## From “ars technica“: “Black holes can’t trash info about what they swallow—and that’s a problem”

From “ars technica“

10.3.22
Paul Sutter

Solving the information paradox could unlock quantum gravity and unification of forces.

Aaron Horowitz/Getty Images.

Three numbers.

Just three numbers—that’s all it takes to completely, unequivocally, 100 percent describe a black hole in general relativity. If I tell you the mass and electric charge and spin (i.e. angular momentum) of a black hole we’re done. That’s all we’ll ever know about it and all we’ll ever need to describe its features.

Those three numbers allow us to calculate everything about how a black hole will interact with its environment, how objects around it will respond to it, and how the black hole will evolve in the future.

For all their ferocious gravitational abilities and their unholy exotic natures, black holes are surprisingly simple. If I give you two black holes with the exact same mass, charge, and spin, you wouldn’t be able to tell them apart. If I swapped their places without you looking, you wouldn’t know that I did it.

This also means that when you see a fully formed black hole, you have no idea what made it. Any combination of mass squeezed into a sufficiently small volume could have done the job. It could have been the ultra-dense core of a dying star. It could have been an extremely dense litter of adorable kittens squashed into oblivion.

As long as the mass, charge, and spin are the same, the history is irrelevant. No information about the original material that created the black hole survives. Or does it?

Founding charters

“Information” is a bit of a loaded term; it can take on various definitions depending on who you ask and what mood they’re in. In physics, the concept of information is tightly linked to our understanding of how physical systems evolve and how we construct our theories of physics.

We like to think that physics is a relatively useful paradigm for understanding the Universe we live in. One of the ways that physics is useful is its power of prediction. If I give you a list of all the information about a system, I should be able to apply my laws and theories of physics to tell you how that system will evolve. The reverse is also true. If I tell you the state of a system now, you can run all the math backward to figure out how the system got to its present state.

These two concepts are known as determinism (I can predict the future) and reversibility (I can read the past) and are pretty much the foundational core of physics. If our theories of physics didn’t have these properties, we wouldn’t be able to get much work done.

These two concepts also apply to quantum mechanics. Yes, quantum mechanics puts strict limits on what we can measure about the Universe, but that doesn’t mean all bets are off. Instead, we can simply replace a sharply defined classical state with a fuzzier quantum state and move on with our lives; the quantum state evolves according to the Schrödinger equation, which upholds both determinism and reversibility, so we’re all good.

This one-two punch of determinism and reversibility means that, in terms of physics, information must be preserved during any process. It can’t be either created or destroyed—if we were to add or remove information willy-nilly, we wouldn’t be able to predict the future or read the past. Any loss or gain means there would either be missing information or extra information, so all of physics would crumble to dust.

There are many processes that appear to destroy information, but that’s only because we’re not keeping careful enough track. Take, for example, the burning of a book. If I gave you a pile of ashes, this would appear to be irreversible: There’s no way you could put the book back together. But if you have a sufficiently powerful microscope at your disposal (and a lot of patience) and got to watch me in the act of burning the book, you could—in principle at least, which is good enough—watch and track the motion of every single molecule in the process. You could then reverse all those motions and all those interactions to reconstruct the book. Information is not lost when you burn a book; it’s merely scrambled.

In the traditional, classical view of black holes, all this business about information is not a problem at all. The information that went into building the black hole is simply locked away behind the event horizon—the one-way boundary at the black hole’s surface that makes it so unique. Once there, the information will never be seen in this Universe again. Whether the black hole was formed from dying stars or squashed kittens, it doesn’t practically matter. The information may not be destroyed, but it’s permanently hidden from our prying eyes.

Hawking’s surprise

At least, that’s what we thought until the mid-1970s, when famed astrophysicist Stephen Hawking discovered that black holes aren’t entirely… well, black.

Hawking was exploring the nature of quantum fields near the event horizons of black holes when he discovered an unusual property. The interaction of the event horizon with the quantum fields triggered the emission of radiation; light and particles could escape from the otherwise inescapable event horizons, causing the black holes to lose mass and eventually evaporate.

Curiously, Hawking found that the radiation emitted by a black hole was perfectly thermal, meaning that it contained no information whatsoever except for that regarding the mass, charge, and spin of the black hole. Thus was born the black hole information paradox. Unlike if it were burned, were a book to fall into a black hole, there’s no way we could reconstruct the words from the radiation that came out. After the black hole radiated away all its mass and disappeared in a poof of particles, all the information about all the objects (books, stars, kittens, etc.) that fell in to create the black hole would disappear along with it.

But as we went over earlier, information can’t just disappear, so this was a bit of a puzzle.

The problem languished for decades, with physicists arguing back and forth (and even changing their minds!) about how to fix it. Hawking’s calculations could be wrong, but that would mean we were missing something important about the nature of quantum field theory—which was well-tested. Or our understanding of gravity could be wrong, although that was well-tested, too. Or we needed to give up our cherished notions of the conservation of information… which was also well-tested.

It won’t be spoiling the rest of this article to tell you that we still do not have a solution to the paradox. But in studying this troubling problem, physicists have come up with several interesting clues that are helping us move in what’s hopefully the right direction.

Information wants to be free

The first major clue came in the late 1990s when theoretical physicist Juan Maldacena calculated the entropy of a black hole. In a nutshell, this calculation of the entropy was a count of all the missing information that gets locked behind an event horizon. He found that the amount of entropy inside a black hole is proportional to the radius squared—and thus proportional to the surface area of the black hole. (That’s in contrast to the radius cubed, which is proportional to the volume.)

For example, if you take a standard black hole and add one single bit of information to it (as encoded by, say, a single photon with a wavelength equal to the radius of the black hole) its surface area will increase by exactly the square of the Planck length.

Leading from Hawking’s insight, this result suggested that the most important property of a black hole—the place where we should focus our attention and efforts—was not the infinitely dense singularity in the center but the surface of the event horizon, which separates the insides of a black hole from the Universe outside.

The relationship between a black hole’s surface and its entropy also dovetailed nicely with another concept evolving out of the string theory community at the time, something known as the “holographic principle.”

String theory is an attempt to develop a theory of everything, a complete description of all the forces of nature under a single unifying framework. That attempt hasn’t seen a lot of success because nobody has been able to use string theory to develop a quantum theory of gravity—all the math just gets too complex to solve. So several physicists in the ’90s wondered if there was a way to simplify the problem. Instead of trying to work through the nasty problem of quantum gravity in our normal four-dimensional Universe, maybe we could encode all the information contained in the Universe onto an imaginary three-dimensional boundary and get an easier version of the math.

Maldacena was able to provide a realization of that idea via what’s called the AdS/CFT correspondence. It works like this. You start by trying to solve a problem involving quantum gravity in a particular kind of Universe called anti-de Sitter space (AdS, which has no matter or radiation inside it but does have positive cosmological constant). Mathematically, you can project all the information in that Universe onto its surface. Once you make that transformation, your impossible-to-solve quantum gravity problem turns into a merely very-difficult-to-solve problem in conformal field theory (that’s the CFT part), which is a kind of quantum field theory that doesn’t include gravity at all. You can then solve your problem and translate the solution back into the full-dimensional Universe and move on with your life.

This correspondence between the information within a volume and the information present on that volume’s surface is the holographic principle (named so because holograms store 3D information on a 2D surface). The correspondence has yet to be proven mathematically, but it has turned out to be useful for solving various kinds of specialized problems in the realm of high-energy physics.

What does this have to do with black holes? The fact that a black hole’s information content is related directly to its surface and not its volume seems to be a major clue that the resolution to the paradox may come from using the AdS/CFT correspondence, which recasts problems involving extended objects with gravity into surface-layer problems without gravity. Leaving aside the slightly uncomfortable fact that the inside of a black hole is definitely not an anti-de Sitter space, perhaps the black holes are trying to tell us something fundamental not just about the nature of gravity but about reality itself.

It was based on this correspondence that Hawking declared a winner in the love-it-or-leave-it debate regarding the preservation of information. Based on the AdS/CFT holographic picture of the Universe, information must be preserved (somehow) on the surface of a black hole and end up leaving the black hole (somehow) via Hawking radiation. If you threw a book into a black hole and kept careful track of the particles emitted over the next few trillions of years, you should be able to put the book back together again.

Somehow.

The “promised land” of quantum gravity

The “how” part of this story has been keeping some physicists up late at night for the past 20 years. One particular line of thinking has been to closely examine the nature of spacetime near the event horizon. In Hawking’s original approach, he assumed that a large enough black hole would curve space in the region of the horizon, but only mildly so. But we know from our (limited and incomplete) forays into quantum gravity that we may have to account for a more dramatic curvature. To fully answer the question of “what’s gravity up to around an event horizon?” we may also have to fold in the same kind of quantum fuzziness that underlies theories of subatomic particles.

When we do that, however, we typically get uncontrollable infinities popping up everywhere in the math because such theories need to account for every possible exotic shape that spacetime can take. This is generally why we don’t have a theory of quantum gravity. That said, some brave theorists have dared to venture into those uncharted waters and have discovered some clever tricks (really hardcore stuff, too, like imaginary wormholes threading together in a complex mathematical space) to untangle some of the equations, showing that it may be possible to create scenarios where information can leak into the Hawking process.

Still other theorists have rejected this string-theory-driven approach to black holes and focus instead on the nature of space-time at the singularity. Their approaches consider whether space and time might come in discrete little chunks, the same way that energy levels and angular momentum do. In this view, the singularity is not an infinitely dense point but merely a really tiny one. And when the black hole evaporates, it doesn’t disappear completely—instead, it leaves behind a nugget of information-rich material. But those approaches run into major hurdles of their own, like having to figure out how to make the transition from a black hole with an inescapable horizon to a lump of matter existing bare naked in the Universe.

Ultimately, physicists remain intrigued by the information paradox because it potentially exposes a feature of quantum gravity and makes it available to our examination. Quantum gravity is usually the domain of the ultra-exotic: the initial moments of the Big Bang or unachievable particle collider energies. But black holes are real things in the real Universe; with enough determination, we could reach out and dip a toe into an event horizon.

If we can solve the information paradox, we just might be able to unlock quantum gravity, the unification of the forces, and more.

five-ways-keep-your-child-safe-school-shootings

Stem Education Coalition

Ars Technica was founded in 1998 when Founder & Editor-in-Chief Ken Fisher announced his plans for starting a publication devoted to technology that would cater to what he called “alpha geeks”: technologists and IT professionals. Ken’s vision was to build a publication with a simple editorial mission: be “technically savvy, up-to-date, and more fun” than what was currently popular in the space. In the ensuing years, with formidable contributions by a unique editorial staff, Ars Technica became a trusted source for technology news, tech policy analysis, breakdowns of the latest scientific advancements, gadget reviews, software, hardware, and nearly everything else found in between layers of silicon.

Ars Technica innovates by listening to its core readership. Readers have come to demand devotedness to accuracy and integrity, flanked by a willingness to leave each day’s meaningless, click-bait fodder by the wayside. The result is something unique: the unparalleled marriage of breadth and depth in technology journalism. By 2001, Ars Technica was regularly producing news reports, op-eds, and the like, but the company stood out from the competition by regularly providing long thought-pieces and in-depth explainers.

And thanks to its readership, Ars Technica also accomplished a number of industry leading moves. In 2001, Ars launched a digital subscription service when such things were non-existent for digital media. Ars was also the first IT publication to begin covering the resurgence of Apple, and the first to draw analytical and cultural ties between the world of high technology and gaming. Ars was also first to begin selling its long form content in digitally distributable forms, such as PDFs and eventually eBooks (again, starting in 2001).

## From Astrobites : “Could Stripped Stars be False Positives in the Search for the Missing Black Holes?”

From Astrobites

10.3.22
Aldo Panfichi

Authors: Julia Bodensteiner et al.

Status: Published on ESO’s The Messenger [open access]

Unraveling the mysteries behind the fates of the most massive stars is key to understanding the present state of the universe. This is because massive stars are origins of elements heavier than helium, as a result of thermonuclear interactions in their cores; as well as being sources of electromagnetic radiation, strong stellar winds, and supernovae, which help seed these elements throughout the cosmos. Since the most massive stars end their lives as black holes, understanding the distribution and characteristics of these objects is key to understanding the lifecycle of said stars.

The problem with searching for black holes, however, is that by their very nature, they are nearly impossible to detect on their own. We infer their existence through two main techniques. The first is when a black hole accretes material from a stellar binary companion – this gas and dust can form an accretion disk around the black hole, heating up and emitting x-ray radiation. The second is from the detection of gravitational waves that occur when a black hole merges with another compact object.

In our galaxy, we have detected around 100 or so black holes from X-ray binaries. However, since we expect most massive stars to end their lives as black holes, theories suggest we should see ~10^7 stellar-mass black holes in the Milky Way. As such, it is suspected that the vast majority of black holes are what we call quiescent – that is, they do not accrete enough to show up on x-ray observations, and thus can only be detected via gravitational effects on other nearby bodies.

Searching Spectroscopically

To date there have been only a handful of reported candidate quiescent black holes. These have all been in binary systems, whose initial signature was detected through spectroscopy and radial velocity measurements. In short, if looking at the light spectrum of a star shows its spectral lines varying sinusoidally, as if orbiting a companion, but there are no appropriate lines that vary in opposite cadence, it could represent an unseen companion that does not emit light – such as a black hole.

The authors of today’s paper, however, caution that a black hole need not be the only explanation for this. There could instead be a companion star that is emitting light, but is not detected due to low-quality data or being relatively faint compared to the much brighter companion. Alternatively, it could be rotating so fast that its spectral lines are broad and shallow, and thus are much less distinguishable, among other theories.

In particular, the authors look in detail at two systems – LB-1 and HR 6819 – whose initial spectra prompted them to be reported as quiescent black holes orbited by a B-type star (luminous, blue, and usually more massive than the sun). However, subsequent analyses have proposed that they are instead binary star systems that consist of a B-type star whose atmosphere has been stripped, and another luminous star.

The spectra of LB-1 and HR 6819 both share similar features that are shown in Figure 1. In particular, in this wavelength region there are two bright, stationary, broad emission lines, and two dark, narrow, shallow absorption lines, which vary sinusoidally in time. The absorption lines are those of the B-type star, and vary on a scale of tens of days. The emission lines are instead characteristic of a classical Be star – a specific kind of B-type star that contains an emitting circumstellar gaseous disk.

Figure 1: Spectra of HR 6189, cut around the Fe II spectral line region at 5316 Angstroms, over the full orbital period of 40 days. The top panel shows the two bright, stationary emission lines of a classical Be star, and two darker, sinusoidally-varying absorption lines from a typical B-type star. The bottom panel shows three normalized spectra taken at three different phases in the orbit. Figure 2 in the paper.

The initial hypothesis was that since the Be emission lines appear stationary, the B-star and Be star did not orbit one another closely. Either the B-star must orbit with an invisible companion, and the Be emission corresponded to either an unrelated third star which appeared in the spectra due to chance superposition, or this was a triple star system and the Be-star orbited much further away. These ideas were backed up by calculations which showed that if the B-type star had its typical mass of ~5 solar masses, the Be star would need to have an unphysical mass to have such an effect on the radial velocity of the B-type star’s spectral lines.

The Stripped Star Solution

However, subsequent studies have since suggested that such a triple system would most likely be unstable. Furthermore, the Be star’s emission lines do in fact seem to show a very small, subtle variation in opposite cadence to the B-star’s absorption lines; thus the two stars could in fact be orbiting one another, removing the need for a third, invisible companion. If this is the case, then, how do we justify the non-physicality of the Be star’s estimated mass? The projected orbital velocity of the B-type stars, based on the movement of their spectral lines, is much larger than it should be in comparison to that of the Be stars, in both the LB-1 and HR 6819 systems.

We can resolve this by reinterpreting the physical nature of the B-type star. If we assume its mass to be on the order of ~0.5 solar masses, rather than the typical ~5-6, the radial velocities would make sense. Under this interpretation, the B-type star is not a standard main-sequence B-type star, but is instead in a “post-mass-transfer” phase – a star that has been fully ‘stripped’ by its binary companion, losing the majority of its mass, while its companion accreted all that matter and angular momentum, spinning up into a rapidly rotating Be star. As the outer hydrogen layers were stripped away from the B-type star, its now exposed Helium core would puff outwards and re-contract into a new equilibrium phase. In the early contraction phase, its luminosity and surface temperature can appear to overlap with those of a typical main-sequence B-type star, and thus it could be easily confused for one. If this is the case, then said B-type star would continue contracting over millions of years, eventually becoming a sub-dwarf OB star. The start of the contraction phase, however, is the brightest and most easily spectroscopically detectable phase of this evolution, and so it makes sense that these systems are detected in this phase.

Figure 2: Two hypotheses for the observed spectra of HR 6819. The first scenario corresponds to a stripped B-type star and a Be star orbiting each other. The second scenario shows a normal B-type star orbiting a black hole, with a Be star forming a part of this triple system, orbiting from much further away. Figure 3 in the paper.

The authors posit that high-resolution interferometry might be the definitive way to determine whether these systems contain quiescent black holes or stripped B-type stars. The binary scenario has the two companions orbiting at 1-2 milliarcsecond separations, with an orbital period on the order of tens of days. On the other hand, the triple scenario should have the Be star orbiting much further apart, and appearing stationary on month-long timescales. Initial observations of HR 6819 from the GRAVITY instrument at the VLT Interferometer seem to favor the binary hypothesis, and further observations in April-September of 2022 will allow for the derivation of stellar parameters such as an accurate mass of the stripped B-type star. Similarly, GRAVITY observations of LB-1 are planned for this year, and will hopefully shed light on the nature of that system as well.

With the possible elimination of these two candidates, however, the search for the missing quiescent black holes continues, and the authors hope that the lessons learned from these two systems pushes for an interdisciplinary approach to finding and characterizing these objects, in particular with ongoing and upcoming large scale surveys on the horizon.

What do we do?

Astrobites is a daily astrophysical literature journal written by graduate students in astronomy. Our goal is to present one interesting paper per day in a brief format that is accessible to undergraduate students in the physical sciences who are interested in active research.

Reading a technical paper from an unfamiliar subfield is intimidating. It may not be obvious how the techniques used by the researchers really work or what role the new research plays in answering the bigger questions motivating that field, not to mention the obscure jargon! For most people, it takes years for scientific papers to become meaningful.

Our goal is to solve this problem, one paper at a time. In 5 minutes a day reading Astrobites, you should not only learn about one interesting piece of current work, but also get a peek at the broader picture of research in a new area of astronomy.

## From Tohoku University[東北大学](JP): “Research News”

From Tohoku University[東北大学](JP)

9.30.22

Figure 2.

Photon spectrum of a reconnection-driven flare from M87. Parameters are M = 6.3 × 109 M⊙, $\dot{m}=5\times {10}^{-5}$, fl = 1.5, and ξhl = 0.5. The blue-dashed, green-dotted, and red-solid lines are for the high-energy flaring state, the low-energy flaring state, and their sum, respectively. The data points are obtained from Table A8 in EHT MWL Science Working Group et al. (2021), which is in the quiescent state. Our model predicts flares of ∼10 times higher luminosity. The black- and gray-dotted lines are sensitivity curves for HiZ-GUNDAM (2 × 104 s: Yonetoku et al. 2020) and AMEGO (106 s: McEnery et al. 2019), respectively.

Figure 3.

Photon spectrum of a reconnection-driven flare from Sgr A* (solid red line). Parameters are M = 4.0 × 106 M⊙, $\dot{m}=6\times {10}^{-7}$, fl =0.6, and ξhl = 0.5. The X-ray flare data (cyan and magenta regions) are taken from Nowak et al. (2012) and Barrière et al. (2014), respectively. The black-dashed line is the sensitivity curve for FORCE (100 s: Nakazawa et al. 2018).

See the science paper for instructive images.

Galaxies, including our Milky Way, host supermassive black holes in their centers, and their masses are millions to billions of times larger than the Sun. Some supermassive black holes launch fast-moving plasma outflows which emit strong radio signals, known as radio jets.

Radio jets were first discovered in the 1970s. But much remains unknown about how they are produced, especially their energy source and plasma loading mechanism.

Recently, the Event Horizon Telescope Collaboration uncovered radio images of a nearby black hole at the center of the giant elliptical galaxy M87. The observation supported the theory that the spin of the black hole powers radio jets but did little to clarify the plasma loading mechanism.

Now, a research team, led by Tohoku University astrophysicists, has proposed a promising scenario that clarifies plasma loading mechanism into radio jets.

Recent studies have claimed that black holes are highly magnetized because magnetized plasma inside galaxies carries magnetic fields into the black hole. Then, neighboring magnetic energy transiently releases its energy via magnetic reconnection, energizing the plasma surrounding the black hole. This magnetic reconnection provides the energy source for solar flares.

Plasmas in solar flares give off ultraviolet and X-rays; whereas the magnetic reconnection around the black hole can cause gamma-ray emission since the released energy per plasma particle is much higher than that for a solar flare.

The present scenario proposes that the emitted gamma rays interact with each other and produce copious electron-positron pairs, which are loaded into the radio jets.

This explains the large amount of plasma observed in radio jets, consistent with the M87 observations. Additionally, the scenario makes note that radio signal strengths vary from black hole to black hole. For example, radio jets around Sgr A* – the supermassive black hole in our Milky Way – are too faint and undetectable by current radio facilities.

Also, the scenario predicts short-term X-ray emission when plasma is loaded into radio jets. These X-ray signals are missed with current X-ray detectors, but they are observable by planned X-ray detectors.

“Under this scenario, future X-ray astronomy will be able to unravel the plasma loading mechanism into radio jets, a long-standing mystery of black holes,” points out Shigeo Kimura, lead author of the study.

Details of Kimura and his team’s research were published in The Astrophysical Journal Letters on September 29, 2022.

five-ways-keep-your-child-safe-school-shootings

Stem Education Coalition

Tohoku University (東北大学](JP), located in Sendai, Miyagi in the Tōhoku Region, Japan, is a Japanese national university. It was the third Imperial University in Japan, the first three Designated National University along with the The University of Tokyo[(東京大] (JP) and Kyoto University [京都大学](JP) and selected as a Top Type university of Top Global University Project by the Japanese government. In 2020 and 2021, the Times Higher Education Tohoku University was ranked No. 1 university in Japan.

In 2016, Tohoku University had 10 faculties, 16 graduate schools and 6 research institutes, with a total enrollment of 17,885 students. The university’s three core values are “Research First [研究第一主義],” “Open-Doors [門戸開放],” and “Practice-Oriented Research and Education [実学尊重].”

Faculties

Arts and Letters
Education
Law
Economics
Science
Medicine
Dentistry
Pharmaceutical Sciences
Engineering
Mechanical and Aerospace Engineering
Information and Intelligent Systems
Applied Chemistry, Chemical Engineering and Bio molecular Engineering
Materials Science and Engineering
Civil Engineering and Architecture
Agriculture

Arts and Letters
Education
Law
Economics and Management
Science
Medicine
Dentistry
Pharmaceutical Sciences
Engineering
Agricultural Sciences
International Cultural Studies
Information Sciences
Life Sciences
Environmental Studies
Educational Informatics Research Division / Education Division

Law School
School of Public Policy
Accounting School

Research institutes

Research Institute of Electrical Communication [電気通信研究所]
Institute of Development, Aging and Cancer [加齢医学研究所]
Institute of Fluid Science [流体科学研究所]
Institute for Materials Research,IMR [金属材料研究所]

National Collaborative Research Institute

Institute of Multidisciplinary Research for Advanced Materials [多元物質科学研究所]

International Research Institute of Disaster Science [災害科学国際研究所]

## From “Quanta Magazine” : “A Black Hole’s Orbiting Ring of Light Could Encrypt Its Inner Secrets”

From “Quanta Magazine”

9.8.22
Thomas Lewton

The photon ring, which glows orange in this visualization of light flowing around a black hole, contains a succession of images of the entire universe. Credit: Olena Shmahalo for Quanta Magazine; Source: Jeremy Schnittman/ NASA’s Goddard Space Flight Center.

When photons hurtle toward a black hole, most are sucked into its depths, never to return, or gently deflected away. A rare few, however, skirt the hole, making a series of abrupt U-turns. Some of these photons keep circling the black hole practically forever.

Described by astrophysicists as a “cosmic movie camera” and an “infinite light trap,” the resulting ring of orbiting photons is among the weirdest phenomena in nature. If you detect the photons, “you’re going to see every object in the universe infinitely many times,” said Sam Gralla, a physicist at the University of Arizona.

But unlike the iconic event horizon of a black hole — the boundary within which gravity is so strong that nothing can escape — the photon ring, which orbits the hole farther away, has never received much attention from theorists. It makes sense that researchers have been preoccupied with the event horizon, since it marks the edge of their knowledge about the universe. Throughout most of the cosmos, gravity tracks with curves in space and time as described by Albert Einstein’s General Theory of Relativity. But spacetime warps so much inside black holes that General Relativity breaks down there. Quantum Gravity theorists seeking a truer, quantum description of gravity have therefore looked to the horizon for answers.

“I had taken the view that the event horizon was what we needed to understand,” said Andrew Strominger, a leading black hole and quantum gravity theorist at Harvard University. “And I thought of the photon ring as some sort of technical, complicated thing which didn’t have any deep significance.”

Now Strominger is making his own U-turn and trying to convince other theorists to join him. “We’re exploring, excitedly, the possibility that the photon ring is the thing that you have to understand to unlock the secrets of Kerr black holes,” he said, referring to the kind of spinning black holes created when stars die and gravitationally collapse. (The photon ring forms concurrently.)

In a paper posted online in May and recently accepted for publication in Classical Quantum Gravity, Strominger and his collaborators revealed that the photon ring around a spinning black hole has an unexpected kind of symmetry — a way that it can be transformed and still stay the same. The symmetry suggests that the ring may encode information about the hole’s quantum structure. “This symmetry smells like something to do with the central problem of understanding the quantum dynamics of black holes,” he said. The discovery has led researchers to debate whether the photon ring might even be part of a black hole’s “holographic dual” — a quantum system that’s exactly equivalent to the black hole itself, and which the black hole can be thought of as emerging out of like a hologram.

“It opens up a very interesting avenue for understanding the holography of these [black hole] geometries,” said Alex Maloney, a theorist at McGill University in Canada who was not involved in the research. “The new symmetry organizes the structure of black holes far from the event horizon, and I think that’s very exciting.”

Photons that make a single U-turn around a black hole before flying away from it create an image of a ring, labeled n = 1 in the video. Photons that redirect twice before flying away from the hole form an image of a thinner ring within the first ring, labeled n = 2 in the video, and so on.
Credit: Harvard-Smithsonian Center for Astrophysics.

Much more theoretical study is needed before researchers can say for sure whether, or in what way, the photon ring encodes a black hole’s inner contents. But at the very least, theorists say the new paper has detailed a precise test for any quantum system claiming to be the black hole’s holographic dual. “It’s a target for a holographic description,” said Juan Maldacena of the Institute for Advanced Study in Princeton, New Jersey, one of the original architects of holography.

Hiding in the Photon Ring

Part of the excitement about the photon ring is that, unlike the event horizon, it’s actually visible. In fact, Strominger’s U-turn toward these rings happened because of a photograph: the first-ever image of a black hole.

When the Event Horizon Telescope (EHT) unveiled it in 2019, “I cried,” he said. “It’s amazingly beautiful.”

Elation soon spiraled into confusion. The black hole in the image had a thick ring of light around it, but physicists on the EHT team didn’t know whether this light was the product of the hole’s chaotic surrounding environment, or if it included the black hole’s photon ring. They went to Strominger and his theorist colleagues for help interpreting the image. Together, they browsed the huge databank of computer simulations that the EHT team was using to disentangle the physical processes that produce light around black holes. In these simulated images, they could see the thin, bright ring embedded in the larger, fuzzier orange doughnut of light.

“When you look at all the simulations, you can’t miss it,” said Shahar Hadar of the University of Haifa in Israel, who collaborated with Strominger and the EHT physicists on the research while at Harvard. The formation of the photon ring seems to be a “universal effect” that happens around all black holes, Hadar said.

Unlike the maelstrom of energetic colliding particles and fields that surrounds black holes, the theorists determined, the sharp line of the photon ring carries direct information about the black hole’s properties, including its mass and amount of spin. “It’s definitely the most beautiful and compelling way to really see the black hole,” said Strominger.

The collaboration of astronomers, simulators and theorists found that the EHT’s actual photograph, which shows the black hole at the center of the nearby galaxy Messier 87, isn’t sharp enough to resolve the photon ring, although it isn’t far off. They argued in a 2020 paper [Science Advances (below)] that future, higher-resolution telescopes should easily see photon rings. (A new paper [The Astrophysical Journal (below)] claims to have found the ring in the EHT’s 2019 image by applying an algorithm to remove layers from the original data, but the claim has been met with skepticism.)

Still, having stared at photon rings for so long in the simulations, Strominger and his colleagues began to wonder if their form hinted at an even deeper meaning.

A Surprising Symmetry

Photons that make a single U-turn around a black hole and then zip toward Earth would appear to us as a single ring of light. Photons that make two U-turns around the hole appear as a fainter, thinner subring within the first ring. And photons that make three U-turns appear as a subring within that subring, and so on, creating nested rings, each fainter and thinner than the last.

Light from the inner subrings has made more orbits and was therefore captured before the light from outer subrings, resulting in a series of time-delayed snapshots of the surrounding universe. “Together, the set of subrings are akin to the frames of a movie, capturing the history of the visible universe as seen from the black hole,” the collaboration wrote in the 2020 paper.

Strominger said that when he and his collaborators looked at the EHT pictures, “we were like: ‘Hey, there’s an infinite number of copies of the universe right there at that screen? Couldn’t that be where the holographic dual lives?’”

The researchers realized that the ring’s concentric structure is suggestive of a group of symmetries called conformal symmetry. A system that has conformal symmetry exhibits “scale invariance,” meaning it looks the same when you zoom in or out. In this case, each photon subring is an exact, demagnified copy of the previous subring. Moreover, a conformally symmetric system stays the same when translated forward or backward in time and when all spatial coordinates are inverted, shifted and then inverted again.

Strominger encountered conformal symmetry in the 1990s when it turned up in a special kind of five-dimensional black hole he was studying. By precisely understanding the details of this symmetry, he and Cumrun Vafa found a novel way to connect general relativity to the quantum world, at least inside these extreme kinds of black holes. They imagined cutting out the black hole and replacing its event horizon with what they called a holographic plate, a surface containing a quantum system of particles that respect conformal symmetry. They showed that the system’s properties correspond to properties of the black hole, as if the black hole is a higher-dimensional hologram of the conformal quantum system. In this way, they built a bridge between the description of a black hole according to general relativity and its quantum mechanical description.

In 1997, Maldacena extended this same holographic principle to an entire toy universe. He discovered a “universe in a bottle,” in which a conformally symmetric quantum system living on the bottle’s surface exactly mapped onto properties of space-time and gravity in the bottle’s interior. It was as if the interior was a “universe” that projected from its lower-dimensional surface like a hologram.

The discovery led many theorists to believe that the real universe is a hologram. The hitch is that Maldacena’s universe in a bottle differs from our own. It’s filled with a type of space-time that’s negatively curved, which gives it a surface-like outer boundary. Our universe is thought to be flat, and theorists have little idea what the holographic dual of flat space-time looks like. “We need to get back to the real world, while taking inspiration from what we learned from these hypothetical worlds,” Strominger said.

And so the group decided to study a realistic spinning black hole sitting in flat space-time, like those photographed by the Event Horizon Telescope. “The first questions to ask are: Where does the holographic dual live? And what are the symmetries?” said Hadar.

Searching for the Holographic Dual

Historically, conformal symmetry has proved a trustworthy guide in the search for quantum systems that holographically map onto systems with gravity. “Saying conformal symmetry and black hole in the same sentence to a quantum gravity theorist is like waving red meat in front of a dog,” said Strominger.

Starting from the description of spinning black holes in general relativity, called the Kerr metric, the group began to look for hints of conformal symmetry. They imagined hitting the black hole with a hammer to make it ring like a bell. These slowly fading vibrations are like the gravitational waves created when, say, two black holes collide. The black hole will ring with some resonant frequencies that depend on the shape of space-time (that is, on the Kerr metric) just as the ringing tones of a bell depend on its shape.

Figuring out the exact pattern of vibrations is unfeasible because the Kerr metric is so complicated. So the team approximated the pattern by only considering high-frequency vibrations, which result from hitting the black hole very hard. They noticed a relationship between the pattern of waves at these high energies and the structure of the black hole’s photon rings. The pattern “turns out to be completely governed by the photon ring,” said Alex Lupsasca of the Vanderbilt Initiative for Gravity, Waves and Fluids in Tennessee, who co-authored the new paper with Strominger, Hadar and Daniel Kapec of Harvard.

A pivotal moment came in the summer of 2020 during the Covid-19 pandemic. Blackboards and benches were set up on the grass outside Harvard’s Jefferson physics lab, and the researchers could finally meet up in person. They worked out that, like the conformal symmetry which relates each photon ring to the next subring, the successive tones of a ringing black hole are related to each other by conformal symmetry. This relationship between the photon rings and the black hole vibrations could be a “harbinger” of holography, said Strominger.

Another clue that the photon ring may hold special significance comes from the counterintuitive way the ring relates to the black hole’s geometry. “It’s very, very weird,” Hadar said. “As you move along different points on the photon ring, you are actually probing different radii” or depths into the black hole.

These findings imply to Strominger that the photon ring, rather than the event horizon, is a “natural candidate” for part of the holographic plate of a spinning black hole.

If so, there may be a new way to picture what happens to information about objects that fall into black holes — a long-standing mystery known as the black hole information paradox. Recent calculations indicate that this information is somehow preserved by the universe as a black hole slowly evaporates. Strominger now speculates that the information might be stored in the holographic plate. “Perhaps information doesn’t really fall into the black hole, but it sort of stays in a cloud around outside the black hole, which probably extends to the photon ring,” he said. “But we don’t understand how it’s coded in there, or exactly how that works.”

A Call to Theorists

Strominger and company’s hunch that the holographic dual lives in or around the photon ring has been met with skepticism by some quantum gravity theorists, who see it as too bold an extrapolation from the ring’s conformal symmetry. “Where the holographic dual lives is a much deeper question than: What is the symmetry?” said Daniel Harlow, a quantum gravity and black hole theorist at the Massachusetts Institute of Technology. Although he is in favor of further research on the issue, Harlow stresses that a convincing holographic duality, in this case, must show how the properties of the photon ring, such as individual photons’ orbits and frequencies, mathematically map onto the fine-grained quantum details of the black hole.

Nevertheless, several experts said that the new research offers a useful needle that any proposed holographic dual must thread: The dual must be able to encode the unusual vibration pattern of a spinning black hole after it has been struck like a bell. “Demanding the quantum system that describes the black hole reproduces all of that complexity is an incredibly powerful constraint — and one that we’ve never tried to exploit before,” said Strominger. Eva Silverstein, a theoretical physicist at Stanford University, said, “It seems like a very nice piece of theoretical data for people to try to reproduce when attempting a holographic dual description.”

Maldacena agreed, saying, “One would like to understand how to incorporate this into a holographic dual. So it will probably stimulate some research in that direction.”

Maloney suspects that the newfound symmetry of the photon ring will spur interest among both theorists and observers. If hoped-for upgrades to the Event Horizon Telescope get funded, it could start to detect photon rings within a few years.

Future measurements of these rings won’t directly test holography, though — rather, the data will allow extreme tests of general relativity near black holes. It’s up to theorists to determine with pen-and-paper calculations if the structure of the infinite light traps around black holes can mathematically encrypt the secrets within.

Stem Education Coalition

Formerly known as Simons Science News, Quanta Magazine is an editorially independent online publication launched by the Simons Foundation to enhance public understanding of science. Why Quanta? Albert Einstein called photons “quanta of light.” Our goal is to “illuminate science.” At Quanta Magazine, scientific accuracy is every bit as important as telling a good story. All of our articles are meticulously researched, reported, edited, copy-edited and fact-checked.

## From The Stanford University Kavli Institute for Particle Astrophysics and Cosmology : “The Inescapable Astrophysical Attraction of Black Holes”

From The Stanford University Kavli Institute for Particle Astrophysics and Cosmology

7.26.22

Kavli institute-affiliated researcher Adi Foord follows her inspiration while inspiring others.

Much like how black holes irreversibly trap matter that strays too close, researchers who encounter these astounding objects in their careers find it is nearly impossible to pull themselves away.

Adi Foord can attest to the powerful scientific allure of black holes. Now a Porat Postdoctoral Fellow at the Kavli Institute for Particle Astrophysics and Cosmology (KIPAC) at Stanford University, Foord had always had an interest in physics growing up. Astronomy appeared on Foord’s radar, though, only after she took a course her senior year of high school. She recalls the tremendous support of her teacher, “Mr. P.”

Foord’s research focus is on dual AGN—astronomer-speak for pairs of supermassive black holes in the cores of galaxies that, as their host galaxies merge to form a single galaxy will likewise, in time, merge together into a single, even more supermassive black hole.

The “AGN” bit refers to “active galactic nucleus,” the term for when these supermassive black holes actively devour matter and spew out stunning amounts of energy and radiation. AGN are accordingly some of the brighter objects found in the universe.

Researchers like Foord are eager to study the relatively short-lived phase, cosmically speaking, when colossal black holes come into close quarters, whirl about each other, and eventually coalesce.

This celestial dance is tumultuous and has far-reaching effects. As the objects’ intensely strong gravitational fields rip at each other, bystander matter is revved up and blazes energetically, in turn affecting the formation of stars galaxy-wide as the black holes’ original galaxies become one.

“We think that mergers are some of the most formative years in a supermassive black hole’s and galaxy’s life, where the black hole can grow quickly, undergo violent periods where they launch jets, and change the properties of the galaxy it sits in,” says Foord.

Because the black hole merger process “only” lasts tens of millions of years, there are only so many of these events that can be observed given the universe’s multi-billion-year history. “It’s not that easy to find these pairs of merging SMBHs,” says Foord, “so I’m hoping to expand the sample size.”

Foord relies chiefly on observations from NASA’s Chandra X-ray Observatory to detect the telltale high-energy X-ray signals from dual AGNs.

The hope is that a better understanding of these fleeting, yet major phases in the lives of supermassive black holes will shed light on broader mysteries about these objects in general, and especially with regard to their murky origins.

“I think it’s fascinating that we’ve observed over one million or so supermassive black holes, and yet we still don’t know some fundamental aspects about them, like how and when they are formed,” says Foord.

Otherwise largely successful cosmology models struggle to account for how so much mass could have accumulated so quickly to form the supermassive black holes that evidently existed surprisingly early in cosmic history. Logic suggests that supermassive black holes can form directly from somehow pooling billions of times the sun’s mass in the early universe, or that big black holes form from the rapid build-up mergers of many smaller black holes, or that an inherently pretty good-sized black hole can voraciously consume matter in its environment in order to go supermassive. More data is needed to disentangle these roots.

Foord aims to study the environments created when black hole-hosting galaxies come together to learn more about the matter-gobbling and merger pathways taken by black holes.

“Black holes’ environments may play a really important role in how easily they can eat material and grow, and how likely they are to merge with other nearby supermassive black holes,” says Foord. “The cosmic environment evolves throughout our universe’s history, so I’m interested in how this influences the evolution of supermassive black holes.”

In addition to her research, Foord enjoys communicating about science to the public. In June, Foord gave a KIPAC public lecture, entitled “Catching a Supermassive Black Hole in the Act.” Foord also does special outreach to high school students through the three-week summer outreach effort called the Stanford Program for Inspiring the Next Generation of Women in Physics (SPINWIP). Like herself back in high school, the students in this program might find true inspiration when introduced to the thrilling world of astrophysics.

“Support and encouraging women in science is very important to me and I’m so thankful that I’ve had various opportunities at KIPAC to do so, such as teaching high school girls about supermassive black holes through SPINWIP, working with students on merging supermassive black hole data projects, and getting to present to the public about exciting supermassive black hole research results,” Foord says.

Thanks to her outreach, many other budding researchers might heed the call of astrophysics and feel the irresistible pull of black hole science.

five-ways-keep-your-child-safe-school-shootings

Stem Education Coalition

The Kavli Institute for Particle Astrophysics and Cosmology, is an independent laboratory of Stanford University. Initiated with a generous grant from Fred Kavli and The Kavli Foundation, KIPAC is housed at The DOE’s SLAC National Accelerator Laboratory and in the Varian Physics and Physics Astrophysics buildings on the Stanford campus. The lab is funded in part by Stanford University and the Department of Energy.

Leland and Jane Stanford founded Stanford University to “promote the public welfare by exercising an influence on behalf of humanity and civilization.” Stanford opened its doors in 1891, and more than a century later, it remains dedicated to finding solutions to the great challenges of the day and to preparing our students for leadership in today’s complex world. Stanford, is an American private research university located in Stanford, California on an 8,180-acre (3,310 ha) campus near Palo Alto. Since 1952, more than 54 Stanford faculty, staff, and alumni have won the Nobel Prize, including 19 current faculty members.

Stanford University, officially Leland Stanford Junior University, is a private research university located in Stanford, California. Stanford was founded in 1885 by Leland and Jane Stanford in memory of their only child, Leland Stanford Jr., who had died of typhoid fever at age 15 the previous year. Stanford is consistently ranked as among the most prestigious and top universities in the world by major education publications. It is also one of the top fundraising institutions in the country, becoming the first school to raise more than a billion dollars in a year.

Leland Stanford was a U.S. senator and former governor of California who made his fortune as a railroad tycoon. The school admitted its first students on October 1, 1891, as a coeducational and non-denominational institution. Stanford University struggled financially after the death of Leland Stanford in 1893 and again after much of the campus was damaged by the 1906 San Francisco earthquake. Following World War II, provost Frederick Terman supported faculty and graduates’ entrepreneurialism to build self-sufficient local industry in what would later be known as Silicon Valley.

The university is organized around seven schools: three schools consisting of 40 academic departments at the undergraduate level as well as four professional schools that focus on graduate programs in law, medicine, education, and business. All schools are on the same campus. Students compete in 36 varsity sports, and the university is one of two private institutions in the Division I FBS Pac-12 Conference. It has gained 126 NCAA team championships, and Stanford has won the NACDA Directors’ Cup for 24 consecutive years, beginning in 1994–1995. In addition, Stanford students and alumni have won 270 Olympic medals including 139 gold medals.

As of October 2020, 84 Nobel laureates, 28 Turing Award laureates, and eight Fields Medalists have been affiliated with Stanford as students, alumni, faculty, or staff. In addition, Stanford is particularly noted for its entrepreneurship and is one of the most successful universities in attracting funding for start-ups. Stanford alumni have founded numerous companies, which combined produce more than $2.7 trillion in annual revenue, roughly equivalent to the 7th largest economy in the world (as of 2020). Stanford is the alma mater of one president of the United States (Herbert Hoover), 74 living billionaires, and 17 astronauts. It is also one of the leading producers of Fulbright Scholars, Marshall Scholars, Rhodes Scholars, and members of the United States Congress. Stanford University was founded in 1885 by Leland and Jane Stanford, dedicated to Leland Stanford Jr, their only child. The institution opened in 1891 on Stanford’s previous Palo Alto farm. Jane and Leland Stanford modeled their university after the great eastern universities, most specifically Cornell University. Stanford opened being called the “Cornell of the West” in 1891 due to faculty being former Cornell affiliates (either professors, alumni, or both) including its first president, David Starr Jordan, and second president, John Casper Branner. Both Cornell and Stanford were among the first to have higher education be accessible, nonsectarian, and open to women as well as to men. Cornell is credited as one of the first American universities to adopt this radical departure from traditional education, and Stanford became an early adopter as well. Despite being impacted by earthquakes in both 1906 and 1989, the campus was rebuilt each time. In 1919, The Hoover Institution on War, Revolution and Peace was started by Herbert Hoover to preserve artifacts related to World War I. The Stanford Medical Center, completed in 1959, is a teaching hospital with over 800 beds. The DOE’s SLAC National Accelerator Laboratory(originally named the Stanford Linear Accelerator Center), established in 1962, performs research in particle physics. Land Most of Stanford is on an 8,180-acre (12.8 sq mi; 33.1 km^2) campus, one of the largest in the United States. It is located on the San Francisco Peninsula, in the northwest part of the Santa Clara Valley (Silicon Valley) approximately 37 miles (60 km) southeast of San Francisco and approximately 20 miles (30 km) northwest of San Jose. In 2008, 60% of this land remained undeveloped. Stanford’s main campus includes a census-designated place within unincorporated Santa Clara County, although some of the university land (such as the Stanford Shopping Center and the Stanford Research Park) is within the city limits of Palo Alto. The campus also includes much land in unincorporated San Mateo County (including the SLAC National Accelerator Laboratory and the Jasper Ridge Biological Preserve), as well as in the city limits of Menlo Park (Stanford Hills neighborhood), Woodside, and Portola Valley. Non-central campus Stanford currently operates in various locations outside of its central campus. On the founding grant: Jasper Ridge Biological Preserve is a 1,200-acre (490 ha) natural reserve south of the central campus owned by the university and used by wildlife biologists for research. SLAC National Accelerator Laboratory is a facility west of the central campus operated by the university for the Department of Energy. It contains the longest linear particle accelerator in the world, 2 miles (3.2 km) on 426 acres (172 ha) of land. Golf course and a seasonal lake: The university also has its own golf course and a seasonal lake (Lake Lagunita, actually an irrigation reservoir), both home to the vulnerable California tiger salamander. As of 2012 Lake Lagunita was often dry and the university had no plans to artificially fill it. Off the founding grant: Hopkins Marine Station, in Pacific Grove, California, is a marine biology research center owned by the university since 1892. Study abroad locations: unlike typical study abroad programs, Stanford itself operates in several locations around the world; thus, each location has Stanford faculty-in-residence and staff in addition to students, creating a “mini-Stanford”. Redwood City campus for many of the university’s administrative offices located in Redwood City, California, a few miles north of the main campus. In 2005, the university purchased a small, 35-acre (14 ha) campus in Midpoint Technology Park intended for staff offices; development was delayed by The Great Recession. In 2015 the university announced a development plan and the Redwood City campus opened in March 2019. The Bass Center in Washington, DC provides a base, including housing, for the Stanford in Washington program for undergraduates. It includes a small art gallery open to the public. China: Stanford Center at Peking University, housed in the Lee Jung Sen Building, is a small center for researchers and students in collaboration with Beijing University [北京大学](CN) (Kavli Institute for Astronomy and Astrophysics at Peking University(CN) (KIAA-PKU). Administration and organization Stanford is a private, non-profit university that is administered as a corporate trust governed by a privately appointed board of trustees with a maximum membership of 38. Trustees serve five-year terms (not more than two consecutive terms) and meet five times annually.[83] A new trustee is chosen by the current trustees by ballot. The Stanford trustees also oversee the Stanford Research Park, the Stanford Shopping Center, the Cantor Center for Visual Arts, Stanford University Medical Center, and many associated medical facilities (including the Lucile Packard Children’s Hospital). The board appoints a president to serve as the chief executive officer of the university, to prescribe the duties of professors and course of study, to manage financial and business affairs, and to appoint nine vice presidents. The provost is the chief academic and budget officer, to whom the deans of each of the seven schools report. Persis Drell became the 13th provost in February 2017. As of 2018, the university was organized into seven academic schools. The schools of Humanities and Sciences (27 departments), Engineering (nine departments), and Earth, Energy & Environmental Sciences (four departments) have both graduate and undergraduate programs while the Schools of Law, Medicine, Education and Business have graduate programs only. The powers and authority of the faculty are vested in the Academic Council, which is made up of tenure and non-tenure line faculty, research faculty, senior fellows in some policy centers and institutes, the president of the university, and some other academic administrators, but most matters are handled by the Faculty Senate, made up of 55 elected representatives of the faculty. The Associated Students of Stanford University (ASSU) is the student government for Stanford and all registered students are members. Its elected leadership consists of the Undergraduate Senate elected by the undergraduate students, the Graduate Student Council elected by the graduate students, and the President and Vice President elected as a ticket by the entire student body. Stanford is the beneficiary of a special clause in the California Constitution, which explicitly exempts Stanford property from taxation so long as the property is used for educational purposes. Endowment and donations The university’s endowment, managed by the Stanford Management Company, was valued at$27.7 billion as of August 31, 2019. Payouts from the Stanford endowment covered approximately 21.8% of university expenses in the 2019 fiscal year. In the 2018 NACUBO-TIAA survey of colleges and universities in the United States and Canada, only Harvard University, the University of Texas System, and Yale University had larger endowments than Stanford.

In 2006, President John L. Hennessy launched a five-year campaign called the Stanford Challenge, which reached its $4.3 billion fundraising goal in 2009, two years ahead of time, but continued fundraising for the duration of the campaign. It concluded on December 31, 2011, having raised a total of$6.23 billion and breaking the previous campaign fundraising record of $3.88 billion held by Yale. Specifically, the campaign raised$253.7 million for undergraduate financial aid, as well as $2.33 billion for its initiative in “Seeking Solutions” to global problems,$1.61 billion for “Educating Leaders” by improving K-12 education, and $2.11 billion for “Foundation of Excellence” aimed at providing academic support for Stanford students and faculty. Funds supported 366 new fellowships for graduate students, 139 new endowed chairs for faculty, and 38 new or renovated buildings. The new funding also enabled the construction of a facility for stem cell research; a new campus for the business school; an expansion of the law school; a new Engineering Quad; a new art and art history building; an on-campus concert hall; a new art museum; and a planned expansion of the medical school, among other things. In 2012, the university raised$1.035 billion, becoming the first school to raise more than a billion dollars in a year.

Research centers and institutes

DOE’s SLAC National Accelerator Laboratory
Stanford Research Institute, a center of innovation to support economic development in the region.
Hoover Institution, a conservative American public policy institution and research institution that promotes personal and economic liberty, free enterprise, and limited government.
Hasso Plattner Institute of Design, a multidisciplinary design school in cooperation with the Hasso Plattner Institute of University of Potsdam [Universität Potsdam](DE) that integrates product design, engineering, and business management education).
Martin Luther King Jr. Research and Education Institute, which grew out of and still contains the Martin Luther King Jr. Papers Project.
John S. Knight Fellowship for Professional Journalists
Center for Ocean Solutions
Together with UC Berkeley and UC San Francisco, Stanford is part of the Biohub, a new medical science research center founded in 2016 by a $600 million commitment from Facebook CEO and founder Mark Zuckerberg and pediatrician Priscilla Chan. Discoveries and innovation Natural sciences Biological synthesis of deoxyribonucleic acid (DNA) – Arthur Kornberg synthesized DNA material and won the Nobel Prize in Physiology or Medicine 1959 for his work at Stanford. First Transgenic organism – Stanley Cohen and Herbert Boyer were the first scientists to transplant genes from one living organism to another, a fundamental discovery for genetic engineering. Thousands of products have been developed on the basis of their work, including human growth hormone and hepatitis B vaccine. Laser – Arthur Leonard Schawlow shared the 1981 Nobel Prize in Physics with Nicolaas Bloembergen and Kai Siegbahn for his work on lasers. Nuclear magnetic resonance – Felix Bloch developed new methods for nuclear magnetic precision measurements, which are the underlying principles of the MRI. Computer and applied sciences ARPANETStanford Research Institute, formerly part of Stanford but on a separate campus, was the site of one of the four original ARPANET nodes. Internet—Stanford was the site where the original design of the Internet was undertaken. Vint Cerf led a research group to elaborate the design of the Transmission Control Protocol (TCP/IP) that he originally co-created with Robert E. Kahn (Bob Kahn) in 1973 and which formed the basis for the architecture of the Internet. Frequency modulation synthesis – John Chowning of the Music department invented the FM music synthesis algorithm in 1967, and Stanford later licensed it to Yamaha Corporation. Google – Google began in January 1996 as a research project by Larry Page and Sergey Brin when they were both PhD students at Stanford. They were working on the Stanford Digital Library Project (SDLP). The SDLP’s goal was “to develop the enabling technologies for a single, integrated and universal digital library” and it was funded through the National Science Foundation, among other federal agencies. Klystron tube – invented by the brothers Russell and Sigurd Varian at Stanford. Their prototype was completed and demonstrated successfully on August 30, 1937. Upon publication in 1939, news of the klystron immediately influenced the work of U.S. and UK researchers working on radar equipment. RISCARPA funded VLSI project of microprocessor design. Stanford and University of California- Berkeley are most associated with the popularization of this concept. The Stanford MIPS would go on to be commercialized as the successful MIPS architecture, while Berkeley RISC gave its name to the entire concept, commercialized as the SPARC. Another success from this era were IBM’s efforts that eventually led to the IBM POWER instruction set architecture, PowerPC, and Power ISA. As these projects matured, a wide variety of similar designs flourished in the late 1980s and especially the early 1990s, representing a major force in the Unix workstation market as well as embedded processors in laser printers, routers and similar products. SUN workstation – Andy Bechtolsheim designed the SUN workstation for the Stanford University Network communications project as a personal CAD workstation, which led to Sun Microsystems. Businesses and entrepreneurship Stanford is one of the most successful universities in creating companies and licensing its inventions to existing companies; it is often held up as a model for technology transfer. Stanford’s Office of Technology Licensing is responsible for commercializing university research, intellectual property, and university-developed projects. The university is described as having a strong venture culture in which students are encouraged, and often funded, to launch their own companies. Companies founded by Stanford alumni generate more than$2.7 trillion in annual revenue, equivalent to the 10th-largest economy in the world.

Some companies closely associated with Stanford and their connections include:

Hewlett-Packard, 1939, co-founders William R. Hewlett (B.S, PhD) and David Packard (M.S).
Silicon Graphics, 1981, co-founders James H. Clark (Associate Professor) and several of his grad students.
Sun Microsystems, 1982, co-founders Vinod Khosla (M.B.A), Andy Bechtolsheim (PhD) and Scott McNealy (M.B.A).
Cisco, 1984, founders Leonard Bosack (M.S) and Sandy Lerner (M.S) who were in charge of Stanford Computer Science and Graduate School of Business computer operations groups respectively when the hardware was developed.[163]
Yahoo!, 1994, co-founders Jerry Yang (B.S, M.S) and David Filo (M.S).
Google, 1998, co-founders Larry Page (M.S) and Sergey Brin (M.S).
LinkedIn, 2002, co-founders Reid Hoffman (B.S), Konstantin Guericke (B.S, M.S), Eric Lee (B.S), and Alan Liu (B.S).
Instagram, 2010, co-founders Kevin Systrom (B.S) and Mike Krieger (B.S).
Snapchat, 2011, co-founders Evan Spiegel and Bobby Murphy (B.S).
Coursera, 2012, co-founders Andrew Ng (Associate Professor) and Daphne Koller (Professor, PhD).

Student body

Stanford enrolled 6,996 undergraduate and 10,253 graduate students as of the 2019–2020 school year. Women comprised 50.4% of undergraduates and 41.5% of graduate students. In the same academic year, the freshman retention rate was 99%.

Stanford awarded 1,819 undergraduate degrees, 2,393 master’s degrees, 770 doctoral degrees, and 3270 professional degrees in the 2018–2019 school year. The four-year graduation rate for the class of 2017 cohort was 72.9%, and the six-year rate was 94.4%. The relatively low four-year graduation rate is a function of the university’s coterminal degree (or “coterm”) program, which allows students to earn a master’s degree as a 1-to-2-year extension of their undergraduate program.

As of 2010, fifteen percent of undergraduates were first-generation students.

Athletics

As of 2016 Stanford had 16 male varsity sports and 20 female varsity sports, 19 club sports and about 27 intramural sports. In 1930, following a unanimous vote by the Executive Committee for the Associated Students, the athletic department adopted the mascot “Indian.” The Indian symbol and name were dropped by President Richard Lyman in 1972, after objections from Native American students and a vote by the student senate. The sports teams are now officially referred to as the “Stanford Cardinal,” referring to the deep red color, not the cardinal bird. Stanford is a member of the Pac-12 Conference in most sports, the Mountain Pacific Sports Federation in several other sports, and the America East Conference in field hockey with the participation in the inter-collegiate NCAA’s Division I FBS.

Its traditional sports rival is the University of California, Berkeley, the neighbor to the north in the East Bay. The winner of the annual “Big Game” between the Cal and Cardinal football teams gains custody of the Stanford Axe.

Stanford has had at least one NCAA team champion every year since the 1976–77 school year and has earned 126 NCAA national team titles since its establishment, the most among universities, and Stanford has won 522 individual national championships, the most by any university. Stanford has won the award for the top-ranked Division 1 athletic program—the NACDA Directors’ Cup, formerly known as the Sears Cup—annually for the past twenty-four straight years. Stanford athletes have won medals in every Olympic Games since 1912, winning 270 Olympic medals total, 139 of them gold. In the 2008 Summer Olympics, and 2016 Summer Olympics, Stanford won more Olympic medals than any other university in the United States. Stanford athletes won 16 medals at the 2012 Summer Olympics (12 gold, two silver and two bronze), and 27 medals at the 2016 Summer Olympics.

The unofficial motto of Stanford, selected by President Jordan, is Die Luft der Freiheit weht. Translated from the German language, this quotation from Ulrich von Hutten means, “The wind of freedom blows.” The motto was controversial during World War I, when anything in German was suspect; at that time the university disavowed that this motto was official.
Hail, Stanford, Hail! is the Stanford Hymn sometimes sung at ceremonies or adapted by the various University singing groups. It was written in 1892 by mechanical engineering professor Albert W. Smith and his wife, Mary Roberts Smith (in 1896 she earned the first Stanford doctorate in Economics and later became associate professor of Sociology), but was not officially adopted until after a performance on campus in March 1902 by the Mormon Tabernacle Choir.
“Uncommon Man/Uncommon Woman”: Stanford does not award honorary degrees, but in 1953 the degree of “Uncommon Man/Uncommon Woman” was created to recognize individuals who give rare and extraordinary service to the University. Technically, this degree is awarded by the Stanford Associates, a voluntary group that is part of the university’s alumni association. As Stanford’s highest honor, it is not conferred at prescribed intervals, but only when appropriate to recognize extraordinary service. Recipients include Herbert Hoover, Bill Hewlett, Dave Packard, Lucile Packard, and John Gardner.
Big Game events: The events in the week leading up to the Big Game vs. UC Berkeley, including Gaieties (a musical written, composed, produced, and performed by the students of Ram’s Head Theatrical Society).
“Viennese Ball”: a formal ball with waltzes that was initially started in the 1970s by students returning from the now-closed Stanford in Vienna overseas program. It is now open to all students.
“Full Moon on the Quad”: An annual event at Main Quad, where students gather to kiss one another starting at midnight. Typically organized by the Junior class cabinet, the festivities include live entertainment, such as music and dance performances.
“Band Run”: An annual festivity at the beginning of the school year, where the band picks up freshmen from dorms across campus while stopping to perform at each location, culminating in a finale performance at Main Quad.
“Mausoleum Party”: An annual Halloween Party at the Stanford Mausoleum, the final resting place of Leland Stanford Jr. and his parents. A 20-year tradition, the “Mausoleum Party” was on hiatus from 2002 to 2005 due to a lack of funding, but was revived in 2006. In 2008, it was hosted in Old Union rather than at the actual Mausoleum, because rain prohibited generators from being rented. In 2009, after fundraising efforts by the Junior Class Presidents and the ASSU Executive, the event was able to return to the Mausoleum despite facing budget cuts earlier in the year.
Former campus traditions include the “Big Game bonfire” on Lake Lagunita (a seasonal lake usually dry in the fall), which was formally ended in 1997 because of the presence of endangered salamanders in the lake bed.

Award laureates and scholars

Stanford’s current community of scholars includes:

19 Nobel Prize laureates (as of October 2020, 85 affiliates in total)
171 members of the National Academy of Sciences
109 members of National Academy of Engineering
76 members of National Academy of Medicine
288 members of the American Academy of Arts and Sciences
19 recipients of the National Medal of Science
1 recipient of the National Medal of Technology
4 recipients of the National Humanities Medal
49 members of American Philosophical Society
56 fellows of the American Physics Society (since 1995)
4 Pulitzer Prize winners
31 MacArthur Fellows
4 Wolf Foundation Prize winners
2 ACL Lifetime Achievement Award winners
14 AAAI fellows
2 Presidential Medal of Freedom winners

## From Perimeter Institute (CA): “The photon ring:: a black hole ready for its close-up”

From Perimeter Institute (CA)

8.16.22
Colin Hunter

Scientists have discerned a sharp ring of light created by photons whipping around the back of a supermassive black hole in a vivid confirmation of theoretical prediction.

The emission from Messier 87* has now been resolved into a bright, thin ring (orange colormap), arising from the infinite sequence of additional images of the emission region, and the more diffuse primary image, produced by the photons that come directly toward Earth (in blue contours). When viewed at the imaging resolution of the Event Horizon Telescope, the two components blur together. However, by separately searching for the thin ring, it is possible to sharpen the view of Messier 87*, isolating the fingerprint of strong gravity. Credit: Broderick et al.

When scientists unveiled humanity’s historic first image of a black hole in 2019 – depicting a dark core encircled by a fiery aura of material falling toward it – they believed even richer imagery and insights were waiting to be teased out of the data.

Simulations predicted that, hidden behind the glare of the diffuse orange glow, there should be a thin, bright ring of light created by photons flung around the back of the black hole by its intense gravity.

A team of researchers led by astrophysicist Avery Broderick used sophisticated imaging algorithms to essentially “remaster” the original imagery of the supermassive black hole at the centre of the Messier 87 galaxy.

“We turned off the searchlight to see the fireflies,” explains Broderick, an associate faculty member at Perimeter Institute and the University of Waterloo. “We have been able to do something profound – to resolve a fundamental signature of gravity around a black hole.”

Capturing the photon ring of a black hole. Perimeter Institute (CA)

By essentially “peeling off” elements of the imagery, says co-author Hung-Yi Pu, an assistant professor at National Taiwan Normal University, “the environment around the black hole can then be clearly revealed.”

To accomplish this, the team employed a new imaging algorithm within the EHT analysis framework THEMIS to isolate and extract the distinct ring feature from the original observations of the M87 black hole – as well as detect the telltale footprint of a powerful jet blasting outward from the black hole.

Anatomy of a black hole image. Perimeter Institute (CA)

The researchers’ findings both confirm theoretical predictions and offer new ways to explore these mysterious objects, which are believed to reside at the heart of most galaxies.

Black holes were long considered unseeable until scientists coaxed them out of hiding with a globe-spanning network of telescopes, the Event Horizon Telescope (EHT). Using eight observatories on four continents, all pointed at the same spot in the sky and linked together with nanosecond timing; the EHT researchers observed two black holes in 2017.

The EHT collaboration first unveiled the supermassive black hole in M87 in 2019, and then in 2022, the comparatively small but tumultuous black hole at the heart of our own Milky Way galaxy, called Sagittarius A* (or Sgr A*).

Supermassive black holes occupy the centre of most galaxies, packing an incredible amount of mass and energy into a small space. The Messier 87 black hole, for example, is two quadrillion (that’s a two followed by 15 zeros) times more massive than Earth.

The Messier 87 image scientists unveiled in 2019 was a landmark, but the researchers felt they could sharpen the image and glean new insights by working smarter, not harder. They applied new software techniques to reconstruct the original 2017 data in search of phenomena that theories and models predicted were lurking beneath the surface. The new, resulting image depicts the photon ring, comprised of a series of increasingly sharp sub-rings, which the team then stacked to get the full image.

The black hole photon ring in context. Perimeter Institute (CA)

“The approach we took involved leveraging our theoretical understanding of how these black holes look to build a customized model for the EHT data,” says Dominic Pesce, a team member based at the Center for Astrophysics | Harvard & Smithsonian. “This model decomposes the reconstructed image into the two pieces that we care most about, so we can study both pieces individually rather than blended together.”

The result was possible because the EHT is a “computational instrument at its heart,” says Broderick. “It is as dependent on algorithms as it is upon steel. Cutting-edge algorithmic developments have allowed us to probe key features of the image while rendering the remainder in the EHT’s native resolution.”

The researchers’ findings were published on August 16 in The Astrophysical Journal.

_________________________________________
Event Horizon Telescope Array

About the Event Horizon Telescope (EHT)

The EHT consortium consists of 13 stakeholder institutes; The Academia Sinica Institute of Astronomy & Astrophysics [中央研究院天文及天文物理研究所](TW) , The University of Arizona, The University of Chicago, The East Asian Observatory, Goethe University Frankfurt [Goethe-Universität](DE), Institut de Radioastronomie Millimétrique, Large Millimeter Telescope, The MPG Institute for Radio Astronomy[MPG Institut für Radioastronomie](DE), MIT Haystack Observatory, The National Astronomical Observatory of Japan[[国立天文台](JP), The Perimeter Institute for Theoretical Physics (CA), Radboud University [Radboud Universiteit](NL) and The Center for Astrophysics | Harvard & Smithsonian.
_________________________________________

five-ways-keep-your-child-safe-school-shootings

Stem Education Coalition

Perimeter Institute (CA) is a leading centre for scientific research, training and educational outreach in foundational theoretical physics. Founded in 1999 in Waterloo, Ontario, Canada, its mission is to advance our understanding of the universe at the most fundamental level, stimulating the breakthroughs that could transform our future. Perimeter also trains the next generation of physicists through innovative programs, and shares the excitement and wonder of science with students, teachers and the general public.

Perimeter’s research encompasses nine fields:

Cosmology
Mathematical physics
Particle Physics
Quantum fields and strings
Quantum foundations
Quantum gravity
Quantum information
Quantum matter
Strong gravity

## From “Quanta Magazine” : “What Drives Galaxies? The Milky Way’s Black Hole May Be the Key”

From “Quanta Magazine”

8.23.22
Thomas Lewton

Olena Shmahalo for Quanta Magazine

On May 12, at nine simultaneous press conferences around the world, astrophysicists revealed the first image of the black hole at the heart of the Milky Way.

_________________________________________
Event Horizon Telescope Array

About the Event Horizon Telescope (EHT)

The EHT consortium consists of 13 stakeholder institutes; The Academia Sinica Institute of Astronomy & Astrophysics [中央研究院天文及天文物理研究所](TW) , The University of Arizona, The University of Chicago, The East Asian Observatory, Goethe University Frankfurt [Goethe-Universität](DE), Institut de Radioastronomie Millimétrique, Large Millimeter Telescope, The MPG Institute for Radio Astronomy[MPG Institut für Radioastronomie](DE), MIT Haystack Observatory, The National Astronomical Observatory of Japan[[国立天文台](JP), The Perimeter Institute for Theoretical Physics (CA), Radboud University [Radboud Universiteit](NL) and The Center for Astrophysics | Harvard & Smithsonian.
_________________________________________

At first, awesome though it was, the painstakingly produced image of the ring of light around our galaxy’s central pit of darkness seemed to merely prove what experts already expected: The Milky Way’s supermassive black hole exists, it is spinning, and it obeys Albert Einstein’s General Theory of Relativity.

And yet, on closer inspection, things don’t quite stack up.

From the brightness of the bagel of light, researchers have estimated how quickly matter is falling onto SGR A* — the name given to the Milky Way’s central black hole. The answer is: not quickly at all. “It’s clogged up to a little trickle,” said Priya Natarajan, a cosmologist at Yale University, comparing the galaxy to a broken shower head. Somehow only a thousandth of the matter that’s flowing into the Milky Way from the surrounding intergalactic medium makes it all the way down and into the hole. “That’s revealing a huge problem,” Natarajan said. “Where is this gas going? What is happening to the flow? It’s very clear that our understanding of black hole growth is suspect.”

Over the past quarter century, astrophysicists have come to recognize what a tight-knit, dynamic relationship exists between many galaxies and the black holes at their centers.

“There’s been a really huge transition in the field,” says Ramesh Narayan, a theoretical astrophysicist at Harvard University. “The surprise was that black holes are important as shapers and controllers of how galaxies evolve.”

These giant holes — concentrations of matter so dense that gravity prevents even light from escaping — are like the engines of galaxies, but researchers are only beginning to understand how they operate. Gravity draws dust and gas inward to the galactic center, where it forms a swirling accretion disk around the supermassive black hole, heating up and turning into white-hot plasma. Then, when the black hole engulfs this matter (either in dribs and drabs or in sudden bursts), energy is spat back out into the galaxy in a feedback process. “When you grow a black hole, you are producing energy and dumping it into the surroundings more efficiently than through any other process we know of in nature,” said Eliot Quataert, a theoretical astrophysicist at Princeton University. This feedback affects star formation rates and gas flow patterns throughout the galaxy.
But researchers have only vague ideas about supermassive black holes’ “active” episodes, which turn them into so-called active galactic nuclei (AGNs). “What is the triggering mechanism? What is the off switch? These are the fundamental questions that we’re still trying to get at,” said Kirsten Hall of the Harvard-Smithsonian Center for Astrophysics.

Stellar feedback, which occurs when a star explodes as a supernova, is known to have similar effects as AGN feedback on a smaller scale. These stellar engines are easily big enough to regulate small “dwarf” galaxies, whereas only the giant engines of supermassive black holes can dominate the evolution of the largest “elliptical” galaxies.

Size-wise, the Milky Way, a typical spiral galaxy, sits in the middle. With few obvious signs of activity at its center, our galaxy was long thought to be dominated by stellar feedback. But several recent observations suggest that AGN feedback shapes it as well. By studying the details of the interplay between these feedback mechanisms in our home galaxy — and grappling with puzzles like the current dimness of SGR A* — astrophysicists hope to figure out how galaxies and black holes co-evolve in general. The Milky Way “is becoming the most powerful astrophysical laboratory,” said Natarajan. By serving as a microcosm, it “may hold the key.”

Galactic Engines

By the late 1990s, astronomers generally accepted the presence of black holes in galaxies’ centers. By then they could see close enough to these invisible objects to deduce their mass from the movements of stars around them. A strange correlation emerged: The more massive a galaxy is, the heavier its central black hole. “This was particularly tight, and it was totally revolutionary. Somehow the black hole is talking to the galaxy,” said Tiziana Di Matteo, an astrophysicist at Carnegie Mellon University.

The correlation is surprising when you consider that the black hole — big as it is — is a scant fraction of the galaxy’s size. (SGR A* weighs roughly 4 million suns, for instance, while the Milky Way measures some 1.5 trillion solar masses.) Because of this, the black hole’s gravity only pulls with any strength on the innermost region of the galaxy.

To Martin Rees, the United Kingdom’s Astronomer Royal, AGN feedback offered a natural way to connect the relatively tiny black hole to the galaxy at large. Two decades earlier, in the 1970s, Rees correctly hypothesized that supermassive black holes power the luminous jets observed in some far-off, brightly glowing galaxies called quasars. He even proposed, along with Donald Lynden-Bell, that a black hole would explain why the Milky Way’s center glows. Could these be signs of a general phenomenon that governs the size of supermassive black holes everywhere?

The idea was that the more matter a black hole swallows, the brighter it gets, and the increased energy and momentum blows gas outward. Eventually, the outward pressure stops gas from falling into the black hole. “That will terminate the growth. In a hand-wavy way, that was the reasoning,” said Rees. Or, in Di Matteo’s words, “the black hole eats and then swallows.” A very big galaxy puts more weight on the central black hole, making it harder to blow gas outward, and so the black hole grows bigger before it swallows.

Yet few astrophysicists were convinced that the energy of infalling matter could be ejected in such a dramatic way. “When I was doing my thesis, we were all obsessed with black holes as a point of no return — just gas going in,” said Natarajan, who helped develop the first AGN feedback models as Rees’ graduate student. “Everyone had to do it very cautiously and gingerly as it was so radical.”

Confirmation of the feedback idea came a few years later, from computer simulations developed by Di Matteo and the astrophysicists Volker Springel and Lars Hernquist. “We wanted to reproduce the amazing zoo of galaxies that we see in the real universe,” Di Matteo said. They knew the basic picture: Galaxies start out small and dense in the early universe. Wind the clock forward and gravity smashes these dwarfs together in a blaze of spectacular mergers, forming rings, whirlpools, cigars and every shape in between. Galaxies grow in size and variety until, after enough collisions, they become big and smooth. “It ends up in a blob,” said Di Matteo. In the simulations, she and her colleagues could re-create these large featureless blobs, called elliptical galaxies, by merging spiral galaxies many times. But there was a problem.

While spiral galaxies like the Milky Way have many young stars that glow blue, giant elliptical galaxies only contain very old stars that glow red. “They are red and dead,” said Springel, of the Max Planck Institute for Astrophysics in Garching, Germany. But every time the team ran their simulation, it spat out ellipticals that glowed blue. Whatever was switching off star formation hadn’t been captured in their computer model.

Then, Springel said, “we had the idea to augment our galaxy mergers with supermassive black holes in the center. We let these black holes swallow gas and release energy until the whole thing flew apart, like a pressure cooker pot. Suddenly, the elliptical galaxy would stop star formation and would become red and dead.”

“My jaw dropped,” he added. “We did not expect [the effect] to be so extreme.”

By reproducing red-and-dead ellipticals, the simulation bolstered the black hole feedback theories of Rees and Natarajan. A black hole, despite its relatively tiny size, can talk to the galaxy as a whole through feedback. Over the last two decades, the computer models have been refined and expanded to simulate large swaths of the cosmos, and they broadly match the eclectic galaxy zoo we see around us. These simulations also show that ejected energy from black holes fills the space between galaxies with hot gas that otherwise should have already cooled and turned into stars. “People are convinced by now that supermassive black holes are very plausible engines,” said Springel. “No one has come up with a successful model without black holes.”

Mysteries of Feedback

Yet the computer simulations are still surprisingly blunt.

As matter creeps inward to the accretion disk around a black hole, friction causes energy to be pushed back out; the amount of energy lost this way is something the coders put into their simulations by hand through trial and error. It’s a sign that the details are still elusive. “There’s a possibility that in some instances we’re getting the right answer for the wrong reason,” said Quataert. “Maybe we’re not capturing what is actually the most important thing about how black holes grow and how they dump energy into their surroundings.”

The truth is that astrophysicists don’t really know how AGN feedback works. “We know how important it is. But it’s escaping us exactly what causes this feedback,” said Di Matteo. “The key, key problem is that we don’t understand feedback deeply, physically.”

They know that some energy is emitted as radiation, which gives the centers of active galaxies their characteristic bright glow. Strong magnetic fields cause matter to fly out from the accretion disk too, either as diffuse galactic winds or in powerful narrow jets. The mechanism by which black holes are thought to launch jets, called the Blandford-Znajek process, was identified in the 1970s, but what determines the beam’s power, and how much of its energy gets absorbed by the galaxy, is “still an open unsolved problem,” said Narayan. The galactic wind, which emanates spherically from the accretion disk and so tends to interact more directly with the galaxy than the narrow jets, is even more mysterious. “The billion-dollar question is: How is the energy coupling to the gas?” said Springel.

Jets emerging from the black hole in the center of the galaxy Cygnus A create massive interstellar blobs, visible here in radio waves. Credit: NRAO/AUI/NSF.

One sign that there’s still a problem is that the black holes in state-of-the-art cosmological simulations end up smaller [MNRAS (below)] than the observed sizes of real supermassive black holes in some systems. To switch off star formation and create red-and-dead galaxies, the simulations need black holes to eject so much energy that they choke off the inward flux of matter, so that the black holes stop growing. “The feedback in the simulations is too aggressive; it stunts the growth prematurely,” Natarajan said.

The Milky Way exemplifies the opposite problem: Simulations typically predict that a galaxy of its size should have a black hole between three and 10 times bigger than Sagittarius A* is.

By taking a closer look at the Milky Way and nearby galaxies, researchers hope we can begin to unravel precisely how AGN feedback works.

Milky Way Ecosystem

In December 2020, researchers with the eROSITA X-ray telescope reported that they had spotted a pair of bubbles stretching tens of thousands of light-years above and below the Milky Way.

The vast bubbles of X-rays resembled equally baffling bubbles of gamma rays that, 10 years earlier, the Fermi Gamma-ray Space Telescope detected emanating from the galaxy.

Two origin theories of the Fermi bubbles were still being hotly debated. Some astrophysicists suggested that they were a relic of a jet that shot out of SGR A* millions of years ago. Others thought the bubbles were the accumulated energy of many stars exploding near the galactic center — a kind of stellar feedback.

When Hsiang-Yi Karen Yang of National Tsing Hua University in Taiwan saw the image of the eROSITA X-ray bubbles, she “started jumping up and down.” It was clear to Yang that the X-rays could have a common origin with the gamma rays if both were generated by the same AGN jet. (The X-rays would come from shocked gas in the Milky Way rather than from the jet itself.) Along with coauthors Ellen Zweibel and Mateusz Ruszkowski, she set about building a computer model. The results, published in Nature Astrophysics [below] this past spring, not only replicate the shape of the observed bubbles and a bright shock front, but predict that they formed over the course of 2.6 million years (expanding outward from a jet that was active for 100,000 years) — far too quickly to be explained by stellar feedback.

The finding suggests that AGN feedback may be far more important in run-of-the-mill disk galaxies like the Milky Way than researchers used to think. The picture that’s emerging is akin to that of an ecosystem, Yang said, where AGN and stellar feedback are intertwined with the diffuse, hot gas that surrounds galaxies, called the circumgalactic medium. Different effects and flow patterns will dominate in different galaxy types and at different times.

A case study of the Milky Way’s past and present could unveil the interplay of these processes. Europe’s Gaia space telescope, for example, has mapped the precise positions and movements of millions of the Milky Way’s stars, allowing astrophysicists to retrace the history of its mergers with smaller galaxies.

Such merger events have been hypothesized to activate supermassive black holes by shaking matter into them, causing them to suddenly brighten and even launch jets. “There’s a big debate in the field as to whether or not mergers are important,” said Quataert. The Gaia star data suggests that the Milky Way did not undergo a merger at the time that the Fermi and eROSITA bubbles formed, disfavoring mergers as the triggers of the AGN jet.

The Gaia spacecraft’s measurements of the positions and velocities of millions of stars and other objects in and around the Milky Way have allowed astronomers to unravel the history of the galaxy’s mergers with smaller galaxies. These mergers left traces in the form of streams of stars. Credit: S. Payne-Wardenaar / K. Malhan, MPIA.

Alternatively, blobs of gas may just happen to collide with the black hole and activate it. It might chaotically switch between eating, belching out energy as jets and galactic winds, and pausing.

The Event Horizon Telescope’s recent image of Sagittarius A* [above], which reveals its current trickle of infalling matter, presents a new puzzle to solve. Astrophysicists already knew that not all of the gas that is drawn into a galaxy will make it to the black hole horizon, since galactic winds push outward against this accretion flow. But the strength of the winds required to explain such an extremely tapered flow is unrealistic. “When I do simulations, I don’t see a huge wind,” said Narayan. “It’s not the kind of wind you need for a complete explanation of what’s going on.”

Nested Simulations

Part of the challenge in understanding how galaxies work is the huge difference between the length scales at play in stars and black holes and the scales of entire galaxies and their surroundings. When simulating a physical process on a computer, researchers pick a scale and include relevant effects at that scale. But in galaxies, big and small effects interact.

“The black hole is truly tiny, compared to the big galaxy, and you cannot put them all in one single humongous simulation,” said Narayan. “Each regime needs information from the other guy, but doesn’t know how to make the connection.”

To try and bridge this gap, Narayan, Natarajan and colleagues are launching a project that will use nested simulations to build a coherent model of how gas flows through the Milky Way and the nearby active galaxy Messier 87. “You allow information to come from the galaxy to tell the black hole what to do, and then you allow the information from the black hole to go back and tell the galaxy what to do,” Narayan said. “It’s a loop that goes round and round and round.”

The simulations should help clarify the flow pattern of the diffuse gas in and around galaxies. (Further observations of the circumgalactic medium by the James Webb Space Telescope will help as well.) “That’s a critical part of this whole ecosystem,” Quataert said. “How do you get the gas down to the black hole to drive all the energy that goes back out?”

Crucially, in the new scheme, all inputs and outputs between simulations of different scales must be consistent, leaving fewer dials to twiddle. “If the simulation is set up properly, it will self-consistently decide how much gas should reach the black hole,” Narayan said. “We can look into it and ask: Why did it not eat all the gas? Why was it so fussy and take so little of the available gas?” The group hopes to create a series of snapshots of the galaxies during different phases of their evolution.

For now, much about these galactic ecosystems is still a hunch. “It’s really a new era, where people are starting to think about these overlapping scenarios,” said Yang. “I don’t have a clear answer, but I hope I will in a few years.”

Science papers:
MNRAS
Nature Astronomy

Stem Education Coalition

Formerly known as Simons Science News, Quanta Magazine is an editorially independent online publication launched by the Simons Foundation to enhance public understanding of science. Why Quanta? Albert Einstein called photons “quanta of light.” Our goal is to “illuminate science.” At Quanta Magazine, scientific accuracy is every bit as important as telling a good story. All of our articles are meticulously researched, reported, edited, copy-edited and fact-checked.

## From The National Aeronautics and Space Administration Chandra X-ray telescope: “NGC 4424:: NASA Telescopes Capture Stellar Delivery Service for Black Hole”

8.18.22

Credit: A. Graham et al./X-ray: NASA/CXC/Swinburne Univ. of Technology/; Optical: NASA/ESA/STScI.

NGC 4424 is a spiral galaxy in the Virgo galaxy cluster that is absorbing the collision of a smaller one.

Data from NASA’s Chandra X-ray Observatory provides evidence for a supermassive black hole in the smaller galaxy.

The smaller galaxy has likely acted as a black hole “delivery service” for NGC 4424.

A cluster of stars remaining after the smaller galaxy has had most of its stars stripped away has been nicknamed “Nikhuli,” a name relating to the Tulini festival for the harvest..

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Astronomers may have witnessed a galaxy’s black hole delivery system in action. A new study using data from NASA’s Chandra X-ray Observatory and Hubble Space Telescope outlines how a large black hole may have been delivered to the spiral galaxy NGC 4424 by another, smaller galaxy.

NGC 4424 is located about 54 million light-years from Earth in the Virgo galaxy cluster.

The main panel of this image, which has been previously released, shows a wide-field view of this galaxy in optical light from Hubble. The image is about 45,000 light-years wide. The center of this galaxy is expected to host a large black hole estimated to contain a mass between about 60,000 and 100,000 Suns. There are also likely to be millions of stellar-mass black holes, which contain between about 5 and 30 solar masses, spread throughout the galaxy.

The inset features a close-up view of NGC 4424 that shows Chandra X-ray data (blue), plus infrared data from Hubble (red) that has had infrared light from a model of NGC 4424 subtracted from the image to show other faint features. This inset image is about 1,160 light-years across. The elongated red object is a cluster of stars that the authors of the new study have nicknamed “Nikhuli,” a name relating to the Tulini festive period of celebrating and wishing for a rich harvest. This name is taken from the Sumi language from the Indian state of Nagaland. The Chandra data shows a point source of X-rays.

Close-up view of NGC 4424 (Credit: A. Graham et al./X-ray: NASA/CXC/Swinburne Univ. of Technology/; Optical: NASA/ESA/STScI).

The researchers determined Nikhuli is likely the center of a small galaxy that has had most of its stars stripped away as it collides with the larger galaxy NGC 4424. Nikhuli has also been stretched out by gravitational forces as it falls towards the center of NGC 4424, giving it an elongated shape. Currently, Nikhuli is about 1,300 light-years from the center of NGC 4424, or about 20 times closer than the Earth is to the Milky Way’s giant black hole.

One possible explanation for the Chandra X-ray source in the inset is that matter from Nikhuli is falling rapidly into a stellar-mass black hole. However, because these smaller black holes are expected to be rare in a cluster the size of Nikhuli, the authors argue it is more likely from material falling slowly onto a more massive black hole weighing between about 40,000 and 150,000 Suns. This is similar to the expected size of the black hole in the center of NGC 4424. These results imply that Nikhuli is likely acting as a delivery system for NGC 4424’s supply of black holes, in this case bringing along a massive one. If the center of NGC 4424 contains a massive black hole, Nikhuli’s massive black hole should end up orbiting it. The distance separating the pair should then shrink until gravitational waves are produced and the two massive black holes merge with each other.

A paper describing these results appeared in the December 2021 issue of The Astrophysical Journal [below]. The authors of the study are Alister Graham (Swinburne Astronomy Online, Australia), Roberto Soria (University of the Chinese Academy of Sciences in Beijing, China), Bogdan Ciambur (The Paris Observatory, France), Benjamin Davis (New York University in Abu Dhabi, United Arab Emirates), and Douglas Swartz (NASA’s Marshall Space Flight Center in Huntsville, Alabama).

Quick Look: NASA Telescopes Capture Stellar Delivery Service for Black Hole.

Science paper:
The Astrophysical Journal

Stem Education Coalition

NASA’s Marshall Space Flight Center in Huntsville, Ala., manages the Chandra program for NASA’s Science Mission Directorate in Washington. The Smithsonian Astrophysical Observatory controls Chandra’s science and flight operations from Cambridge, Mass.
In 1976 the Chandra X-ray Observatory (called AXAF at the time) was proposed to National Aeronautics and Space Administration by Riccardo Giacconi and Harvey Tananbaum. Preliminary work began the following year at NASA’s Marshall Space Flight Center and the Harvard Smithsonian Center for Astrophysics. In the meantime, in 1978, NASA launched the first imaging X-ray telescope, Einstein (HEAO-2), into orbit. Work continued on the AXAF project throughout the 1980s and 1990s. In 1992, to reduce costs, the spacecraft was redesigned. Four of the twelve planned mirrors were eliminated, as were two of the six scientific instruments. AXAF’s planned orbit was changed to an elliptical one, reaching one third of the way to the Moon’s at its farthest point. This eliminated the possibility of improvement or repair by the space shuttle but put the observatory above the Earth’s radiation belts for most of its orbit. AXAF was assembled and tested by TRW (now Northrop Grumman Aerospace Systems) in Redondo Beach, California.

AXAF was renamed Chandra as part of a contest held by NASA in 1998, which drew more than 6,000 submissions worldwide. The contest winners, Jatila van der Veen and Tyrel Johnson (then a high school teacher and high school student, respectively), suggested the name in honor of Nobel Prize–winning Indian-American astrophysicist Subrahmanyan Chandrasekhar. He is known for his work in determining the maximum mass of white dwarf stars, leading to greater understanding of high energy astronomical phenomena such as neutron stars and black holes. Fittingly, the name Chandra means “moon” in Sanskrit.

Originally scheduled to be launched in December 1998, the spacecraft was delayed several months, eventually being launched on July 23, 1999, at 04:31 UTC by Space Shuttle Columbia during STS-93. Chandra was deployed from Columbia at 11:47 UTC. The Inertial Upper Stage’s first stage motor ignited at 12:48 UTC, and after burning for 125 seconds and separating, the second stage ignited at 12:51 UTC and burned for 117 seconds. At 22,753 kilograms (50,162 lb), it was the heaviest payload ever launched by the shuttle, a consequence of the two-stage Inertial Upper Stage booster rocket system needed to transport the spacecraft to its high orbit.

Chandra has been returning data since the month after it launched. It is operated by the SAO at the Chandra X-ray Center in Cambridge, Massachusetts, with assistance from Massachusetts Institute of Technology and Northrop Grumman Space Technology. The ACIS CCDs suffered particle damage during early radiation belt passages. To prevent further damage, the instrument is now removed from the telescope’s focal plane during passages.

Although Chandra was initially given an expected lifetime of 5 years, on September 4, 2001, NASA extended its lifetime to 10 years “based on the observatory’s outstanding results.” Physically Chandra could last much longer. A 2004 study performed at the Chandra X-ray Center indicated that the observatory could last at least 15 years.

In July 2008, the International X-ray Observatory, a joint project between European Space Agency [La Agencia Espacial Europea] [Agence spatiale européenne][Europäische Weltraumorganisation](EU), NASA and Japan Aerospace Exploration Agency (JAXA) (国立研究開発法人宇宙航空研究開発機構], was proposed as the next major X-ray observatory but was later cancelled. ESA later resurrected a downsized version of the project as the Advanced Telescope for High Energy Astrophysics (ATHENA), with a proposed launch in 2028.

On October 10, 2018, Chandra entered safe mode operations, due to a gyroscope glitch. NASA reported that all science instruments were safe. Within days, the 3-second error in data from one gyro was understood, and plans were made to return Chandra to full service. The gyroscope that experienced the glitch was placed in reserve and is otherwise healthy.

The National Aeronautics and Space Administration (NASA) is the agency of the United States government that is responsible for the nation’s civilian space program and for aeronautics and aerospace research.

President Dwight D. Eisenhower established the National Aeronautics and Space Administration (NASA) in 1958 with a distinctly civilian (rather than military) orientation encouraging peaceful applications in space science. The National Aeronautics and Space Act was passed on July 29, 1958, disestablishing NASA’s predecessor, the National Advisory Committee for Aeronautics (NACA). The new agency became operational on October 1, 1958.

Since that time, most U.S. space exploration efforts have been led by NASA, including the Apollo moon-landing missions, the Skylab space station, and later the Space Shuttle. Currently, NASA is supporting the International Space Station and is overseeing the development of the Orion Multi-Purpose Crew Vehicle and Commercial Crew vehicles. The agency is also responsible for the Launch Services Program (LSP) which provides oversight of launch operations and countdown management for unmanned NASA launches. Most recently, NASA announced a new Space Launch System that it said would take the agency’s astronauts farther into space than ever before and lay the cornerstone for future human space exploration efforts by the U.S.

NASA science is focused on better understanding Earth through the Earth Observing System, advancing heliophysics through the efforts of the Science Mission Directorate’s Heliophysics Research Program, exploring bodies throughout the Solar System with advanced robotic missions such as New Horizons, and researching astrophysics topics, such as the Big Bang, through the Great Observatories [NASA/ESA Hubble, NASA Chandra, NASA Spitzer, and associated programs.] NASA shares data with various national and international organizations such as from [JAXA]Greenhouse Gases Observing Satellite.

## From Stoney Brook University – SUNY : “Scientists Take Another Theoretical Step to Uncovering the Mystery of Dark Matter and Black Holes”

From Stoney Brook University – SUNY

8.16.22

A star (orange) that gets close to a supermassive black hole (black) can be tidally disrupted by the black hole’s strong gravitational pull. According to a new study, If ultra-light bosons exist (purple), they can affect the spin of the black hole, which in turn affects the rate at which tidal disruption events occur. Credit: Peizhi Du.

Much of the matter in the universe remains unknown and undefined yet theoretical physicists continue to gain clues to the properties of dark matter and black holes. A study by a team of scientists including three from Stony Brook University proposes a novel method to search for new particles not currently contained in the standard model of particle physics. Their method, published in Nature Communications [below], could shed light on the nature of dark matter.

The three Stony Brook authors include Rouven Essig, PhD, Professor in the C. N. Yang Institute for Theoretical Physics (YITP); Rosalba Perna, PhD, Professor in the Department of Physics and Astronomy, and Peizhi Du, PhD, postdoctoral researcher at the YITP.

Stars that pass close to the supermassive black holes located in the center of galaxies can be disrupted by tidal forces, leading to flares that are observed as bright transient events in sky surveys. The rate for these events to occur depends on the black hole spins, which in turn can be affected by ultra-light bosons (hypothetical particles with minute masses) due to superradiance. The research team performed a detailed analysis of these effects, and they discovered that searches for stellar tidal-disruptions have the potential to uncover the existence of ultra-light bosons.

According to co-author Rouven Essig, the team demonstrated that due to the dependence of the stellar disruption rates on the black hole’s spin, and given that ultra-light bosons uniquely affect such spins because of the superradiant instability, stellar tidal disruption rate measurements can be used to probe these new particles.

Additionally, the researchers suggest that with the enormous dataset of stellar tidal disruptions that is provided by the Vera Rubin Observatory, these data in combination with the researchers’ work can be used to discover or rule out a variety of ultra-light boson models over wide regions of parameter space.

Their analysis also indicates that measurements of stellar tidal disruption rates may be used to constrain a variety of supermassive black hole spin distributions and determine if close-to maximal spins are preferred.

“The potential implications of our findings are profound. The discovery of new ultra-light bosons in stellar tidal disruption surveys would be revolutionary for fundamental physics,” says Essig.

“These new particles could be the dark matter, and thus the work could open up windows into a complex dark sector that hints toward more fundamental descriptions of nature such as string theory. Our proposal may have other applications too, as measurements of supermassive black hole spins can be used to study the black hole’s formation history,” says Rosalba Perna.

“And ultimately, if these ultra-light bosons exist they will affect how stars that get close to a supermassive black hole are disrupted by the black hole’s strong gravitational pull,” adds Peizhi.

The Stony Brook team worked with Dr. Daniel Egana-Ugrinovic, a postdoctoral researcher at the Perimeter Institute, and Dr. Giacomo Fragione, a Research Assistant Professor at Northwestern University.

The Stony Brook research component was supported by the Department of Energy (Grant No. DE-SC0009854), the Simons Foundation (Simons Investigator in Physics Award 623940), the National Science Foundation (Awards PHY-1915093 and AST-2006839), and the US-Israel Binational Science Foundation (Grant No. 2016153).

Science paper:
Nature Communications

five-ways-keep-your-child-safe-school-shootings

Stem Education Coalition

Stony Brook University-SUNY’s reach extends from its 1,039-acre campus on Long Island’s North Shore–encompassing the main academic areas, an 8,300-seat stadium and sports complex and Stony Brook Medicine–to Stony Brook Manhattan, a Research and Development Park, four business incubators including one at Calverton, New York, and the Stony Brook Southampton campus on Long Island’s East End. Stony Brook also co-manages Brookhaven National Laboratory, joining Princeton, the University of Chicago, Stanford, and the University of California on the list of major institutions involved in a research collaboration with a national lab.

And Stony Brook is still growing. To the students, the scholars, the health professionals, the entrepreneurs and all the valued members who make up the vibrant Stony Brook community, this is a not only a great local and national university, but one that is making an impact on a global scale.

## From The University of Chicago: “Black hole collisions could help us measure how fast the universe is expanding”

From The University of Chicago

8.15.22
Louise Lerner

UChicago astronomers propose ‘spectral siren’ method to understand evolution of the universe.

In a new study, two University of Chicago astrophysicists laid out a method for how to use pairs of colliding black holes (shown as an artist’s rendition above) to measure how fast our universe is expanding.
Illustration credit: Simulating eXtreme Spacetimes (SXS) Project

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LIGO-VIRGO-KAGRA-GEO 600-LIGO-India-ESA/NASA LISA

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A black hole is usually where information goes to disappear—but scientists may have found a trick to use its last moments to tell us about the history of the universe.

In a new study [Physical Review Letters (below)], two University of Chicago astrophysicists laid out a method for how to use pairs of colliding black holes to measure how fast our universe is expanding—and thus understand how the universe evolved, what it is made out of, and where it’s going.

In particular, the scientists think the new technique, which they call a “spectral siren,” may be able to tell us about the otherwise elusive “teenage” years of the universe.

A cosmic ruler

A major ongoing scientific debate is exactly how fast the universe is expanding—a number called the Hubble constant. The different methods available so far yield slightly different answers, and scientists are eager to find alternate ways to measure this rate. Checking the accuracy of this number is especially important because it affects our understanding of fundamental questions like the age, history and makeup of the universe.

The new study offers a way to make this calculation, using special detectors that pick up the cosmic echoes of black hole collisions.

Occasionally, two black holes will slam into each other—an event so powerful that it literally creates a ripple in space-time that travels across the universe. Here on Earth, the U.S. Laser Interferometer Gravitational-Wave Observatory (LIGO) and the Italian observatory Virgo can pick up those ripples, which are called gravitational waves.

Over the past few years, LIGO and Virgo have collected the readings from almost 100 pairs of black holes colliding.

The signal from each collision contains information about how massive the black holes were. But the signal has been traveling across space, and during that time the universe has expanded, which changes the properties of the signal. “For example, if you took a black hole and put it earlier in the universe, the signal would change and it would look like a bigger black hole than it really is,” explained UChicago astrophysicist Daniel Holz, one of the two authors on the paper.

If scientists can figure out a way to measure how that signal changed, they can calculate the expansion rate of the universe. The problem is calibration: How do they know how much it changed from the original?

In their new paper, Holz and first author Jose María Ezquiaga suggest that they can use our newfound knowledge about the whole population of black holes as a calibration tool. For example, current evidence suggests that most of the detected black holes have between five and 40 times the mass of our sun. “So we measure the masses of the nearby black holes and understand their features, and then we look further away and see how much those further ones appear to have shifted,” said Ezquiaga, a NASA Einstein Postdoctoral Fellow and Kavli Institute for Cosmological Physics Fellow working with Holz at UChicago. “And this gives you a measure of the expansion of the universe.”

The authors dub it the “spectral siren” method, a new approach to the ‘standard siren’ method which Holz and collaborators have been pioneering. (The name is a reference to the ‘standard candle’ methods also used in astronomy.)

The scientists are excited because in the future, as LIGO’s capabilities expand, the method may provide a unique window into the “teenage” years of the universe—about 10 billion years ago—that are hard to study with other methods.

Researchers can use the cosmic microwave background [CMB] to look at the very earliest moments of the universe, and they can look around at galaxies near our own galaxy to study the universe’s more recent history.

But the in-between period is harder to reach, and it’s an area of special scientific interest.

“It’s around that time that we switched from dark matter being the predominant force in the universe to dark energy taking over, and we are very interested in studying this critical transition,” said Ezquiaga.

The other advantage of this method, the authors said, is that there are fewer uncertainties created by gaps in our scientific knowledge. “By using the entire population of black holes, the method can calibrate itself, directly identifying and correcting for errors,” Holz said. The other methods used to calculate the Hubble constant rely on our current understanding of the physics of stars and galaxies, which involves a lot of complicated physics and astrophysics. This means the measurements might be thrown off quite a bit if there’s something we don’t yet know.

By contrast, this new black hole method relies almost purely on Einstein’s theory of gravity, which is well-studied and has stood up against all the ways scientists have tried to test it so far.

The more readings they have from all black holes, the more accurate this calibration will be. “We need preferably thousands of these signals, which we should have in a few years, and even more in the next decade or two,” said Holz. “At that point it would be an incredibly powerful method to learn about the universe.”

Science paper:
Physical Review Letters

five-ways-keep-your-child-safe-school-shootings

Stem Education Coalition

The University of Chicago is an urban research university that has driven new ways of thinking since 1890. Our commitment to free and open inquiry draws inspired scholars to our global campuses, where ideas are born that challenge and change the world.

We empower individuals to challenge conventional thinking in pursuit of original ideas. Students in the College develop critical, analytic, and writing skills in our rigorous, interdisciplinary core curriculum. Through graduate programs, students test their ideas with University of Chicago scholars, and become the next generation of leaders in academia, industry, nonprofits, and government.

University of Chicago research has led to such breakthroughs as discovering the link between cancer and genetics, establishing revolutionary theories of economics, and developing tools to produce reliably excellent urban schooling. We generate new insights for the benefit of present and future generations with our national and affiliated laboratories: DOE’s Argonne National Laboratory, DOE’s Fermi National Accelerator Laboratory , and the Marine Biological Laboratory in Woods Hole, Massachusetts.
The University of Chicago is enriched by the city we call home. In partnership with our neighbors, we invest in Chicago’s mid-South Side across such areas as health, education, economic growth, and the arts. Together with our medical center, we are the largest private employer on the South Side.

In all we do, we are driven to dig deeper, push further, and ask bigger questions—and to leverage our knowledge to enrich all human life. Our diverse and creative students and alumni drive innovation, lead international conversations, and make masterpieces. Alumni and faculty, lecturers and postdocs go on to become Nobel laureates, CEOs, university presidents, attorneys general, literary giants, and astronauts. The University of Chicago is a private research university in Chicago, Illinois. Founded in 1890, its main campus is located in Chicago’s Hyde Park neighborhood. It enrolled 16,445 students in Fall 2019, including 6,286 undergraduates and 10,159 graduate students. The University of Chicago is ranked among the top universities in the world by major education publications, and it is among the most selective in the United States.

The university is composed of one undergraduate college and five graduate research divisions, which contain all of the university’s graduate programs and interdisciplinary committees. Chicago has eight professional schools: the Law School, the Booth School of Business, the Pritzker School of Medicine, the School of Social Service Administration, the Harris School of Public Policy, the Divinity School, the Graham School of Continuing Liberal and Professional Studies, and the Pritzker School of Molecular Engineering. The university has additional campuses and centers in London, Paris, Beijing, Delhi, and Hong Kong, as well as in downtown Chicago.

University of Chicago scholars have played a major role in the development of many academic disciplines, including economics, law, literary criticism, mathematics, religion, sociology, and the behavioralism school of political science, establishing the Chicago schools in various fields. Chicago’s Metallurgical Laboratory produced the world’s first man-made, self-sustaining nuclear reaction in Chicago Pile-1 beneath the viewing stands of the university’s Stagg Field. Advances in chemistry led to the “radiocarbon revolution” in the carbon-14 dating of ancient life and objects. The university research efforts include administration of DOE’s Fermi National Accelerator Laboratory and DOE’s Argonne National Laboratory, as well as the U Chicago Marine Biological Laboratory in Woods Hole, Massachusetts (MBL). The university is also home to the University of Chicago Press, the largest university press in the United States. The Barack Obama Presidential Center is expected to be housed at the university and will include both the Obama presidential library and offices of the Obama Foundation.

The University of Chicago’s students, faculty, and staff have included 100 Nobel laureates as of 2020, giving it the fourth-most affiliated Nobel laureates of any university in the world. The university’s faculty members and alumni also include 10 Fields Medalists, 4 Turing Award winners, 52 MacArthur Fellows, 26 Marshall Scholars, 27 Pulitzer Prize winners, 20 National Humanities Medalists, 29 living billionaire graduates, and have won eight Olympic medals.

The University of Chicago is enriched by the city we call home. In partnership with our neighbors, we invest in Chicago’s mid-South Side across such areas as health, education, economic growth, and the arts. Together with our medical center, we are the largest private employer on the South Side.

Research

According to the National Science Foundation, University of Chicago spent \$423.9 million on research and development in 2018, ranking it 60th in the nation. It is classified among “R1: Doctoral Universities – Very high research activity” and is a founding member of the Association of American Universities and was a member of the Committee on Institutional Cooperation from 1946 through June 29, 2016, when the group’s name was changed to the Big Ten Academic Alliance. The University of Chicago is not a member of the rebranded consortium, but will continue to be a collaborator.

The university operates more than 140 research centers and institutes on campus. Among these are the Oriental Institute—a museum and research center for Near Eastern studies owned and operated by the university—and a number of National Resource Centers, including the Center for Middle Eastern Studies. Chicago also operates or is affiliated with several research institutions apart from the university proper. The university manages DOE’s Argonne National Laboratory, part of the United States Department of Energy’s national laboratory system, and co-manages DOE’s Fermi National Accelerator Laboratory, a nearby particle physics laboratory, as well as a stake in the Apache Point Observatory in Sunspot, New Mexico.
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Apache Point Observatory, near Sunspot, New Mexico Altitude 2,788 meters (9,147 ft).
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Faculty and students at the adjacent Toyota Technological Institute at Chicago collaborate with the university. In 2013, the university formed an affiliation with the formerly independent Marine Biological Laboratory in Woods Hole, Mass. Although formally unrelated, the National Opinion Research Center is located on Chicago’s campus.

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