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  • richardmitnick 1:49 pm on November 10, 2022 Permalink | Reply
    Tags: "Death of a star reveals midsize black hole lurking in a dwarf galaxy", A flare of radiation briefly outshone the combined stellar light of the host dwarf galaxy., An intermediate-mass black hole lurking undetected in a dwarf galaxy revealed itself to astronomers when it gobbled up an unlucky star that strayed too close., Astronomers discovered a star being ripped apart by a black hole in the galaxy SDSS J152120.07+140410.5 850 million light years away., , , , , , , Only a minuscule fraction of dwarf galaxies is known to host intermediate-mass black holes., Scientists can use tidal disruption events not only to find more intermediate-mass black holes in quiet dwarf galaxies but also to measure their masses., , TDE: tidal disruption event,   

    From The University of California-Santa Cruz: “Death of a star reveals midsize black hole lurking in a dwarf galaxy” 

    From The University of California-Santa Cruz

    11.10.22
    Tim Stephens
    stephens@ucsc.edu

    1
    Astronomers discovered a star being ripped apart by a black hole in the galaxy SDSS J152120.07+140410.5, 850 million light years away. Researchers pointed NASA’s Hubble Space Telescope to examine the aftermath, called AT 2020neh, which is shown in the center of the image. Hubble’s ultraviolet camera saw a ring of stars being formed around the nucleus of the galaxy where AT 2020neh is located. Credit: Ryan Foley/UC Santa Cruz/NASA, ESA.

    An intermediate-mass black hole lurking undetected in a dwarf galaxy revealed itself to astronomers when it gobbled up an unlucky star that strayed too close. The shredding of the star, known as a “tidal disruption event” or TDE, produced a flare of radiation that briefly outshone the combined stellar light of the host dwarf galaxy and could help scientists better understand the relationships between black holes and galaxies.

    The flare was captured by astronomers with the Young Supernova Experiment (YSE), a survey designed to detect cosmic explosions and transient astrophysical events. An international team led by scientists at UC Santa Cruz, the Niels Bohr Institute at the University of Copenhagen, and Washington State University reported the discovery in a paper published November 10 in Nature Astronomy [below].

    “This discovery has created widespread excitement because we can use tidal disruption events not only to find more intermediate-mass black holes in quiet dwarf galaxies, but also to measure their masses,” said coauthor Ryan Foley, an assistant professor of astronomy and astrophysics at UC Santa Cruz who helped plan the YSE survey.

    First author Charlotte Angus at the Niels Bohr Institute said the team’s findings provide a baseline for future studies of midsize black holes.

    “The fact that we were able to capture this midsize black hole whilst it devoured a star offered us a remarkable opportunity to detect what otherwise would have been hidden from us,” Angus said. “What is more, we can use the properties of the flare itself to better understand this elusive group of middle-weight black holes, which could account for the majority of black holes in the centers of galaxies.”

    Supermassive black holes are found at the centers of all massive galaxies, including our own Milky Way. Astronomers conjecture that these massive beasts, with millions or billions of times the mass of the sun, could have grown from smaller “intermediate-mass” black holes with thousands to hundreds of thousands of solar masses.

    One theory for how such massive black holes were assembled is that the early universe was rampant with small dwarf galaxies with intermediate-mass black holes. Over time, these dwarf galaxies would have merged or been gobbled up by more massive galaxies, their cores combining each time to build up the mass in the center of the growing galaxy. This merger process would eventually create the supermassive black holes seen today.

    “If we can understand the population of intermediate-mass black holes out there—how many there are and where they are located—we can help determine if our theories of supermassive black hole formation are correct,” said coauthor Enrico Ramirez-Ruiz, professor of astronomy and astrophysics at UCSC and Niels Bohr Professor at the University of Copenhagen.

    But do all dwarf galaxies have midsize black holes?

    “That’s difficult to assert, because detecting intermediate-mass black holes is extremely challenging,” Ramirez-Ruiz said.

    Classic black hole hunting techniques, which look for actively feeding black holes, are often not sensitive enough to uncover black holes in the centers of dwarf galaxies. As a result, only a minuscule fraction of dwarf galaxies is known to host intermediate-mass black holes. Finding more midsize black holes with tidal disruption events could help to settle the debate about how supermassive black holes form.

    “One of the biggest open questions in astronomy is currently how supermassive black holes form,” said coauthor Vivienne Baldassare, professor of physics and astronomy at Washington State University.

    Data from the Young Supernova Experiment enabled the team to detect the first signs of light as the black hole began to eat the star. Capturing this initial moment was pivotal to unlocking how big the black hole was, because the duration of these events can be used to measure the mass of the central black hole. This method, which until now had only been shown to work well for supermassive black holes, was first proposed by Ramirez-Ruiz and coauthor Brenna Mockler at UC Santa Cruz.

    “This flare was incredibly fast, but because our YSE data gave us so much early information about the event, we were really able to pin down the mass of the black hole using it,” Angus said.

    This study was based on data from observatories around the world, including the W. M. Keck Observatory in Hawaii, the Nordic Optical Telescope, UC’s Lick Observatory [below], NASA’s Hubble Space Telescope, the international Gemini Observatory, the Palomar Observatory, and the Pan-STARRS Survey at Haleakala Observatory.



    Science paper:
    Nature Astronomy

    See the full article here .


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    UC Santa Cruz campus.

    The University of California-Santa Cruz, opened in 1965 and grew, one college at a time, to its current (2008-09) enrollment of more than 16,000 students. Undergraduates pursue more than 60 majors supervised by divisional deans of humanities, physical & biological sciences, social sciences, and arts. Graduate students work toward graduate certificates, master’s degrees, or doctoral degrees in more than 30 academic fields under the supervision of the divisional and graduate deans. The dean of the Jack Baskin School of Engineering oversees the campus’s undergraduate and graduate engineering programs.

    UCSC is the home base for the Lick Observatory.

    UCO Lick Observatory’s 36-inch Great Refractor telescope housed in the South (large) Dome of main building.

    UC Santa Cruz Lick Observatory Since 1888 Mt Hamilton, in San Jose, California, Altitude 1,283 m (4,209 ft)

    UC Observatories Lick Automated Planet Finder fully robotic 2.4-meter optical telescope at Lick Observatory, situated on the summit of Mount Hamilton, east of San Jose, California, USA.

    The UCO Lick C. Donald Shane telescope is a 120-inch (3.0-meter) reflecting telescope located at the Lick Observatory, Mt Hamilton, in San Jose, California, Altitude 1,283 m (4,209 ft).

    Search for extraterrestrial intelligence expands at Lick Observatory
    New instrument scans the sky for pulses of infrared light
    March 23, 2015
    By Hilary Lebow
    Astronomers are expanding the search for extraterrestrial intelligence into a new realm with detectors tuned to infrared light at UC’s Lick Observatory. A new instrument, called NIROSETI, will soon scour the sky for messages from other worlds.

    “Infrared light would be an excellent means of interstellar communication,” said Shelley Wright, an assistant professor of physics at UC San Diego who led the development of the new instrument while at the University of Toronto’s Dunlap Institute for Astronomy & Astrophysics.

    Wright worked on an earlier SETI project at Lick Observatory as a UC Santa Cruz undergraduate, when she built an optical instrument designed by UC Berkeley researchers. The infrared project takes advantage of new technology not available for that first optical search.

    Infrared light would be a good way for extraterrestrials to get our attention here on Earth, since pulses from a powerful infrared laser could outshine a star, if only for a billionth of a second. Interstellar gas and dust is almost transparent to near infrared, so these signals can be seen from great distances. It also takes less energy to send information using infrared signals than with visible light.

    The NIROSETI instrument saw first light on the Nickel 1-meter Telescope at Lick Observatory on March 15, 2015. (Photo by Laurie Hatch.)
    Astronomers are expanding the search for extraterrestrial intelligence into a new realm with detectors tuned to infrared light at UC’s Lick Observatory. A new instrument, called NIROSETI, will soon scour the sky for messages from other worlds.

    Alumna Shelley Wright, now an assistant professor of physics at UC San Diego, discusses the dichroic filter of the NIROSETI instrument, developed at the U Toronto Dunlap Institute for Astronomy and Astrophysics (CA) and brought to The University of California-San Diego and installed at the UC Santa Cruz Lick Observatory Nickel Telescope (Photo by Laurie Hatch). “Infrared light would be an excellent means of interstellar communication,” said Shelley Wright, an assistant professor of physics at The University of California-San Diego who led the development of the new instrument while at the U Toronto Dunlap Institute for Astronomy and Astrophysics (CA).


    NIROSETI team from left to right Rem Stone UCO Lick Observatory Dan Werthimer, UC Berkeley; Jérôme Maire, U Toronto; Shelley Wright, The University of California-San Diego Patrick Dorval, U Toronto; Richard Treffers, Starman Systems. (Image by Laurie Hatch).

    Wright worked on an earlier SETI project at Lick Observatory as a UC Santa Cruz undergraduate, when she built an optical instrument designed by University of California-Berkeley researchers. The infrared project takes advantage of new technology not available for that first optical search.

    Infrared light would be a good way for extraterrestrials to get our attention here on Earth, since pulses from a powerful infrared laser could outshine a star, if only for a billionth of a second. Interstellar gas and dust is almost transparent to near infrared, so these signals can be seen from great distances. It also takes less energy to send information using infrared signals than with visible light.

    Frank Drake, professor emeritus of astronomy and astrophysics at UC Santa Cruz and director emeritus of the SETI Institute, said there are several additional advantages to a search in the infrared realm.

    Frank Drake with his Drake Equation. Credit Frank Drake.

    Drake Equation, Frank Drake, Seti Institute.

    “The signals are so strong that we only need a small telescope to receive them. Smaller telescopes can offer more observational time, and that is good because we need to search many stars for a chance of success,” said Drake.

    The only downside is that extraterrestrials would need to be transmitting their signals in our direction, Drake said, though he sees this as a positive side to that limitation. “If we get a signal from someone who’s aiming for us, it could mean there’s altruism in the universe. I like that idea. If they want to be friendly, that’s who we will find.”

    Scientists have searched the skies for radio signals for more than 50 years and expanded their search into the optical realm more than a decade ago. The idea of searching in the infrared is not a new one, but instruments capable of capturing pulses of infrared light only recently became available.

    “We had to wait,” Wright said. “I spent eight years waiting and watching as new technology emerged.”

    Now that technology has caught up, the search will extend to stars thousands of light years away, rather than just hundreds. NIROSETI, or Near-Infrared Optical Search for Extraterrestrial Intelligence, could also uncover new information about the physical universe.

     
  • richardmitnick 12:39 pm on October 5, 2022 Permalink | Reply
    Tags: "A Stellar ‘Light Switch’ Orbiting a Black Hole", 600 days after the dimming began the ‘light switch’ was flipped and the X-ray and UV emission from AT2018fyk have returned to close to pre-dimming levels., 600 days after the initial discovery there was a sharp decrease in the brightness of the X-ray and UV emission., , , , , , TDE: tidal disruption event, The event was called AT2018fyk and further analysis found that the emission was coming from the nucleus of a galaxy named LCRS B224721.6−450748.   

    From Astrobites : “A Stellar ‘Light Switch’ Orbiting a Black Hole” 

    Astrobites bloc

    From Astrobites

    10.5.22
    Evan Lewis

    Title: The rebrightening of AT2018fyk as a repeating partial tidal disruption event

    Authors: T. Wevers, E.R. Coughlin, D.R. Pasham, M. Guolo, Y. Sun, S. Wen, P.G. Jonker, A. Zabludoff, A. Malyali, R. Arcodia, Z. Liu, A. Merloni, A. Rau, I. Grotova, P. Short, Z. Cao

    First Author’s Institution: The European Southern Observatory [La Observatorio Europeo Austral] [Observatoire européen austral][Europaiche Sûdsternwarte] (EU)(CL)
    Status: Submitted to ApJ Letters [open access]

    Out in the center of a distant galaxy, a star is being torn apart as it circles the drain around an enormous black hole! Today’s paper reports on the re-emergence of X-ray and UV emission from a star orbiting a supermassive black hole (SMBH). After being discovered, this emission suddenly flicked off and stayed undetectable for ~600 days, before it quickly returned like a light switch being turned back on after a blackout– making this a very dynamic system to study.

    In 2018, optical emission from the star was discovered by the All-Sky Automated Survey for Supernovae (ASASSN), a supernova search using 24 telescopes around the world which can see objects 50,000 times dimmer than we can see with our naked eyes!

    The event was called AT2018fyk and further analysis found that the emission was coming from the nucleus of a galaxy named LCRS B224721.6−450748. These super catchy and memorable names are thanks to astronomers using astrometric coordinates and dates of discovery to name new objects, since there are too many in the sky to give each a unique name! But 600 days after the initial discovery there was a sharp decrease in the brightness of the X-ray and UV emission, with the X-ray emission plummeting to less than 1/6,000th of its original brightness. For 600 days, this dimming persisted, suggesting that the star had been torn apart by the gravitational pull of the black hole, and all of the stellar material had fallen onto the surface of the black hole, leaving nothing behind. This is known as a tidal disruption event (TDE), since the tidal forces (yes, the same ones that cause the ocean tides on Earth!) rip the star apart.

    However, today’s authors report that 600 days after the dimming began the ‘light switch’ was flipped and the X-ray and UV emission from AT2018fyk have returned to close to pre-dimming levels. In most tidal disruptions, the star is totally torn apart and the emission slowly fades, never to return– so their hypothesis is that this event was only a partial TDE, where the core of the star remained intact while only the outer layers were stripped away.

    1
    Figure 1: Cartoons illustrating the evolution of the star/SMBH system over time. The binary system is torn apart in panels a) and b), the stellar material begins to fall onto the black hole in panel c), the star moves away from the black hole in panel e), and the tidal disruption begins once again in panel f). Figure 3 from today’s paper.

    Figure 1 shows a schematic which illustrates the key phases of AT2018fyk’s history. The origins of this system are unique- given the previously estimated SMBH mass, a star should theoretically take at least a few thousand years to make one full orbit around the central black hole– way longer than the timescales of a few years that we’re seeing! But, if the star was originally part of a binary system, the black hole can disrupt the binary, pulling one star into an orbit around the black hole while the other star is shot at extremely high speeds away from the galaxy. Panels a) and b) of Figure 1 show this process, with the yellow dot representing the star’s ex-binary companion (now called a hypervelocity star) which is flung off into space.

    Panel c), at t=0, matches up with the initial discovery of the system, with material falling onto the surface of the supermassive black hole and getting heated up, which creates X-rays. This process is called accretion, or stellar fallback. Panel e), at t=600 days after discovery, shows that at this point the core of the star has moved farther away from the SMBH, and the stellar material remains gravitationally attracted to the stellar core, so it has stopped falling onto the SMBH– this is the point at which the X-ray and UV emission got much dimmer. At t=1200 days (the focus of this paper), what remains of the star has moved back into the region where the outer material of the star will be pulled onto the SMBH, and the emission ‘turns on’ once again.

    2
    Figure 2- the light curve of the stellar/SMBH system over time, since its discovery. Both the UV (green diamond; from Swift) and X-ray (black, from Swift/XMM-Newton/Chandra/eROSITA) light curves are shown. The x-axis is measured in days, with t=0 equal to the discovery of the system. Top left panel of Figure 1 from today’s paper.

    Figure 2 shows the light curve, or the luminosity of the emission over time, in the UV (green) and X-ray (black) wavelength ranges over the course of the observational history of AT2018fyk. Letters A-D represent the first 600 days of bright emission: at first, the UV emission is brighter (higher up on the y-axis) than the X-ray emission, but they switch around letter C. Why do we observe this behavior? At early times, the gas surrounding SMBH will be optically thick, but when the star moves away and the rate of fallback declines, the gas is able to expand and cool, becoming more optically thin (puffier) so it’s easier to see through to the hot inner region of the system, leading to brighter X-ray emission. At letter E, the dimming period begins as the star moves away from the SMBH, and the emission brightness drops sharply into its “quiescent” state. Finally, at letter F, the bright emission returns at similar luminosity levels to before, implying that the same star has orbited back around to a point where material is falling onto the SMBH.

    The authors predict that there will be another sharp brightness decline in August 2023 and, if the star survives this second encounter, a third episode of re-brightening should begin around March 2025. This gives astronomers an exciting prediction to look forward to confirming or denying, as we continue to learn about exotic systems like this!

    See the full article here .


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    Why read Astrobites?

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

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

     
  • richardmitnick 3:39 pm on June 23, 2022 Permalink | Reply
    Tags: "A star’s demise is connected to a neutrino outburst", , Ground based Neutrino Observation, , , , On 1 October 2019 the IceCube Neutrino Observatory in Antarctica detected a 0.2 PeV neutrino., , , , Recently the Zwicky Transient Facility observed another TDE that was coincident with a high-energy neutrino detected by IceCube., Seven hours later the Zwicky Transient Facility observed optical an emission in the direction of the incoming neutrino., TDE: tidal disruption event, The optical emission was caused by a bright transient phenomenon known as a tidal disruption event (TDE)., The prospect of high-energy neutrinos being formed by tidal forces ripping apart a star near a supermassive black hole has garnered new support.   

    From “Physics Today” : “A star’s demise is connected to a neutrino outburst” 

    Physics Today bloc

    From “Physics Today”

    23 Jun 2022
    Alex Lopatka

    The prospect of high-energy neutrinos being formed by tidal forces ripping apart a star near a supermassive black hole has garnered new support.

    (S. Reusch et al., Phys. Rev. Lett. 128, 221101, 2022.)

    1
    Technicians install a camera at the Zwicky Transient Facility. Credit: Caltech/Palomar.

    On 1 October 2019 the IceCube Neutrino Observatory in Antarctica detected a 0.2 PeV neutrino.

    Seven hours later the Zwicky Transient Facility in California followed up with a wide-field survey of the sky at optical and IR wavelengths. The facility observed optical emission in the direction of the incoming neutrino.

    Researchers concluded [Nature Astronomy] that the two observations could be connected after studying the exceptional energy flux of the emission, its location within the reported uncertainty region of the high-energy neutrino, and some modeling results. The optical emission was caused by a bright transient phenomenon known as a tidal disruption event (TDE), and that particular one had first been observed one year before the neutrino. Such events occur when stars get close enough to supermassive black holes to experience spaghettification—the stretching and compression of an object into a long, thin shape due to the black hole’s extreme tidal forces. (See the article by Suvi Gezari, Physics Today, May 2014, page 37.)

    A theory paper [Nature Astronomy] proposed that neutrinos with energies above 100 TeV, like the 2019 sighting, could be produced in relativistic jets of plasma, which are composed of stellar debris that’s flung outward after such an event. TDEs and many other sources for high-energy neutrinos have been debated in the literature. But with only one reported TDE–neutrino association researchers haven’t been able to conclusively establish TDEs as high-energy neutrino sources.

    3
    Credit: S. Reusch et al., Phys. Rev. Lett. 128, 221101 (2022)

    Recently the Zwicky Transient Facility observed another TDE that was coincident with a high-energy neutrino detected by IceCube. Simeon Reusch, Marek Kowalski, and their colleagues estimated that the probability of a second such pairing happening by chance is 0.034%, lending more credence to TDEs as a source for high-energy neutrinos.

    The second TDE caused a long-duration optical flare which reached its peak luminosity in August 2019. The neutrino was detected by IceCube in May 2020, by which point the flare’s flux had decreased by about 30% from its peak. Such flares often last several months, though this one was still detectable as of June 2022.

    To better understand how the unusually long-lasting TDE may have produced high-energy neutrinos, the research team simulated three mechanisms. The figure shows the predicted neutrino flux as a function of energy, and the vertical dotted line indicates the energy of the neutrino observed by IceCube. Any of the three mechanisms could reasonably explain the neutrino. Besides relativistic jets, a TDE could also generate an accretion disk, and emission from its corona or a subrelativistic wind of ejected material may generate neutrinos too.

    Other uncertainties remain. The radio-emission measurements of the flare, for example, mean that it could have originated from an active galactic nucleus instead of a TDE. In addition, IceCube’s statistical analysis cannot rule out that the neutrino may have formed from atmospheric processes on Earth.

    Although it’ll take more observations to lower those uncertainties, the latest detection of a TDE–neutrino pairing reinforces the significance of TDEs as neutrino sources. And if the association is true, TDEs would have to be surprisingly efficient particle accelerators, a possibility that could only be further studied with more comprehensive multimessenger data.

    See the full article here .

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  • richardmitnick 9:03 am on June 7, 2022 Permalink | Reply
    Tags: "Neutrinos from a Black Hole Snack", An event named AT2019fdr from November 2019., , , , , , , TDE: tidal disruption event   

    From “Physics News” : “Neutrinos from a Black Hole Snack” 

    About Physics

    From “Physics News”

    June 3, 2022
    Mark Buchanan

    Researchers have found new evidence that high-energy neutrinos are emitted when a black hole gobbles up a hapless star.

    1

    Doomed star. When a star is torn apart by a black hole—as shown in this artist’s representation—high-energy neutrinos can be produced. An observatory at the South Pole has detected a neutrino that appears to have come from one of these events.
    Credit: NASA/CXC/M.Weiss.

    Neutrinos of extremely high energy routinely strike Earth. Physicists suspect these particles are created in cosmic processes involving black holes, but exactly which process dominates this production remains uncertain. Now astronomers report the detection of a high-energy neutrino linked directly to a tidal disruption event (TDE)—the violent shredding of a star by the intense gravity of a nearby black hole [1]. This observation is the second strong association of a high-energy neutrino with such a star-devouring event, allowing researchers to make a crude initial estimate of how many neutrinos are produced through this mechanism.

    High-energy neutrinos—roughly those in the TeV energy range and above—give physicists information on some of the most violent astrophysical events in the Universe, many occurring well outside our Galaxy. Because neutrinos interact with matter so weakly, they travel unaltered over immense distances from their original production sites. Theoretical models—backed by observations—have linked them to a wide variety of potential sources, including active galactic nuclei, which are supermassive black holes that produce beams of energetic particles as they devour surrounding gas. TDEs offer another possibility, as copious neutrinos should be generated if a black hole tears apart a nearby orbiting star (see Research News: “Revolution” for Alternative Black Hole Probe). Most generation scenarios involve large black holes.

    Currently, however, researchers remain unable to estimate the relative importance of these distinct processes. For example, active galactic nuclei are far more common than TDEs, but the latter could emit a very high percentage of their energy as neutrinos. As a result, “We don’t really know where the majority of high-energy cosmic neutrinos come from,” says physicist Marek Kowalski of Humboldt University in Germany. Knowing the neutrino origins would help researchers understand the extreme astrophysical events that generate some of the most energetic cosmic rays in the Universe.

    Last year, Kowalski and his colleagues reported the first coincidence detection of a neutrino and a TDE [2]. The neutrino was spotted by the IceCube Neutrino Observatory—an array of detectors buried deep within the ice near the South Pole.

    _____________________________________________________
    U Wisconsin IceCube neutrino observatory

    U Wisconsin IceCube Neutrino Observatory neutrino detector at the at the Amundsen-Scott South Pole Station in Antarctica South Pole, elevation of 2,835 metres (9,301 feet).
    IceCube employs more than 5000 detectors lowered on 86 strings into almost 100 holes in the Antarctic ice NSF B. Gudbjartsson, IceCube Collaboration.

    Lunar Icecube

    IceCube Gen-2 DeepCore PINGU annotated

    IceCube neutrino detector interior.

    IceCube DeepCore annotated.

    IceCube Gen-2 DeepCore PINGU annotated

    DM-Ice II at IceCube annotated.


    _____________________________________________________

    The researchers found that the neutrino’s location in the sky corresponded to a long-lived burst of radiation that exhibited TDE signatures in archived astronomical data.


    DESY, Science Communication Lab.
    The animation depicts a tidal disruption event of the kind believed to have produced a recently detected high-energy neutrino. The event begins when a star orbits too close to a supermassive black hole, causing it to stretch out into long noodle-like strands, in a process called “spaghettification.” The star’s torn-up remnants spiral into the black hole, driving reactions that create high-energy neutrinos and other particles.

    Adding to this earlier finding, Kowalski and colleagues now report finding a second TDE closely linked to a different neutrino, which was detected on 30 May 2020 by IceCube. The researchers discovered the association by using computers to sort through a database of astronomical observations collected by the Zwicky Transient Facility, California, which uses a wide-view, optical camera to scan the entire Northern Sky every two days.

    In their search, the team discovered an event named AT2019fdr from November 2019, which was closely associated with the most likely direction of the high-energy neutrino. Exploiting data from other telescopes, they also identified specific radiative signatures expected for a TDE.

    This association is strong evidence, the researchers argue, that this neutrino was created during a years-long radiative flare released by the black-hole–star interaction. Based on a preliminary statistical analysis, they estimate that there is only a 0.034% probability that the neutrino’s direction just happened by chance to match that of the TDE. But they say that further work on localizing the neutrino direction could change this estimate.

    “This is certainly a major result,” says astrophysicist Nicholas Stone of the Racah Institute of Physics in Israel. He says that the first observed association gave credence to TDEs being sources for high-energy neutrinos, but it was hard to be confident with just one event. “With a second neutrino-TDE association, we are now on much firmer footing.”

    This second detection does more than just bolster confidence in the earlier detection, says team member Simeon Reusch, a Ph.D. student of Kowalski’s. It also makes possible a crude estimate of the TDE contribution to high-energy neutrino production. Comparing these two observations with the full catalog of cosmic neutrinos detected by the IceCube observatory, the researchers conclude that at least 7.8% of high-energy neutrinos must be coming from TDEs. “Because tidal disruption events are so rare, our findings indicate that they are probably extremely efficient neutrino factories,” Kowalski says.

    References

    S. Reusch et al., “Candidate tidal disruption event AT2019fdr coincident with a high-energy neutrino,” Phys. Rev. Lett. 128, 221101 (2022).
    R. Stein et al., “A tidal disruption event coincident with a high-energy neutrino,” Nat. Astron. 5, 510 (2021).

    See the full article here .

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    Physicists are drowning in a flood of research papers in their own fields and coping with an even larger deluge in other areas of physics. How can an active researcher stay informed about the most important developments in physics? Physics News highlights a selection of papers from the Physical Review journals. In consultation with expert scientists, the editors choose these papers for their importance and/or intrinsic interest. To highlight these papers, Physics News features three kinds of articles: Viewpoints are commentaries written by active researchers, who are asked to explain the results to physicists in other subfields. Focus stories are written by professional science writers in a journalistic style and are intended to be accessible to students and non-experts. Synopses are brief editor-written summaries. Physics News provides a much-needed guide to the best in physics, and we welcome your comments.

     
  • richardmitnick 12:24 pm on October 16, 2021 Permalink | Reply
    Tags: "A Mysterious 'Ghost Particle' Probably Didn't Come From a Black Hole's Meal After All", A high-energy neutrino traced back to a violent encounter between a black hole and a star needs a different origin story new research has found., , , TDE: tidal disruption event, The encounter known as AT2019dsg   

    From Northwestern University (US) and Harvard-Smithsonian Center for Astrophysics (US) via Science Alert (US) : “A Mysterious ‘Ghost Particle’ Probably Didn’t Come From a Black Hole’s Meal After All” 

    Northwestern U bloc

    From Northwestern University (US)

    and

    Harvard-Smithsonian Center for Astrophysics (US)

    via

    ScienceAlert

    Science Alert (US)

    16 OCTOBER 2021
    MICHELLE STARR

    1
    Animation of AT2019dsg. (DESY Electron Synchrotron[ Deütsches Elektronen-Synchrotron](DE), Science Communication Lab)

    A high-energy neutrino traced back to a violent encounter between a black hole and a star needs a different origin story new research has found.

    An analysis of radio waves emitted by the encounter, known as AT2019dsg, has shown that it was fairly ordinary, at least as far as a black hole tearing apart a star goes. That means that the event wasn’t energetic enough to produce the neutrino months later – that the events were merely coincidental.

    “Instead of seeing the bright jet of material needed for this, we see a fainter radio outflow of material,” said astronomer Kate Alexander of Northwestern University. “Instead of a powerful firehose, we see a soft wind.”

    The death of a star by a black hole isn’t a neat and tidy process. When an errant star comes close enough to a black hole that it’s snared by the latter object’s gravity, the colossal tidal force of the black hole – the product of its gravitational field – first stretches and then pulls the star so hard that it’s torn apart.

    This is called a tidal disruption event (TDE). It releases a brilliant flare of light, glowing brightly as half of the debris from the disintegrated star swirls into a disc around the black hole, generating immense heat and light before it’s pulled inexorably beyond the event horizon. The other half of the debris gets flung out into space.

    AT2019dsg, first detected on 9 April 2019, was just such an event, from a galaxy 750 million light-years away. X-ray and radio observations confirmed a supermassive black hole 30 million times the mass of the Sun undergoing a TDE. Nearly six months later, on 1 October 2019, a neutrino called IC191001A was detected at the IceCube neutrino detector in Antarctica, clocking in at a whopping energy level of over 200 teraelectronvolts.

    Neutrinos are called ‘ghost particles’ because their mass is almost zero, they travel at near light-speed, and they don’t really interact with normal matter; to a neutrino, the Universe would be all but incorporeal.

    Occasionally, however, they do interact, and this is how IceCube works. When a neutrino interacts with the Antarctic ice, it can create a flash of light. With detectors tunneled deep under that ice, those flashes really stand out.

    Based on characteristics such as how the light propagates, and how bright it is, scientists can work out the energy level of the neutrino, and the direction from whence it came. IC191001A came from the direction of AT2019dsg, so closely that scientists calculated just a 0.2 percent chance that the neutrino and TDE were unrelated.

    But that raised some significant issues.

    “If this neutrino somehow came from AT2019dsg, it begs the question: Why haven’t we spotted neutrinos associated with supernovae at this distance or closer?” said astronomer Yvette Cendes of the Center for Astrophysics | Harvard & Smithsonian (US).

    “They are much more common and have the same energy velocities.”

    The research team, led by Cendes, used the Atacama Large Millimeter/submillimeter Array in Chile to observe AT2019dsg for over 500 days in radio wavelengths.

    They found that the TDE continued to brighten in radio wavelengths for around 200 days, at which point it peaked and began to slowly dim.

    They also calculated the total amount of energy in the TDE outflow: It was about as much energy emitted by the Sun over 30 million years. That’s pretty standard for a TDE, as well as type Ib and type Ic supernovae.

    In order to produce a neutrino as energetic as IC191001A, the energy of the outflow would need to have been around 1,000 times greater.

    In addition, it would need to have had a strange geometry, which AT2019dsg’s outflow did not. AT2019dsg is really rather ordinary, after all. Since IC191001A is not ordinary, a new explanation might be warranted.

    But there’s a lot we still don’t know about neutrinos, and TDEs for that matter. This means AT2019dsg is going to continue being of interest.

    “We’re probably going to check in on this one again,” Cendes said. “This particular black hole is still feeding.”

    The research has been published in The Astrophysical Journal.

    See the full article here .

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    Please help promote STEM in your local schools.

    Stem Education Coalition

    The Harvard-Smithsonian Center for Astrophysics (US) combines the resources and research facilities of the Harvard College Observatory(US) and the Smithsonian Astrophysical Observatory(US) under a single director to pursue studies of those basic physical processes that determine the nature and evolution of the universe. The Smithsonian Astrophysical Observatory(US) is a bureau of the Smithsonian Institution(US), founded in 1890. The Harvard College Observatory, founded in 1839, is a research institution of the Faculty of Arts and Sciences, Harvard University(US), and provides facilities and substantial other support for teaching activities of the Department of Astronomy.

    Founded in 1973 and headquartered in Cambridge, Massachusetts, the CfA leads a broad program of research in astronomy, astrophysics, Earth and space sciences, as well as science education. The CfA either leads or participates in the development and operations of more than fifteen ground- and space-based astronomical research observatories across the electromagnetic spectrum, including the forthcoming Giant Magellan Telescope(CL) and the Chandra X-ray Observatory(US), one of NASA’s Great Observatories.

    Hosting more than 850 scientists, engineers, and support staff, the CfA is among the largest astronomical research institutes in the world. Its projects have included Nobel Prize-winning advances in cosmology and high energy astrophysics, the discovery of many exoplanets, and the first image of a black hole. The CfA also serves a major role in the global astrophysics research community: the CfA’s Astrophysics Data System(ADS)(US), for example, has been universally adopted as the world’s online database of astronomy and physics papers. Known for most of its history as the “Harvard-Smithsonian Center for Astrophysics”, the CfA rebranded in 2018 to its current name in an effort to reflect its unique status as a joint collaboration between Harvard University and the Smithsonian Institution. The CfA’s current Director (since 2004) is Charles R. Alcock, who succeeds Irwin I. Shapiro (Director from 1982 to 2004) and George B. Field (Director from 1973 to 1982).

    The Center for Astrophysics | Harvard & Smithsonian is not formally an independent legal organization, but rather an institutional entity operated under a Memorandum of Understanding between Harvard University and the Smithsonian Institution. This collaboration was formalized on July 1, 1973, with the goal of coordinating the related research activities of the Harvard College Observatory (HCO) and the Smithsonian Astrophysical Observatory (SAO) under the leadership of a single Director, and housed within the same complex of buildings on the Harvard campus in Cambridge, Massachusetts. The CfA’s history is therefore also that of the two fully independent organizations that comprise it. With a combined lifetime of more than 300 years, HCO and SAO have been host to major milestones in astronomical history that predate the CfA’s founding.

    History of the Smithsonian Astrophysical Observatory (SAO)

    Samuel Pierpont Langley, the third Secretary of the Smithsonian, founded the Smithsonian Astrophysical Observatory on the south yard of the Smithsonian Castle (on the U.S. National Mall) on March 1,1890. The Astrophysical Observatory’s initial, primary purpose was to “record the amount and character of the Sun’s heat”. Charles Greeley Abbot was named SAO’s first director, and the observatory operated solar telescopes to take daily measurements of the Sun’s intensity in different regions of the optical electromagnetic spectrum. In doing so, the observatory enabled Abbot to make critical refinements to the Solar constant, as well as to serendipitously discover Solar variability. It is likely that SAO’s early history as a solar observatory was part of the inspiration behind the Smithsonian’s “sunburst” logo, designed in 1965 by Crimilda Pontes.

    In 1955, the scientific headquarters of SAO moved from Washington, D.C. to Cambridge, Massachusetts to affiliate with the Harvard College Observatory (HCO). Fred Lawrence Whipple, then the chairman of the Harvard Astronomy Department, was named the new director of SAO. The collaborative relationship between SAO and HCO therefore predates the official creation of the CfA by 18 years. SAO’s move to Harvard’s campus also resulted in a rapid expansion of its research program. Following the launch of Sputnik (the world’s first human-made satellite) in 1957, SAO accepted a national challenge to create a worldwide satellite-tracking network, collaborating with the United States Air Force on Project Space Track.

    With the creation of National Aeronautics and Space Administration(US) the following year and throughout the space race, SAO led major efforts in the development of orbiting observatories and large ground-based telescopes, laboratory and theoretical astrophysics, as well as the application of computers to astrophysical problems.

    History of Harvard College Observatory (HCO)

    Partly in response to renewed public interest in astronomy following the 1835 return of Halley’s Comet, the Harvard College Observatory was founded in 1839, when the Harvard Corporation appointed William Cranch Bond as an “Astronomical Observer to the University”. For its first four years of operation, the observatory was situated at the Dana-Palmer House (where Bond also resided) near Harvard Yard, and consisted of little more than three small telescopes and an astronomical clock. In his 1840 book recounting the history of the college, then Harvard President Josiah Quincy III noted that “…there is wanted a reflecting telescope equatorially mounted…”. This telescope, the 15-inch “Great Refractor”, opened seven years later (in 1847) at the top of Observatory Hill in Cambridge (where it still exists today, housed in the oldest of the CfA’s complex of buildings). The telescope was the largest in the United States from 1847 until 1867. William Bond and pioneer photographer John Adams Whipple used the Great Refractor to produce the first clear Daguerrotypes of the Moon (winning them an award at the 1851 Great Exhibition in London). Bond and his son, George Phillips Bond (the second Director of HCO), used it to discover Saturn’s 8th moon, Hyperion (which was also independently discovered by William Lassell).

    Under the directorship of Edward Charles Pickering from 1877 to 1919, the observatory became the world’s major producer of stellar spectra and magnitudes, established an observing station in Peru, and applied mass-production methods to the analysis of data. It was during this time that HCO became host to a series of major discoveries in astronomical history, powered by the Observatory’s so-called “Computers” (women hired by Pickering as skilled workers to process astronomical data). These “Computers” included Williamina Fleming; Annie Jump Cannon; Henrietta Swan Leavitt; Florence Cushman; and Antonia Maury, all widely recognized today as major figures in scientific history. Henrietta Swan Leavitt, for example, discovered the so-called period-luminosity relation for Classical Cepheid variable stars, establishing the first major “standard candle” with which to measure the distance to galaxies. Now called “Leavitt’s Law”, the discovery is regarded as one of the most foundational and important in the history of astronomy; astronomers like Edwin Hubble, for example, would later use Leavitt’s Law to establish that the Universe is expanding, the primary piece of evidence for the Big Bang model.

    Upon Pickering’s retirement in 1921, the Directorship of HCO fell to Harlow Shapley (a major participant in the so-called “Great Debate” of 1920). This era of the observatory was made famous by the work of Cecelia Payne-Gaposchkin, who became the first woman to earn a Ph.D. in astronomy from Radcliffe College (a short walk from the Observatory). Payne-Gapochkin’s 1925 thesis proposed that stars were composed primarily of hydrogen and helium, an idea thought ridiculous at the time. Between Shapley’s tenure and the formation of the CfA, the observatory was directed by Donald H. Menzel and then Leo Goldberg, both of whom maintained widely recognized programs in solar and stellar astrophysics. Menzel played a major role in encouraging the Smithsonian Astrophysical Observatory to move to Cambridge and collaborate more closely with HCO.

    Joint history as the Center for Astrophysics (CfA)

    The collaborative foundation for what would ultimately give rise to the Center for Astrophysics began with SAO’s move to Cambridge in 1955. Fred Whipple, who was already chair of the Harvard Astronomy Department (housed within HCO since 1931), was named SAO’s new director at the start of this new era; an early test of the model for a unified Directorship across HCO and SAO. The following 18 years would see the two independent entities merge ever closer together, operating effectively (but informally) as one large research center.

    This joint relationship was formalized as the new Harvard–Smithsonian Center for Astrophysics on July 1, 1973. George B. Field, then affiliated with UC Berkeley(US), was appointed as its first Director. That same year, a new astronomical journal, the CfA Preprint Series was created, and a CfA/SAO instrument flying aboard Skylab discovered coronal holes on the Sun. The founding of the CfA also coincided with the birth of X-ray astronomy as a new, major field that was largely dominated by CfA scientists in its early years. Riccardo Giacconi, regarded as the “father of X-ray astronomy”, founded the High Energy Astrophysics Division within the new CfA by moving most of his research group (then at American Sciences and Engineering) to SAO in 1973. That group would later go on to launch the Einstein Observatory (the first imaging X-ray telescope) in 1976, and ultimately lead the proposals and development of what would become the Chandra X-ray Observatory. Chandra, the second of NASA’s Great Observatories and still the most powerful X-ray telescope in history, continues operations today as part of the CfA’s Chandra X-ray Center. Giacconi would later win the 2002 Nobel Prize in Physics for his foundational work in X-ray astronomy.

    Shortly after the launch of the Einstein Observatory, the CfA’s Steven Weinberg won the 1979 Nobel Prize in Physics for his work on electroweak unification. The following decade saw the start of the landmark CfA Redshift Survey (the first attempt to map the large scale structure of the Universe), as well as the release of the Field Report, a highly influential Astronomy & Astrophysics Decadal Survey chaired by the outgoing CfA Director George Field. He would be replaced in 1982 by Irwin Shapiro, who during his tenure as Director (1982 to 2004) oversaw the expansion of the CfA’s observing facilities around the world.

    CfA-led discoveries throughout this period include canonical work on Supernova 1987A, the “CfA2 Great Wall” (then the largest known coherent structure in the Universe), the best-yet evidence for supermassive black holes, and the first convincing evidence for an extrasolar planet.

    The 1990s also saw the CfA unwittingly play a major role in the history of computer science and the internet: in 1990, SAO developed SAOImage, one of the world’s first X11-based applications made publicly available (its successor, DS9, remains the most widely used astronomical FITS image viewer worldwide). During this time, scientists at the CfA also began work on what would become the Astrophysics Data System (ADS), one of the world’s first online databases of research papers. By 1993, the ADS was running the first routine transatlantic queries between databases, a foundational aspect of the internet today.

    The CfA Today

    Research at the CfA

    Charles Alcock, known for a number of major works related to massive compact halo objects, was named the third director of the CfA in 2004. Today Alcock overseas one of the largest and most productive astronomical institutes in the world, with more than 850 staff and an annual budget in excess of $100M. The Harvard Department of Astronomy, housed within the CfA, maintains a continual complement of approximately 60 Ph.D. students, more than 100 postdoctoral researchers, and roughly 25 undergraduate majors in astronomy and astrophysics from Harvard College. SAO, meanwhile, hosts a long-running and highly rated REU Summer Intern program as well as many visiting graduate students. The CfA estimates that roughly 10% of the professional astrophysics community in the United States spent at least a portion of their career or education there.

    The CfA is either a lead or major partner in the operations of the Fred Lawrence Whipple Observatory, the Submillimeter Array, MMT Observatory, the South Pole Telescope, VERITAS, and a number of other smaller ground-based telescopes. The CfA’s 2019-2024 Strategic Plan includes the construction of the Giant Magellan Telescope as a driving priority for the Center.

    CFA Harvard Smithsonian Submillimeter Array on MaunaKea, Hawaii, USA, Altitude 4,205 m (13,796 ft).

    South Pole Telescope SPTPOL. The SPT collaboration is made up of over a dozen (mostly North American) institutions, including The University of Chicago (US); The University of California Berkeley (US); Case Western Reserve University (US); Harvard/Smithsonian Astrophysical Observatory (US); The University of Colorado, Boulder; McGill(CA) University, The University of Illinois, Urbana-Champaign;The University of California, Davis; Ludwig Maximilians Universität München(DE); DOE’s Argonne National Laboratory; and The National Institute for Standards and Technology. The University of California, Davis; Ludwig Maximilians Universität München(DE); DOE’s Argonne National Laboratory; and The National Institute for Standards and Technology. It is funded by the National Science Foundation(US).

    Along with the Chandra X-ray Observatory, the CfA plays a central role in a number of space-based observing facilities, including the recently launched Parker Solar Probe, Kepler Space Telescope, the Solar Dynamics Observatory (SDO), and HINODE. The CfA, via the Smithsonian Astrophysical Observatory, recently played a major role in the Lynx X-ray Observatory, a NASA-Funded Large Mission Concept Study commissioned as part of the 2020 Decadal Survey on Astronomy and Astrophysics (“Astro2020”). If launched, Lynx would be the most powerful X-ray observatory constructed to date, enabling order-of-magnitude advances in capability over Chandra.

    NASA Parker Solar Probe Plus named to honor Pioneering Physicist Eugene Parker.

    SAO is one of the 13 stakeholder institutes for the Event Horizon Telescope Board, and the CfA hosts its Array Operations Center. In 2019, the project revealed the first direct image of a black hole.

    The result is widely regarded as a triumph not only of observational radio astronomy, but of its intersection with theoretical astrophysics. Union of the observational and theoretical subfields of astrophysics has been a major focus of the CfA since its founding.

    In 2018, the CfA rebranded, changing its official name to the “Center for Astrophysics | Harvard & Smithsonian” in an effort to reflect its unique status as a joint collaboration between Harvard University and the Smithsonian Institution. Today, the CfA receives roughly 70% of its funding from NASA, 22% from Smithsonian federal funds, and 4% from the National Science Foundation. The remaining 4% comes from contributors including the United States Department of Energy, the Annenberg Foundation, as well as other gifts and endowments.

    Northwestern South Campus
    South Campus

    Northwestern University (US) is a private research university in Evanston, Illinois. Founded in 1851 to serve the former Northwest Territory, the university is a founding member of the Big Ten Conference.

    On May 31, 1850, nine men gathered to begin planning a university that would serve the Northwest Territory.

    Given that they had little money, no land and limited higher education experience, their vision was ambitious. But through a combination of creative financing, shrewd politicking, religious inspiration and an abundance of hard work, the founders of Northwestern University were able to make that dream a reality.

    In 1853, the founders purchased a 379-acre tract of land on the shore of Lake Michigan 12 miles north of Chicago. They established a campus and developed the land near it, naming the surrounding town Evanston in honor of one of the University’s founders, John Evans. After completing its first building in 1855, Northwestern began classes that fall with two faculty members and 10 students.
    Twenty-one presidents have presided over Northwestern in the years since. The University has grown to include 12 schools and colleges, with additional campuses in Chicago and Doha, Qatar.

    Northwestern is known for its focus on interdisciplinary education, extensive research output, and student traditions. The university provides instruction in over 200 formal academic concentrations, including various dual degree programs. The university is composed of eleven undergraduate, graduate, and professional schools, which include the Kellogg School of Management, the Pritzker School of Law, the Feinberg School of Medicine, the Weinberg College of Arts and Sciences, the Bienen School of Music, the McCormick School of Engineering and Applied Science, the Medill School of Journalism, the School of Communication, the School of Professional Studies, the School of Education and Social Policy, and The Graduate School. As of fall 2019, the university had 21,946 enrolled students, including 8,327 undergraduates and 13,619 graduate students.

    Valued at $12.2 billion, Northwestern’s endowment is among the largest university endowments in the United States. Its numerous research programs bring in nearly $900 million in sponsored research each year.

    Northwestern’s main 240-acre (97 ha) campus lies along the shores of Lake Michigan in Evanston, 12 miles north of Downtown Chicago. The university’s law, medical, and professional schools, along with its nationally ranked Northwestern Memorial Hospital, are located on a 25-acre (10 ha) campus in Chicago’s Streeterville neighborhood. The university also maintains a campus in Doha, Qatar and locations in San Francisco, California, Washington, D.C. and Miami, Florida.

    As of October 2020, Northwestern’s faculty and alumni have included 1 Fields Medalist, 22 Nobel Prize laureates, 40 Pulitzer Prize winners, 6 MacArthur Fellows, 17 Rhodes Scholars, 27 Marshall Scholars, 23 National Medal of Science winners, 11 National Humanities Medal recipients, 84 members of the American Academy of Arts and Sciences, 10 living billionaires, 16 Olympic medalists, and 2 U.S. Supreme Court Justices. Northwestern alumni have founded notable companies and organizations such as the Mayo Clinic, The Blackstone Group, Kirkland & Ellis, U.S. Steel, Guggenheim Partners, Accenture, Aon Corporation, AQR Capital, Booz Allen Hamilton, and Melvin Capital.

    The foundation of Northwestern University can be traced to a meeting on May 31, 1850, of nine prominent Chicago businessmen, Methodist leaders, and attorneys who had formed the idea of establishing a university to serve what had been known from 1787 to 1803 as the Northwest Territory. On January 28, 1851, the Illinois General Assembly granted a charter to the Trustees of the North-Western University, making it the first chartered university in Illinois. The school’s nine founders, all of whom were Methodists (three of them ministers), knelt in prayer and worship before launching their first organizational meeting. Although they affiliated the university with the Methodist Episcopal Church, they favored a non-sectarian admissions policy, believing that Northwestern should serve all people in the newly developing territory by bettering the economy in Evanston.

    John Evans, for whom Evanston is named, bought 379 acres (153 ha) of land along Lake Michigan in 1853, and Philo Judson developed plans for what would become the city of Evanston, Illinois. The first building, Old College, opened on November 5, 1855. To raise funds for its construction, Northwestern sold $100 “perpetual scholarships” entitling the purchaser and his heirs to free tuition. Another building, University Hall, was built in 1869 of the same Joliet limestone as the Chicago Water Tower, also built in 1869, one of the few buildings in the heart of Chicago to survive the Great Chicago Fire of 1871. In 1873 the Evanston College for Ladies merged with Northwestern, and Frances Willard, who later gained fame as a suffragette and as one of the founders of the Woman’s Christian Temperance Union (WCTU), became the school’s first dean of women (Willard Residential College, built in 1938, honors her name). Northwestern admitted its first female students in 1869, and the first woman was graduated in 1874.

    Northwestern fielded its first intercollegiate football team in 1882, later becoming a founding member of the Big Ten Conference. In the 1870s and 1880s, Northwestern affiliated itself with already existing schools of law, medicine, and dentistry in Chicago. Northwestern University Pritzker School of Law is the oldest law school in Chicago. As the university’s enrollments grew, these professional schools were integrated with the undergraduate college in Evanston; the result was a modern research university combining professional, graduate, and undergraduate programs, which gave equal weight to teaching and research. By the turn of the century, Northwestern had grown in stature to become the third largest university in the United States after Harvard University(US) and the University of Michigan(US).

    Under Walter Dill Scott’s presidency from 1920 to 1939, Northwestern began construction of an integrated campus in Chicago designed by James Gamble Rogers, noted for his design of the Yale University(US) campus, to house the professional schools. The university also established the Kellogg School of Management and built several prominent buildings on the Evanston campus, including Dyche Stadium, now named Ryan Field, and Deering Library among others. In the 1920s, Northwestern became one of the first six universities in the United States to establish a Naval Reserve Officers Training Corps (NROTC). In 1939, Northwestern hosted the first-ever NCAA Men’s Division I Basketball Championship game in the original Patten Gymnasium, which was later demolished and relocated farther north, along with the Dearborn Observatory, to make room for the Technological Institute.

    After the golden years of the 1920s, the Great Depression in the United States (1929–1941) had a severe impact on the university’s finances. Its annual income dropped 25 percent from $4.8 million in 1930-31 to $3.6 million in 1933-34. Investment income shrank, fewer people could pay full tuition, and annual giving from alumni and philanthropists fell from $870,000 in 1932 to a low of $331,000 in 1935. The university responded with two salary cuts of 10 percent each for all employees. It imposed hiring and building freezes and slashed appropriations for maintenance, books, and research. Having had a balanced budget in 1930-31, the university now faced deficits of roughly $100,000 for the next four years. Enrollments fell in most schools, with law and music suffering the biggest declines. However, the movement toward state certification of school teachers prompted Northwestern to start a new graduate program in education, thereby bringing in new students and much needed income. In June 1933, Robert Maynard Hutchins, president of the University of Chicago(US), proposed a merger of the two universities, estimating annual savings of $1.7 million. The two presidents were enthusiastic, and the faculty liked the idea; many Northwestern alumni, however, opposed it, fearing the loss of their Alma Mater and its many traditions that distinguished Northwestern from Chicago. The medical school, for example, was oriented toward training practitioners, and alumni feared it would lose its mission if it were merged into the more research-oriented University of Chicago Medical School. The merger plan was ultimately dropped. In 1935, the Deering family rescued the university budget with an unrestricted gift of $6 million, bringing the budget up to $5.4 million in 1938-39. This allowed many of the previous spending cuts to be restored, including half of the salary reductions.

    Like other American research universities, Northwestern was transformed by World War II (1939–1945). Regular enrollment fell dramatically, but the school opened high-intensity, short-term programs that trained over 50,000 military personnel, including future president John F. Kennedy. Northwestern’s existing NROTC program proved to be a boon to the university as it trained over 36,000 sailors over the course of the war, leading Northwestern to be called the “Annapolis of the Midwest.” Franklyn B. Snyder led the university from 1939 to 1949, and after the war, surging enrollments under the G.I. Bill drove dramatic expansion of both campuses. In 1948, prominent anthropologist Melville J. Herskovits founded the Program of African Studies at Northwestern, the first center of its kind at an American academic institution. J. Roscoe Miller’s tenure as president from 1949 to 1970 saw an expansion of the Evanston campus, with the construction of the Lakefill on Lake Michigan, growth of the faculty and new academic programs, and polarizing Vietnam-era student protests. In 1978, the first and second Unabomber attacks occurred at Northwestern University. Relations between Evanston and Northwestern became strained throughout much of the post-war era because of episodes of disruptive student activism, disputes over municipal zoning, building codes, and law enforcement, as well as restrictions on the sale of alcohol near campus until 1972. Northwestern’s exemption from state and municipal property-tax obligations under its original charter has historically been a source of town-and-gown tension.

    Although government support for universities declined in the 1970s and 1980s, President Arnold R. Weber was able to stabilize university finances, leading to a revitalization of its campuses. As admissions to colleges and universities grew increasingly competitive in the 1990s and 2000s, President Henry S. Bienen’s tenure saw a notable increase in the number and quality of undergraduate applicants, continued expansion of the facilities and faculty, and renewed athletic competitiveness. In 1999, Northwestern student journalists uncovered information exonerating Illinois death-row inmate Anthony Porter two days before his scheduled execution. The Innocence Project has since exonerated 10 more men. On January 11, 2003, in a speech at Northwestern School of Law’s Lincoln Hall, then Governor of Illinois George Ryan announced that he would commute the sentences of more than 150 death-row inmates.

    In the 2010s, a 5-year capital campaign resulted in a new music center, a replacement building for the business school, and a $270 million athletic complex. In 2014, President Barack Obama delivered a seminal economics speech at the Evanston campus.

    Organization and administration

    Governance

    Northwestern is privately owned and governed by an appointed Board of Trustees, which is composed of 70 members and, as of 2011, has been chaired by William A. Osborn ’69. The board delegates its power to an elected president who serves as the chief executive officer of the university. Northwestern has had sixteen presidents in its history (excluding interim presidents). The current president, economist Morton O. Schapiro, succeeded Henry Bienen whose 14-year tenure ended on August 31, 2009. The president maintains a staff of vice presidents, directors, and other assistants for administrative, financial, faculty, and student matters. Kathleen Haggerty assumed the role of interim provost for the university in April 2020.

    Students are formally involved in the university’s administration through the Associated Student Government, elected representatives of the undergraduate students, and the Graduate Student Association, which represents the university’s graduate students.

    The admission requirements, degree requirements, courses of study, and disciplinary and degree recommendations for each of Northwestern’s 12 schools are determined by the voting members of that school’s faculty (assistant professor and above).

    Undergraduate and graduate schools

    Evanston Campus:

    Weinberg College of Arts and Sciences (1851)
    School of Communication (1878)
    Bienen School of Music (1895)
    McCormick School of Engineering and Applied Science (1909)
    Medill School of Journalism (1921)
    School of Education and Social Policy (1926)
    School of Professional Studies (1933)

    Graduate and professional

    Evanston Campus

    Kellogg School of Management (1908)
    The Graduate School

    Chicago Campus

    Feinberg School of Medicine (1859)
    Kellogg School of Management (1908)
    Pritzker School of Law (1859)
    School of Professional Studies (1933)

    Northwestern University had a dental school from 1891 to May 31, 2001, when it closed.

    Endowment

    In 1996, Princess Diana made a trip to Evanston to raise money for the university hospital’s Robert H. Lurie Comprehensive Cancer Center at the invitation of then President Bienen. Her visit raised a total of $1.5 million for cancer research.

    In 2003, Northwestern finished a five-year capital campaign that raised $1.55 billion, exceeding its fundraising goal by $550 million.

    In 2014, Northwestern launched the “We Will” campaign with a fundraising goal of $3.75 billion. As of December 31, 2019, the university has received $4.78 billion from 164,026 donors.

    Sustainability

    In January 2009, the Green Power Partnership (sponsored by the EPA) listed Northwestern as one of the top 10 universities in the country in purchasing energy from renewable sources. The university matches 74 million kilowatt hours (kWh) of its annual energy use with Green-e Certified Renewable Energy Certificates (RECs). This green power commitment represents 30 percent of the university’s total annual electricity use and places Northwestern in the EPA’s Green Power Leadership Club. The Initiative for Sustainability and Energy at Northwestern (ISEN), supporting research, teaching and outreach in these themes, was launched in 2008.

    Northwestern requires that all new buildings be LEED-certified. Silverman Hall on the Evanston campus was awarded Gold LEED Certification in 2010; Wieboldt Hall on the Chicago campus was awarded Gold LEED Certification in 2007, and the Ford Motor Company Engineering Design Center on the Evanston campus was awarded Silver LEED Certification in 2006. New construction and renovation projects will be designed to provide at least a 20% improvement over energy code requirements where feasible. At the beginning of the 2008–09 academic year, the university also released the Evanston Campus Framework Plan, which outlines plans for future development of the university’s Evanston campus. The plan not only emphasizes sustainable building construction, but also focuses on reducing the energy costs of transportation by optimizing pedestrian and bicycle access. Northwestern has had a comprehensive recycling program in place since 1990. The university recycles over 1,500 tons of waste, or 30% of all waste produced on campus, each year. All landscape waste at the university is composted.

    Academics

    Education and rankings

    Northwestern is a large, residential research university, and is frequently ranked among the top universities in the United States. The university is a leading institution in the fields of materials engineering, chemistry, business, economics, education, journalism, and communications. It is also prominent in law and medicine. Accredited by the Higher Learning Commission and the respective national professional organizations for chemistry, psychology, business, education, journalism, music, engineering, law, and medicine, the university offers 124 undergraduate programs and 145 graduate and professional programs. Northwestern conferred 2,190 bachelor’s degrees, 3,272 master’s degrees, 565 doctoral degrees, and 444 professional degrees in 2012–2013. Since 1951, Northwestern has awarded 520 honorary degrees. Northwestern also has chapters of academic honor societies such as Phi Beta Kappa (Alpha of Illinois), Eta Kappa Nu, Tau Beta Pi, Eta Sigma Phi (Beta Chapter), Lambda Pi Eta, and Alpha Sigma Lambda (Alpha Chapter).

    The four-year, full-time undergraduate program comprises the majority of enrollments at the university. Although there is no university-wide core curriculum, a foundation in the liberal arts and sciences is required for all majors; individual degree requirements are set by the faculty of each school. The university heavily emphasizes interdisciplinary learning, with 72% of undergrads combining two or more areas of study. Northwestern’s full-time undergraduate and graduate programs operate on an approximately 10-week academic quarter system with the academic year beginning in late September and ending in early June. Undergraduates typically take four courses each quarter and twelve courses in an academic year and are required to complete at least twelve quarters on campus to graduate. Northwestern offers honors, accelerated, and joint degree programs in medicine, science, mathematics, engineering, and journalism. The comprehensive doctoral graduate program has high coexistence with undergraduate programs.

    Despite being a mid-sized university, Northwestern maintains a relatively low student to faculty ratio of 6:1.

    Research

    Northwestern was elected to the Association of American Universities (US)in 1917 and is classified as an R1 university, denoting “very high” research activity. Northwestern’s schools of management, engineering, and communication are among the most academically productive in the nation. The university received $887.3 million in research funding in 2019 and houses over 90 school-based and 40 university-wide research institutes and centers. Northwestern also supports nearly 1,500 research laboratories across two campuses, predominately in the medical and biological sciences.

    Northwestern is home to the Center for Interdisciplinary Exploration and Research in Astrophysics, Northwestern Institute for Complex Systems, Nanoscale Science and Engineering Center, Materials Research Center, Center for Quantum Devices, Institute for Policy Research, International Institute for Nanotechnology, Center for Catalysis and Surface Science, Buffet Center for International and Comparative Studies, the Initiative for Sustainability and Energy at Northwestern, and the Argonne/Northwestern Solar Energy Research Center among other centers for interdisciplinary research.

    Student body

    Northwestern enrolled 8,186 full-time undergraduate, 9,904 full-time graduate, and 3,856 part-time students in the 2019–2020 academic year. The freshman retention rate for that year was 98%. 86% of students graduated after four years and 92% graduated after five years. These numbers can largely be attributed to the university’s various specialized degree programs, such as those that allow students to earn master’s degrees with a one or two year extension of their undergraduate program.

    The undergraduate population is drawn from all 50 states and over 75 foreign countries. 20% of students in the Class of 2024 were Pell Grant recipients and 12.56% were first-generation college students. Northwestern also enrolls the 9th-most National Merit Scholars of any university in the nation.

    In Fall 2014, 40.6% of undergraduate students were enrolled in the Weinberg College of Arts and Sciences, 21.3% in the McCormick School of Engineering and Applied Science, 14.3% in the School of Communication, 11.7% in the Medill School of Journalism, 5.7% in the Bienen School of Music, and 6.4% in the School of Education and Social Policy. The five most commonly awarded undergraduate degrees are economics, journalism, communication studies, psychology, and political science. The Kellogg School of Management’s MBA, the School of Law’s JD, and the Feinberg School of Medicine’s MD are the three largest professional degree programs by enrollment. With 2,446 students enrolled in science, engineering, and health fields, the largest graduate programs by enrollment include chemistry, integrated biology, material sciences, electrical and computer engineering, neuroscience, and economics.

    Athletics

    Northwestern is a charter member of the Big Ten Conference. It is the conference’s only private university and possesses the smallest undergraduate enrollment (the next-smallest member, the University of Iowa, is roughly three times as large, with almost 22,000 undergraduates).

    Northwestern fields 19 intercollegiate athletic teams (8 men’s and 11 women’s) in addition to numerous club sports. 12 of Northwestern’s varsity programs have had NCAA or bowl postseason appearances. Northwestern is one of five private AAU members to compete in NCAA Power Five conferences (the other four being Duke, Stanford, USC, and Vanderbilt) and maintains a 98% NCAA Graduation Success Rate, the highest among Football Bowl Subdivision schools.

    In 2018, the school opened the Walter Athletics Center, a $270 million state of the art lakefront facility for its athletics teams.

    Nickname and mascot

    Before 1924, Northwestern teams were known as “The Purple” and unofficially as “The Fighting Methodists.” The name Wildcats was bestowed upon the university in 1924 by Wallace Abbey, a writer for the Chicago Daily Tribune, who wrote that even in a loss to the University of Chicago, “Football players had not come down from Evanston; wildcats would be a name better suited to “[Coach Glenn] Thistletwaite’s boys.” The name was so popular that university board members made “Wildcats” the official nickname just months later. In 1972, the student body voted to change the official nickname to “Purple Haze,” but the new name never stuck.

    The mascot of Northwestern Athletics is “Willie the Wildcat”. Prior to Willie, the team mascot had been a live, caged bear cub from the Lincoln Park Zoo named Furpaw, who was brought to the playing field on game days to greet the fans. After a losing season however, the team decided that Furpaw was to blame for its misfortune and decided to select a new mascot. “Willie the Wildcat” made his debut in 1933, first as a logo and then in three dimensions in 1947, when members of the Alpha Delta fraternity dressed as wildcats during a Homecoming Parade.

    Traditions

    Northwestern’s official motto, “Quaecumque sunt vera,” was adopted by the university in 1890. The Latin phrase translates to “Whatsoever things are true” and comes from the Epistle of Paul to the Philippians (Philippians 4:8), in which St. Paul admonishes the Christians in the Greek city of Philippi. In addition to this motto, the university crest features a Greek phrase taken from the Gospel of John inscribed on the pages of an open book, ήρης χάριτος και αληθείας or “the word full of grace and truth” (John 1:14).
    Alma Mater is the Northwestern Hymn. The original Latin version of the hymn was written in 1907 by Peter Christian Lutkin, the first dean of the School of Music from 1883 to 1931. In 1953, then Director-of-Bands John Paynter recruited an undergraduate music student, Thomas Tyra (’54), to write an English version of the song, which today is performed by the Marching Band during halftime at Wildcat football games and by the orchestra during ceremonies and other special occasions.
    Purple became Northwestern’s official color in 1892, replacing black and gold after a university committee concluded that too many other universities had used these colors. Today, Northwestern’s official color is purple, although white is something of an official color as well, being mentioned in both the university’s earliest song, Alma Mater (1907) (“Hail to purple, hail to white”) and in many university guidelines.
    The Rock, a 6-foot high quartzite boulder donated by the Class of 1902, originally served as a water fountain. It was painted over by students in the 1940s as a prank and has since become a popular vehicle of self-expression on campus.
    Armadillo Day, commonly known as Dillo Day, is the largest student-run music festival in the country. The festival is hosted every Spring on Northwestern’s Lakefront.
    Primal Scream is held every quarter at 9 p.m. on the Sunday before finals week. Students lean out of windows or gather in courtyards and scream to help relieve stress.
    In the past, students would throw marshmallows during football games, but this tradition has since been discontinued.

    Philanthropy

    One of Northwestern’s most notable student charity events is Dance Marathon, the most established and largest student-run philanthropy in the nation. The annual 30-hour event is among the most widely-attended events on campus. It has raised over $1 million for charity ever year since 2011 and has donated a total of $13 million to children’s charities since its conception.

    The Northwestern Community Development Corps (NCDC) is a student-run organization that connects hundreds of student volunteers to community development projects in Evanston and Chicago throughout the year. The group also holds a number of annual community events, including Project Pumpkin, a Halloween celebration that provides over 800 local children with carnival events and a safe venue to trick-or-treat each year.

    Many Northwestern students participate in the Freshman Urban Program, an initiative for students interested in community service to work on addressing social issues facing the city of Chicago, and the university’s Global Engagement Studies Institute (GESI) programs, including group service-learning expeditions in Asia, Africa, or Latin America in conjunction with the Foundation for Sustainable Development.

    Several internationally recognized non-profit organizations were established at Northwestern, including the World Health Imaging, Informatics and Telemedicine Alliance, a spin-off from an engineering student’s honors thesis.
    Media

    Print

    Established in 1881, The Daily Northwestern is the university’s main student newspaper and is published on weekdays during the academic year. It is directed entirely by undergraduate students and owned by the Students Publishing Company. Although it serves the Northwestern community, the Daily has no business ties to the university and is supported wholly by advertisers.
    North by Northwestern is an online undergraduate magazine established in September 2006 by students at the Medill School of Journalism. Published on weekdays, it consists of updates on news stories and special events throughout the year. It also publishes a quarterly print magazine.
    Syllabus is the university’s undergraduate yearbook. It is distributed in late May and features a culmination of the year’s events at Northwestern. First published in 1885, the yearbook is published by Students Publishing Company and edited by Northwestern students.
    Northwestern Flipside is an undergraduate satirical magazine. Founded in 2009, it publishes a weekly issue both in print and online.
    Helicon is the university’s undergraduate literary magazine. Established in 1979, it is published twice a year: a web issue is released in the winter and a print issue with a web complement is released in the spring.
    The Protest is Northwestern’s quarterly social justice magazine.
    The Northwestern division of Student Multicultural Affairs supports a number of publications for particular cultural groups including Ahora, a magazine about Hispanic and Latino/a culture and campus life; Al Bayan, published by the Northwestern Muslim-cultural Student Association; BlackBoard Magazine, a magazine centered around African-American student life; and NUAsian, a magazine and blog on Asian and Asian-American culture and issues.
    The Northwestern University Law Review is a scholarly legal publication and student organization at Northwestern University School of Law. Its primary purpose is to publish a journal of broad legal scholarship. The Law Review publishes six issues each year. Student editors make the editorial and organizational decisions and select articles submitted by professors, judges, and practitioners, as well as student pieces. The Law Review also publishes scholarly pieces weekly on the Colloquy.
    The Northwestern Journal of Technology and Intellectual Property is a law review published by an independent student organization at Northwestern University School of Law.
    The Northwestern Interdisciplinary Law Review is a scholarly legal publication published annually by an editorial board of Northwestern undergraduates. Its mission is to publish interdisciplinary legal research, drawing from fields such as history, literature, economics, philosophy, and art. Founded in 2008, the journal features articles by professors, law students, practitioners, and undergraduates. It is funded by the Buffett Center for International and Comparative Studies and the Office of the Provost.

    Web-based

    Established in January 2011, Sherman Ave is a humor website that often publishes content on Northwestern student life. Most of its staff writers are current Northwestern undergraduates writing under various pseudonyms. The website is popular among students for its interviews of prominent campus figures, Freshman Guide, and live-tweeting coverage of football games. In Fall 2012, the website promoted a satiric campaign to end the Vanderbilt University football team’s custom of clubbing baby seals.
    Politics & Policy is dedicated to the analysis of current events and public policy. Established in 2010 by students at the Weinberg College of Arts and Sciences, School of Communication, and Medill School of Journalism, the publication reaches students on more than 250 college campuses around the world. Run entirely by undergraduates, it is published several times a week and features material ranging from short summaries of events to extended research pieces. The publication is financed in part by the Buffett Center.
    Northwestern Business Review is a campus source for business news. Founded in 2005, it has an online presence as well as a quarterly print schedule.
    TriQuarterly Online (formerly TriQuarterly) is a literary magazine published twice a year featuring poetry, fiction, nonfiction, drama, literary essays, reviews, blog posts, and art.
    The Queer Reader is Northwestern’s first radical feminist and LGBTQ+ publication.

    Radio, film, and television

    WNUR (89.3 FM) is a 7,200-watt radio station that broadcasts to the city of Chicago and its northern suburbs. WNUR’s programming consists of music (jazz, classical, and rock), literature, politics, current events, varsity sports (football, men’s and women’s basketball, baseball, softball, and women’s lacrosse), and breaking news on weekdays.
    Studio 22 is a student-run production company that produces roughly ten films each year. The organization financed the first film Zach Braff directed, and many of its films have featured students who would later go into professional acting, including Zach Gilford of Friday Night Lights.
    Applause for a Cause is currently the only student-run production company in the nation to create feature-length films for charity. It was founded in 2010 and has raised over $5,000 to date for various local and national organizations across the United States.
    Northwestern News Network is a student television news and sports network, serving the Northwestern and Evanston communities. Its studios and newsroom are located on the fourth floor of the McCormick Tribune Center on Northwestern’s Evanston campus. NNN is funded by the Medill School of Journalism.

     
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