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  • richardmitnick 8:57 am on March 26, 2015 Permalink | Reply
    Tags: , , Black Holes,   

    From Space.com: “The Strangest Black Holes in the Universe” 2013 But Interesting 

    space-dot-com logo

    SPACE.com

    July 08, 2013
    Charles Q. Choi

    Black holes are gigantic cosmic monsters, exotic objects whose gravity is so strong that not even light can escape their clutches.

    The Biggest Black Holes
    1
    Credit: Pete Marenfeld

    Nearly all galaxies are thought to harbor at their cores supermassive black holes millions to billions of times the mass of our sun. Scientists recently discovered the largest black holes known in two nearby galaxies.

    One of these galaxies, known as NGC 3842 — the brightest galaxy in the Leo cluster nearly 320 million light years away — has a central black hole containing 9.7 billion solar masses. The other, NGC 4889, the brightest galaxy in the Coma cluster more than 335 million light years away, has a black hole of comparable or larger mass.

    3
    NGC 4889
    Credit: Sloan Digital Sky Survey, Spitzer Space Telescope
    Sloan Digital Sky Survey Telescope
    SDSS telescope

    NASA Spitzer Telescope
    NASA/Spitzer

    The Smallest Black Hole
    2
    Credit: NASA/Goddard Space Flight Center/CI Lab

    The gravitational range, or “event horizon,” of these black holes is about five times the distance from the sun to Pluto. For comparison, these blaVck holes are 2,500 times as massive as the black hole at the center of the Milky Way galaxy, whose event horizon is one-fifth the orbit of Mercury.

    The smallest black hole discovered to date may be less than three times the mass of our sun. This would put this little monster, officially called IGR J17091-3624, near the theoretical minimum limit needed for a black hole to be stable. As tiny as this black hole may be, it looks fierce, capable of 20 million mph winds (32 million kph) — the fastest yet observed from a stellar-mass black hole by nearly 10 times.

    Cannibalistic Black Holes
    3
    Credit: X-ray: NASA/CXC/SAO/G.Fabbiano et al; Optical: NASA/STScI

    NASA Chandra schematic
    NASA/Chandra

    NASA Hubble Telescope
    NASA/ESA Hubble [not in notes but in credit]

    Black holes devour anything unlucky enough to drift too close, including other black holes. Scientists recently detected the monstrous black hole at the heart of one galaxy getting consumed by a still larger black hole in another.

    The discovery is the first of its kind. Astronomers had witnessed the final stages of the merging of galaxies of equal mass — so-called major mergers — but minor mergers between galaxies and smaller companions had long eluded researchers.

    Using NASA’s Chandra X-ray Observatory, investigators detected two black holes at the center of a galaxy dubbed NGC3393, with one black hole about 30 million times the mass of the sun and the other at least 1 million times the mass of the sun, separated from each other by only about 490 light-years.

    Bullet-shooting Black Hole
    4
    Credit: Greg Sivakoff/University of Alberta

    Black holes are known for sucking in matter, but researchers find they can shoot it out as well. Observations of a black hole called H1743-322, which harbors five to 10 times the mass of the sun and is located about 28,000 light-years from Earth, revealed it apparently pulled matter off a companion star, then spat some of it back out as gigantic “bullets” of gas moving at nearly a quarter the speed of light.

    The Oldest Known Black Hole
    5
    Credit: ESO/M. Kornmesser

    The oldest black hole found yet, officially known as ULAS J1120+0641, was born about 770 million years after the Big Bang that created our universe. (Scientists think the Big Bang occurred about 13.7 billion years ago.)

    The ancient age of this black hole actually poses some problems for astronomers. This brilliant enigma appears to be 2 billion times the mass of the sun. How black holes became so massive so soon after the Big Bang is difficult to explain.

    The Brightest Black Hole
    6
    Credit: HST

    Although the gravitational pulls of black holes are so strong that even light cannot escape, they also make up the heart of quasars, the most luminous, most powerful and most energetic objects in the universe.

    As supermassive black holes at the centers of galaxies suck in surrounding gas and dust, they can spew out huge amounts of energy. The brightest quasar we see in the visible range is 3C 273, which lies about 3 billion light-years away.

    Rogue Black Holes
    7
    Credit: David A. Aguilar (CfA)

    When galaxies collide, black holes can get kicked away from the site of the crash to roam freely through space. The first known such rogue black hole, SDSSJ0927+2943, may be approximately 600 million times the mass of the sun and hurtle through space at a whopping 5.9 million mph (9.5 million kph). Hundreds of rogue black holes might wander the Milky Way.

    Middleweight Black Holes
    8
    Credit: NASA

    Scientists have long thought that black holes come in three sizes — essentially small, medium and large. Relatively small black holes holding the mass of a few suns are common, while supermassive black holes millions to billions of solar masses are thought to lurk at the heart of nearly every galaxy. One more massive than four million suns, for example, is thought to hide in the center of the Milky Way.

    However, middle-weight black holes had eluded astronomers for years. Scientists recently discovered an intermediate-mass black hole, called HLX-1 (Hyper-Luminous X-ray source 1), approximately 290 million light-years from Earth, which appears to be about 20,000 solar masses in size.

    Medium-size black holes are thought to be the building blocks of supermassive black holes, so understanding more about them can shed light on how these monsters and the galaxies that surround them evolved.

    Fastest-spinning Black Hole
    9
    Credit: NASA / NASA / CXC / M.Weiss

    Black holes can whirl the fabric of space around themselves at extraordinary speeds. One black hole called GRS 1915+105, in the constellation Aquila (The Eagle) about 35,000 light-years from Earth, is spinning more than 950 times per second.

    An item placed on the edge of the black hole’s event horizon — the edge past which nothing can escape — would spin around it at a speed of more than 333 million mph (536 million kph), or about half the speed of light.

    Tabletop Black Holes
    10
    Credit: Chris Kuklewicz

    Black holes are thankfully quite far away from Earth, but this distance makes it difficult to gather clues that could help solve the many mysteries that surround them. However, researchers are now recreating the enigmatic properties of black holes on tabletops.

    For instance, black holes possess gravitational pulls so powerful that nothing, including light, can escape after falling past a border known as the event horizon. Scientists have created an artificial event horizon in the lab using fiber optics. They have also recreated the so-called Hawking radiation thought to escape from black holes.

    See the full article here.

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  • richardmitnick 6:46 am on March 26, 2015 Permalink | Reply
    Tags: , , Black Holes,   

    From ESO: “Best View Yet of Dusty Cloud Passing Galactic Centre Black Hole” 


    European Southern Observatory

    26 March 2015
    Andreas Eckart
    University of Cologne
    Cologne, Germany
    Email: eckart@ph1.uni-koeln.de

    Monica Valencia-S.
    University of Cologne
    Cologne, Germany
    Email: mvalencias@ph1.uni-koeln.de

    Richard Hook
    ESO, Public Information Officer
    Garching bei München, Germany
    Tel: +49 89 3200 6655
    Cell: +49 151 1537 3591
    Email: rhook@eso.org

    VLT observations confirm that G2 survived close approach and is a compact object

    Temp 0

    The best observations so far of the dusty gas cloud G2 confirm that it made its closest approach to the supermassive black hole at the centre of the Milky Way in May 2014 and has survived the experience. The new result from ESO’s Very Large Telescope shows that the object appears not to have been significantly stretched and that it is very compact. It is most likely to be a young star with a massive core that is still accreting material. The black hole itself has not yet shown any increase in activity.

    A supermassive black hole with a mass four million times that of the Sun lies at the heart of the Milky Way galaxy. It is orbited by a small group of bright stars and, in addition, an enigmatic dusty cloud, known as G2, has been tracked on its fall towards the black hole over the last few years. Closest approach, known as peribothron, was predicted to be in May 2014.

    The great tidal forces in this region of very strong gravity were expected to tear the cloud apart and disperse it along its orbit. Some of this material would feed the black hole and lead to sudden flaring and other evidence of the monster enjoying a rare meal. To study these unique events, the region at the galactic centre has been very carefully observed over the last few years by many teams using large telescopes around the world.

    A team led by Andreas Eckart (University of Cologne, Germany) has observed the region using ESO’s Very Large Telescope (VLT) [1] over many years, including new observations during the critical period from February to September 2014, just before and after the peribothron event in May 2014. These new observations are consistent with earlier ones made using the Keck Telescope on Hawaii [2].

    Keck Observatory
    Keck Observatory Interior
    UCO/Keck

    The images of infrared light coming from glowing hydrogen show that the cloud was compact both before and after its closest approach, as it swung around the black hole.

    As well as providing very sharp images, the SINFONI instrument on the VLT also splits the light into its component infrared colours and hence allows the velocity of the cloud to be estimated [3].

    ESO SINFONI
    SINFONI

    Before closest approach, the cloud was found to be travelling away from the Earth at about ten million kilometres/hour and, after swinging around the black hole, it was measured to be approaching the Earth at about twelve million kilometres/hour.

    Florian Peissker, a PhD student at the University of Cologne in Germany, who did much of the observing, says: “Being at the telescope and seeing the data arriving in real time was a fascinating experience,” and Monica Valencia-S., a post-doctoral researcher also at the University of Cologne, who then worked on the challenging data processing adds: “It was amazing to see that the glow from the dusty cloud stayed compact before and after the close approach to the black hole.”

    Although earlier observations had suggested that the G2 object was being stretched, the new observations did not show evidence that the cloud had become significantly smeared out, either by becoming visibly extended, or by showing a larger spread of velocities.

    In addition to the observations with the SINFONI instrument the team has also made a long series of measurements of the polarisation of the light coming from the supermassive black hole region using the NACO instrument on the VLT.

    ESO NACO
    NACO

    These, the best such observations so far, reveal that the behaviour of the material being accreted onto the black hole is very stable, and — so far — has not been disrupted by the arrival of material from the G2 cloud.

    The resilience of the dusty cloud to the extreme gravitational tidal effects so close to the black hole strongly suggest that it surrounds a dense object with a massive core, rather than being a free-floating cloud. This is also supported by the lack, so far, of evidence that the central monster is being fed with material, which would lead to flaring and increased activity.

    Andreas Eckart sums up the new results: “We looked at all the recent data and in particular the period in 2014 when the closest approach to the black hole took place. We cannot confirm any significant stretching of the source. It certainly does not behave like a coreless dust cloud. We think it must be a dust-shrouded young star.”

    Notes

    [1] These are very difficult observations as the region is hidden behind thick dust clouds, requiring observations in infrared light. And, in addition, the events occur very close to the black hole, requiring adaptive optics to get sharp enough images. The team used the SINFONI instrument on ESO’s Very Large Telescope and also monitored the behaviour of the central black hole region in polarised light using the NACO instrument.

    [2] The VLT observations are both sharper (because they are made at shorter wavelengths) and also have additional measurements of velocity from SINFONI and polarisation measurement using the NACO instrument.

    [3] Because the dusty cloud is moving relative to Earth — away from Earth before closest approach to the black hole and towards Earth afterwards — the Doppler shift changes the observed wavelength of light. These changes in wavelength can be measured using a sensitive spectrograph such as the SINFONI instrument on the VLT. It can also be used to measure the spread of velocities of the material, which would be expected if the cloud was extended along its orbit to a significant extent, as had previously been reported.

    More information

    This research was presented in a paper Monitoring the Dusty S-Cluster Object (DSO/G2) on its Orbit towards the Galactic Center Black Hole by M. Valencia-S. et al. in the journal Astrophysical Journal Letters.

    The team is composed of M. Valencia-S. (Physikalisches Institut der Universität zu Köln, Germany), A. Eckart (Universität zu Köln; Max-Planck-Institut für Radioastronomie, Bonn, Germany [MPIfR]), M. Zajacek (Universität zu Köln; MPIfR; Astronomical Institute of the Academy of Sciences Prague, Czech Republic), F. Peissker (Universität zu Köln), M. Parsa (Universität zu Köln), N. Grosso (Observatoire Astronomique de Strasbourg, France), E. Mossoux (Observatoire Astronomique de Strasbourg), D. Porquet (Observatoire Astronomique de Strasbourg), B. Jalali (Universität zu Köln), V. Karas (Astronomical Institute of the Academy of Sciences Prague), S. Yazici (Universität zu Köln), B. Shahzamanian (Universität zu Köln), N. Sabha (Universität zu Köln), R. Saalfeld (Universität zu Köln), S. Smajic (Universität zu Köln), R. Grellmann (Universität zu Köln), L. Moser (Universität zu Köln), M. Horrobin (Universität zu Köln), A. Borkar (Universität zu Köln), M. García-Marín (Universität zu Köln), M. Dovciak (Astronomical Institute of the Academy of Sciences Prague), D. Kunneriath (Astronomical Institute of the Academy of Sciences Prague), G. D. Karssen (Universität zu Köln), M. Bursa (Astronomical Institute of the Academy of Sciences Prague), C. Straubmeier (Universität zu Köln) and H. Bushouse (Space Telescope Science Institute, Baltimore, Maryland, USA).

    See the full article here.

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    ESO is the foremost intergovernmental astronomy organisation in Europe and the world’s most productive ground-based astronomical observatory by far. It is supported by 16 countries: Austria, Belgium, Brazil, the Czech Republic, Denmark, France, Finland, Germany, Italy, the Netherlands, Poland, Portugal, Spain, Sweden, Switzerland and the United Kingdom, along with the host state of Chile. ESO carries out an ambitious programme focused on the design, construction and operation of powerful ground-based observing facilities enabling astronomers to make important scientific discoveries. ESO also plays a leading role in promoting and organising cooperation in astronomical research. ESO operates three unique world-class observing sites in Chile: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope, the world’s most advanced visible-light astronomical observatory and two survey telescopes. VISTA works in the infrared and is the world’s largest survey telescope and the VLT Survey Telescope is the largest telescope designed to exclusively survey the skies in visible light. ESO is a major partner in ALMA, the largest astronomical project in existence. And on Cerro Armazones, close to Paranal, ESO is building the 39-metre European Extremely Large Telescope, the E-ELT, which will become “the world’s biggest eye on the sky”.

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  • richardmitnick 5:19 am on February 25, 2015 Permalink | Reply
    Tags: , Black Holes, , Stephen Hawking   

    From NOVA: “Stephen Hawking Serves Up Scrambled Black Holes” 

    PBS NOVA

    NOVA

    04 Feb 2014
    Greg Kestin

    1
    Out of the firewall and into the frying pan? Credit: Flickr/Pheexies, under a Creative Commons license.

    Toast or spaghetti?

    That’s the question that physicists have been trying to answer for the last year and a half. After agreeing for decades that anything—or anyone—unlucky enough to fall into a black hole would be ripped and stretched into spaghetti-like strands by the overwhelming gravity, theorists are now contending with the possibility that infalling matter is instead incinerated by a “toasty” wall of fire at the black hole’s horizon. Now, Stephen Hawking has proposed a radical solution: nixing one of the most infamous characteristics of a black hole, its event horizon, or point of no return.

    2
    Stephen Hawking

    The original “spaghetti” scenario follows directly from [Albert] Einstein’s theory of general relativity, which describes how gravity stretches the fabric of space and time. A black hole warps that fabric into a bottomless pit; if you get too close, you reach a point of no return called the horizon, where the slope becomes so steep that you can never climb back out. Inside, the gravity gets stronger and stronger until it tears you limb from limb.

    The first hint that there was a flaw in this picture of a black hole came in 1975, when Stephen Hawking came upon a paradox. He realized that, over a very long time, a black hole will “evaporate”—that is, its mass and energy will gradually leak out as radiation, revealing nothing of what the black hole once contained. This was a shocking conclusion because it suggested that black holes destroy information, a fundamental violation of quantum mechanics, which insists that information be conserved.

    How exactly does black hole evaporation imply that information is destroyed? Let’s say you are reading the last copy of “Romeo and Juliet,” and when you get to the end, grief overcomes you (sorry for the spoiler) and you throw the book into a black hole. After the book falls past the horizon, gravity shreds its pages, and finally it is violently compressed into the central point of the black hole. Then you wait as the black hole slowly evaporates by randomly shooting off particles from its glowing edges without any concern for Romeo or Juliet. As the black hole winks out of existence, only these random subatomic particles remain, floating in space. Where did the Montagues and Capulets go? They are lost forever. You could have thrown in “The Cat in The Hat” and the particles left after evaporation would be indistinguishable from the Shakespearian remnants.

    Hawking realized that something had to give. Either quantum mechanics had to change to accommodate information loss, or Einstein’s theory of gravity was flawed.

    Over the past 40 years theorists have battled in the “black hole wars,” trying to resolve this paradox. Two decades ago, most physicists declared a truce, agreeing to consider the inside and the outside of the black hole as separate spaces. If something falls into the black hole, it has gone to another realm, so just stop thinking about it and its fate, they counseled. This argument was largely accepted until July 2012, when UC Santa Barbara physicist Joseph Polchinski and his colleagues realized the paradox was even more puzzling.

    Polchinski began with a similar thought experiment, but instead of Shakespeare, he imagined tossing entangled particles (particles that are quantum mechanically linked) toward a black hole. What happens, he asked, if one particle falls in the black hole and the other flies out into space? This creates a big problem: We can’t think of the two realms (inside and outside of the black hole) separately because they are tied together by the entangled particles.

    Polchinski proposed a new solution that ripped apart Einstein’s idea of a black hole—literally. If there were something to prevent entanglement across the horizon, he thought, then there would be no problem. So he came up with something called a firewall: a wall of radiation at the black hole’s horizon that burns up anything that hits it. This wall is a tear in space-time that nothing can go through.

    Is incineration finally the solution to the black hole information paradox? The father of the paradox, Stephen Hawking, recently put in his two cents (two pages, actually) in a very brief paper in which he argues against not just firewalls, but also event horizons as an ultimate point-of-no-return. This argument relies on quantum fluctuations in space-time that prevent a horizon from existing at a sharp boundary. He instead proposes a temporary “apparent horizon” that stores matter/energy (and information), chaotically scrambles it, and radiates it back out. This means that, as far as quantum mechanics is concerned, information is not lost; it is just extremely garbled. As Polchinski describes it, “It almost sounds like he is replacing the firewall with a chaos-wall!”

    Are you skeptical? If so, you are in good company. Polchinski, for one, is hesitant, saying “It is not clear what [Hawking’s] picture is. There are no calculations.”

    Steve Giddings, a theoretical physicist at the University of California, Santa Barbara, shares in this reluctance:

    “The big question has been how information escapes a black hole, and what that tells us about faster-than-light signaling or a more serious breakdown of spacetime; the effects Hawking describes don’t appear sufficient to address this.”

    Hawking’s new idea will need some flesh on its bones before we can truly embrace it, but if you don’t like spaghetti or toast, at least you have a third option now: scrambled black holes.

    See the full article here.

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    NOVA is the highest rated science series on television and the most watched documentary series on public television. It is also one of television’s most acclaimed series, having won every major television award, most of them many times over.

     
  • richardmitnick 9:18 am on February 13, 2015 Permalink | Reply
    Tags: , , Black Holes, Interstellar -The Movie,   

    From phys.org: “Interstellar technology throws light on spinning black holes” 

    physdotorg
    phys.org

    Feb 13, 2015

    1

    The team responsible for the Oscar-nominated visual effects at the centre of Christopher Nolan’s epic, Interstellar, have turned science fiction into science fact by providing new insights into the powerful effects of black holes.

    In a paper published today, 13 February, in IOP Publishing’s journal Classical and Quantum Gravity, the team describe the innovative computer code that was used to generate the movie’s iconic images of the wormhole, black hole and various celestial objects, and explain how the code has led them to new science discoveries.

    Using their code, the Interstellar team, comprising London-based visual effects company Double Negative and Caltech theoretical physicist Kip Thorne, found that when a camera is close up to a rapidly spinning black hole, peculiar surfaces in space, known as caustics, create more than a dozen images of individual stars and of the thin, bright plane of the galaxy in which the black hole lives. They found that the images are concentrated along one edge of the black hole’s shadow.

    These multiple images are caused by the black hole dragging space into a whirling motion and stretching the caustics around itself many times. It is the first time that the effects of caustics have been computed for a camera near a black hole, and the resulting images give some idea of what a person would see if they were orbiting around a hole.

    The discoveries were made possible by the team’s computer code, which, as the paper describes, mapped the paths of millions of lights beams and their evolving cross-sections as they passed through the black hole’s warped spacetime. The computer code was used to create images of the movie’s wormhole and the black hole, Gargantua, and its glowing accretion disk, with unparalleled smoothness and clarity.

    It showed portions of the accretion disk swinging up over the top and down under Gargantua’s shadow, and also in front of the shadow’s equator, producing an image of a split shadow that has become iconic for the movie.

    This weird distortion of the glowing disk was caused by gravitational lensing—a process by which light beams from different parts of the disk, or from distant stars, are bent and distorted by the black hole, before they arrive at the movie’s simulated camera.

    This lensing happens because the black hole creates an extremely strong gravitational field, literally bending the fabric of spacetime around itself, like a bowling ball lying on a stretched out bed sheet.

    Early in their work on the movie, with the black hole encircled within a rich field of distant stars and nebulae instead of an accretion disk, the team found that the standard approach of using just one light ray for one pixel in a computer code—in this instance, for an IMAX picture, a total of 23 million pixels—resulted in flickering as the stars and nebulae moved across the screen.

    Co-author of the study and chief scientist at Double Negative, Oliver James, said: “To get rid of the flickering and produce realistically smooth pictures for the movie, we changed our code in a manner that has never been done before. Instead of tracing the paths of individual light rays using [Albert] Einstein’s equations—one per pixel—we traced the distorted paths and shapes of light beams.”

    Co-author of the study Kip Thorne said: “This new approach to making images will be of great value to astrophysicists like me. We, too, need smooth images.”

    Oliver James continued: “Once our code, called DNGR for Double Negative Gravitational Renderer, was mature and creating the images you see in the movie Interstellar, we realised we had a tool that could easily be adapted for scientific research.”

    In their paper, the team report how they used DNGR to carry out a number of research simulations exploring the influence of caustics—peculiar, creased surfaces in space—on the images of distant star fields as seen by a camera near a fast spinning black hole.

    “A light beam emitted from any point on a caustic surface gets focussed by the black hole into a bright cusp of light at a given point,” James continued. “All of the caustics, except one, wrap around the sky many times when the camera is close to the black hole. This sky-wrapping is caused by the black hole’s spin, dragging space into a whirling motion around itself like the air in a whirling tornado, and stretching the caustics around the black hole many times.”

    As each caustic passes by a star, it either creates two new images of the star as seen by the camera, or annihilates two old images of the star. As the camera orbits around the black hole, film clips from the DNGR simulations showed that the caustics were constantly creating and annihilating a huge number of stellar images.

    The team identified as many as 13 simultaneous images of the same star, and as many as 13 images of the thin, bright plane of the galaxy in which the black hole lives.

    These multiple images were only seen when the black hole was spinning rapidly and only near the side of the black hole where the hole’s whirling space was moving toward the camera, which they deduced was because the space whirl was ‘flinging’ the images outward from the hole’s shadow edge. On the shadow’s opposite side, where space is whirling away from the camera, the team deduced that there were also multiple images of each star, but that the whirl of space compressed them inward, so close to the black hole’s shadow that they could not be seen in the simulations.

    See the full article here.

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    Phys.org™ (formerly Physorg.com) is a leading web-based science, research and technology news service which covers a full range of topics. These include physics, earth science, medicine, nanotechnology, electronics, space, biology, chemistry, computer sciences, engineering, mathematics and other sciences and technologies. Launched in 2004, Phys.org’s readership has grown steadily to include 1.75 million scientists, researchers, and engineers every month. Phys.org publishes approximately 100 quality articles every day, offering some of the most comprehensive coverage of sci-tech developments world-wide. Quancast 2009 includes Phys.org in its list of the Global Top 2,000 Websites. Phys.org community members enjoy access to many personalized features such as social networking, a personal home page set-up, RSS/XML feeds, article comments and ranking, the ability to save favorite articles, a daily newsletter, and other options.

     
  • richardmitnick 9:44 pm on January 30, 2015 Permalink | Reply
    Tags: , , Black Holes, McDonald Observatory   

    From McDonald Observatory: “Black Hole Chokes on a Swallowed Star” 

    McDonald Observatory bloc

    McDonald Observatory

    A five-year analysis of an event captured by a tiny telescope at McDonald Observatory and followed up by telescopes on the ground and in space has led astronomers to believe they witnessed a giant black hole tear apart a star. The work is published this month in The Astrophysical Journal.

    1
    When a star encounters a black hole, tidal forces stretch the star into an elongated blob before tearing it apart, as seen in these images from a computer simulation by James Guillochon of Harvard University.

    On January 21, 2009, the ROTSE IIIb telescope at McDonald caught the flash of an extremely bright event. The telescope’s wide field of view takes pictures of large swathes of sky every night, looking for newly exploding stars as part of the ROTSE Supernova Verification Project (RSVP). Software then compares successive photos to find bright “new” objects in the sky — transient events like the explosion of a star or a gamma-ray burst.

    McDonald Observatory ROTSE-IIIb Telescope
    ROTSE-IIIb telescope

    With a magnitude of -22.5, this 2009 event was as bright as the “superluminous supernovae” (a new category of the brightest stellar explosions known) that the ROTSE team discovered at McDonald in recent years. The team nicknamed the 2009 event “Dougie,” after a character in the cartoon South Park. (Its technical name is ROTSE3J120847.9+430121.)

    The team thought Dougie might be a supernova, and set about looking for its host galaxy (which would be much too faint for ROTSE to see). They found that the Sloan Digital Sky Survey [SDSS] had mapped a faint red galaxy at Dougie’s location. The team followed that up with new observations of the galaxy with one of the giant Keck telescopes in Hawaii, pinpointing the galaxy’s distance at three billion light-years.

    Sloan Digital Sky Survey Telescope
    SDSS Telescope

    Keck Observatory
    Keck Observatory

    These deductions meant Dougie had a home — but just what was he? Team members had four possibilities: a superluminous supernova; a merger of two neutron stars; a gamma-ray burst; or a “tidal disruption event” — a star being pulled apart as it neared its host galaxy’s central black hole.

    2
    Simulation of gravitational lensing by a black hole, which distorts the image of a galaxy in the background

    To narrow it down, they studied Dougie in various ways. They made ultraviolet observations with the orbiting Swift telescope, and took many spectra from the ground with the 9.2-meter Hobby-Eberly Telescope at McDonald. Finally, they used computer models of how the light from different possible physical processes that might explain how Dougie would behave — how it varies in brightness over time, and what chemical signatures it might show — and compared them to Dougie’s actual behavior.

    NASA SWIFT Telescope
    NASA/Swift

    In detail, Dougie did not look like a supernova. The neutron star merger and gamma-ray burst possibilities were similarly eliminated.

    “When we discovered this new object, it looked similar to supernovae we had known already,” said lead author Jozsef Vinko of the University of Szeged in Hungary. “But when we kept monitoring its light variation, we realized that this was something nobody really saw before. Finding out that it was probably a supermassive black hole eating a star was a fascinating experience,” Vinko said.

    Team member J. Craig Wheeler, leader of the supernova group at The University of Texas at Austin, elaborated. “We got the idea that it might be a ‘tidal disruption’ event,” he said, explaining that means that the enormous gravity of a black hole pulls on one side of the star harder than the other side, creating tides that rip the star apart.

    “A star wanders near a black hole, the star’s side nearer the black hole is pulled” on more than the star’s far side, he said. “These especially large tides can be strong enough that you pull the star out into a noodle” shape.

    The star “doesn’t fall directly into the black hole,” Wheeler said. “It might form a disk first. But the black hole is destined to swallow most of that material.”

    Though astronomers have seen black holes swallow stars before — though less than a dozen times — this one is special even in that rare company: It’s not going down easy.

    Models by team members James Guillochon of Harvard and Enrico Ramirez-Ruiz at the University of California, Santa Cruz, showed that the disrupted stellar matter was generating so much radiation that it pushed back on the infall. The black hole was choking on the rapidly infalling matter.

    Based on the characteristics of the light from Dougie, and their deductions of the star’s original mass, the team has determined that Dougie started out as a Sun-like star, before being ripped apart.

    Their observations of the host galaxy, coupled with Dougie’s behavior, led them to surmise that the galaxy’s central black hole has the “rather modest” mass of about a million Suns, Wheeler said.

    Delving into Dougie’s behavior has unexpectedly resulted in learning more about small, distant galaxies, Wheeler said, musing “Who knew this little guy had a black hole?”

    The paper’s lead author, Jozsef Vinko, began the project while on sabbatical at The University of Texas at Austin. The team also includes Robert Quimby of San Diego State University, who started the search for supernovae using ROTSE IIIb (then called the Texas Supernova Search, now RSVP) and discovered the category of superluminous supernovae while a graduate student at The University of Texas at Austin.

    See the full article here.

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    McDonald Observatory Campus

    Telescopes Are Windows To the Universe

    Astronomers use them to study everything from the asteroids and planets in our own solar system to galaxies billions of light-years away in space and time. Though they bring the mysteries of the universe to us, their workings are anything but mysterious. They gather and focus light from objects in the sky, so that it can be directed into an instrument attached to the telescope, and ultimately, studied in detail by a scientist. At McDonald Observatory, we have several telescopes, built at various times since the Observatory’s founding in the 1930s.

    Here is an introduction to the telescopes that McDonald Observatory astronomers use for their research:

    McDonald Observatory Hobby-Eberly Telescope
    Hobby-Eberly Telescope

    McDonald Observatory Harlan J Smith Telescope
    Harlan J. Smith Telescope

    McDonald Observatory Otto Struve telescope
    Otto Struve Telescope

    McDonald Observatory .8 meter telescope
    0.8-meter Telescope

    McDonald Observatory .9 meter telescope
    0.9-meter Telescope

    McDonald Observatory Rebecca Gale  Telescope Park
    Rebecca Gale Telescope Park

     
  • richardmitnick 11:46 am on January 30, 2015 Permalink | Reply
    Tags: , Black Holes,   

    From phys.org: “Black holes do not exist where space and time do not exist, says new theory” 

    physdotorg
    phys.org

    Jan 30, 2015
    Lisa Zyga

    1
    This artist’s concept depicts a supermassive black hole at the center of a galaxy. The blue color here represents radiation pouring out from material very close to the black hole. The grayish structure surrounding the black hole, called a torus, is made up of gas and dust. Credit: NASA/JPL-Caltech

    The quintessential feature of a black hole is its “point of no return,” or what is more technically called its event horizon. When anything—a star, a particle, or wayward human—crosses this horizon, the black hole’s massive gravity pulls it in with such force that it is impossible to escape. At least, this is what happens in traditional black hole models based on general relativity. In general, the existence of the event horizon is responsible for most of the strange phenomena associated with black holes.

    In a new paper, physicists Ahmed Farag Ali, Mir Faizal, and Barun Majunder have shown that, according to a new generalization of [Albert] Einstein’s theory of gravity called “gravity’s rainbow,” it is not possible to define the position of the event horizon with arbitrary precision. If the event horizon can’t be defined, then the black hole itself effectively does not exist.

    “In gravity’s rainbow, space does not exist below a certain minimum length, and time does not exist below a certain minimum time interval,” Ali, a physicist at the Zewail City of Science and Technology and Benha University, both in Egypt, told Phys.org. “So, all objects existing in space and occurring at a time do not exist below that length and time interval [which are associated with the Planck scale]. As the event horizon is a place in space which exists at a point in time, it also does not exist below that scale.”

    When Ali talks about “all objects,” he literally means everything around us, including ourselves.

    “We also do not exist physically below that length and time interval,” he said. “However, for us, our house, our car, etc., it does not matter if we do not exist at any one point of space and time, as long as we exist beyond a certain interval. However, for the event horizon it does matter, and this causes the main difference in our calculations.”

    Gravity’s rainbow

    Gravity’s rainbow arises from attempts to develop a theory that combines both the theory of general relativity and quantum mechanics. To fully solve the problems related to black holes, or even the beginning of our universe, physicists require a theory of quantum gravity.

    “Even though no one has been able to discover such a theory, there are various candidates,” Ali said. “These include ideas like taking space and time as fundamentally discrete, or using some mathematical loops as a fundamental quantity to construct space and time, or even replacing particles by tiny strings, and many other exotic ideas.

    “What many of these models have in common is that it can be inferred from them that the energy of a particle cannot get as large as possible, but that there is a maximum energy that any particle can reach. This restriction can be easily combined with Einstein’s special theory of relativity, and the resultant theory is called the doubly special theory of relativity, or DSR.”

    As the physicists explain, it is possible to generalize DSR to include gravity, and this theory is called gravity’s rainbow.

    “General relativity predicts that the geometry of space and time curves in the presence of matter, and this causes gravity to exist,” Ali said. “Gravity’s rainbow predicts that this curvature also depends on the energy of the observer measuring it. So, in gravity’s rainbow, gravity acts differently on particles with different energies. This difference is very small for objects like the Earth. However, it becomes significant for objects like black holes.”

    Information paradox

    The point of the work is not simply to abolish one of the defining features of a black hole, but rather the results could resolve the 40-year-old black hole information paradox that began with work by Stephen Hawking back in the 1970s. At that time, Hawking proposed that black holes emit radiation as they rotate, causing them to lose mass faster than they gain mass, so that they steadily evaporate and eventually disappear altogether.

    The paradox in this scenario is that Hawking radiation originates from the mass of objects that fell into the black hole, but (in theory) the radiation does not carry complete information about these objects as it radiates away from the black hole. Eventually this radiation is expected to cause the black hole to evaporate completely. So the question then arises: where does the information about the objects go?

    In everyday life, shredding or burning paper documents may be common practice to destroy information, but according to quantum theory, information can never be completely destroyed. In principle, the initial state of a system can always be determined by using information about its final state. But Hawking radiation can’t determine the initial state of anything.

    Many proposals have been put forth to solve this paradox, including the possibility that some information slowly leaks out over time, that information is stored deep inside the black hole, and that Hawking radiation actually does contain complete information.

    One of the most developed explanations of the paradox is called black hole complementarity, which is based on the idea that an observer falling into a black hole and an observer watching from a distance see two completely different things. The in-going observer sees information (in the form of himself) pass through the black hole’s event horizon, but to a distant observer it appears that the in-going observer never actually reaches the event horizon due to the strange effect in general relativity of time dilation. Instead, the distant observer sees the information being reflected away from the event horizon in the form of radiation. Since the two observers cannot communicate, there is no paradox (though to many people, such a solution may sound even stranger than the paradox itself).

    Planck-scale limits

    In their new paper, Ali, Faizal, and Majunder show that something very different happens in black hole complementarity when there is no event horizon below a certain length and time interval, as suggested by gravity’s rainbow. Instead of it appearing to the distant observer that it takes an infinite amount of time for the in-going observer to reach the event horizon, in the new theory, that time is finite. In other words, the distant observer eventually sees the in-going observer fall into the black hole.

    Using this new insight gained from gravity’s rainbow, Ali, Faizal, and Majumder claim that the mysteries surrounding a black hole arise from the fact that space and time are being described at a scale at which they do not exist.

    “If we restrict our description to scales at which space and time exist, then the apparent paradoxes associated with black holes seem to naturally resolve,” Ali said. “For example, as the information paradox depends on the existence of the event horizon, and an event horizon like all objects does not exist below a certain length and time interval, then there is no absolute information paradox in gravity’s rainbow. The absence of an effective horizon means that there is nothing absolutely stopping information from going out of the black hole.”

    Beyond black holes

    In addition to offering a solution to the black hole information paradox, the physicists explain that the existence of minimum length and time intervals reminds us that it is important to know what questions one is allowed to ask in physics to get the correct answer. The scientists explain this idea using the analogy of a metal rod:

    “We can ask, how much will a rod bend at a given force without breaking the rod? When we apply a force so great that it breaks the rod, it is meaningless to talk of bending that rod. In the same way, in gravity’s rainbow, it becomes meaningless to talk of space below a certain length scale, and time below a certain interval.

    “The most important lesson from this paper is that space and time exist only beyond a certain scale,” Ali concluded. “There is no space and time below that scale. Hence, it is meaningless to define particles, matter, or any object, including black holes, that exist in space and time below that scale. Thus, as long as we keep ourselves confined to the scales at which both space and time exist, we get sensible physical answers. However, when we try to ask questions at length and time intervals that are below the scales at which space and time exist, we end up getting paradoxes and problems.”

    See the full article here.

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    About Phys.org in 100 Words

    Phys.org™ (formerly Physorg.com) is a leading web-based science, research and technology news service which covers a full range of topics. These include physics, earth science, medicine, nanotechnology, electronics, space, biology, chemistry, computer sciences, engineering, mathematics and other sciences and technologies. Launched in 2004, Phys.org’s readership has grown steadily to include 1.75 million scientists, researchers, and engineers every month. Phys.org publishes approximately 100 quality articles every day, offering some of the most comprehensive coverage of sci-tech developments world-wide. Quancast 2009 includes Phys.org in its list of the Global Top 2,000 Websites. Phys.org community members enjoy access to many personalized features such as social networking, a personal home page set-up, RSS/XML feeds, article comments and ranking, the ability to save favorite articles, a daily newsletter, and other options.

     
    • academix2015 8:00 pm on January 30, 2015 Permalink | Reply

      The way a black hole bends space and time, how can they exist altogether? The natural effect of infinitesimal bending action ought to be a total crunch.

      Like

    • richardmitnick 9:58 pm on January 30, 2015 Permalink | Reply

      Thanks for reading.

      Like

  • richardmitnick 3:46 pm on January 26, 2015 Permalink | Reply
    Tags: , Black Holes,   

    From phys.org: “The cosmic seeds of black holes” 

    physdotorg
    phys.org

    Jan 19, 2015
    No Writer Credit

    1
    Simulation of the collapse of gas in the very early universe into a small black hole, the first step in producing a more massive black hole that will become the seed for the future development of a galaxy. (The scale of the image is 20 au; one au – astronomical unit – is the average distance of the Earth from the Sun.

    Supermassive black holes with millions or billions of solar-masses of material are found at the nuclei of most galaxies. During the embryonic stages of these galaxies they are thought to play an important role, acting as seeds around which material collected. During the later lifetime of galaxies they can power dramatic outflowing jets of material (among other phenomena) as infalling dust and gas accretes onto the disks that typically surround them. These active, later phases of supermassive black holes can result in turning galaxies into an extremely bright objects like quasars, whose luminosities allow them to be seen at cosmic distances. In fact, quasars have recently been detected from eras less than a billion years after the big bang.

    But where do all these black holes come from – especially the ones present in the early universe!? The explosive death of massive stars, one nominal route, can take many hundreds of millions of years while the star itself coalesces from ambient gas and then evolves, after which material must be added to the black hole seed to grow it into a supermassive monster. It is not clear that there is enough time in the early universe for this to happen. A second method has been proposed for these cosmic seeds, the direct collapse of primordial gas into seedlings that are much more massive – about ten thousand solar-masses – than are those present in stellar ashes.

    Computer simulations have struggled for years to predict what happens in direct collapse, with mixed successes. CfA astronomers Fernando Becerra, Thomas Greif, and Lars Hernquist, and a colleague, have just published the most detailed 3-D simulation of the process in the early universe with an amazingly fine spatial scale precision—as small as the solar-system—and spanning a factor of over ten trillion in size and twenty orders of magnitude (a factor of one hundred million trillion) in gas density. They find that a small protostellar-like core of only 0.1 solar-masses can develop in only a few years from a suitable environment and then can grow into a supermassive black hole in only millions of years. In particular, they find that fragmentation, which had been predicted to disrupt the growth of these seedlings, is not a serious problem. Their result is a significant step towards explaining the cosmic origins of the seeds of galaxies.

    See the full article here.

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    About Phys.org in 100 Words

    Phys.org™ (formerly Physorg.com) is a leading web-based science, research and technology news service which covers a full range of topics. These include physics, earth science, medicine, nanotechnology, electronics, space, biology, chemistry, computer sciences, engineering, mathematics and other sciences and technologies. Launched in 2004, Phys.org’s readership has grown steadily to include 1.75 million scientists, researchers, and engineers every month. Phys.org publishes approximately 100 quality articles every day, offering some of the most comprehensive coverage of sci-tech developments world-wide. Quancast 2009 includes Phys.org in its list of the Global Top 2,000 Websites. Phys.org community members enjoy access to many personalized features such as social networking, a personal home page set-up, RSS/XML feeds, article comments and ranking, the ability to save favorite articles, a daily newsletter, and other options.

     
  • richardmitnick 6:47 pm on January 8, 2015 Permalink | Reply
    Tags: , , , Black Holes, ,   

    From Caltech: “Unusual Light Signal Yields Clues About Elusive Black Hole Merger” 

    Caltech Logo
    Caltech

    01/07/2015
    Ker Than

    The central regions of many glittering galaxies, our own Milky Way included, harbor cores of impenetrable darkness—black holes with masses equivalent to millions, or even billions, of suns. What is more, these supermassive black holes and their host galaxies appear to develop together, or “co-evolve.” Theory predicts that as galaxies collide and merge, growing ever more massive, so too do their dark hearts.

    bh
    Simulation of gravitational lensing by a black hole, which distorts the image of a galaxy in the background


    ESOCast
    Astronomers using ESO’s Very Large Telescope have discovered a gas cloud with several times the mass of the Earth accelerating towards the black hole at the centre of the Milky Way. This is the first time ever that the approach of such a doomed cloud to a supermassive black hole has been observed. This ESOcast explains the new results and includes spectacular simulations of how the cloud will break up over the next few years.
    Credit: ESO.

    ESO VLT Interferometer
    ESO VLT Interior
    ESO/VLT

    Black holes by themselves are impossible to see, but their gravity can pull in surrounding gas to form a swirling band of material called an accretion disk. The spinning particles are accelerated to tremendous speeds and release vast amounts of energy in the form of heat and powerful X-rays and gamma rays. When this process happens to a supermassive black hole, the result is a quasar—an extremely luminous object that outshines all of the stars in its host galaxy and that is visible from across the universe. “Quasars are valuable probes of the evolution of galaxies and their central black holes,” says George Djorgovski, professor of astronomy and director of the Center for Data-Driven Discovery at Caltech.

    In the January 7 issue of the journal Nature, Djorgovski and his collaborators report on an unusual repeating light signal from a distant quasar that they say is most likely the result of two supermassive black holes in the final phases of a merger—something that is predicted from theory but which has never been observed before. The discovery could help shed light on a long-standing conundrum in astrophysics called the “final parsec problem,” which refers to the failure of theoretical models to predict what the final stages of a black hole merger look like or even how long the process might take. “The end stages of the merger of these supermassive black hole systems are very poorly understood,” says the study’s first author, Matthew Graham, a senior computational scientist at Caltech. “The discovery of a system that seems to be at this late stage of its evolution means we now have an observational handle on what is going on.”

    Djorgovski and his team discovered the unusual light signal emanating from quasar PG 1302-102 after analyzing results from the Catalina Real-Time Transient Survey (CRTS), which uses three ground telescopes in the United States and Australia to continuously monitor some 500 million celestial light sources strewn across about 80 percent of the night sky. “There has never been a data set on quasar variability that approaches this scope before,” says Djorgovski, who directs the CRTS. “In the past, scientists who study the variability of quasars might only be able to follow some tens, or at most hundreds, of objects with a limited number of measurements. In this case, we looked at a quarter million quasars and were able to gather a few hundred data points for each one.”

    “Until now, the only known examples of supermassive black holes on their way to a merger have been separated by tens or hundreds of thousands of light years,” says study coauthor Daniel Stern, a scientist at NASA’s Jet Propulsion Laboratory. “At such vast distances, it would take many millions, or even billions, of years for a collision and merger to occur. In contrast, the black holes in PG 1302-102 are, at most, a few hundredths of a light year apart and could merge in about a million years or less.”

    Djorgovski and his team did not set out to find a black hole merger. Rather, they initially embarked on a systematic study of quasar brightness variability in the hopes of finding new clues about their physics. But after screening the data using a pattern-seeking algorithm that Graham developed, the team found 20 quasars that seemed to be emitting periodic optical signals. This was surprising, because the light curves of most quasars are chaotic—a reflection of the random nature by which material from the accretion disk spirals into a black hole. “You just don’t expect to see a periodic signal from a quasar,” Graham says. “When you do, it stands out.”

    Of the 20 periodic quasars that CRTS identified, PG 1302-102 was the best example. It had a strong, clean signal that appeared to repeat every five years or so. “It has a really nice smooth up-and-down signal, similar to a sine wave, and that just hasn’t been seen before in a quasar,” Graham says.

    The team was cautious about jumping to conclusions. “We approached it with skepticism but excitement as well,” says study coauthor Eilat Glikman, an assistant professor of physics at Middlebury College in Vermont. After all, it was possible that the periodicity the scientists were seeing was just a temporary ordered blip in an otherwise chaotic signal. To help rule out this possibility, the scientists pulled in data about the quasar from previous surveys to include in their analysis. After factoring in the historical observations (the scientists had nearly 20 years’ worth of data about quasar PG 1302-102), the repeating signal was, encouragingly, still there.

    The team’s confidence increased further after Glikman analyzed the quasar’s light spectrum. The black holes that scientists believe are powering quasars do not emit light, but the gases swirling around them in the accretion disks are traveling so quickly that they become heated into glowing plasma. “When you look at the emission lines in a spectrum from an object, what you’re really seeing is information about speed—whether something is moving toward you or away from you and how fast. It’s the Doppler effect,” Glikman says. “With quasars, you typically have one emission line, and that line is a symmetric curve. But with this quasar, it was necessary to add a second emission line with a slightly different speed than the first one in order to fit the data. That suggests something else, such as a second black hole, is perturbing this system.”

    Avi Loeb, who chairs the astronomy department at Harvard University, agreed with the team’s assessment that a “tight” supermassive black hole binary is the most likely explanation for the periodic signal they are seeing. “The evidence suggests that the emission originates from a very compact region around the black hole and that the speed of the emitting material in that region is at least a tenth of the speed of light,” says Loeb, who did not participate in the research. “A secondary black hole would be the simplest way to induce a periodic variation in the emission from that region, because a less dense object, such as a star cluster, would be disrupted by the strong gravity of the primary black hole.”

    In addition to providing an unprecedented glimpse into the final stages of a black hole merger, the discovery is also a testament to the power of “big data” science, where the challenge lies not only in collecting high-quality information but also devising ways to mine it for useful information. “We’re basically moving from having a few pictures of the whole sky or repeated observations of tiny patches of the sky to having a movie of the entire sky all the time,” says Sterl Phinney, a professor of theoretical physics at Caltech, who was also not involved in the study. “Many of the objects in the movie will not be doing anything very exciting, but there will also be a lot of interesting ones that we missed before.”

    It is still unclear what physical mechanism is responsible for the quasar’s repeating light signal. One possibility, Graham says, is that the quasar is funneling material from its accretion disk into luminous twin plasma jets that are rotating like beams from a lighthouse. “If the glowing jets are sweeping around in a regular fashion, then we would only see them when they’re pointed directly at us. The end result is a regularly repeating signal,” Graham says.

    Another possibility is that the accretion disk that encircles both black holes is distorted. “If one region is thicker than the rest, then as the warped section travels around the accretion disk, it could be blocking light from the quasar at regular intervals. This would explain the periodicity of the signal that we’re seeing,” Graham says. Yet another possibility is that something is happening to the accretion disk that is causing it to dump material onto the black holes in a regular fashion, resulting in periodic bursts of energy.

    “Even though there are a number of viable physical mechanisms behind the periodicity we’re seeing—either the precessing jet, warped accretion disk or periodic dumping—these are all still fundamentally caused by a close binary system,” Graham says.

    Along with Djorgovski, Graham, Stern, and Glikman, additional authors on the paper, A possible close supermassive black hole binary in a quasar with optical periodicity, include Andrew Drake, a computational scientist and co-principal investigator of the CRTS sky survey at Caltech; Ashish Mahabal, a staff scientist in computational astronomy at Caltech; Ciro Donalek, a computational staff scientist at Caltech; Steve Larson, a senior staff scientist at the University of Arizona; and Eric Christensen, an associate staff scientist at the University of Arizona. Funding for the study was provided by the National Science Foundation.

    See the full article here.

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    The California Institute of Technology (commonly referred to as Caltech) is a private research university located in Pasadena, California, United States. Caltech has six academic divisions with strong emphases on science and engineering. Its 124-acre (50 ha) primary campus is located approximately 11 mi (18 km) northeast of downtown Los Angeles. “The mission of the California Institute of Technology is to expand human knowledge and benefit society through research integrated with education. We investigate the most challenging, fundamental problems in science and technology in a singularly collegial, interdisciplinary atmosphere, while educating outstanding students to become creative members of society.”
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  • richardmitnick 12:40 pm on December 31, 2014 Permalink | Reply
    Tags: , , , Black Holes, ,   

    From SPACE.com: ” Mystery Object Appears Near Milky Way’s Monster Black Hole” 

    space-dot-com logo

    SPACE.com

    December 30, 2014
    Calla Cofield

    A mystery object at the center of the galaxy has astronomers scratching their heads, and a new piece of information won’t be solving the case before the New Year.

    In yet another twist to a saga of astronomical proportions, astronomers have identified what they say is a gas cloud that made a tight orbit around the supermassive black hole at the center of the Milky Way galaxy 13 years ago. The object could be one in a series of gas clouds, the second of which may soon become a snack for the black hole.

    The newly discovered object has been dubbed G1. An object known as G2 has been in the news for more than a year, ever since astronomers at the Max Planck Institute for Extraterrestrial Physics in Germany hypothesized that it was a gas cloud. If that is true, it should lose some of its material to the supermassive black hole at the center of the Milky Way (known as Sagittarius A* or Sgr A*). This giant black hole — its name is pronounced Sagittarius A(star) — doesn’t dine on material often, so the event would be a rare chance for astronomers to watch a black hole eat.

    sa
    Sagittarius A*. This image was taken with NASA’s Chandra X-Ray Observatory. Ellipses indicate light echoes.

    NASA Chandra Telescope
    NASA Chandra schematic
    NASA/Chandra

    While the scientists at Max Planck contend that G2 is a gas cloud, a group of researchers at the University of California, Los Angeles, led by astrophysicist Andrea Ghez, argue that G2 is more likely a star surrounded by a layer of dust and gas. Over the summer, G2 made its closest approach to the black hole and was not torn apart. Ghez and her group argued that this was a knockout punch for the gas cloud theory — clear evidence that G2 is a solid body.

    g
    Using a combination of simulation and high-resolution images, researchers at the Max Planck Institute concluded that the G1 object (blue) would have taken a path very similar to the G2 object (red) around the super massive black hole at the center of the Milky Way Galaxy (marked with an “x”).
    Credit: Max Planck Institute for Extraterrestrial Physics

    But the researchers at the Max Planck institute countered with an explanation for how G2 could have remained intact even if it is a gas cloud. Their theory incorporates the idea that G2 was once part of a larger gas cloud that subsequently broke up into smaller gas clouds that all follow the same path, like beads on a string. This “beading” of gas has been observed in the universe before. If additional clouds of gas could be identified following the same path as G2, that would strongly indicate that G2 is a gas cloud and not a star, the scientists say.

    In their newest paper, the Max Planck group provides a computer model that retraces the path of G1. According to their research, G1 followed a path nearly identical to G2. The model does make certain assumptions about G1’s motion — for example, that it decelerated near closest approach to the black hole.

    “The good agreement of the model with the data renders the idea that G1 and G2 are part of the same gas streamer highly plausible,” Stefan Gillessen, a co-author on the new research, said a statement.

    The new study was first published on the online preprint journal arXiv.org and has been accepted to the Astrophysical Journal.

    See the full article here.

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  • richardmitnick 9:38 am on November 20, 2014 Permalink | Reply
    Tags: , , , , Black Holes, ,   

    From AAAS: “What powers a black hole’s mighty jets?” 

    AAAS

    AAAS

    19 November 2014
    Daniel Clery

    Black holes have a reputation for devouring everything in their path. But some of them like to give as well as receive. A small fraction of supermassive black holes—the ginormous ones that lurk at the centers of galaxies—fire off light-speed jets of particles as they snack. A new survey of more than 200 of these cosmic beasts finds that the jets are much more powerful than scientists thought. Astronomers don’t know what powers jets, but this new result, the team says, supports one proposed explanation: The jets are tapping into the rotational energy of the black hole itself.

    bh
    A black hole’s gravity can heat up the disk around it to shine brightly, but what powers the jets some of them produce remains a mystery. (NASA/JPL-Caltech)

    “It’s very exciting,” says Andrew Fabian, director of the Institute of Astronomy at the University of Cambridge in the United Kingdom, who was not involved in the research. “It’s long been debated whether this is possible.”

    About 1% of supermassive black holes have an “accretion disk” of gas and dust swirling around them. When material from this disk falls toward the black hole, the plunging debris gets so hot that it shines more brightly than the whole rest of its galaxy. One in 10 of these active black holes also produces jets that fire out particles at 99.995% of the speed of light. Astrophysicists suspect that accretion disks produce the jets, but they don’t know how.

    To get a better idea, a team led by astrophysicist Gabriele Ghisellini of the National Institute for Astrophysics in Merate, Italy, surveyed archival data and picked out a sample of 217 bright supermassive black holes for which they could find gamma ray observations (which reveal the brightness of the jets) and optical observations (to get the luminosity of the accretion disks). Key to the survey were data from NASA’s Fermi Gamma-ray Space Telescope, launched in 2008. “It took time to build up a collection of samples with the required information,” Ghisellini says.

    NASA Fermi Telescope
    NASA/Fermi

    Plotting the luminosity of the accretion disks against the gamma ray power of their jets, the team reports online today in Nature that there is a clear linear relationship between the two. The brighter the disk, the more powerful the jets—cementing the idea that accretion disks and jets are linked. But in terms of total power being beamed out into space, Ghisellini says, most of the jets were producing 10 times that of their accretion disks. “There must be another engine, not just the gravitational energy [of accreting matter falling toward the black hole].”

    The most popular explanation of how jets form is that the fast-spinning accretion disk, which contains charged particles, will produce a powerful magnetic field that is in contact with the black hole. If the black hole is spinning, it drags on the field, winding it into a tight cone at the rotational poles of the black hole. It is this twisted field that accelerates particles away from the black hole as jets and, in the process, extracts energy from the rotation of the black hole. Ghisellini says the group’s finding that jets are so much more powerful than accretion disks shows that disks alone can’t power the jets; the black hole’s spin must also be involved.

    Fabian says he still has a “slight reservation” about the assertion that the results prove the role of black hole spin. It’s also possible, he says, that the magnetic field is sucking power out of the accretion disk, making it appear less bright.

    “The next step for science is to measure the spin of a black hole,” Ghisellini says, to see whether spin rate is related to jet power. “But it is very hard to measure.” Fabian says researchers using NASA’s NuSTAR x-ray telescope have measured the spin rate of stellar-sized black holes formed from just one or a few stars. Confusingly, some of these small spinning black holes have jets and some don’t. “There must be some other parameter [defining whether a black hole has jets], but we don’t know what that is,” Fabian says.

    NASA NuSTAR
    NASA/Nu-STAR

    So although evidence is mounting that black hole spin is powering jets, astrophysicists may have to wait until they can measure the spin of a supermassive black hole before they can nail it. Ghisellini thinks Europe’s Athena x-ray observatory will be able to do the job, but he’s got a long wait ahead: Athena’s launch is slated for 2028.

    ESA Athena spacecraft
    Athena

    See the full article here.

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