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  • richardmitnick 9:00 am on September 12, 2019 Permalink | Reply
    Tags: Black Holes, , , University of Hawai’i   

    From University of Hawaii via Science Alert: “Black Holes May Hide Cores of Pure Dark Energy That Keep The Universe Expanding 

    From University of Hawaii

    via

    ScienceAlert

    Science Alert

    12 SEP 2019
    MIKE MCRAE

    1
    (Just_Super/iStock)

    A fifty-year-old hypothesis predicting the existence of bodies dubbed Generic Objects of Dark Energy (GEODEs) is getting a second look in light of a proposed correction to assumptions we use to model the way our Universe expands.

    If this new version of a classic cosmological model is correct, some black holes could hide cores of pure dark energy, pushing our Universe apart at the seams.

    University of Hawai’i astrophysicist Kevin Croker and mathematician Joel Weiner teamed up to challenge the broadly accepted notion that when it comes to the Universe’s growing waistline, its contents are largely irrelevant.

    “For 80 years, we’ve generally operated under the assumption that the Universe, in broad strokes, was not affected by the particular details of any small region,” said Croker.

    “It is now clear that general relativity can observably connect collapsed stars – regions the size of Honolulu – to the behaviour of the Universe as a whole, over a thousand billion billion times larger.”

    Not only could this alternative interpretation of fundamental physics change how we understand the Universe’s expansion, but we might need to also consider how that growth might affect compact objects like the cores of collapsing stars.

    The fact that space has been steadily adding real estate for the past 13.8 billion years is by now a widely accepted feature of our Universe.

    The set of equations we use to describe this expansion was first put to paper just under a century ago by the Russian physicist Alexander Friedmann. They provided a solution to Einstein’s theory of general relativity that now underpins our big picture model of cosmology.

    As useful as Friedmann’s equations have been, they’re based on the assumption that any matter floating around inside this expanding space is more or less made of the same kind of stuff, and spread out fairly evenly.

    This means we tend to ignore the swirls of stars and galaxies – just like we might not include ducks in the hydrodynamics of a lake.

    But Croker and Weiner wonder what might happen to space and the objects it contains if we made some reasonable changes to the assumptions that inform these equations.

    The consequences aren’t trivial.

    According to their adjusted model, the averaged contributions of our metaphorical ducks might affect the lake’s water after all.

    What’s more, the lake’s expansion would also affect how the ducks swim, causing them to lose or gain energy depending on their species.

    Theoretically, this interpretation would mean we need to take the Universe’s growth into account when describing certain phenomena, such as the death of a star.

    In 1966, a Russian physicist named Erast Gliner considered how some densities of space close to the Big Bang might look – in terms of relativity – like a vacuum that could counter the effects of gravity.

    His solution would look like a black hole from the outside. But inside would be a bubble of energy shoving against the surrounding Universe.

    Half a century later, astrophysicists are on the hunt for just such a pushing power that might be responsible for the Universe’s expansion picking up speed over time.

    Today we refer to this undescribed force as dark energy, but could Gliner’s pockets of relativistic nothingness be the source of our Universe’s accelerating expansion?

    Based on Croker and Weiner’s work, if just a few ancient stars were to have collapsed into Gliner’s GEODEs instead of the more typical puckered space of a singularity, their average effect on expanding space would look just like dark energy.

    The pair go further, applying their corrected model to the first observation of gravitational waves from a black hole collision as measured by LIGO.

    To make the math fit, it’s assumed the stars that formed the merging black holes formed in a low-metallicity environment, which makes them somewhat rare.

    Technically, the energy of a GEODE should evolve as the Universe grows, effectively compacting as a cosmological equivalent of a ‘blueshift’.

    If the merging black holes were GEODEs, according to the researchers, there’d be no need to assume the black holes were born in an unusual patch of space.

    “What we have shown is that if GEODEs do exist, then they can easily give rise to observed phenomena that presently lack convincing explanations,” the researchers said.

    “We anticipate numerous other observational consequences of a GEODE scenario, including many ways to exclude it. We’ve barely begun to scratch the surface.”

    Testing assumptions like these is a vital part of physics. We’re a long way off including GEODEs in any official astrophysical zoo of weird objects, but it’s possible these could be the dark hearts of the Universe we’ve been looking for.

    This research was published in The Astrophysical Journal.

    See the full article here .

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  • richardmitnick 12:05 pm on September 8, 2019 Permalink | Reply
    Tags: , , , , Black Holes, , Craig Callender, , Second law of thermodynamics,   

    From WIRED: “Are We All Wrong About Black Holes?” 

    Wired logo

    From WIRED

    09.08.2019
    Brendan Z. Foster

    1
    Craig Callender, a philosopher of science at the University of California San Diego, argues that the connection between black holes and thermodynamics is less ironclad than assumed.Photograph: Peggy Peattie/Quanta Magazine

    In the early 1970s, people studying general relativity, our modern theory of gravity, noticed rough similarities between the properties of black holes and the laws of thermodynamics. Stephen Hawking proved that the area of a black hole’s event horizon—the surface that marks its boundary—cannot decrease. That sounded suspiciously like the second law of thermodynamics, which says entropy—a measure of disorder—cannot decrease.

    Yet at the time, Hawking and others emphasized that the laws of black holes only looked like thermodynamics on paper; they did not actually relate to thermodynamic concepts like temperature or entropy.

    Then in quick succession, a pair of brilliant results—one by Hawking himself—suggested that the equations governing black holes were in fact actual expressions of the thermodynamic laws applied to black holes. In 1972, Jacob Bekenstein argued that a black hole’s surface area was proportional to its entropy [Physical Review D], and thus the second law similarity was a true identity. And in 1974, Hawking found that black holes appear to emit radiation [Nature]—what we now call Hawking radiation—and this radiation would have exactly the same “temperature” in the thermodynamic analogy.

    This connection gave physicists a tantalizing window into what many consider the biggest problem in theoretical physics—how to combine quantum mechanics, our theory of the very small, with general relativity. After all, thermodynamics comes from statistical mechanics, which describes the behavior of all the unseen atoms in a system. If a black hole is obeying thermodynamic laws, we can presume that a statistical description of all its fundamental, indivisible parts can be made. But in the case of a black hole, those parts aren’t atoms. They must be a kind of basic unit of gravity that makes up the fabric of space and time.

    Modern researchers insist that any candidate for a theory of quantum gravity must explain how the laws of black hole thermodynamics arise from microscopic gravity, and in particular, why the entropy-to-area connection happens. And few question the truth of the connection between black hole thermodynamics and ordinary thermodynamics.

    But what if the connection between the two really is little more than a rough analogy, with little physical reality? What would that mean for the past decades of work in string theory, loop quantum gravity, and beyond? Craig Callender, a philosopher of science at the University of California, San Diego, argues that the notorious laws of black hole thermodynamics may be nothing more than a useful analogy stretched too far [Phil Sci]. The interview has been condensed and edited for clarity.

    Why did people ever think to connect black holes and thermodynamics?

    Callender: In the early ’70s, people noticed a few similarities between the two. One is that both seem to possess an equilibrium-like state. I have a box of gas. It can be described by a small handful of parameters—say, pressure, volume, and temperature. Same thing with a black hole. It might be described with just its mass, angular momentum, and charge. Further details don’t matter to either system.

    Nor does this state tell me what happened beforehand. I walk into a room and see a box of gas with stable values of pressure, volume and temperature. Did it just settle into that state, or did that happen last week, or perhaps a million years ago? Can’t tell. The black hole is similar. You can’t tell what type of matter fell in or when it collapsed.

    The second feature is that Hawking proved that the area of black holes is always non-decreasing. That reminds one of the thermodynamic second law, that entropy always increases. So both systems seem to be heading toward simply described states.

    Now grab a thermodynamics textbook, locate the laws, and see if you can find true statements when you replace the thermodynamic terms with black hole variables. In many cases you can, and the analogy improves.

    Hawking then discovers Hawking radiation, which further improves the analogy. At that point, most physicists start claiming the analogy is so good that it’s more than an analogy—it’s an identity! That’s a super-strong and surprising claim. It says that black hole laws, most of which are features of the geometry of space-time, are somehow identical to the physical principles underlying the physics of steam engines.

    Because the identity plays a huge role in quantum gravity, I want to reconsider this identity claim. Few in the foundations of physics have done so.

    So what’s the statistical mechanics for black holes?

    Well, that’s a good question. Why does ordinary thermodynamics hold? Well, we know that all these macroscopic thermodynamic systems are composed of particles. The laws of thermodynamics turn out to be descriptions of the most statistically likely configurations to happen from the microscopic point of view.

    Why does black hole thermodynamics hold? Are the laws also the statistically most likely way for black holes to behave? Although there are speculations in this direction, so far we don’t have a solid microscopic understanding of black hole physics. Absent this, the identity claim seems even more surprising.

    What led you to start thinking about the analogy?

    Many people are worried about whether theoretical physics has become too speculative. There’s a lot of commentary about whether holography, the string landscape—all sorts of things—are tethered enough to experiment. I have similar concerns. So my former Ph.D. student John Dougherty and I thought, where did it all start?

    To our mind a lot of it starts with this claimed identity between black holes and thermodynamics. When you look in the literature, you see people say, “The only evidence we have for quantum gravity, the only solid hint, is black hole thermodynamics.”

    If that’s the main thing we’re bouncing off for quantum gravity, then we ought to examine it very carefully. If it turns out to be a poor clue, maybe it would be better to spread our bets a little wider, instead of going all in on this identity.

    What problems do you see with treating a black hole as a thermodynamic system?

    I see basically three. The first problem is: What is a black hole? People often think of black holes as just kind of a dark sphere, like in a Hollywood movie or something; they’re thinking of it like a star that collapsed. But a mathematical black hole, the basis of black hole thermodynamics, is not the material from the star that’s collapsed. That’s all gone into the singularity. The black hole is what’s left.

    The black hole isn’t a solid thing at the center. The system is really the entire space-time.

    Yes, it’s this global notion for which black hole thermodynamics was developed, in which case the system really is the whole space-time.

    Here is another way to think about the worry. Suppose a star collapses and forms an event horizon. But now another star falls past this event horizon and it collapses, so it’s inside the first. You can’t think that each one has its own little horizon that is behaving thermodynamically. It’s only the one horizon.

    Here’s another. The event horizon changes shape depending on what’s about to be thrown into it. It’s clairvoyant. Weird, but there is nothing spooky here so long as we remember that the event horizon is only defined globally. It’s not a locally observable quantity.

    The picture is more counterintuitive than people usually think. To me, if the system is global, then it’s not at all like thermodynamics.

    The second objection is: Black hole thermodynamics is really a pale shadow of thermodynamics. I was surprised to see the analogy wasn’t as thorough as I expected it to be. If you grab a thermodynamics textbook and start replacing claims with their black hole counterparts, you will not find the analogy goes that deep.


    Craig Callender explains why the connection between black holes and thermodynamics is little more than an analogy.

    For instance, the zeroth law of thermodynamics sets up the whole theory and a notion of equilibrium — the basic idea that the features of the system aren’t changing. And it says that if one system is in equilibrium with another — A with B, and B with C — then A must be in equilibrium with C. The foundation of thermodynamics is this equilibrium relation, which sets up the meaning of temperature.

    The zeroth law for black holes is that the surface gravity of a black hole, which measures the gravitational acceleration, is a constant on the horizon. So that assumes temperature being constant is the zeroth law. That’s not really right. Here we see a pale shadow of the original zeroth law.

    The counterpart of equilibrium is supposed to be “stationary,” a technical term that basically says the black hole is spinning at a constant rate. But there’s no sense in which one black hole can be “stationary with” another black hole. You can take any thermodynamic object and cut it in half and say one half is in equilibrium with the other half. But you can’t take a black hole and cut it in half. You can’t say that this half is stationary with the other half.

    Here’s another way in which the analogy falls flat. Black hole entropy is given by the black hole area. Well, area is length squared, volume is length cubed. So what do we make of all those thermodynamic relations that include volume, like Boyle’s law? Is volume, which is length times area, really length times entropy? That would ruin the analogy. So we have to say that volume is not the counterpart of volume, which is surprising.

    The most famous connection between black holes and thermodynamics comes from the notion of entropy. For normal stuff, we think of entropy as a measure of the disorder of the underlying atoms. But in the 1970s, Jacob Bekenstein said that the surface area of a black hole’s event horizon is equivalent to entropy. What’s the basis of this?

    This is my third concern. Bekenstein says, if I throw something into a black hole, the entropy vanishes. But this can’t happen, he thinks, according to the laws of thermodynamics, for entropy must always increase. So some sort of compensation must be paid when you throw things into a black hole.

    Bekenstein notices a solution. When I throw something into the black hole, the mass goes up, and so does the area. If I identify the area of the black hole as the entropy, then I’ve found my compensation. There is a nice deal between the two—one goes down while the other one goes up—and it saves the second law.

    When I saw that I thought, aha, he’s thinking that not knowing about the system anymore means its entropy value has changed. I immediately saw that this is pretty objectionable, because it identifies entropy with uncertainty and our knowledge.

    There’s a long debate in the foundations of statistical mechanics about whether entropy is a subjective notion or an objective notion. I’m firmly on the side of thinking it’s an objective notion. I think trees unobserved in a forest go to equilibrium regardless of what anyone knows about them or not, that the way heat flows has nothing to do with knowledge, and so on.

    Chuck a steam engine behind the event horizon. We can’t know anything about it apart from its mass, but I claim it can still do as much work as before. If you don’t believe me, we can test this by having a physicist jump into the black hole and follow the steam engine! There is only need for compensation if you think that what you can no longer know about ceases to exist.

    Do you think it’s possible to patch up black hole thermodynamics, or is it all hopeless?

    My mind is open, but I have to admit that I’m deeply skeptical about it. My suspicion is that black hole “thermodynamics” is really an interesting set of relationships about information from the point of view of the exterior of the black hole. It’s all about forgetting information.

    Because thermodynamics is more than information theory, I don’t think there’s a deep thermodynamic principle operating through the universe that causes black holes to behave the way they do, and I worry that physics is all in on it being a great hint for quantum gravity when it might not be.

    Playing the role of the Socratic gadfly in the foundations of physics is sometimes important. In this case, looking back invites a bit of skepticism that may be useful going forward.

    See the full article here .

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  • richardmitnick 11:50 am on August 24, 2019 Permalink | Reply
    Tags: , , , Black Holes, , ,   

    From Ethan Siegel: “Ask Ethan: Can Black Holes And Dark Matter Interact?” 

    From Ethan Siegel
    Aug 24, 2019

    1.
    A by now iconic illustration of an active black hole, one that accretes matter and accelerates a portion of it outwards in two perpendicular jets. The normal matter undergoing an acceleration like this describes how quasars work extremely well. The matter that falls into a black hole, of any variety, will be responsible for additional growth in both mass and event horizon size for the black hole, whether it’s normal matter or dark matter. (MARK A. GARLICK)

    Black holes are regions of extreme gravity, but dark matter barely interacts at all. Do they play well together?

    Black holes are some of the most extreme objects in the Universe: the only locations where there’s so much energy in a tiny volume of space that an event horizon gets created. When they form, atoms, nuclei, and even fundamental particles themselves are crushed down to an arbitrarily small volume — to a singularity — in our three-dimensional space. At the same time, everything that falls past the event horizon is forever doomed, simply adding to the black hole’s gravitational pull. What does that mean for dark matter? Patreon supporter kilobug asks:

    “How does dark matter interact with black holes? Does it get sucked into the singularity like normal matter, contributing to the mass of the black hole? If so, when the black hole evaporates through Hawking radiation, what happens to [it]?”

    To answer this, we have to start at the beginning: with what a black hole actually is.

    Here on Earth, if you want to send something into space, you need to overcome the Earth’s gravitational pull. The way we normally think about this is in terms of balancing two forms of energy: the gravitational potential energy provided by the Earth itself at its surface, compared with the kinetic energy you’d have to add to your payload to escape from Earth’s gravitational pull.

    If you balance these energies, you can derive your escape velocity: how fast you’d have to make an object go for it to eventually achieve an arbitrarily large distance away from the Earth. Even though the Earth has an atmosphere, providing resistance to that motion and requiring us to impart even more energy to a payload than the escape velocity would imply, escape velocity is still a useful physical concept for us to consider.

    2
    If the Earth had no atmosphere, then firing a cannonball at a particular speed would be enough to determine whether it fell back to Earth (A, B), remained in a stable orbit around Earth (C, D), or escaped from Earth’s gravitational pull (E). For all objects that aren’t black holes, all five of these trajectories are possible. For objects that are black holes, trajectories like C, D, and E are impossible inside the event horizon. (WIKIMEDIA COMMONS USER BRIAN BRONDEL)

    For our planet, that calculated speed — or escape velocity — is somewhere around 25,000 mph (or 11.2 km/s), which the rockets we’ve developed on Earth can actually achieve. Multi-stage rockets have been launching spacecraft beyond the reach of Earth’s gravity since the 1960s, and out of even the Sun’s gravitational reach since the 1970s. But this is still only possible because of how far away we are from the surface of the Sun at the location of Earth’s orbit.

    3
    The very first launch from NASA’s Cape Kennedy space center was of the Apollo 4 rocket. Although it accelerated no faster than a sportscar, the key to its success was that the acceleration was sustained for so long, enabling payloads to escape Earth’s atmosphere and enter orbit. Eventually, multi-stage rockets would enable humans to escape the gravitational pull of the Earth entirely. The Saturn V rockets later took humanity to the Moon. (NASA)

    If we were instead on the surface of the Sun, the speed we’d need to achieve to escape the Sun’s gravitational pull — escape velocity — would be much greater: about 55 times as great, or 617.5 km/s. When our Sun dies, it will contract down to a white dwarf, of about 50% the Sun’s current mass but only the physical size of Earth. In this case, its escape velocity will be about 4.570 km/s, or about 1.5% the speed of light.

    4
    Sirius A and B, a normal (Sun-like) star and a white dwarf star. There are stars that get their energy from gravitational contraction, but they are the white dwarfs, which are millions of times fainter than the stars we’re more familiar with. It wasn’t until we understood nuclear fusion that we began to comprehend how stars shine. (NASA, ESA AND G. BACON (STScI))

    There’s a valuable lesson in comparing the Sun, as it is today, to the Sun’s far-future fate as a white dwarf. As more and more mass gets concentrated into a small region of space, the speed required to escape this object rises. If you allowed that mass density to rise, either by compressing it into a smaller volume or adding more mass to the same volume, your escape velocity would get closer and closer to the speed of light.

    That’s the key limit. Once your escape velocity at the object’s surface reaches or exceeds the speed of light, it isn’t just that light can’t get out, it’s mandatory (in General Relativity) that everything within that object inevitably collapses down to and/or falls into the central singularity. The reason is simple: the fabric of space itself falls towards the central regions faster than the speed of light. Your speed limit is less than the speed at which the space beneath your feet moves, and hence, there’s no escape.

    5
    Both inside and outside the event horizon, space flows like either a moving walkway or a waterfall, depending on how you want to visualize it. At the event horizon, even if you ran (or swam) at the speed of light, there would be no overcoming the flow of spacetime, which drags you into the singularity at the center. Outside the event horizon, though, other forces (like electromagnetism) can frequently overcome the pull of gravity, causing even infalling matter to escape. (ANDREW HAMILTON / JILA / UNIVERSITY OF COLORADO)

    So if you’re at any point away from a central singularity and you’re trying to hold a more distant object up against gravitational collapse, you can’t do it; collapse is inevitable. And the most common way to crest past this limit in the first place is simple: just begin with a star more massive than about 20–40 times the mass of our Sun.

    Like all true stars, it lives its life by burning through the nuclear fuel in its core region. When that fuel gets used up, the center implodes under its own gravity, creating a catastrophic supernova explosion. The outer layers are expelled, but the central region, being massive enough, collapses to a black hole. These “stellar mass” black holes, spanning an approximate range from 8-to-40 solar masses, will grow over time, as they consume any matter or energy that dares to venture too nearby. Even if you move at the speed of light when you cross the event horizon, you’ll never get out again.

    6
    The anatomy of a very massive star throughout its life, culminating in a Type II Supernova. At the end of its life, if the core is massive enough, the formation of a black hole is absolutely unavoidable. (NICOLE RAGER FULLER FOR THE NSF)

    In fact, once you cross the event horizon, it’s an inevitability that you’ll encounter the central singularity. And from the perspective of an outside observer, once you cross the event horizon’s boundary, all you do is add to the mass, energy, charge, and angular momentum of the black hole.

    From outside a black hole, we have no way to gain information about what it was initially composed of. A (neutral) black hole made from protons and electrons, neutrons, dark matter, or even antimatter would all appear identical. In fact, there are only three properties at all that we can observe about a black hole from an external location:

    1.its mass,
    2.its electric charge,
    3.and its angular momentum (or intrinsic rotational spin).

    7
    An iconic illustration of heavily curved spacetime, outside the event horizon of a black hole. As you get closer and closer to the mass’s location, space becomes more severely curved, eventually leading to a location from within which even light cannot escape: the event horizon. The radius of that location is set by the mass, charge, and angular momentum of the black hole, the speed of light, and the laws of General Relativity alone. (PIXABAY USER JOHNSONMARTIN)

    Dark matter, even though we know what it is, is known to have mass but not electric charge.

    Fritz Zwicky discovered Dark Matter when observing the movement of the Coma Cluster., Vera Rubin a Woman in STEM denied the Nobel, did most of the work on Dark Matter.

    Fritz Zwicky from http:// palomarskies.blogspot.com

    Coma cluster via NASA/ESA Hubble

    Astronomer Vera Rubin at the Lowell Observatory in 1965, worked on Dark Matter (The Carnegie Institution for Science)


    Vera Rubin measuring spectra, worked on Dark Matter (Emilio Segre Visual Archives AIP SPL)


    Vera Rubin, with Department of Terrestrial Magnetism (DTM) image tube spectrograph attached to the Kitt Peak 84-inch telescope, 1970. https://home.dtm.ciw.edu The LSST, or Large Synoptic Survey Telescope is to be named the Vera C. Rubin Observatory by an act of the U.S. Congress.

    LSST telescope, currently under construction at Cerro Pachón Chile, a 2,682-meter-high mountain in Coquimbo Region, in northern Chile, alongside the existing Gemini South and Southern Astrophysical Research Telescopes, altitude 2,663 m (8,737 ft),

    The angular momentum it adds to the black hole is entirely dependent on its initial infalling trajectory. If you were interested in other quantum numbers — for example, because you were thinking about the black hole information paradox — you’d be chagrined to learn that dark matter doesn’t have them.

    Dark matter has no color charge, baryon number, lepton number, lepton family number, etc. And because black holes form from the deaths of supermassive stars (i.e., normal, baryonic matter), the initial composition of a newly-formed black hole is always approximately 100% normal matter and 0% dark matter. Even though there’s no definitive way to tell what black holes are made of from the outside alone, we’ve witnessed the direct formation of a black hole from a progenitor star; no dark matter was involved.

    8
    The visible/near-IR photos from Hubble show a massive star, about 25 times the mass of the Sun, that has winked out of existence, with no supernova or other explanation. Direct collapse is the only reasonable candidate explanation, and is one known way, in addition to supernovae or neutron star mergers, to form a black hole for the first time. (NASA/ESA/C. KOCHANEK (OSU)). Two different cameras on Hubble. Image on the left is from WFPC2. Image on the right is from WFC3. Very important and Ethan makes no comment about that.

    NASA/Hubble WFPC2. No longer in service.

    NASA/ESA Hubble WFC3

    There’s a good reason to believe that dark matter doesn’t play a role in the initial formation of black holes, but will play a role in the growth of black holes over time: from the ways it does and does not interact.

    Remember that dark matter interacts only gravitationally, unlike normal matter, which interacts via the gravitational, weak, electromagnetic and strong forces. Yes, there’s perhaps five times as much dark matter total in large galaxies and clusters as there is normal matter, but that’s summed up over the entire huge halo. In a typical galaxy, that dark matter halo extends for a million light-years or more, spherically, in all directions. Contrast that with the normal matter, which is concentrated in a disk that occupies just 0.01% the dark matter’s volume.

    9
    A clumpy dark matter halo with varying densities and a very large, diffuse structure, as predicted by simulations, with the luminous part of the galaxy shown for scale. Since dark matter is everywhere, it should affect the motion of everything around it. The volume occupied by a typical dark matter halo is around 10,000 times as great as the volume occupied by the normal matter. (NASA, ESA, AND T. BROWN AND J. TUMLINSON (STScI))

    Black holes tend to form in the inner regions of the galaxy, where the normal matter is dominant over dark matter. Consider just the region of space where we’re located: around our Sun. If we drew a sphere that was 100 AU in radius (where one AU is the distance of the Earth from the Sun) around our Solar System, we’d enclose all the planets, moons, asteroids and pretty much the entire Kuiper belt. We’d also enclose a fair amount of dark matter in that volume.

    Quantitatively, though, the baryonic mass — the normal matter — inside this sphere would be dominated by our Sun, and would weigh about 2 × 10³⁰ kg. (Everything else, combined, adds just another 0.2% to that total.) On the other hand, the total amount of dark matter in that same sphere? Only about 1 × 10¹⁹ kg, or just 0.0000000005% the mass of the normal matter in that same region. All the dark matter combined is about the same mass as a modest asteroid like Juno.

    10
    In the solar system, to a first approximation, the Sun determines the orbits of the planets. To a second approximation, all the other masses (like planets, moons, asteroids, etc.) play a large role. But to add in dark matter, we’d have to get incredibly sensitive: the entire contribution of all the dark matter within 100 AU of the Sun is about the same contribution as the mass of Juno, the asteroid belt’s 11th largest asteroid (by volume). (WIKIPEDIA USER DREG743)

    Over time, dark matter and normal matter both will collide with this black hole, getting absorbed and adding to its mass. The vast majority of black hole mass growth will come from normal matter and not dark matter, although at some point, about 10²² years into the future, the rate of black hole decay will finally surpass the rate of black hole growth.

    The Hawking radiation process results in the emission of particles and photons from outside the black hole’s event horizon, conserving all the energy, charge and angular momentum from the black hole’s insides. Perhaps the information encoded on the surface is somehow encoded in the radiation, too: this is the essence of the black hole information paradox.

    11
    Encoded on the surface of the black hole can be bits of information, proportional to the event horizon’s surface area. When the black hole decays, it decays to a state of thermal radiation. Whether that information survives and is encoded in the radiation or not, and if so, how, is not a question that our current theories can provide the answer to. (T.B. BAKKER / DR. J.P. VAN DER SCHAAR, UNIVERSITEIT VAN AMSTERDAM)

    This process may take anywhere from 10⁶⁷ to 10¹⁰⁰ years, depending on the black hole’s mass. But what comes out is simply thermal, blackbody radiation.

    This means that some dark matter will come out of black holes, but that’s expected to be completely independent of whether a substantial amount of dark matter went into the black hole in the first place. All a black hole has memory of, once things have fallen in, is a small set of quantum numbers, and the amount of dark matter that went into it isn’t one of them. What comes out, at least in terms of particle content, isn’t going to be the same as what you put in!

    12
    The event horizon of a black hole is a spherical or spheroidal region from which nothing, not even light, can escape. Although conventional blackbody radiation is emitted from outside the event horizon, it is unclear where, when, or how the entropy/information encoded on the surface behaves in a merger scenario. (NASA; DANA BERRY, SKYWORKS DIGITAL, INC.)

    If you do the math, you’ll find that black holes will use both normal matter and dark matter as a food source, but that normal matter will dominate the rate of growth of the black hole, even over long, cosmic timescales. When the Universe is more than a billion times as old as it is today, black holes will still owe more than 99% of their mass to normal matter, and less than 1% to dark matter.

    Dark matter is neither a good food source for black holes, nor is it (information-wise) an interesting one. What a black hole gains from eating dark matter is no different than what it gains from shining a flashlight into it. Only the mass/energy content, like you’d get from E = mc², matters. Black holes and dark matter do interact, but their effects are so small that even ignoring dark matter entirely still gives you a great description of black holes: past, present, and future.

    See the full article here .

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    “Starts With A Bang! is a blog/video blog about cosmology, physics, astronomy, and anything else I find interesting enough to write about. I am a firm believer that the highest good in life is learning, and the greatest evil is willful ignorance. The goal of everything on this site is to help inform you about our world, how we came to be here, and to understand how it all works. As I write these pages for you, I hope to not only explain to you what we know, think, and believe, but how we know it, and why we draw the conclusions we do. It is my hope that you find this interesting, informative, and accessible,” says Ethan

     
  • richardmitnick 9:16 am on August 6, 2019 Permalink | Reply
    Tags: , , , Black Holes, ,   

    From Science Alert: “Astronomers Just Found an Absolutely Gargantuan Black Hole The Mass of 40 Billion Suns” 

    ScienceAlert

    From Science Alert

    6 AUG 2019
    MICHELLE STARR

    1
    Abell 85. (NASA/CXC/SAO/A.Vikhlinin et al./SDSS)

    Black holes can get pretty big, but there’s a special class that is the biggest of the big, absolute yawning monster black holes. And astronomers seem to have found an absolute specimen, clocking in at 40 billion times the mass of the Sun.

    It’s at the centre of a galaxy called Holmberg 15A, a supergiant elliptical galaxy around 700 million light-years away, which in turn sits at the centre of the Abell 85 galaxy cluster.

    The object is one of the biggest black holes ever found, and the biggest found by tracking the movement of the stars around it.

    Previous calculations based on the dynamics of the galaxy and the cluster had resulted in Holm 15A* mass estimates of up to 310 billion times the mass of the Sun. However, these were all indirect measurements of the black hole. This new research marks the first direct measurement; the paper has been submitted to The Astrophysical Journal, and awaits peer review.

    “We use orbit-based, axisymmetric Schwarzschild models to analyse the stellar kinematics of Holm 15A from new high-resolution, wide-field spectral observations obtained with MUSE at the VLT.

    ESO MUSE on the VLT on Yepun (UT4)

    ESO VLT at Cerro Paranal in the Atacama Desert, •ANTU (UT1; The Sun ),
    •KUEYEN (UT2; The Moon ),
    •MELIPAL (UT3; The Southern Cross ), and
    •YEPUN (UT4; Venus – as evening star).
    elevation 2,635 m (8,645 ft) from above Credit J.L. Dauvergne & G. Hüdepohl atacama photo,

    We find a supermassive black hole (SMBH) with a mass of (4.0 ± 0.80) × 10^10 solar masses at the center of Holm 15A,” the researchers wrote in their paper.

    “This is the most massive black hole with a direct dynamical detection in the local Universe.”

    Now, it’s not the most massive black hole ever detected – that would be the quasar TON 618, which apparently has a black hole clocking in at 66 billion times the mass of the Sun, based on indirect measurements.

    But Holm 15A* is up there. At 40 billion solar masses, the black hole’s event horizon (also known as the Schwarzschild radius) would be huge, engulfing the orbits of all the planets in the Solar System, and then some.

    Quite a lot of some. Pluto is, on average, 39.5 astronomical units (AU) from the Sun. The heliopause – where the solar wind is no longer strong enough to push against interstellar space – is thought to be around 123 AU.

    At the mass of Holm 15A* as determined by the new paper, its Schwarzschild radius would be around 790 AU.

    Try to imagine something that size. The mind reels.

    In fact, it’s even bigger than other measurements taken by the researchers have suggested – which may explain why Holm 15A*’s mass has been difficult to pin down via indirect methods.

    “The SMBH of Holm 15A is not only the most massive one to date, it is also four to nine times larger than expected given the galaxy’s bulge stellar mass and the galaxy’s stellar velocity dispersion,” the researchers wrote.

    However, it fits the model of a collision between two early-type galaxies with depleted cores. That’s when there are not many stars in the core, based on what is expected from the number of stars in the outer regions of the galaxy.

    “We find that black hole masses in cored galaxies, including Holm 15A, scale inversely with the central stellar surface brightness and mass density, respectively,” the researchers wrote.

    They intend to continue studying the breathtaking beast, conducting more complex and detailed modelling and comparing their results against their observations, to try to figure out exactly how the black hole formed.

    In turn, that can help figure out how often such a merger takes place – and therefore how many such ultramassive black holes are yet to be discovered.

    See the full article here .


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  • richardmitnick 9:03 am on July 31, 2019 Permalink | Reply
    Tags: A0620-00- a binary star system 3300 light-years away- holds a dark secret: One of its stars isn’t a star at all but rather a black hole., , Along Unruh’s imaginary river a waterfall plunges at a supersonic speed—faster than the speed of sound in water., , , , Black Holes, Black holes were first theorized in 1784 by English clergyman and astronomer John Michell., Building black hole models, , Eight years later in 1980 Unruh realized that the equations of motion for sound in the waterfall analogy were identical to those describing light at the horizon of a black hole., , , In 1972 William “Bill” Unruh a physicist at the University of British Columbia Vancouver connected gravity to fluid dynamics in an analogy, Most physicists believe that black holes don’t truly destroy information and that information is preserved in Hawking radiation but that conjecture may be impossible to test directly., physicists use everything from water to exotic ultracold states of matter to mimic black holes, , Stephen Hawking revolutionized the field by proposing that that something could in fact escape from a black hole., Today, Unruh’s work was rediscovered as physicists began probing gravity theoretically and experimentally with analog models., What happens if a fellow fish goes over the falls? You- a blind fish- cannot know; you will never hear it scream because the waterfall will drag the sound down faster than it can travel up., William “Bill” Unruh: “Imagine that you are a blind fish and are also a physicist living in a river” Unruh wrote.   

    From Symmetry: “Gravity’s Waterfall” 

    Symmetry Mag
    From Symmetry

    07/30/19
    Daniel Garisto

    Physicists are using analog black holes to better understand gravity.

    1
    Illustration by Sandbox Studio, Chicago with Ariel Davis

    A0620-00, a binary star system 3300 light-years away, holds a dark secret: One of its stars isn’t a star at all, but a black hole. As far as we know, this is the black hole closest to our planet. Astronomers know it’s there only because its partner star appears to be dancing alone, pulled along by an invisible lead.

    In recent years, scientists have found ways to study black holes, listening to the gravitational waves they unleash when they collide, and even creating an image of one by combining information from radio telescopes around the world.

    MIT /Caltech Advanced aLigo


    VIRGO Collaboration

    But our knowledge of black holes remains limited. No one will ever be able to test a real one in a lab, and with current technology, it would take about 50 million years for a probe to reach A0620-00.

    So scientists are figuring out how to make do with substitutes—analogs to black holes that may hold answers to mysteries about gravity and quantum mechanics.

    Building black hole models

    In 1972, William “Bill” Unruh, a physicist at the University of British Columbia, Vancouver, connected gravity to fluid dynamics in an analogy: “Imagine that you are a blind fish, and are also a physicist, living in a river,” Unruh wrote.

    Along Unruh’s imaginary river, a waterfall plunges at a supersonic speed—faster than the speed of sound in water. What happens if a fellow fish goes over the falls? You, a blind fish, cannot know; you will never hear it scream because the waterfall will drag the sound down faster than it can travel up.

    Unruh used this piscine drama to explain a property of black holes: Like sound that passes over the edge of the supersonic waterfall, light that crosses the horizon of a black hole cannot escape.

    The analogy turned out to be more accurate than Unruh initially thought. Eight years later, in 1980, he realized that the equations of motion for sound in the waterfall analogy were identical to those describing light at the horizon of a black hole.

    At the time, his research drew little attention—it was cited just four times in the decade after it was published. But in the ’90s, Unruh’s work was rediscovered as physicists began probing gravity theoretically and experimentally with analog models.

    Today, physicists use everything from water to exotic ultracold states of matter to mimic black holes. Proponents of the analogs say that these models have confirmed theoretical predictions about black holes. But many physicists still doubt that analogs can predict what happens where gravity warps spacetime so violently.

    Black holes were first theorized in 1784, by English clergyman and astronomer John Michell, who calculated that for a large enough star, “all light emitted from such a body would be made to return towards it, by its own proper gravity.”

    The idea was mostly put aside until the 20th century, when Einstein’s general theory of relativity overturned the paradigm of Newtonian gravity. Luminaries like Karl Schwarzchild, Subrahmanyan Chandrasekhar and John Archibald Wheeler developed theory about these monsters from which nothing could escape. But in 1974, a young physicist named Stephen Hawking revolutionized the field by proposing that that something could, in fact, escape from a black hole.

    Due to random quantum fluctuations in the fabric of spacetime, pairs of virtual particles and antiparticles pop into existence all the time, throughout the universe. Most of the time, these pairs annihilate instantly, disappearing back into the void. But, Hawking theorized, the horizon of a black hole could separate a pair: One particle would be sucked in, while the other would zoom away as a now real particle.

    Because of a mathematical quirk in Hawking radiation, swallowed virtual particles effectively have negative energy. Black holes that gobble up these particles shrink. To an observer, Hawking radiation would look a lot like a black hole spitting up what it swallowed and getting smaller.

    However, Hawking radiation is random and carries no information about the inside of a black hole—remember that the emitted particle comes from just outside the horizon. This creates a paradox: Quantum mechanics rests on the premise that information is never destroyed, but if particles emitted as Hawking radiation are truly random, information would be lost forever.

    Most physicists believe that black holes don’t truly destroy information and that information is preserved in Hawking radiation, but that conjecture may be impossible to test directly. “The temperature of Hawking radiation is very small—it’s much smaller than the background radiation of the universe,” says Hai Son Nguyen, a physicist at the Institute of Nanotechnology of Lyon. “That’s why we will never be able to observe Hawking radiation from a real black hole.”

    What about something that behaved a lot like a black hole? In his 1980 paper, Unruh calculated that phonons—quantum units of sound analogous to photons, quantum units of light—would be the Hawking radiation emitted from his analog black hole.

    Unruh was initially bleak about the prospects of actually making such a measurement, calling it “an extremely slim possibility.” But as more physicists joined Unruh in theorizing about analogs to black holes in the ’90s, the possibility of measuring Hawking radiation became a difficult, but achievable goal.

    Over the waterfall

    There are many different analog models of black holes, but they all have one aspect in common: a horizon. Mathematically, horizons are defined as the boundary beyond which events cannot escape—like the edge of Unruh’s waterfall. Because they can separate pairs of particles, any horizon creates a form of Hawking radiation.

    “Understanding of the phenomenology associated with the presence of horizons in different analog systems provides hints about phenomena that might also be present in the gravitational realm,” writes Carlos Barceló, a theoretical physicist at the Astrophysical Institute of Andalucia.

    Often, it’s useful to start with a simple analog like water, says Silke Weinfurtner, a physicist at the University of Nottingham. It’s possible to create a horizon by running water quickly enough over an obstacle; if the conditions are just right, surface waves are thwarted at the obstacle.

    But to properly measure the smallest—quantum-level—effects of a black hole, you need a quantum analog. Bose-Einstein condensates, or BECs, are typically ultracold gases like rubidium that are ruled by quantum effects odd enough to qualify them as another state of matter. Subtle quantum effects like Hawking radiation hidden by the noise present in normal fluids become apparent in BECs.

    Analog black holes can even use light as a fluid. The fluid is made of quasiparticles called polaritons, which are the collective state of a photon that couples to an electric field. Enough polaritons behave as a quantum fluid of light. So when the flow of polaritons goes faster than the speed of sound in the polariton fluid, just like Unruh’s waterfall, a horizon forms. Hawking radiation from this fluid of light still comes in the form of phonons.

    Some black hole analogs are “optical” because their Hawking radiation comes in photons. In optical fibers—like the type we send data through—intense laser pulses can create a horizon. The pulse changes the physical properties of the fiber, slowing down the speed of light within the fiber. This makes the leading edge of the pulse a horizon: Slowed light cannot escape past the pulse any more than sound can escape up out of Unruh’s waterfall.

    To date, though, experimental evidence of Hawking radiation in any of these analogs has been lacking in support—with one exception.

    In May, Jeff Steinhauer published his latest paper, with the strongest evidence yet for Hawking radiation. Steinhauer, a physicist at the Technion in Haifa, Israel, has been working on the problem for over a decade, chipping away relentlessly at the extremely difficult experimental task, largely on his own.

    Focusing a laser on rubidium gas, a BEC, Steinhauer created a high-energy region. Particles move from high-energy regions to low-energy regions, so the rubidium gas wanted to escape the laser. The edge of the laser here functioned as the horizon for the rubidium gas, similar to a waterfall that it could go over but not come back up. Steinhauer used the set-up to study the Hawking radiation resulting from quantum fluctuations separated by the horizon.

    The temperature of Hawking radiation—how much energy the emitted phonons have, in this case—depends on the slope of the horizon, or waterfall. The steeper it is, the higher the energy of the radiation. This is why Hawking radiation is low temperature for a black hole: A weak force like gravity doesn’t make for a steep horizon.

    By measuring the slope, and then separately measuring the energy of radiated phonons, Steinhauer was able to get corroboration for his data.

    Previous experiments from Steinhauer and others have claimed to find Hawking radiation [PhysicsWorld], but have lacked the rigor of this latest result. This time, Steinhauer and some other physicists believe he has observed Hawking radiation.

    “I think we verified Hawking’s calculation,” Steinhauer says. “He had a calculation with certain assumptions and approximations, and we have the same approximations, and so mathematically it’s equivalent.”

    However, Steinhauer points out, it’s quite possible that Hawking radiation works differently for black holes because of quantum gravity. Critics also claim phonons may not be perfect analogs to photons.

    Many physicists who work on quantum gravity are dismissive of the latest results, according to reporting in Quanta.

    Weinfurtner acknowledges the criticism and agrees that analogs cannot strictly prove anything about black holes. But to physicists working on analogs, the facsimiles of black holes are already worthwhile. “What we’re doing is already on its own really interesting,” she says. “We’re deepening our understanding of the analog gravity systems, and the hope is that such experiments stimulate new theoretical black hole studies.”

    3

    See the full article here .


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    Symmetry is a joint Fermilab/SLAC publication.


     
  • richardmitnick 12:55 pm on July 3, 2019 Permalink | Reply
    Tags: , , , Black Holes, , ,   

    From NASA Chandra: “X-rays Spot Spinning Black Holes Across Cosmic Sea” 

    NASA Chandra Banner

    NASA/Chandra Telescope


    From NASA Chandra

    2019-07-03

    1
    Quasars. Credit: NASA/CXC/Univ. of Oklahoma/X. Dai et al.

    Like whirlpools in the ocean, spinning black holes in space create a swirling torrent around them. However, black holes do not create eddies of wind or water. Rather, they generate disks of gas and dust heated to hundreds of millions of degrees that glow in X-ray light.

    Using data from NASA’s Chandra X-ray Observatory and chance alignments across billions of light years, astronomers have deployed a new technique to measure the spin of five supermassive black holes. The matter in one of these cosmic vortices is swirling around its black hole at greater than about 70% of the speed of light.

    The astronomers took advantage of a natural phenomenon called a gravitational lens.

    Gravitational Lensing NASA/ESA

    With just the right alignment, the bending of space-time by a massive object, such as a large galaxy, can magnify and produce multiple images of a distant object, as predicted by Einstein.

    In this latest research, astronomers used Chandra and gravitational lensing to study five quasars, each consisting of a supermassive black hole rapidly consuming matter from a surrounding accretion disk. Gravitational lensing of the light from each of these quasars by an intervening galaxy has created multiple images of each quasar, as shown by these Chandra images of four of the targets. The sharp imaging ability of Chandra is needed to separate the multiple, lensed images of each quasar.

    The key advance made by researchers in this study was that they took advantage of “microlensing,” where individual stars in the intervening, lensing galaxy provided additional magnification of the light from the quasar.

    Gravitational microlensing, S. Liebes, Physical Review B, 133 (1964): 835

    A higher magnification means a smaller region is producing the X-ray emission.

    The researchers then used the property that a spinning black hole is dragging space around with it and allows matter to orbit closer to the black hole than is possible for a non-spinning black hole. Therefore, a smaller emitting region corresponding to a tight orbit generally implies a more rapidly spinning black hole. The authors concluded from their microlensing analysis that the X-rays come from such a small region that the black holes must be spinning rapidly.

    The results showed that one of the black holes, in the lensed quasar called the “Einstein Cross,” (labeled Q2237 in the image above) is spinning at, or almost at, the maximum rate possible. This corresponds to the event horizon, the black hole’s point of no return, spinning at the speed of light, which is about 670 million miles per hour. Four other black holes in the sample are spinning, on average, at about half this maximum rate.

    For the Einstein Cross the X-ray emission is from a part of the disk that is less than about 2.5 times the size of the event horizon, and for the other 4 quasars the X-rays come from a region four to five times the size of the event horizon.

    How can these black holes spin so quickly? The researchers think that these supermassive black holes likely grew by accumulating most of their material over billions of years from an accretion disk spinning with a similar orientation and direction of spin, rather than from random directions. Like a merry-go-round that keeps getting pushed in the same direction, the black holes kept picking up speed.

    The X-rays detected by Chandra are produced when the accretion disk surrounding the black hole creates a multimillion-degree cloud, or corona above the disk near the black hole. X-rays from this corona reflect off the inner edge of the accretion disk, and the strong gravitational forces near the black hole distort the reflected X-ray spectrum, that is, the amount of X-rays seen at different energies. The large distortions seen in the X-ray spectra of the quasars studied here imply that the inner edge of the disk must be close to the black holes, giving further evidence that they must be spinning rapidly.

    The quasars are located at distances ranging from 9.8 billion to 10.9 billion light years from Earth, and the black holes have masses between 160 and 500 million times that of the sun. These observations were the longest ever made with Chandra of gravitationally lensed quasars, with total exposure times ranging between 1.7 and 5.4 days.

    A paper describing these results is published in the July 2nd issue of The Astrophysical Journal. The authors are Xinyu Dai, Shaun Steele and Eduardo Guerras from the University of Oklahoma in Norman, Oklahoma, Christopher Morgan from the United States Naval Academy in Annapolis, Maryland, and Bin Chen from Florida State University in Tallahassee, Florida.

    See the full article here .


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    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.

     
  • richardmitnick 8:33 am on May 25, 2019 Permalink | Reply
    Tags: , , , Black Holes, , , , ,   

    From European Space Agency: “Two merging black holes” 

    ESA Space For Europe Banner

    From European Space Agency

    1

    20/05/2019

    Black holes are among the most fascinating objects in the Universe. Enclosing huge amounts of mass in relatively small regions, these compact objects have enormous densities that give rise to some of the strongest gravitational fields in the cosmos, so strong that nothing can escape – not even light.

    This artistic impression shows two black holes that are spiralling towards each other and will eventually coalesce. A black hole merger was first detected in 2015 by LIGO, the Laser Interferometer Gravitational-Wave Observatory, which detected the gravitational waves – fluctuations in the fabric of spacetime – created by the giant collision.

    Black holes and gravitational waves are both predictions of Albert Einstein’s general relativity, which was presented in 1915 and remains to date the best theory to describe gravity across the Universe.

    Karl Schwarzschild derived the equations for black holes in 1916, but they remained rather a theoretical curiosity for several decades, until X-ray observations performed with space telescopes could finally probe the highly energetic emission from matter in the vicinity of these extreme objects. The first ever image of a black hole’s dark silhouette, cast against the light from matter in its immediate surrounding, was only captured recently by the Event Horizon Telescope and published just last month.

    As for gravitational waves, it was Einstein himself who predicted their existence from his theory, also in 1916, but it would take another century to finally observe these fluctuations. Since 2015, the ground-based LIGO and Virgo observatories have assembled over a dozen detections, and gravitational-wave astronomy is a burgeoning new field of research.

    But another of Einstein’s predictions found observational proof much sooner: the gravitational bending of light, which was demonstrated only a few years after the theory had appeared, during a total eclipse of the Sun in 1919.

    In the framework of general relativity, any object with mass bends the fabric of spacetime, deflecting the path of anything that passes nearby – including light. An artistic view of this distortion, also known as gravitational lensing, is depicted in this representation of two merging black holes.

    One hundred years ago, astronomers set out to test general relativity, observing whether and by how much the mass of the Sun deflects the light of distant stars. This experiment could only be performed by obscuring the Sun’s light to reveal the stars around it, something that is possible during a total solar eclipse.

    On 29 May 1919, Sir Arthur Eddington observed the distant stars around the Sun during an eclipse from the island of Príncipe, in West Africa, while Andrew Crommelin performed similar observations in Sobral, in the north east of Brazil.

    Eddington/Einstein exibition of gravitational lensing solar eclipse of 29 May 1919

    The results, presented six months later, indicated that stars observed near the solar disc during the eclipse were slightly displaced, with respect to their normal position in the sky, roughly by the amount predicted by Einstein’s theory for the Sun’s mass to have deflected their light.

    “Lights All Askew in the Heavens,” headlined the New York Times in November 1919 to announce the triumph of Einstein’s new theory. This inaugurated a century of exciting experiments investigating gravity on Earth and in space, proving general relativity more and more precisely.

    We have made giant leaps over the past hundred years, but there is still much for us to discover. Athena, ESA’s future X-ray observatory, will investigate in unprecedented detail the supermassive black holes that sit at the centre of galaxies.


    LISA, another future ESA mission, will detect gravitational waves from orbit, looking for the low-frequency fluctuations that are released when two supermassive black holes merge and can only be detected from space.

    ESA/NASA eLISA

    ESA/NASA eLISA space based, the future of gravitational wave research

    Both missions are currently in the study phase, and are scheduled to launch in the early 2030s. If Athena and LISA could operate jointly for at least a few years, they could perform a unique experiment: observing the merger of supermassive black holes both in gravitational waves and X-rays, using an approach known as multi-messenger astronomy.

    We have never observed such a merger before: we need LISA to detect the gravitational waves and tell us where to look in the sky, then we need Athena to observe it with high precision in X-rays to see how the mighty collision affects the gas surrounding the black holes. We don’t know what happens during such a cosmic clash so this experiment, much like the eclipse of 1919 that first proved Einstein’s theory, is set to shake our understanding of gravity and the Universe.

    See the full article here .


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    Please help promote STEM in your local schools.

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    The European Space Agency (ESA), established in 1975, is an intergovernmental organization dedicated to the exploration of space, currently with 19 member states. Headquartered in Paris, ESA has a staff of more than 2,000. ESA’s space flight program includes human spaceflight, mainly through the participation in the International Space Station program, the launch and operations of unmanned exploration missions to other planets and the Moon, Earth observation, science, telecommunication as well as maintaining a major spaceport, the Guiana Space Centre at Kourou, French Guiana, and designing launch vehicles. ESA science missions are based at ESTEC in Noordwijk, Netherlands, Earth Observation missions at ESRIN in Frascati, Italy, ESA Mission Control (ESOC) is in Darmstadt, Germany, the European Astronaut Centre (EAC) that trains astronauts for future missions is situated in Cologne, Germany, and the European Space Astronomy Centre is located in Villanueva de la Cañada, Spain.

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  • richardmitnick 8:01 am on May 10, 2019 Permalink | Reply
    Tags: "Q&A: SLAC/Stanford researchers prepare for a new quantum revolution", , Black Holes, , , , , , , , Quantum squeezing, , The most exciting opportunities in quantum control make use of a phenomenon known as entanglement   

    From SLAC National Accelerator Lab- “Q&A: SLAC/Stanford researchers prepare for a new quantum revolution” 

    From SLAC National Accelerator Lab

    May 9, 2019
    Manuel Gnida

    Monika Schleier-Smith and Kent Irwin explain how their projects in quantum information science could help us better understand black holes and dark matter.

    The tech world is abuzz about quantum information science (QIS). This emerging technology explores bizarre quantum effects that occur on the smallest scales of matter and could potentially revolutionize the way we live.

    Quantum computers would outperform today’s most powerful supercomputers; data transfer technology based on quantum encryption would be more secure; exquisitely sensitive detectors could pick up fainter-than-ever signals from all corners of the universe; and new quantum materials could enable superconductors that transport electricity without loss.

    In December 2018, President Trump signed the National Quantum Initiative Act into law, which will mobilize $1.2 billion over the next five years to accelerate the development of quantum technology and its applications. Three months earlier, the Department of Energy had already announced $218 million in funding for 85 QIS research awards.

    The Fundamental Physics and Technology Innovation directorates of DOE’s SLAC National Accelerator Laboratory recently joined forces with Stanford University on a new initiative called Q-FARM to make progress in the field. In this Q&A, two Q-FARM scientists explain how they will explore the quantum world through projects funded by DOE QIS awards in high-energy physics.

    Monika Schleier-Smith, assistant professor of physics at Stanford, wants to build a quantum simulator made of atoms to test how quantum information spreads. The research, she said, could even lead to a better understanding of black holes.

    Kent Irwin, professor of physics at Stanford and professor of photon science and of particle physics and astrophysics at SLAC, works on quantum sensors that would open new avenues to search for the identity of the mysterious dark matter that makes up most of the universe.

    1
    Monika Schleier-Smith and Kent Irwin are the principal investigators of three quantum information science projects in high-energy physics at SLAC. (Farrin Abbott/Dawn Harmer/SLAC National Accelerator Laboratory)

    What exactly is quantum information science?

    Irwin: If we look at the world on the smallest scales, everything we know is already “quantum.” On this scale, the properties of atoms, molecules and materials follow the rules of quantum mechanics. QIS strives to make significant advances in controlling those quantum effects that don’t exist on larger scales.

    Schleier-Smith: We’re truly witnessing a revolution in the field in the sense that we’re getting better and better at engineering systems with carefully designed quantum properties, which could pave the way for a broad range of future applications.

    What does quantum control mean in practice?

    Schleier-Smith: The most exciting opportunities in quantum control make use of a phenomenon known as entanglement – a type of correlation that doesn’t exist in the “classical,” non-quantum world. Let me give you a simple analogy: Imagine that we flip two coins. Classically, whether one coin shows heads or tails is independent of what the other coin shows. But if the two coins are instead in an entangled quantum state, looking at the result for one “coin” automatically determines the result for the other one, even though the coin toss still looks random for either coin in isolation.

    Entanglement thus provides a fundamentally new way of encoding information – not in the states of individual “coins” or bits but in correlations between the states of different qubits. This capability could potentially enable transformative new ways of computing, where problems that are intrinsically difficult to solve on classical computers might be more efficiently solved on quantum ones. A challenge, however, is that entangled states are exceedingly fragile: any measurement of the system – even unintentional – necessarily changes the quantum state. So a major area of quantum control is to understand how to generate and preserve this fragile resource.

    At the same time, certain quantum technologies can also take advantage of the extreme sensitivity of quantum states to perturbations. One application is in secure telecommunications: If a sender and receiver share information in the form of quantum bits, an eavesdropper cannot go undetected, because her measurement necessarily changes the quantum state.

    Another very promising application is quantum sensing, where the idea is to reduce noise and enhance sensitivity by controlling quantum correlations, for instance, through quantum squeezing.

    What is quantum squeezing?

    Irwin: Quantum mechanics sets limits on how we can measure certain things in nature. For instance, we can’t perfectly measure both the position and momentum of a particle. The very act of measuring one changes the other. This is called the Heisenberg uncertainty principle. When we search for dark matter, we need to measure an electromagnetic signal extremely well, but Heisenberg tells us that we can’t measure the strength and timing of this signal without introducing uncertainty.

    Quantum squeezing allows us to evade limits on measurement set by Heisenberg by putting all the uncertainty into one thing (which we don’t care about), and then measuring the other with much greater precision. So, for instance, if we squeeze all of the quantum uncertainty in an electromagnetic signal into its timing, we can measure its strength much better than quantum mechanics would ordinarily allow. This lets us search for an electromagnetic signal from dark matter much more quickly and sensitively than is otherwise possible.

    2
    Kent Irwin (at left with Dale Li) leads efforts at SLAC and Stanford to build quantum sensors for exquisitely sensitive detectors. (Andy Freeberg/SLAC National Accelerator Laboratory)

    What types of sensors are you working on?

    Irwin: My team is exploring quantum techniques to develop sensors that could break new ground in the search for dark matter.

    We’ve known since the 1930s that the universe contains much more matter than the ordinary type that we can see with our eyes and telescopes – the matter made up of atoms. Whatever dark matter is, it’s a new type of particle that we don’t understand yet. Most of today’s dark matter detectors search for relatively heavy particles, called weakly interacting massive particles, or WIMPs.

    PandaX II Dark Matter experiment at Jin-ping Underground Laboratory (CJPL) in Sichuan, China

    DEAP Dark Matter detector, The DEAP-3600, suspended in the SNOLAB deep in Sudbury’s Creighton Mine

    LBNL LZ project at SURF, Lead, SD, USA

    But what if dark matter particles were so light that they wouldn’t leave a trace in those detectors? We want to develop sensors that would be able to “see” much lighter dark matter particles.

    There would be so many of these very light dark matter particles that they would behave much more like waves than individual particles. So instead of looking for collisions of individual dark matter particles within a detector, which is how WIMP detectors work, we want to look for dark matter waves, which would be detected like a very weak AM radio signal.

    In fact, we even call one of our projects “Dark Matter Radio.” It works like the world’s most sensitive AM radio. But it’s also placed in the world’s most perfect radio shield, made up of a material called a superconductor, which keeps all normal radio waves out. However, unlike real AM radio signals, dark matter waves would be able to go right through the shield and produce a signal. So we are looking for a very weak AM radio station made by dark matter at an unknown frequency.

    Quantum sensors can make this radio much more sensitive, for instance by using quantum tricks such as squeezing and entanglement. So the Dark Matter Radio will not only be the world’s most sensitive AM radio; it will also be better than the Heisenberg uncertainty principle would normally allow.

    What are the challenges of QIS?

    Schleier-Smith: There is a lot we need to learn about controlling quantum correlations before we can make broad use of them in future applications. For example, the sensitivity of entangled quantum states to perturbations is great for sensor applications. However, for quantum computing it’s a major challenge because perturbations of information encoded in qubits will introduce errors, and nobody knows for sure how to correct for them.

    To make progress in that area, my team is studying a question that is very fundamental to our ability to control quantum correlations: How does information actually spread in quantum systems?

    The model system we’re using for these studies consists of atoms that are laser-cooled and optically trapped. We use light to controllably turn on interactions between the atoms, as a means of generating entanglement. By measuring the speed with which quantum information can spread in the system, we hope to understand how to design the structure of the interactions to generate entanglement most efficiently. We view the system of cold atoms as a quantum simulator that allows us to study principles that are also applicable to other physical systems.

    In this area of quantum simulation, one major thrust has been to advance understanding of solid-state systems, by trapping atoms in arrays that mimic the structure of a crystalline material. In my lab, we are additionally working to extend the ideas and tools of quantum simulation in new directions. One prospect that I am particularly excited about is to use cold atoms to simulate what happens to quantum information in black holes.

    3
    Monika Schleier-Smith (at center with graduate students Emily Davis and Eric Cooper) uses laser-cooled atoms in her lab at Stanford to study the transfer of quantum information. (Dawn Harmer/SLAC National Accelerator Laboratory)

    What do cold atoms have to do with black holes?

    Schleier-Smith: The idea that there might be any connection between quantum systems we can build in the lab and black holes has its origins in a long-standing theoretical problem: When particles fall into a black hole, what happens to the information they contained? There were compelling arguments that the information should be lost, but that would contradict the laws of quantum mechanics.

    More recently, theoretical physicists – notably my Stanford colleague Patrick Hayden – found a resolution to this problem: We should think of the black hole as a highly chaotic system that “scrambles” the information as fast as physically possible. It’s almost like shredding documents, but quantum information scrambling is much richer in that the result is a highly entangled quantum state.

    Although precisely recreating such a process in the lab will be very challenging, we hope to look at one of its key features already in the near term. In order for information scrambling to happen, information needs to be transferred through space exponentially fast. This, in turn, requires quantum interactions to occur over long distances, which is quite counterintuitive because interactions in nature typically become weaker with distance. With our quantum simulator, we are able to study interactions between distant atoms by sending information back and forth with photons, particles of light.

    What do you hope will happen in QIS over the next few years?

    Irwin: We need to prove that, in real applications, quantum technology is superior to the technology that we already have. We are in the early stages of this new quantum revolution, but this is already starting to happen. The things we’re learning now will help us make a leap in developing future technology, such as universal quantum computers and next-generation sensors. The work we do on quantum sensors will enable new science, not only in dark matter research. At SLAC, I also see potential for quantum-enhanced sensors in X-ray applications, which could provide us with new tools to study advanced materials and understand how biomolecules work.

    Schleier-Smith: QIS offers plenty of room for breakthroughs. There are many open questions we still need to answer about how to engineer the properties of quantum systems in order to harness them for technology, so it’s imperative that we continue to broadly advance our understanding of complex quantum systems. Personally, I hope that we’ll be able to better connect experimental observations with the latest theoretical advances. Bringing all this knowledge together will help us build the technologies of the future.

    See the full article here .


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    Please help promote STEM in your local schools.

    Stem Education Coalition

    SLAC/LCLS


    SLAC/LCLS II projected view


    SLAC is a multi-program laboratory exploring frontier questions in photon science, astrophysics, particle physics and accelerator research. Located in Menlo Park, California, SLAC is operated by Stanford University for the DOE’s Office of Science.

     
  • richardmitnick 9:45 am on April 14, 2019 Permalink | Reply
    Tags: "The Day Feynman Worked Out Black-Hole Radiation on My Blackboard", , , , Black Holes, , ,   

    From Nautilus: “The Day Feynman Worked Out Black-Hole Radiation on My Blackboard” 

    Nautilus

    From Nautilus

    Apr 11, 2019

    The amazing image of a black hole unveiled Wednesday, along with data from the Event Horizon Telescope, may not substantiate Stephen Hawking’s famous theory that radiation, an example of spontaneous emission at the quantum level, is emitted by a black hole.

    The first image of a black hole, Messier 87 Credit Event Horizon Telescope Collaboration, via NSF 4.10.19

    But the news did remind us of a story that physicist and writer Alan Lightman told Nautilus: Richard Feynman came up with the idea for spontaneous emission before Hawking. Here is Lightman in his own words:

    1
    After a few minutes, Richard Feynman had worked out the process of spontaneous emission, which is what Stephen Hawking became famous for a year later.Wikicommons

    “One day at lunch in the Caltech cafeteria, I was with two graduate students, Bill Press and Saul Teukolsky, and Feynman. Bill and Saul were talking about a calculation they had just done. It was a theoretical calculation, purely mathematical, where they looked at what happens if you shine light on a rotating black hole. If you shine it at the right angle, the light will bounce off the black hole with more energy than it came in with. The classical analogue is a spinning top. If you throw a marble at the top at the right angle, the marble will bounce off the top with more velocity than it came in with. The top slows down and the energy, the increased energy of the marble, comes from the spin of the top. As Bill and Saul were talking, Feynman was listening.

    We got up from the table and began walking back through the campus. Feynman said, ‘You know that process you’ve described? It sounds very much like stimulated emission.’ That’s a quantum process in atomic physics where you have an electron orbiting an atom, and a light particle, a photon, comes in. The two particles are emitted and the electron goes to a lower energy state, so the light is amplified by the electron. The electron decreases energy and gives up that extra energy to sending out two photons. Feynman said, ‘What you’ve just described sounds like stimulated emission. According to Einstein, there’s a well-known relationship between stimulated emission and spontaneous emission.’

    Spontaneous emission is when you have an electron orbiting an atom and it just emits a photon all by itself, without any light coming in, and goes to a lower energy state. Einstein had worked out this relationship between stimulated and spontaneous emission. Whenever you have one, you have the other, at the atomic level. That’s well known to graduate students of physics. Feynman said that what Bill and Saul were describing sounded like simulated emission, and so there should be a spontaneous emission process analogous to it.

    We’d been wandering through the campus. We ended up in my office, a tiny little room, Bill, Saul, me, and Feynman. Feynman went to the blackboard and began working out the equations for spontaneous emission from black holes. Up to this point in history, it had been thought that all black holes were completely black, that a black hole could never emit on its own any kind of energy. But Feynman had postulated, after listening to Bill and Saul talk at lunch, that if a spinning black hole can emit with light coming in, it can also emit energy with nothing coming in, if you take into account quantum mechanics.

    After a few minutes, Feynman had worked out the process of spontaneous emission, which is what Stephen Hawking became famous for a year later. Feynman had it all on my blackboard. He wasn’t interested in copying down what he’d written. He just wanted to know how nature worked, and he had just learned that isolated black holes are capable of emitting energy when you take into account quantum effects. After he finished working it out, he brushed his hands together to get the chalk dust off them, and walked out of the office.

    After Feynman left, Bill and Saul and I were looking at the blackboard. We were thinking it was probably important, not knowing how important. Bill and Saul had to go off to some appointment, and so they left the office. A little bit later, I left. But that night I realized this was a major thing that Feynman had done and I needed to hurry back to my office and copy down the equations. But when I got back to my office in the morning, the cleaning lady had wiped the blackboard clean.”

    See the full article here .

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

    Please help promote STEM in your local schools.

    Stem Education Coalition

    Welcome to Nautilus. We are delighted you joined us. We are here to tell you about science and its endless connections to our lives. Each month we choose a single topic. And each Thursday we publish a new chapter on that topic online. Each issue combines the sciences, culture and philosophy into a single story told by the world’s leading thinkers and writers. We follow the story wherever it leads us. Read our essays, investigative reports, and blogs. Fiction, too. Take in our games, videos, and graphic stories. Stop in for a minute, or an hour. Nautilus lets science spill over its usual borders. We are science, connected.

     
  • richardmitnick 10:28 am on March 30, 2019 Permalink | Reply
    Tags: "Hello Quantum Vacuum Nice to See You", , “Back action”, Black Holes, , , , , , Quantum radiation pressure noise, Quantum vacuum or ‘"nothingness"   

    From Louisiana State University: “Hello, Quantum Vacuum, Nice to See You” 

    From Louisiana State University

    March 25, 2019

    Elsa Hahne
    LSU Office of Research & Economic Development
    504-610-1950
    ehahne@lsu.edu

    Mimi LaValle
    LSU Department of Physics & Astronomy
    225-439-5633
    mlavall@lsu.edu

    Thomas Corbitt, associate professor at the LSU Department of Physics & Astronomy, and his team of researchers measure quantum behavior at room temperature, visible to the naked eye, as reported today in the journal Nature.

    1
    Thomas Corbitt in his lab, setting up a complex sequence of lasers.Elsa Hahne/LSU

    Since the historic finding of gravitational waves from two black holes colliding over a billion light years away was made in 2015, physicists are advancing knowledge about the limits on the precision of the measurements that will help improve the next generation of tools and technology used by gravitational wave scientists.

    Artist’s iconic conception of two merging black holes similar to those detected by LIGO Credit LIGO-Caltech/MIT/Sonoma State /Aurore Simonnet

    LSU Department of Physics & Astronomy Associate Professor Thomas Corbitt and his team of researchers now present the first broadband, off-resonance measurement of quantum radiation pressure noise in the audio band, at frequencies relevant to gravitational wave detectors, as reported today in the scientific journal Nature. The research was supported by the National Science Foundation, or NSF, and the results hint at methods to improve the sensitivity of gravitational-wave detectors by developing techniques to mitigate the imprecision in measurements called “back action,” thus increasing the chances of detecting gravitational waves.

    Corbitt and researchers have developed physical devices that make it possible to observe—and hear—quantum effects at room temperature. It is often easier to measure quantum effects at very cold temperatures, while this approach brings them closer to human experience. Housed in miniature models of detectors like LIGO (the Laser Interferometer Gravitational-Wave Observatory, one located in Livingston, La., and the other in Hanford, Wash.), these devices consist of low-loss, single-crystal micro-resonators—each a tiny mirror pad the size of a pin prick, suspended from a cantilever. A laser beam is directed at one of these mirrors, and as the beam is reflected, the fluctuating radiation pressure is enough to bend the cantilever structure, causing the mirror pad to vibrate, which creates noise.


    VIRGO Gravitational Wave interferometer, near Pisa, Italy


    Caltech/MIT Advanced aLigo Hanford, WA, USA installation


    Caltech/MIT Advanced aLigo detector installation Livingston, LA, USA

    Cornell SXS, the Simulating eXtreme Spacetimes (SXS) project

    Gravitational waves. Credit: MPI for Gravitational Physics/W.Benger

    Gravity is talking. Lisa will listen. Dialogos of Eide

    ESA/eLISA the future of gravitational wave research

    Localizations of gravitational-wave signals detected by LIGO in 2015 (GW150914, LVT151012, GW151226, GW170104), more recently, by the LIGO-Virgo network (GW170814, GW170817). After Virgo came online in August 2018


    Skymap showing how adding Virgo to LIGO helps in reducing the size of the source-likely region in the sky. (Credit: Giuseppe Greco (Virgo Urbino group)

    Gravitational wave interferometers use as much laser power as possible in order to minimize the uncertainty caused by the measurement of discrete photons and to maximize the signal-to-noise ratio. These higher power beams increase position accuracy but also increase back action, which is the uncertainty in the number of photons reflecting from a mirror that corresponds to a fluctuating force due to radiation pressure on the mirror, causing mechanical motion. Other types of noise, such as thermal noise, usually dominate over quantum radiation pressure noise, but Corbitt and his team, including collaborators at MIT, have sorted through them. Advanced LIGO and other second and third generation interferometers will be limited by quantum radiation pressure noise at low frequencies when running at their full laser power. Corbitt’s paper in Nature offers clues as to how researchers can work around this when measuring gravitational waves.

    2
    Thomas Corbitt looks through the custom-built device used to measure quantum radiation pressure noise. Elsa Hahne/LSU

    “Given the imperative for more sensitive gravitational wave detectors, it is important to study the effects of quantum radiation pressure noise in a system similar to Advanced LIGO, which will be limited by quantum radiation pressure noise across a wide range of frequencies far from the mechanical resonance frequency of the test mass suspension,” Corbitt said.

    Corbitt’s former academic advisee and lead author of the Nature paper, Jonathan Cripe, graduated from LSU with a Ph.D. in Physics last year and is now a postdoctoral research fellow at the National Institute of Standards and Technology:

    “Day-to-day at LSU, as I was doing the background work of designing this experiment and the micro-mirrors and placing all of the optics on the table, I didn’t really think about the impact of the future results,” Cripe said. “I just focused on each individual step and took things one day at a time. [But] now that we have completed the experiment, it really is amazing to step back and think about the fact that quantum mechanics—something that seems otherworldly and removed from the daily human experience—is the main driver of the motion of a mirror that is visible to the human eye. The quantum vacuum, or ‘nothingness,’ can have an effect on something you can see.”

    Pedro Marronetti, a physicist and NSF program director, notes that it can be tricky to test new ideas for improving gravitational wave detectors, especially when reducing noise that can only be measured in a full-scale interferometer:

    “This breakthrough opens new opportunities for testing noise reduction,” he said. The relative simplicity of the approach makes it accessible by a wide range of research groups, potentially increasing participation from the broader scientific community in gravitational wave astrophysics.”

    For more information from LSU Physics & Astronomy, visit http://www.phys.lsu.edu.

    See the full article here .

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

    Please help promote STEM in your local schools.

    Stem Education Coalition

    Louisiana State University (officially Louisiana State University and Agricultural and Mechanical College, commonly referred to as LSU) is a public coeducational university located in Baton Rouge, Louisiana. The university was founded in 1853 in what is now known as Pineville, Louisiana, under the name Louisiana State Seminary of Learning & Military Academy. The current LSU main campus was dedicated in 1926, consists of more than 250 buildings constructed in the style of Italian Renaissance architect Andrea Palladio, and occupies a 650-acre (2.6 km²) plateau on the banks of the Mississippi River.

    LSU is the flagship institution of the Louisiana State University System. In 2017, the university enrolled over 25,000 undergraduate and over 5,000 graduate students in 14 schools and colleges. Several of LSU’s graduate schools, such as the E.J. Ourso College of Business and the Paul M. Hebert Law Center, have received national recognition in their respective fields of study. Designated as a land-grant, sea-grant and space-grant institution, LSU is also noted for its extensive research facilities, operating some 800 sponsored research projects funded by agencies such as the National Institutes of Health, the National Science Foundation, the National Endowment for the Humanities, and the National Aeronautics and Space Administration.

    LSU’s athletics department fields teams in 21 varsity sports (9 men’s, 12 women’s), and is a member of the NCAA (National Collegiate Athletic Association) and the SEC (Southeastern Conference). The university is represented by its mascot, Mike the Tiger.

     
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