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  • richardmitnick 4:46 pm on January 7, 2021 Permalink | Reply
    Tags: "After decades of effort scientists are finally seeing black holes—or are they?, Andrea Ghez UCLA, , , , , , Richard Genzel-MPE,   

    From Science Magazine: “After decades of effort scientists are finally seeing black holes—or are they? 

    From Science Magazine

    Jan. 7, 2021
    Adrian Cho

    1
    General relativity makes very specific predictions about what black holes are and how they should appear, as shown in this simulation. Credit: GODDARD SPACE FLIGHT CENTER/JEREMY SCHNITTMAN.

    While working on his doctorate in theoretical physics in the early 1970s, Saul Teukolsky solved a problem that seemed purely hypothetical. Imagine a black hole, the ghostly knot of gravity that forms when, say, a massive star burns out and collapses to an infinitesimal point. Suppose you perturb it, as you might strike a bell. How does the black hole respond?

    Teukolsky, then a graduate student at the California Institute of Technology (Caltech), attacked the problem with pencil, paper, and Albert Einstein’s theory of gravity, general relativity. Like a bell, the black hole would oscillate at one main frequency and multiple overtones, he found. The oscillations would quickly fade as the black hole radiated gravitational waves—ripples in the fabric of space itself. It was a sweet problem, says Teukolsky, now at Cornell University. And it was completely abstract—until 5 years ago.

    In February 2016, experimenters with the Laser Interferometer Gravitational-Wave Observatory (LIGO), a pair of huge instruments in Louisiana and Washington, reported the first observation of fleeting gravitational ripples, which had emanated from two black holes, each about 30 times as massive as the Sun, spiraling into each other 1.3 billion light-years away.


    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-Zib

    ESA/eLISA the future of gravitational wave research

    LIGO even sensed the “ring down”: the shudder of the bigger black hole produced by the merger. Teukolsky’s old thesis was suddenly cutting-edge physics.

    The thought that anything I did would ever have implications for anything measurable in my lifetime was so far-fetched that the last 5 years have seemed like living in a dream world,” Teukolsky says. “I have to pinch myself, it doesn’t feel real.”

    Fantastical though it may seem, scientists can now study black holes as real objects. Gravitational wave detectors have spotted four dozen black hole mergers since LIGO’s breakthrough detection. In April 2019, an international collaboration called the Event Horizon Telescope (EHT) produced the first image of a black hole. By training radio telescopes around the globe on the supermassive black hole in the heart of the nearby galaxy Messier 87 (M87), EHT imaged a fiery ring of hot gas surrounding the black hole’s inky “shadow.”

    Messier 87*, The first image of the event horizon of a black hole. This is the supermassive black hole at the center of the galaxy Messier 87. Image via JPL/ Event Horizon Telescope Collaboration released on 10 April 2019.

    EHT map.

    Meanwhile, astronomers are tracking stars that zip close to the black hole in the center of our own Galaxy, following paths that may hold clues to the nature of the black hole itself.

    The observations are already challenging astrophysicists’ assumptions about how black holes form and influence their surroundings. The smaller black holes detected by LIGO and, now, the European gravitational wave detector Virgo in Italy have proved heavier and more varied than expected, straining astrophysicists’ understanding of the massive stars from which they presumably form. And the environment around the supermassive black hole in our Galaxy appears surprisingly fertile, teeming with young stars not expected to form in such a maelstrom. But some scientists feel the pull of a more fundamental question: Are they really seeing the black holes predicted by Einstein’s theory?

    Some theorists say the answer is most likely a ho-hum yes. “I don’t think we’re going to learn anything more about general relativity or the theory of black holes from any of this,” says Robert Wald, a gravitational theorist at the University of Chicago. Others aren’t so sure. “Are black holes strictly the same as you would expect with general relativity or are they different?” asks Clifford Will, a gravitational theorist at the University of Florida. “That’s going to be a major thrust of future observations.” Any anomalies would require a rethink of Einstein’s theory, which physicists suspect is not the final word on gravity, as it doesn’t jibe with the other cornerstone of modern physics, quantum mechanics.

    Using multiple techniques, researchers are already gaining different, complementary views of these strange objects, says Andrea Ghez, an astrophysicist at the University of California, Los Angeles, who shared the 2020 Nobel Prize in Physics for inferring the existence of the supermassive black hole in the heart of our Galaxy. “We’re still a long way from putting a complete picture together,” she says, “but we’re certainly getting more of the puzzle pieces in place.”

    Andrea Ghez has centered her work at the W.M Keck Observatory.

    W.M. Keck Observatory, two ten meter telescopes operated by Caltech and the University of California, Maunakea Hawaii USA, altitude 4,207 m (13,802 ft). Credit: Caltech.

    Consisting of pure gravitational energy, a black hole is a ball of contradictions. It contains no matter, but, like a bowling ball, possesses mass and can spin. It has no surface, but has a size. It behaves like an imposing, weighty object, but is really just a peculiar region of space.

    Or so says general relativity, which Einstein published in 1915. Two centuries earlier, Isaac Newton had posited that gravity is a force that somehow reaches through space to attract massive objects to one another. Einstein went deeper and argued that gravity arises because massive things such as stars and planets warp space and time—more accurately, spacetime—causing the trajectories of freely falling objects to curve into, say, the parabolic arc of a thrown ball.

    Early predictions of general relativity differed only slightly from those of Newton’s theory. Whereas Newton predicted that a planet should orbit its star in an ellipse, general relativity predicts that the orientation of the ellipse should advance slightly, or precess, with each orbit. In the first triumph of the theory, Einstein showed it accounted for the previously unexplained precession of the orbit of the planet Mercury. Only years later did physicists realize the theory also implied something far more radical.

    In 1939, theorist J. Robert Oppenheimer and colleagues calculated that when a sufficiently massive star burned out, no known force could stop its core from collapsing to an infinitesimal point, leaving behind its gravitational field as a permanent pit in spacetime. Within a certain distance of the point, gravity would be so strong that not even light could escape. Anything closer would be cut off from the rest of the universe, David Finkelstein, a theorist at Caltech, argued in 1958. This “event horizon” isn’t a physical surface. An astronaut falling past it would notice nothing special. Nevertheless, reasoned Finkelstein, who died just days before LIGO’s announcement in 2016, the horizon would act like a one-way membrane, letting things fall in, but preventing anything from getting out.

    According to general relativity, these objects—eventually named black holes by famed theorist John Archibald Wheeler—should also exhibit a shocking sameness. In 1963, Roy Kerr, a mathematician from New Zealand, worked out how a spinning black hole of a given mass would warp and twist spacetime. Others soon proved that, in general relativity, mass and spin are the only characteristics a black hole can have, implying that Kerr’s mathematical formula, known as the Kerr metric, describes every black hole there is. Wheeler dubbed the result the no-hair theorem to emphasize that two black holes of the same mass and spin are as indistinguishable as bald pates. Wheeler himself was bald, Teukolsky notes, “so maybe it was bald pride.”

    Some physicists suspected black holes might not exist outside theorists’ imaginations, says Sean Carroll, a theorist at Caltech. Skeptics argued that black holes might be an artifact of general relativity’s subtle math, or that they might only form under unrealistic conditions, such as the collapse of a perfectly spherical star. However, in the late 1960s, Roger Penrose, a theorist at the University of Oxford, dispelled such doubts with rigorous math, for which he shared the 2020 Nobel Prize in Physics. “Penrose exactly proved that, no, no, even if you have a lumpy thing, as long as the density became high enough, it was going to collapse to a black hole,” Carroll says.

    Soon enough, astronomers began to see signs of actual black holes. They spotted tiny x-ray sources, such as Cygnus X-1, each in orbit around a star. Astrophysicists deduced that the x-rays came from gas flowing from the star and heating up as it fell onto the mysterious object. The temperature of the gas and the details of the orbit implied the x-ray source was too massive and too small to be anything but a black hole. Similar reasoning suggested quasars, distant galaxies spewing radiation, are powered by supermassive black holes in their centers.

    But no one could be sure those black holes actually are what theorists had pictured, notes Feryal Özel, an astrophysicist at the University of Arizona (UA). For example, “Very little that we have done so far establishes the presence of an event horizon,” she says. “That is an open question.”

    Now, with multiple ways to peer at black holes, scientists can start to test their understanding and look for surprises that could revolutionize physics. “Even though it’s very unlikely, it would be so amazingly important if we found that there was any deviation” from the predictions of general relativity, Carroll says. “It’s a very high-risk, high-reward question.”

    Scientists hope to answer three specific questions: Do the observed black holes really have event horizons? Are they as featureless as the no-hair theorem says? And do they distort spacetime exactly as the Kerr metric predicts?

    Perhaps the simplest tool for answering them is one that Ghez developed. Since 1995, she and colleagues have used the 10-meter Keck telescope in Hawaii to track stars around a radio source known as Sagittarius A* (Sgr A*) in the center of our Galaxy. In 1998, the stars’ high speeds revealed they orbit an object 4 million times as massive as the Sun. Because Sgr A* packs so much mass into such a small volume, general relativity predicts it must be a supermassive black hole. Reinhard Genzel, an astrophysicist at the Max Planck Institute for Extraterrestrial Physics, independently tracked the stars to reach the same conclusion and shared the Nobel Prize with Ghez.

    Richard Genzel studied back holes at the VLT of the European Southern Observatory.

    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.

    Much of the information comes from a single star, dubbed SO2 by Ghez, which whips around Sgr A* once every 16 years.

    Star S0-2 Andrea Ghez Keck/UCLA Galactic Center Group at SGR A*, the supermassive black hole at the center of the Milky Way.

    Just as the orbit of Mercury around the Sun precesses, so, too, should the orbit of SO2. Ghez and colleagues are now trying to tease out that precession from the extremely complicated data. “We’re right on the cusp,” she says. “We have a signal, but we’re still trying to convince ourselves that it’s real.” (In April 2020, Genzel and colleagues claimed to have seen the precession.)

    If they get a little lucky, Ghez and company hope to look for other anomalies that would probe the nature of the supermassive black hole. Close to the black hole, its spin should modify the precession of a star’s orbit in a way that’s predictable from Kerr’s mathematical description. “If there were stars even closer than the ones they’ve seen—maybe 10 times closer—then you could test whether the Kerr metric is exactly correct,” Will says.

    The star tracking will likely never probe very close to the event horizon of Sgr A*, which could fit within the orbit of Mercury. But EHT, which combines data from 11 radio telescopes or arrays around the world to form, essentially, one big telescope, has offered a closer look at a different supermassive black hole, the 6.5-billion-solar-mass beast in M87.

    The famous image the team released 2 years ago, which resembles a fiery circus hoop, is more complicated than it looks. The bright ring emanates from hot gas, but the dark center is not the black hole itself. Rather it is a “shadow” cast by the black hole as its gravity distorts or “lenses” the light from the gas in front of it. The edge of shadow marks not the event horizon, but rather a distance about 50% farther out where spacetime is distorted just enough so that passing light circles the black hole, neither escaping nor falling into the maw.

    Even so, the image holds clues about the object at its center. The spectrum of the glowing ring could reveal, for example, whether the object has a physical surface rather than an event horizon. Matter crashing onto a surface would shine even brighter than stuff sliding into a black hole, Özel explains. (So far researchers have seen no spectral distortion.) The shadow’s shape can also test the classical picture of a black hole. A spinning black hole’s event horizon should bulge at the equator. However, other effects in general relativity should counteract that effect on the shadow. “Because of a very funky cancellation of squishing in different directions, the shadow still looks circular,” Özel says. “That’s why the shape of the shadow becomes a direct test of the no-hair theorem.”

    Some researchers doubt EHT can image the black hole with enough precision for such tests. Samuel Gralla, a theorist at UA, questions whether EHT is even seeing a black hole shadow or merely viewing the disk of gas swirling around the black hole from the top down, in which case the dark spot is simply the eye of that astrophysical hurricane. But Özel says that even with limited resolution, EHT can contribute significantly to testing general relativity in the conceptual terra incognita around a black hole.

    Gravitational waves, in contrast, convey information straight from the black holes themselves. Churned out when black holes spiral together at half the speed of light, these ripples in spacetime pass unimpeded through ordinary matter. LIGO and Virgo have now detected mergers of black holes with masses ranging from three to 86 solar masses.

    The mergers can probe the black holes in several ways, says Frank Ohme, a gravitational theorist and LIGO member at the Max Planck Institute for Gravitational Physics. Assuming the objects are classical black holes, researchers can calculate from general relativity how the chirplike gravitational wave signal from a merger should speed up, climax in a spike, and then ring down. If the massive partners are actually larger material objects, then as they draw close they should distort each other, altering the peak of the signal. So far, researchers see no alterations, Ohme says.

    The merger produces a perturbed black hole just like the one in Teukolsky’s old thesis, offering another test of general relativity. The final black hole undulates briefly but powerfully, at one main frequency and multiple shorter lived overtones. According to the no-hair theorem, those frequencies and lifetimes only depend on the final black hole’s mass and spin. “If you analyze each mode individually, they all have to point to the same black hole mass and spin or something’s wrong,” Ohme says.

    In September 2019, Teukolsky and colleagues teased out the main vibration and a single overtone from a particularly loud merger. If experimenters can improve the sensitivity of their detectors, Ohme says, they might be able to spot two or three overtones—enough to start to test the no-hair theorem.

    Future instruments may make such tests much easier. The 30-meter optical telescopes being built in Chile and Hawaii should scrutinize the neighborhood of Sgr A* with a resolution roughly 80 times better than current instruments, Ghez says, possibly spying closer stars. Similarly, EHT researchers are adding more radio dishes to their network, which should enable them to image the black hole in M87 more precisely. They’re also trying to image Sgr A*.

    Meanwhile, gravitational wave researchers are already planning the next generation of more sensitive detectors, including the Laser Interferometer Space Antenna (LISA), made up of three satellites flying in formation millions of kilometers apart. To be launched in the 2030s, LISA would be so sensitive that it could spot an ordinary stellar-mass black hole spiraling into a much bigger supermassive black hole in a distant galaxy, says Nicolas Yunes, a theoretical physicist at the University of Illinois, Urbana-Champaign.

    The smaller black hole would serve as a precise probe of the spacetime around the bigger black hole, revealing whether it warps and twists exactly as the Kerr metric dictates. An affirmative result would cement the case that black holes are what general relativity predicts, Yunes says. “But you have to wait for LISA.”

    In the meantime, the sudden observability of black holes has changed the lives of gravitational physicists. Once the domain of thought experiments and elegant but abstract calculations like Teukolsky’s, general relativity and black holes are suddenly the hottest things in fundamental physics, with experts in general relativity feeding vital input to billion-dollar experiments. “I felt this transition very literally myself,” Ohme says. “It was really a small niche community, and with the detection of gravitational waves that all changed.”


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  • richardmitnick 11:00 am on February 23, 2018 Permalink | Reply
    Tags: Andrea Ghez UCLA, , , , , , S0-2 Star is Single and Ready for Big Einstein Test, ,   

    From Keck: “Astronomers Discover S0-2 Star is Single and Ready for Big Einstein Test” 

    Keck Observatory, Maunakea, Hawaii, USA.4,207 m (13,802 ft) above sea level, with Subaru and IRTF (NASA Infrared Telescope Facility). Vadim Kurland


    Keck Observatory

    February 21, 2018
    Mari-Ela Chock, Communications Officer
    (808) 554-0567
    mchock@keck.hawaii.edu

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    Credit: S. SAKAI/The Great Astronomer Andrea Ghez who spotted SgrA* by waching S0-2 Star /W. M. KECK OBSERVATORY/ UCLA GALACTIC CENTER GROUP
    The orbit of S0-2 (light blue) located near the Milky Way’s supermassive black hole will be used to test Einstein’s Theory of General Relativity and generate potentially new gravitational models.

    Andrea Ghez, UCLA

    No companion found for famous young bright star orbiting Milky Way’s supermassive black hole SgrA*.

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    Lead author Devin Chu of Hilo, Hawaii is an astronomy graduate student at UCLA. The Hilo High School and 2014 Dartmouth College alumnus conducts his research with the UCLA Galactic Center Group, which uses the W. M. Keck Observatory on Hawaii Island to obtain scientific data. “Growing up on Hawaii Island, it feels surreal doing important research with telescopes on my home island. I find it so rewarding to be able to return home to conduct observations,” Chu said. Credit: D. CHU

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    The UCLA Galactic Center Group takes a photo together during a visit to Keck Observatory, located atop Maunakea, Hawaii. Members of the group will return to the Observatory this spring to begin observations of S0-2 as the star travels towards its closest distance to the Galactic Center’s supermassive black hole. Credit: UCLA GALACTIC CENTER GROUP

    Astronomers have the “all-clear” for an exciting test of Einstein’s Theory of General Relativity, thanks to a new discovery about S0-2’s star status.

    Up until now, it was thought that S0-2 may be a binary, a system where two stars circle around each other. Having such a partner would have complicated the upcoming gravity test.

    But in a study published recently in The Astrophysical Journal, a team of astronomers led by a UCLA scientist from Hawaii has found that S0-2 does not have a significant other after all, or at least one that is massive enough to get in the way of critical measurements that astronomers need to test Einstein’s theory.

    The researchers made their discovery by obtaining spectroscopic measurements of S0-2 using W. M. Keck Observatory’s OH-Suppressing Infrared Imaging Spectrograph (OSIRIS) and Laser Guide Star Adaptive Optics.

    Keck OSIRIS

    “This is the first study to investigate S0-2 as a spectroscopic binary,” said lead author Devin Chu of Hilo, an astronomy graduate student with UCLA’s Galactic Center Group. “It’s incredibly rewarding. This study gives us confidence that a S0-2 binary system will not significantly affect our ability to measure gravitational redshift.”

    Einstein’s Theory of General Relativity predicts that light coming from a strong gravitational field gets stretched out, or “redshifted.” Researchers expect to directly measure this phenomenon beginning in the spring as S0-2 makes its closest approach to the supermassive black hole at the center of our Milky Way galaxy.

    This will allow the Galactic Center Group to witness the star being pulled at maximum gravitational strength – a point where any deviation to Einstein’s theory is expected to be the greatest.

    “It will be the first measurement of its kind,” said co-author Tuan Do, deputy director of the Galactic Center Group. “Gravity is the least well-tested of the forces of nature. Einstein’s theory has passed all other tests with flying colors so far, so if there are deviations measured, it would certainly raise lots of questions about the nature of gravity!”

    “We have been waiting 16 years for this,” said Chu. “We are anxious to see how the star will behave under the black hole’s violent pull. Will S0-2 follow Einstein’s theory or will the star defy our current laws of physics? We will soon find out!”

    The study also sheds more light on the strange birth of S0-2 and its stellar neighbors in the S-Star Cluster. The fact that these stars exist so close to the supermassive black hole is unusual because they are so young; how they could’ve formed in such a hostile environment is a mystery.

    “Star formation at the Galactic Center is difficult because the brute strength of tidal forces from the black hole can tear gas clouds apart before they can collapse and form stars,” said Do.

    “S0-2 is a very special and puzzling star,” said Chu. “We don’t typically see young, hot stars like S0-2 form so close to a supermassive black hole. This means that S0-2 must have formed a different way.”

    There are several theories that provide a possible explanation, with S0-2 being a binary as one of them. “We were able to put an upper limit on the mass of a companion star for S0-2,” said Chu. This new constraint brings astronomers closer to understanding this unusual object.

    “Stars as massive as S0-2 almost always have a binary companion. We are lucky that having no companion makes the measurements of general relativistic effects easier, but it also deepens the mystery of this star,” said Do.

    The Galactic Center Group now plans to study other S-Stars orbiting the supermassive black hole, in hopes of differentiating between the varying theories that attempt to explain why S0-2 is single.

    See the full article here .

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    Mission
    To advance the frontiers of astronomy and share our discoveries with the world.

    The W. M. Keck Observatory operates the largest, most scientifically productive telescopes on Earth. The two, 10-meter optical/infrared telescopes on the summit of Mauna Kea on the Island of Hawaii feature a suite of advanced instruments including imagers, multi-object spectrographs, high-resolution spectrographs, integral-field spectrometer and world-leading laser guide star adaptive optics systems. Keck Observatory is a private 501(c) 3 non-profit organization and a scientific partnership of the California Institute of Technology, the University of California and NASA.

    Today Keck Observatory is supported by both public funding sources and private philanthropy. As a 501(c)3, the organization is managed by the California Association for Research in Astronomy (CARA), whose Board of Directors includes representatives from the California Institute of Technology and the University of California, with liaisons to the board from NASA and the Keck Foundation.


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  • richardmitnick 7:02 am on September 26, 2017 Permalink | Reply
    Tags: Andrea Ghez UCLA, , , , , , Is S0-2 a Binary Star?   

    From astrobites: “Is S0-2 a Binary Star?” 

    Astrobites bloc

    Astrobites

    Sep 26, 2017
    Philipp Plewa

    Title: Investigating the Binarity of S0-2: Implications for its Origins and Robustness as a Probe of the Laws of Gravity around a Supermassive Black Hole
    Authors: D. S. Chu, T. Do, A. Hees, A. Ghez, S. Naoz, G. Witzel, S. Sakai, S. Chappell, A. K. Gautam, J. R. Lu, K. Matthews
    First Author’s Institution: Department of Physics and Astronomy, University of California, Los Angeles

    Status: Submitted to The Astrophysical Journal, open access

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    S0–102 is a star that is located very close to the centre of the Milky Way, near the radio source Sgr A*, orbiting it with an orbital period of 11.5 years. As of 2012 it is the star with the shortest known period orbiting the black hole at the centre of the Milky Way. This beat the record of 15 years previously set by S0–2. The star was identified by a University of California, Los Angeles team headed by Andrea M. Ghez.

    Andrea Ghez, UCLA

    At its periapsis, its speed exceeds 1% of the speed of light.[3] At that point it is 260 astronomical units (36 light hours, 38.9 billion km) from the centre, while the black hole radius is less than one thousandth of that size (11 million km). It passed that point in 2009 and will be there again in 2020.

    The most exciting discoveries in astronomy all have something in common: They let us marvel at the fact that nature obeys laws of physics. The discovery of S0-2 is one of them. S0-2 (also known as S2) is a fast-moving star that has been observed to follow a full elliptical, 16-year orbit around the Milky Way’s central supermassive black hole, precisely according to Kepler’s laws of planetary motion. Serving as a test particle probe of the gravitational potential, S0-2 provides some of the best constraints on the black hole’s mass and distance yet, being the brightest of the S-stars, which are a group of young main-sequence stars concentrated within the inner 1” (0.13 ly) of the nuclear star cluster.

    The next time S0-2 will reach its closest approach to the black hole, in 2018, there will exist a unique opportunity to detect a deviation from Keplerian motion, namely the relativistic redshift of S0-2’s radial (line-of-sight) velocity, in a direct measurement. In anticipation of this event, the authors of today’s paper investigate possible consequences of S0-2 not being a single star, but a spectroscopic binary, which would complicate this measurement.

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    Figure 1: Top: Radial velocity measurements of S0-2 over time. Bottom: Residual velocities after subtraction of the best-fit model for the orbital motion.

    To search for any periodicity in S0-2’s radial velocity curve that would indicate the presence of a companion star, the authors combine their most recent velocity measurements with previous ones obtained as part of monitoring programs carried out at both the WMKO in Hawaii and the VLT in Chile.


    Keck Observatory, Maunakea, Hawaii, USA.4,207 m (13,802 ft) above sea level

    ESO/VLT at Cerro Paranal, with an elevation of 2,635 metres (8,645 ft) above sea level

    The resulting data set consists of 87 measurements in total, which are spread over 17 years of observations and have a typical uncertainty of a few 10 km/s (Figure 1, top panel). When S0-2 passes the black hole, the relativistic redshift of its radial velocity is predicted to amount to roughly 200 km/s at closest approach, while the radial velocity is expected to change from +4000 to -2000 km/s. S0-2’s actual speed at this time will be close to 8000 km/s, about 2.7% of the speed of light.

    See more at the full article.

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    Astrobites is a daily astrophysical literature journal written by graduate students in astronomy. Our goal is to present one interesting paper per day in a brief format that is accessible to undergraduate students in the physical sciences who are interested in active research.
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    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.
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  • richardmitnick 2:40 pm on May 31, 2017 Permalink | Reply
    Tags: Andrea Ghez UCLA, , , , , , New Method of Searching for Fifth Force   

    From Keck: “New Method of Searching for Fifth Force” 

    Keck Observatory

    Keck Observatory.
    Keck, with Subaru and IRTF (NASA Infrared Telescope Facility). Vadim Kurland

    Keck Observatory

    1

    W. M. Keck Observatory data leads to first of its kind test of Einstein’s theory of General Relativity

    A UCLA-led team has discovered a new way of probing the hypothetical fifth force of nature using two decades of observations at W. M. Keck Observatory, the world’s most scientifically productive ground-based telescope.

    There are four known forces in the universe: electromagnetic force, strong nuclear force, weak nuclear force, and gravitational force. Physicists know how to make the first three work together, but gravity is the odd one out. For decades, there have been theories that a fifth force ties gravity to the others, but no one has been able to prove it thus far.

    “This is really exciting. It’s taken us 20 years to get here, but now our work on studying stars at the center of our galaxy is opening up a new method of looking at how gravity works,” said Andrea Ghez, Director of the UCLA Galactic Center Group and co-author of the study.

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    Andrea Ghez, UCL

    The research is published in the current issue of Physical Review Letters.

    Ghez and her co-workers analyzed extremely sharp images of the center of our galaxy taken with Keck Observatory’s adaptive optics (AO). Ghez used this cutting-edge system to track the orbits of stars near the supermassive black hole located at the center of the Milky Way. Their stellar path, driven by gravity created from the supermassive black hole, could give clues to the fifth force.

    “By watching the stars move over 20 years using very precise measurements taken from Keck Observatory data, you can see and put constraints on how gravity works. If gravitation is driven by something other than Einstein’s theory of General Relativity, you’ll see small variations in the orbital paths of the stars,” said Ghez.

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    The orbits of two stars, S0-2 and S0-38 located near the Milky Way’s supermassive black hole will be used to test Einstein’s theory of General Relativity and potentially generate new gravitational models. IMAGE CREDIT: S. SAKAI/A.GHEZ/W. M. KECK OBSERVATORY/ UCLA GALACTIC CENTER GROUP.

    This is the first time the fifth force theory has been tested in a strong gravitational field such as the one created by the supermassive black hole at the center of the Milky Way. Historically, measurements of our solar system’s gravity created by our sun have been used to try and detect the fifth force, but that has proven difficult because its gravitational field is relatively weak.

    “It’s exciting that we can do this because we can ask a very fundamental question – how does gravity work?” said Ghez. “Einstein’s theory describes it beautifully well, but there’s lots of evidence showing the theory has holes. The mere existence of supermassive black holes tells us that our current theories of how the universe works are inadequate to explain what a black hole is.”

    Ghez and her team, including lead author Aurelien Hees and co-author Tuan Do, both of UCLA, are looking forward to summer of 2018. That is when the star S0-2 will be at its closest distance to our galaxy’s supermassive black hole. This will allow the team to witness the star being pulled at maximum gravitational strength – a point where any deviations to Einstein’s theory is expected to be the greatest.

    About Adaptive Optics
    W. M. Keck Observatory is a distinguished leader in the field of adaptive optics (AO), a breakthrough technology that removes the distortions caused by the turbulence in the Earth’s atmosphere. Keck Observatory pioneered the astronomical use of both natural guide star (NGS) and laser guide star adaptive optics (LGS AO) and our current systems now deliver images three to four times sharper than the Hubble Space Telescope. AO has imaged the four massive planets orbiting the star HR8799, measured the mass of the giant black hole at the center of our Milky Way Galaxy, discovered new supernovae in distant galaxies, and identified the specific stars that were their progenitors.

    See the full article here .

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    Mission
    To advance the frontiers of astronomy and share our discoveries with the world.

    The W. M. Keck Observatory operates the largest, most scientifically productive telescopes on Earth. The two, 10-meter optical/infrared telescopes on the summit of Mauna Kea on the Island of Hawaii feature a suite of advanced instruments including imagers, multi-object spectrographs, high-resolution spectrographs, integral-field spectrometer and world-leading laser guide star adaptive optics systems. Keck Observatory is a private 501(c) 3 non-profit organization and a scientific partnership of the California Institute of Technology, the University of California and NASA.

    Today Keck Observatory is supported by both public funding sources and private philanthropy. As a 501(c)3, the organization is managed by the California Association for Research in Astronomy (CARA), whose Board of Directors includes representatives from the California Institute of Technology and the University of California, with liaisons to the board from NASA and the Keck Foundation.
    Keck UCal

     
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