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  • richardmitnick 5:18 am on June 25, 2016 Permalink | Reply
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    From Southampton: “Black holes and measuring gravitational waves” 

    U Southampton bloc

    University of Southampton

    16 June 2016
    No writer credit found

    1
    Artist’s concept of a supermassive black hole. Credit: NASA – JPL/Caltech

    The supermassive black holes found at the centre of every galaxy, including our own Milky Way, may, on average, be smaller than we thought, according to work led by astronomer Dr Francesco Shankar.

    Sag A*  NASA Chandra X-Ray Observatory 23 July 2014, the supermassive black hole at the center of the Milky Way
    Sag A* NASA Chandra X-Ray Observatory 23 July 2014, the supermassive black hole at the center of the Milky Way

    If he and his colleagues are right, then the gravitational waves produced when they merge will be harder to detect than previously assumed. The international team of scientists published their results in Monthly Notices of the Royal Astronomical Society.

    Supermassive black holes have been found lurking in the cores of all galaxies observed with high enough sensitivity. Despite this, little is known about how they formed. What is known is that the mass of a supermassive black hole at the centre of a galaxy is related to the total mass and the typical speeds (the “velocity dispersion”) of the stars in its host.

    The very existence of this relationship suggests a close co-evolution between black holes and their host galaxies, and understanding their origin is vital for a proper model of how galaxies and black holes form and evolve. This is because many galaxy evolution models invoke powerful winds and/or jets from the central supermassive black hole to control or even stop star formation in the host galaxy (so-called “quasar feedback”). Alternatively, multiple mergers of galaxies – and their central black holes – are also often suggested as the primary drivers behind the evolution of massive galaxies.

    Despite major theoretical and observational efforts in the last decades, it remains unclear whether quasar feedback actually ever occurred in galaxies, and to what extent mergers have truly shaped galaxies and their black holes.

    The new work shows that selection effects – where what is observed is not representative – have significantly biased the view of the local black hole population. This bias has led to significantly overestimated black hole masses. It suggests that modellers should look to velocity dispersion rather than stellar mass as the key to unlocking the decades-old puzzles of both quasar feedback and the history of galaxies.

    With less mass than previously thought, supermassive black holes have on average weaker gravitational fields. Despite this, they were still able to power quasars, making them bright enough to be observed over distances of billions of light years.

    Unfortunately, it also implies a substantial reduction in the expected gravitational wave signal detectable from pulsar timing array experiments. Ripples in spacetime that were first predicted by Albert Einstein in his general theory of relativity in 1915; gravitational waves were finally detected last year and announced by the LIGO team this February.

    LSC LIGO Scientific Collaboration
    Caltech/MIT Advanced aLigo Hanford, WA, USA installation
    Caltech/MIT Advanced aLigo Hanford, WA, USA installation
    Caltech/MIT Advanced aLigo detector installation Livingston, LA, USA
    Caltech/MIT Advanced aLigo detector installation Livingston, LA, USA

    The hope is that coming observatories can observe many more gravitational wave events, and that it will provide astronomers with a new technique for observing the universe.

    VIRGO Gravitational Wave interferometer, near Pisa, Italy
    VIRGO Gravitational Wave interferometer, near Pisa, Italy, not yet taking data.

    Dr Shankar comments: “Gravitational wave astronomy is opening up an entirely new way of observing the universe. Our results though illustrate how challenging a complete census of the gravitational background could be, with the signals from the largest black holes being paradoxically among the most difficult to detect with present technology.”

    Researchers expect pairs of supermassive black holes, found in merging galaxies, to be the strongest sources of gravitational waves in the universe.

    Cornell SXS team. Two merging black holes simulation
    Cornell SXS team. Two merging black holes simulation

    However, the more massive the pairs, the lower the frequencies of the emitted waves, which become inaccessible to ground based interferometers like LIGO. Gravitational waves from supermassive black holes can however be detected from space via dedicated gravitational telescopes (such as the present and future ESA missions LISA pathfinder and eLISA), or by a different method using ‘pulsar timing arrays’.

    ESA/LISA Pathfinder
    ESA/LISA Pathfinder

    ESA/eLISA
    ESA/eLISA

    These devices monitor the collapsed, rapidly rotating remnants of massive stars, which have pulsating signals. Even this method though is still a few years from making a detection, according to a follow-up study by the same team expected to appear in another Monthly Notices paper later this year.

    See the full article here .

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    U Southampton campus

    The University of Southampton is a world-class university built on the quality and diversity of our community. Our staff place a high value on excellence and creativity, supporting independence of thought, and the freedom to challenge existing knowledge and beliefs through critical research and scholarship. Through our education and research we transform people’s lives and change the world for the better.

    Vision 2020 is the basis of our strategy.

    Since publication of the previous University Strategy in 2010 we have achieved much of what we set out to do against a backdrop of a major economic downturn and radical change in higher education in the UK.

    Vision 2020 builds on these foundations, describing our future ambition and priorities. It presents a vision of the University as a confident, growing, outwardly-focused institution that has global impact. It describes a connected institution equally committed to education and research, providing a distinctive educational experience for its students, and confident in its place as a leading international research university, achieving world-wide impact.

     
  • richardmitnick 3:06 pm on May 24, 2016 Permalink | Reply
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    From Hubble: “Hubble finds clues to the birth of supermassive black holes” 

    NASA Hubble Banner

    NASA Hubble Telescope

    Hubble

    24 May 2016
    At ESA/Hubble
    Fabio Pacucci
    Scuola Normale Superiore
    Pisa, Italy
    Email: fabio.pacucci@sns.it

    Andrea Ferrara
    Scuola Normale Superiore
    Pisa, Italy
    Email: andrea.ferrara@sns.it

    Andrea Grazian
    National Institute for Astrophysics
    Rome, Italy
    Email: grazian@oa-roma.inaf.it

    Mathias Jäger
    ESA/Hubble, Public Information Officer
    Garching bei München, Germany
    Tel: +49 176 62397500
    Email: mjaeger@partner.eso.org

    At NASA/Chandra
    Media contacts:
    Felicia Chou / Sean Potter
    Headquarters, Washington
    202-358-0257 / 1536
    felicia.chou@nasa.gov / sean.potter@nasa.gov

    Megan Watzke
    Chandra X-ray Center, Cambridge, Mass.
    617-496-7998
    mwatzke@cfa.harvard.edu

    1

    Astrophysicists have taken a major step forward in understanding how supermassive black holes formed. Using data from Hubble and two other space telescopes, Italian researchers have found the best evidence yet for the seeds that ultimately grow into these cosmic giants.

    For years astronomers have debated how the earliest generation of supermassive black holes formed very quickly, relatively speaking, after the Big Bang. Now, an Italian team has identified two objects in the early Universe that seem to be the origin of these early supermassive black holes. The two objects represent the most promising black hole seed candidates found so far [1].

    The group used computer models and applied a new analysis method to data from the NASA Chandra X-ray Observatory, the NASA/ESA Hubble Space Telescope, and the NASA Spitzer Space Telescope to find and identify the two objects. Both of these newly discovered black hole seed candidates are seen less than a billion years after the Big Bang and have an initial mass of about 100 000 times the Sun.

    NASA/Chandra Telescope
    NASA/Chandra Telescope

    NASA/Spitzer Telescope
    NASA/Spitzer Telescope

    “Our discovery, if confirmed, would explain how these monster black holes were born,” said Fabio Pacucci, lead author of the study, of Scuola Normale Superiore in Pisa, Italy.

    This new result helps to explain why we see supermassive black holes less than one billion years after the Big Bang.

    There are two main theories to explain the formation of supermassive black holes in the early Universe. One assumes that the seeds grow out of black holes with a mass about ten to a hundred times greater than our Sun, as expected for the collapse of a massive star. The black hole seeds then grew through mergers with other small black holes and by pulling in gas from their surroundings. However, they would have to grow at an unusually high rate to reach the mass of supermassive black holes already discovered in the billion years young Universe.

    The new findings support another scenario where at least some very massive black hole seeds with 100 000 times the mass of the Sun formed directly when a massive cloud of gas collapses [2]. In this case the growth of the black holes would be jump started, and would proceed more quickly.

    “There is a lot of controversy over which path these black holes take,” said co-author Andrea Ferrara also of Scuola Normale Superiore. “Our work suggests we are converging on one answer, where black holes start big and grow at the normal rate, rather than starting small and growing at a very fast rate.”

    Andrea Grazian, a co-author from the National Institute for Astrophysics in Italy explains: “Black hole seeds are extremely hard to find and confirming their detection is very difficult. However, we think our research has uncovered the two best candidates so far.”

    Even though both black hole seed candidates match the theoretical predictions, further observations are needed to confirm their true nature. To fully distinguish between the two formation theories, it will also be necessary to find more candidates.

    These results* will appear in the June 21st issue of the Monthly Notices of the Royal Astronomical Society and is available online. The authors of the paper are Fabio Pacucci (SNS, Italy), Andrea Ferrara (SNS), Andrea Grazian (INAF), Fabrizio Fiore (INAF), Emaneule Giallongo (INAF), and Simonetta Puccetti (ASI Science Data Center).

    The team plans to conduct follow-up observations in X-rays and in the infrared range to check whether the two objects have more of the properties expected for black hole seeds. Upcoming observatories, like the NASA/ESA/CSA James Webb Space Telescope and the European Extremely Large Telescope will certainly mark a breakthrough in this field, by detecting even smaller and more distant black holes.

    NASA/ESA/CSA Webb Telescope annotated
    NASA/ESA/CSA Webb Telescope annotated

    ESO/E-ELT,to be on top of Cerro Armazones in the Atacama Desert of northern Chile
    ESO/E-ELT,to be on top of Cerro Armazones in the Atacama Desert of northern Chile

    Notes

    [1] Supermassive black holes contain millions or even billions of times the mass of the Sun. In the modern Universe they can be found in the centre of nearly all large galaxies, including the Milky Way.

    Sag A*  NASA Chandra X-Ray Observatory 23 July 2014, the supermassive black hole at the center of the Milky Way
    Sag A* NASA Chandra X-Ray Observatory 23 July 2014, the supermassive black hole at the center of the Milky Way

    The supermassive black hole in the centre of the Milky Way has a mass of four million solar masses. The two black hole seed candidates would also be the progenitors of two of the modern supermassive black holes.

    [2] Black hole seeds created through the collapse of a massive cloud of gas bypass any other intermediate phases such as the formation and subsequent destruction of a massive star.

    The team of scientists in this study consists of Fabio Pacucci (Scuola Normale Superiore, Italy), Andrea Ferrara (Scuola Normale Superiore, Italy), Andrea Grazian (INAF, Italy), Fabrizio Fiore (INAF, Italy), Emanuele Giallongo (INAF, Italy), Simonetta Puccetti (ASDC-ASI, Italy)

    NASA’s Marshall Space Flight Center in Huntsville, Alabama, manages the Chandra program for NASA’s Science Mission Directorate in Washington. The Smithsonian Astrophysical Observatory in Cambridge, Massachusetts, controls Chandra’s science and flight operations.

    NASA’s Jet Propulsion Laboratory in Pasadena, California, manages the Spitzer Space Telescope mission for NASA’s Science Mission Directorate in Washington, D.C. Science operations are conducted at the Spitzer Science Center at the California Institute of Technology in Pasadena. Spacecraft operations are based at Lockheed Martin Space Systems Company in Littleton, Colorado. Data are archived at the Infrared Science Archive housed at the Infrared Processing and Analysis Center at Caltech. Caltech manages JPL for NASA.

    *Science paper:
    First Identification of Direct Collapse Black Hole Candidates in the Early Universe in CANDELS/GOODS-S

    See the full article here .

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    The Hubble Space Telescope is a project of international cooperation between NASA and the European Space Agency. NASA’s Goddard Space Flight Center manages the telescope. The Space Telescope Science Institute (STScI), is a free-standing science center, located on the campus of The Johns Hopkins University and operated by the Association of Universities for Research in Astronomy (AURA) for NASA, conducts Hubble science operations.

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    AURA Icon

    NASA image

     
  • richardmitnick 11:48 am on April 26, 2016 Permalink | Reply
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    From GIZMODO: “A Dozen Black Holes Are Mysteriously Spewing Energy In the Same Direction” 

    GIZMODO bloc

    GIZMODO

    4.25.16
    Maddie Stone

    NASA Chandra black hole poster
    NASA Chandra black hole poster

    Something strange is going on in a distant corner of our universe. About a dozen supermassive black holes are all shooting enormous jets of energy in roughly the same direction. It could be a cosmic coincidence—but some astronomers suspect there are larger forces at play.

    Supermassive black holes, which are found at the center of nearly all galaxies, periodically erupt, hurling streams of energized plasma into intergalactic space. For instance our galaxy’s own supermassive black hole, Sagittarius A*, will sometimes swallow a star and belch x-ray energy all over the Milky Way.

    Sag A* NASA's Chandra X-Ray Observatory 23 July 2014, the supermassive black hole at the center of the Milky Way
    Sag A* NASA’s Chandra X-Ray Observatory 23 July 2014, the supermassive black hole at the center of the Milky Way

    These eruptions are fascinating to astronomers, but they are typically thought to be independent events.

    Now, a survey of 64 galaxies located halfway across the known universe has revealed a bizarre alignment between the energy jets erupting from a handful of black holes, all of which are located within a hundred million light years of each other. A pattern like this shouldn’t exist, unless it’s being dictated by an even larger structure in our universe.

    Which is exactly what Russ Taylor, lead author of a forthcoming study* in the Monthly Notices of the Royal Astronomical Society, thinks may be happening. As Science News reports, Taylor suspects the eruptions are all being steered by filaments, a sort of scaffolding along which matter congregates on a cosmic scale. If the hypothesis is correct, it could help explain how our universe’s present structure came to be.

    Not everybody is convinced, however. Some astronomers feel the number of galaxies in the study is too small to draw meaningful conclusions, and that the pattern could be chalked up to nothing more than chance. But the idea of a cosmic alignment is intriguing enough that Taylor and his colleagues plan to follow up on it by probing more black holes, and by figuring out the precise distances between the galaxies they’ve already studied.

    I suppose if there’s one takeaway for us puny Earthlings, it’s that there are mind-bogglingly vast forces shaping our universe in ways we’ve only just begun to understand. Keeps your Monday struggle in perspective.

    *Science paper
    Alignments of radio galaxies in deep radio imaging of ELAIS N1

    See the full article here .

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    “We come from the future.”

    GIZMOGO pictorial

     
  • richardmitnick 2:09 pm on April 2, 2016 Permalink | Reply
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    From SPACE.com: “Cataclysm Hunters: The Search for Monster Black-Hole Collisions” 

    space-dot-com logo

    SPACE.com

    April 1, 2016
    Sarah Lewin

    1
    Supermassive black holes at the heart of merging galaxies will circle closer and closer until they come together, releasing a titanic wave of energy. The process may help explain how black holes get so huge to begin with. Credit: NASA

    Julie Comerford has built a career searching for galaxies that contain not one, but two supermassive black holes — light-devouring monsters that have masses millions or billions of times that of the sun. So far, the count is up to 12.

    “The mergers of two supermassive black holes is second only to the Big Bang as the most energetic phenomena in the universe,” Comerford, an astrophysicist at the University of Colorado, Boulder, told Space.com. Yet that titanic, violent dance — essential to galaxy growth and evolution — has not been spotted very often.

    Each galaxy has a supermassive black hole at its core. When two galaxies merge, the two central black holes circle faster and faster, coming closer and closer until they merge into one as well.

    Cornell SXS team. Two merging black holes simulation
    Cornell SXS team. Two merging black holes simulation

    Black holes merging Swinburne Astronomy Productions
    Black holes merging Swinburne Astronomy Productions

    Once light crosses the threshold of a black hole, it can never escape, but galactic sleuths like Comerford have spent years looking for other kinds of evidence revealing those monster black holes headed for a cataclysmic collision.

    Relatively small “stellar mass” black holes form when a huge star dies in a supernova explosion and its core collapses. A black hole can grow as more mass falls into it, but nobody can fully explain how the supermassive ones lurking at the cores of galaxies are able to get so enormous — the one at the center of the Milky Way has a mass 4 million times that of the sun, and it’s comparatively small.

    Sag A* NASA's Chandra X-Ray Observatory 23 July 2014
    Sag A* NASA’s Chandra X-Ray Observatory 23 July 2014, the supermassive black hole at the center of the Milky Way

    The process of two galaxies merging could explain this extraordinary growth.

    “One theory is that maybe a lot of the black hole mass growth actually occurs during galaxy mergers, because that’s when all this gas is being slammed together and funneled towards a black hole — so there’s a lot of fuel available for the black hole to eat and build up its mass,” Comerford said.

    Solving the growth mystery promises to reveal insight into how galaxies, and the black holes at their hearts, grow and change over time. Plus, it should help hone scientists’ newly proven powers of detecting gravitational waves.

    Searching for light

    The ultralarge black holes at the centers of galaxies don’t let any light slip out, but pairs of structures so massive leave their mark on the environment around them in other ways. For one thing, they’re always at the hearts of merging galaxies.

    “The Milky Way just has one central big sphere of stars, so it would not be a good candidate for one of these potential double black holes,” Comerford said. “We’re looking for things that look different from the usual galaxies that you see images of, like a normal spiral galaxy or elliptical galaxy — that’s not what we want. [We want] the ones that look like they’re two merging spheres of stars.”

    That merging process also puts a lot of extra material in the path of each of the black holes, which can gain whirling “accretion disks” of dust around them that glow brightly andemit jets of energy. Supermassive black holes with that kind of ultrabright beacon are called quasars, and they’re far from invisible — in fact, they often outshine the galaxies that surround them.

    2
    This artist’s concept illustrates a quasar, or feeding black hole, similar to APM 08279+5255, where astronomers discovered huge amounts of water vapor. Gas and dust likely form a torus around the central black hole, with clouds of charged gas above and below. Credit: NASA/ESA

    NASA/ESA Hubble Telescope
    NASA/ESA Hubble Telescope

    Comerford first started searching for these double-black-hole galaxies when she was in graduate school. Her group first recognized the black holes by the unusual spectrum of light their host galaxies emit, as measured in big survey studies like the Sloan Digital Sky Survey [SDSS].

    SDSS Telescope at Apache Point, NM, USA
    SDSS Telescope at Apache Point, NM, USA

    Galaxies with a quasar at their center — a supermassive black hole taking in large quantities of material — emit a narrow band of radiation that’s very bright. But the galaxies Comerford was looking for were more complex: Instead of a nice, tall peak indicating the intense glow emitted by the quasar, she saw two peaks — one slightly redder and one slightly bluer.

    The two peaks showed that there were two significant light sources in the system: one moving toward Earth and one moving away. By following up with an X-ray or radio telescope, or with NASA’s Hubble Space Telescope looking in visible light, she could verify that those two light sources were embedded in a merging set of galaxies.

    Comerford’s systematic search could find supermassive black holes that are around 3,000 light-years away from each other — that’s about 1/8 the distance from Earth’s solar system to the center of the galaxy — and that are orbiting one another at about 500,000 mph (800,000 kph). Looking straight at such systems, it might be impossible to distinguish the two quasars from each other because they’d be too close together, so the wavelengths of light emitted provided a crucial first clue.

    More recently, because of the increasing amount of Hubble galaxy imagery available, Comerford has started relying on visual images to pinpoint the supermassive black hole pairs. First, she finds quasar activity in telescope data, and then she checks with a Hubble image of the galaxy to see if it looks like it might be two merging galaxies, with two tight cores of stars that might each surround a supermassive black hole. Finally, she follows up with higher-resolution infrared or radio telescopes to try and distinguish whether there are two separate quasars there.

    4
    Diagrams of 30 merging galaxies. The edges show signal strength from carbon monoxide, while colors show where the gas is moving. Red represents gas moving away from Earth, and blue moving towards.
    Credit: ALMA (ESO/NAOJ/NRAO)/SMA/CARMA/IRAM/J. Ueda et al.

    ESO/NRAO/NAOJ ALMA Array
    ESO/NRAO/NAOJ ALMA Array

    CfA Submillimeter Array Hawaii SAO
    CfA Submillimeter Array Hawaii SAO

    CARMA Array no longer in service
    CARMA Array no longer in service

    IRAM NOEMA interferometer
    IRAM NOEMA interferometer

    “There may be one [supermassive black hole pair] in every something like a thousand to a million galaxies,” Sarah Spolaor, a researcher at the National Radio Astronomy Observatory in New Mexico, told Space.com. “The chance of just finding one by chance is pretty low, but if you have a sky catalog of thousands upon thousands of galaxies, then you’re much more likely to see that kind of weird-looking one that you think, ‘What is that?’ — and it’s maybe a binary black hole.”

    The growing mystery

    Researchers know that supermassive black holes are intimately tied to the galaxies surrounding them. There’s one at every galaxy’s heart, and the galaxy’s size is reflected in the size of the black hole. Even early galaxies, born close to the beginning of the universe, show that correlation. Finding black hole mergers can help solve the mystery of how those black holes got so big, so early in the universe’s history. Plus, even the existence of quasars at all, which can only form once black holes get massive enough, raises questions.

    “Why are we doing this stamp collecting?” Comerford said. “There’s scientific questions that we want to answer, and that is one of the big ones: how do black holes get enough gas in the first place to become a quasar?”

    Researchers know that black holes at the center of merging galaxies ultimately form into one larger supermassive black hole, but it’s unclear whether that’s the whole picture.

    “Galaxy mergers are definitely an effective way to get supermassive black holes to grow,” said Scott Barrows, an astronomer also at the University of Colorado, Boulder. “But how important is this process relative to other processes that could just be happening in a galaxy that’s not interacting?” Barrows said. “There’s not a good consensus on how this works as of yet,” he told Space.com.

    Barrows’ own research searches for supermassive black hole systems where only one black hole has bloomed into a quasar — an indicator, he said, that the black holes are uneven; one is growing faster than the other and taking in more material kicked up in the merger. That uneven matchup could help scientists understand exactly what role the events play in growing black holes and the galaxies surrounding them.

    Besides solving that mystery, a better understanding of the epic systems should reveal more about the overall universe’s evolution, researchers say.

    “Supermassive black holes are thought to play a huge role in how the universe evolves,” Spolaor said. “They are the most massive compact single objects in the universe.”

    See the full article here .

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  • richardmitnick 2:04 pm on January 12, 2016 Permalink | Reply
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    From Symmetry: “Black holes” 

    Symmetry

    01/12/16
    Ali Sundermier

    Let yourself be pulled into the weird world of black holes.

    Temp 1

    Imagine, somewhere in the galaxy, the corpse of a star so dense that it punctures the fabric of space and time. So dense that it devours any surrounding matter that gets too close, pulling it into a riptide of gravity that nothing, not even light, can escape.

    And once matter crosses over the point of no return, the event horizon, it spirals helplessly toward an almost infinitely small point, a point where spacetime is so curved that all our theories break down: the singularity. No one gets out alive.

    Black holes sound too strange to be real. But they are actually pretty common in space. There are dozens known and probably millions more in the Milky Way and a billion times that lurking outside. Scientists also believe there could be a supermassive black hole at the center of nearly every galaxy, including our own. The makings and dynamics of these monstrous warpings of spacetime have been confounding scientists for centuries.

    A history of black holes

    It all started in England in 1665, when an apple broke from the branch of a tree and fell to the ground. Watching from his garden at Woolsthorpe Manor, Isaac Newton began thinking about the apple’s descent: a line of thought that, two decades later, ended with his conclusion that there must be some sort of universal force governing the motion of apples and cannonballs and even planetary bodies. He called it gravity.

    Newton realized that any object with mass would have a gravitational pull. He found that as mass increases, gravity increases. To escape an object’s gravity, you would need to reach its escape velocity. To escape the gravity of Earth, you would need to travel at a rate of roughly 11 kilometers per second.

    It was Newton’s discovery of the laws of gravity and motion that, 100 years later, led Reverend John Michell, a British polymath, to the conclusion that if there were a star much more massive or much more compressed than the sun, its escape velocity could surpass even the speed of light. He called these objects “dark stars.” Twelve years later, French scientist and mathematician Pierre Simon de Laplace arrived at the same conclusion and offered mathematical proof for the existence of what we now know as black holes.

    In 1915, Albert Einstein set forth the revolutionary theory of general relativity, which regarded space and time as a curved four-dimensional object. Rather than viewing gravity as a force, Einstein saw it as a warping of space and time itself. A massive object, such as the sun, would create a dent in spacetime, a gravitational well, causing any surrounding objects, such as the planets in our solar system, to follow a curved path around it.

    A month after Einstein published this theory, German physicist Karl Schwarzschild discovered something fascinating in Einstein’s equations. Schwarzschild found a solution that led scientists to the conclusion that a region of space could become so warped that it would create a gravitational well that no object could escape.

    Up until 1967, these mysterious regions of spacetime had not been granted a universal title. Scientists tossed around terms like “collapsar” or “frozen star” when discussing the dark plots of inescapable gravity. At a conference in New York, physicist John Wheeler popularized the term “black hole.”

    How to find a black hole

    During star formation, gravity compresses matter until it is stopped by the star’s internal pressure. If the internal pressure does not stop the compression, it can result in the formation of a black hole.

    Some black holes are formed when massive stars collapse. Others, scientists believe, were formed very early in the universe, a billion years after the big bang.

    There is no limit to how immense a black hole can be, sometimes more than a billion times the mass of the sun. According to general relativity, there is also no limit to how small they can be (although quantum mechanics suggests otherwise). Black holes grow in mass as they continue to devour their surrounding matter. Smaller black holes accrete matter from a companion star while the larger ones feed off of any matter that gets too close.

    Black holes contain an event horizon, beyond which not even light can escape. Because no light can get out, it is impossible to see beyond this surface of a black hole. But just because you can’t see a black hole, doesn’t mean you can’t detect one.

    Scientists can detect black holes by looking at the motion of stars and gas nearby as well as matter accreted from its surroundings. This matter spins around the black hole, creating a flat disk called an accretion disk. The whirling matter loses energy and gives off radiation in the form of X-rays and other electromagnetic radiation before it eventually passes the event horizon.

    This is how astronomers identified Cygnus X-1 in 1971. Cygnus X-1 was found as part of a binary star system in which an extremely hot and bright star called a blue supergiant formed an accretion disk around an invisible object. The binary star system was emitting X-rays, which are not usually produced by blue supergiants. By calculating how far and fast the visible star was moving, astronomers were able to calculate the mass of the unseen object. Although it was compressed into a volume smaller than the Earth, the object’s mass was more than six times as heavy as our sun.

    Several different experiments study black holes. The Event Horizon Telescope [EHT] will look at black holes in the nucleus of our galaxy and a nearby galaxy, M87. Its resolution is high enough to image flowing gas around the event horizon.

    Event Horizon Telescope map
    EHT

    Scientists can also do reverberation mapping, which uses X-ray telescopes to look for time differences between emissions from various locations near the black hole to understand the orbits of gas and photons around the black hole.

    The Laser Interferometer Gravitational-Wave Observatory, or LIGO, seeks to identify the merger of two black holes, which would emit gravitational radiation, or gravitational waves, as the two black holes merge.

    Caltech Ligo
    MIT/Caltech Advanced LIGO

    In addition to accretion disks, black holes also have winds and incredibly bright jets erupting from them along their rotation axis, shooting out matter and radiation at nearly the speed of light. Scientists are still working to understand how these jets form.

    What we don’t know

    Scientists have learned that black holes are not as black as they once thought them to be. Some information might escape them. In 1974, Stephen Hawking published results that showed that black holes should radiate energy, or Hawking radiation.

    Matter-antimatter pairs are constantly being produced throughout the universe, even outside the event horizon of a black hole. Quantum theory predicts that one particle might be dragged in before the pair has a chance to annihilate, and the other might escape in the form of Hawking radiation. This contradicts the picture general relativity paints of a black hole from which nothing can escape.

    But as a black hole radiates Hawking radiation, it slowly evaporates until it eventually vanishes. So what happens to all the information encoded on its horizon? Does it disappear, which would violate quantum mechanics? Or is it preserved, as quantum mechanics would predict? One theory is that the Hawking radiation contains all of that information. When the black hole evaporates and disappears, it has already preserved the information of everything that fell into it, radiating it out into the universe.

    Black holes give scientists an opportunity to test general relativity in very extreme gravitational fields. They see black holes as an opportunity to answer one of the biggest questions in particle physics theory: Why can’t we square quantum mechanics with general relativity?

    Beyond the event horizon, black holes curve into one of the darkest mysteries in physics. Scientists can’t explain what happens when objects cross the event horizon and spiral towards the singularity. General relativity and quantum mechanics collide and Einstein’s equations explode into infinities. Black holes might even house gateways to other universes called wormholes and violent fountains of energy and matter called white holes, though it seems very unlikely that nature would allow these structures to exist.

    Sometimes reality is stranger than fiction.

    See the full article here .

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    Symmetry is a joint Fermilab/SLAC publication.


     
  • richardmitnick 6:46 am on January 9, 2016 Permalink | Reply
    Tags: , , , Supermassive Black Holes   

    From ESA: “Supermassive and super-hungry” 

    ESASpaceForEuropeBanner
    European Space Agency

    08/01/2016
    No writer credit found

    1
    NASA/ESA Hubble and S. Smartt (Queen’s University Belfast)

    This NASA/ESA Hubble Space Telescope image shows the spiral galaxy NGC 4845, located over 65 million light-years away in the constellation of Virgo (The Virgin). The galaxy’s orientation clearly reveals the galaxy’s striking spiral structure: a flat and dust-mottled disc surrounding a bright galactic bulge.

    NASA Hubble Telescope
    NASA/ESA Hubble

    NGC 4845’s glowing centre hosts a gigantic version of a black hole, known as a supermassive black hole. The presence of a black hole in a distant galaxy like NGC 4845 can be inferred from its effect on the galaxy’s innermost stars; these stars experience a strong gravitational pull from the black hole and whizz around the galaxy’s centre much faster than otherwise.

    From investigating the motion of these central stars, astronomers can estimate the mass of the central black hole — for NGC 4845 this is estimated to be hundreds of thousands times heavier than the Sun. This same technique was also used to discover the supermassive black hole at the centre of our own Milky Way — Sagittarius A* — which hits some four million times the mass of the Sun (potw1340a).

    2
    Sagittarius A*. This image was taken with NASA’s Chandra X-Ray Observatory. Ellipses indicate light echoes.

    NASA Chandra Telescope
    NASA/Chandra

    3
    This image, not unlike a pointillist painting, shows the star-studded centre of the Milky Way towards the constellation of Sagittarius. The crowded centre of our galaxy contains numerous complex and mysterious objects that are usually hidden at optical wavelengths by clouds of dust — but many are visible here in these infrared observations from Hubble.
    However, the most famous cosmic object in this image still remains invisible: the monster at our galaxy’s heart called Sagittarius A*. Astronomers have observed stars spinning around this supermassive black hole (located right in the centre of the image), and the black hole consuming clouds of dust as it affects its environment with its enormous gravitational pull.
    Infrared observations can pierce through thick obscuring material to reveal information that is usually hidden to the optical observer. This is the best infrared image of this region ever taken with Hubble, and uses infrared archive data from Hubble’s Wide Field Camera 3, taken in September 2011. It was posted to Flickr by Gabriel Brammer, a fellow at the European Southern Observatory based in Chile. He is also an ESO photo ambassador. Credit: NASA/ESA Hubble and G. Brammer

    The galactic core of NGC 4845 is not just supermassive, but also super-hungry. In 2013 researchers were observing another galaxy when they noticed a violent flare at the centre of NGC 4845. The flare came from the central black hole tearing up and feeding off an object many times more massive than Jupiter. A brown dwarf or a large planet simply strayed too close and was devoured by the hungry core of NGC 4845.

    See the full article here .

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

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  • richardmitnick 1:02 pm on January 5, 2016 Permalink | Reply
    Tags: , , Supermassive Black Holes,   

    From U Colorado: “Galactic merger reveals an unusual star-deprived black hole” 

    U Colorado

    University of Colorado Boulder

    January 5, 2016
    Julie Comerford, 303-242-2181
    julie.comerford@colorado.edu

    Trent Knoss, CU-Boulder media relations, 303-735-0528
    trent.knoss@colorado.edu

    1
    Image of the galaxy SDSS J1126+2944 taken with the Hubble Space Telescope and the Chandra X-ray Observatory. The arrow points to the black hole that lost most of its stars due to gravitational stripping processes.

    In a season of post-holiday gym memberships, an unusually star-deprived black hole at the site of two merged galaxies is showing that these massive gravitational voids can shed weight too.

    The recently discovered black hole, which does not have the expected number of stars surrounding it, could provide new insight into black hole evolution and behavior, according to recently published research from the University of Colorado Boulder.

    The findings were announced today during a news briefing at the annual meeting of the American Astronomical Society (AAS) being held this week in Kissimmee, Florida.

    Supermassive black holes exist at the centers of all massive galaxies, including the Milky Way, and contain a mass of between 1 million and 1 billion times that of the sun. The mass of a black hole tends to scale with the mass of its galaxy, and each black hole is typically embedded within a large sphere of stars.

    The galaxy SDSS J1126+2944 is the result of a merger between two smaller galaxies, which brought together a pair of supermassive black holes. One of the black holes is surrounded by a typical amount of stars, but the other black hole is strangely “naked” and has a much lower number of associated stars than expected.

    “One black hole is starved of stars, and has 500 times fewer stars associated with it than the other black hole,” said Julie Comerford, an assistant professor in CU-Boulder’s Department of Astrophysical and Planetary Sciences and the lead investigator of the new research. “The question is why there’s such a discrepancy.”

    One possibility, said Comerford, is that extreme gravitational and tidal forces simply stripped away most of the stars from one of the black holes over the course of the galactic merger.

    The other possibility, however, is that the merger actually reveals a rare “intermediate” mass black hole, with a mass of between 100 and 1 million times that of the sun. Intermediate mass black holes are predicted to exist at the centers of dwarf galaxies and thus have a lower number of associated stars. These intermediate mass black holes can grow and one day become supermassive black holes.

    “Theory predicts that intermediate black holes should exist, but they are difficult to pinpoint because we don’t know exactly where to look,” said Scott Barrows, a postdoctoral researcher at CU-Boulder who co-authored the study. “This unusual galaxy may provide a rare glimpse of one of these intermediate mass black holes.”

    If galaxy SDSS J1126+2944 does indeed contain an intermediate black hole, it would provide researchers with an opportunity to test the theory that supermassive black holes evolve from these lower-mass ‘seed’ black holes.

    Images of the galaxy SDSS J1126+2944 were taken with the Hubble Space Telescope and the Chandra X-ray Observatory, a NASA-operated orbital X-ray telescope.

    NASA Hubble Telescope
    NASA/ESA Hubble

    NASA Chandra Telescope
    NASA/Chandra

    Details of the research were recently published in The Astrophysical Journal. The article is also publicly available at arXiv.

    See the full article here .

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    U Colorado Campus

    As the flagship university of the state of Colorado, CU-Boulder is a dynamic community of scholars and learners situated on one of the most spectacular college campuses in the country. As one of 34 U.S. public institutions belonging to the prestigious Association of American Universities (AAU) – and the only member in the Rocky Mountain region – we have a proud tradition of academic excellence, with five Nobel laureates and more than 50 members of prestigious academic academies.

    CU-Boulder has blossomed in size and quality since we opened our doors in 1877 – attracting superb faculty, staff, and students and building strong programs in the sciences, engineering, business, law, arts, humanities, education, music, and many other disciplines.

    Today, with our sights set on becoming the standard for the great comprehensive public research universities of the new century, we strive to serve the people of Colorado and to engage with the world through excellence in our teaching, research, creative work, and service.

     
  • richardmitnick 4:09 pm on December 3, 2015 Permalink | Reply
    Tags: , , , , Supermassive Black Holes   

    From phys.org: “Event Horizon Telescope reveals magnetic fields at Milky Way’s central black hole” 

    physdotorg
    phys.org

    December 3, 2015

    1
    In this artist’s conception, the black hole at the center of our galaxy is surrounded by a hot disk of accreting material. Blue lines trace magnetic fields. The Event Horizon Telescope has measured those magnetic fields for the first time with a resolution six times the size of the event horizon (6 Schwarzschild radii). It found the fields in the disk to be disorderly, with jumbled loops and whorls resembling intertwined spaghetti. In contrast, other regions showed a much more organized pattern, possibly in the region where jets (shown by the narrow yellow streamer) would be generated. Credit: M. Weiss/CfA

    Most people think of black holes as giant vacuum cleaners sucking in everything that gets too close. But the supermassive black holes at the centers of galaxies are more like cosmic engines, converting energy from infalling matter into intense radiation that can outshine the combined light from all surrounding stars. If the black hole is spinning, it can generate strong jets that blast across thousands of light-years and shape entire galaxies. These black hole engines are thought to be powered by magnetic fields. For the first time, astronomers have detected magnetic fields just outside the event horizon of the black hole at the center of our Milky Way galaxy.

    “Understanding these magnetic fields is critical. Nobody has been able to resolve magnetic fields near the event horizon until now,” says lead author Michael Johnson of the Harvard-Smithsonian Center for Astrophysics (CfA). The results appear in the Dec. 4th issue of the journal Science.

    “These magnetic fields have been predicted to exist, but no one has seen them before. Our data puts decades of theoretical work on solid observational ground,” adds principal investigator Shep Doeleman (CfA/MIT), who is assistant director of MIT’s Haystack Observatory.

    This feat was achieved using the Event Horizon Telescope (EHT) – a global network of radio telescopes that link together to function as one giant telescope the size of Earth.

    Event Horizon Telescope map
    EHT map

    Since larger telescopes can provide greater detail, the EHT ultimately will resolve features as small as 15 micro-arcseconds. (An arcsecond is 1/3600 of a degree, and 15 micro-arcseconds is the angular equivalent of seeing a golf ball on the moon.)

    Such resolution is needed because a black hole is the most compact object in the universe. The Milky Way’s central black hole, Sgr A* (Sagittarius A-star), weighs about 4 million times as much as our Sun, yet its event horizon spans only 8 million miles – smaller than the orbit of Mercury.

    2
    Sagittarius A*. This image was taken with NASA’s Chandra X-Ray Observatory. Ellipses indicate light echoes.
    Date 23 July 2014

    NASA Chandra Telescope
    NASA/Chandra

    And since it’s located 25,000 light-years away, this size corresponds to an incredibly small 10 micro-arcseconds across. Fortunately, the intense gravity of the black hole warps light and magnifies the event horizon so that it appears larger on the sky – about 50 micro-arcseconds, a region that the EHT can easily resolve.

    The Event Horizon Telescope made observations at a wavelength of 1.3 mm. The team measured how that light is linearly polarized. On Earth, sunlight becomes linearly polarized by reflections, which is why sunglasses are polarized to block light and reduce glare. In the case of Sgr A*, polarized light is emitted by electrons spiraling around magnetic field lines. As a result, this light directly traces the structure of the magnetic field.

    Sgr A* is surrounded by an accretion disk of material orbiting the black hole.

    3
    Image taken by Hubble space telescope of what may be gas accreting onto a black hole in elliptical galaxy NGC 4261

    The team found that magnetic fields in some regions near the black hole are disorderly, with jumbled loops and whorls resembling intertwined spaghetti. In contrast, other regions showed a much more organized pattern, possibly in the region where jets would be generated.

    They also found that the magnetic fields fluctuated on short time scales of only 15 minutes or so.

    “Once again, the galactic center is proving to be a more dynamic place than we might have guessed,” says Johnson. “Those magnetic fields are dancing all over the place.”

    These observations used astronomical facilities in three geographic locations: the Submillimeter Array and the James Clerk Maxwell Telescope [JCMT](both on Mauna Kea in Hawaii), the Submillimeter Telescope on Mt. Graham in Arizona, and the Combined Array for Research in Millimeter-wave Astronomy (CARMA) near Bishop, California.

    CfA Submillimeter Array Hawaii SAO
    CfA Submillimeter Array

    East Asia Observatory James Clerk Maxwell telescope
    JCMT

    CARMA Array
    CARMA Array

    As the EHT adds more radio dishes around the world and gathers more data, it will achieve greater resolution with the goal of directly imaging a black hole’s event horizon for the first time.

    “The only way to build a telescope that spans the Earth is to assemble a global team of scientists working together. With this result, the EHT team is one step closer to solving a central paradox in astronomy: why are black holes so bright?” states Doeleman.

    More information: Resolved magnetic-field structure and variability near the event horizon of Sagittarius A* Science, http://www.sciencemag.org/lookup/doi/10.1126/science.aac7087

    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 9:06 pm on November 26, 2015 Permalink | Reply
    Tags: , , , , Supermassive Black Holes   

    From ICRAR: “Scientists spot jets from supermassive black hole snacking on a star” 

    International Center for Radio Astronomy Research

    International Centre for Radio Astronomy Research

    27 November, 2015
    Contacts

    Dr Gemma Anderson
    ICRAR – Curtin University
    Ph: +61 8 9266 3577
    M: +61 408 955 483
    E: Gemma.Anderson@icrar.org

    Dr James Miller-Jones
    ICRAR – Curtin University
    Ph: +61 8 9266 3785
    M: +61 488 484 825
    E: James.Miller-Jones@icrar.org

    Pete Wheeler
    Media Contact
    M: +61 423 982 018
    E: Pete.Wheeler@icrar.org

    1
    An artist’s impression of a star being drawn toward a black hole and destroyed, triggering a jet of plasma made from debris left over from the stars destruction.
    Credit: Modified from an original image by Amadeo Bachar.

    Scientists have discovered a hungry black hole swallowing a star at the centre of a nearby galaxy.

    The supermassive black hole was found to have faint jets of material shooting out from it and helps to confirm scientists’ theories about the nature of black holes.

    The discovery was published today in the journal Science.

    Astrophysicist Dr Gemma Anderson, from the Curtin University node of the International Centre for Radio Astronomy Research (ICRAR), said a supermassive black hole swallowing a star is an extreme event in which the star gets ripped apart.

    “It’s very unusual when a supermassive black hole at the centre of a galaxy actually eats a star, we’ve probably only seen about 20 of them,” she said.

    “Everything we know about black holes suggests we should see a jet when this happens but until now they’ve only been detected in a few of the most powerful systems.

    “Now we’ve finally found one in a more normal event.”

    The discovery is the first time scientists have been able to see both a disk of material falling into a black hole, known as an accretion disk, and a jet in a system of this kind.

    ICRAR astrophysicist Dr James Miller-Jones compared the energy produced by the jets in this event to the entire energy output of the Sun over 10 million years.

    He said it was likely all supermassive black holes swallowing stars launched jets but this discovery was made because the black hole is relatively close to Earth and was studied soon after it was first seen.

    The black hole is only 300 million light years away from us and the team (led by Dr Sjoert van Velzen from The Johns Hopkins University in the USA) were able to make their first observations only three weeks after it was found.

    “We’ve shown that it was just a question of looking at the right time and with enough sensitivity,” Dr Miller-Jones said.

    “Then you can show that a jet exists right at the point you think it should.”

    Dr Anderson began the research while working with the 4 PI SKY team at Oxford University but moved to Western Australia in September.

    She said the event was first picked up by the All-sky Automated Survey for Supernovae (ASAS-SN), which is pronounced ‘assassin’ by astronomers, and followed up with the Arcminute Microkelvin Imager (AMI), a radio telescope, located near Cambridge.

    Arcminute Microkelvin Imager
    Arcminute Microkelvin Imager (AMI) Small Array

    “Hopefully with the increased sensitivity of future telescopes like the Square Kilometre Array we’ll be able to detect jets from other supermassive black holes of this type and discover even more about them,” Dr Anderson said.

    Further information:
    For more information about the 4 PI SKY project visit http://www.4pisky.org

    ICRAR is a joint venture between Curtin University and The University of Western Australia with support and funding from the State Government of Western Australia.

    Original publication details:

    ‘A radio jet from the optical and X-ray bright stellar tidal disruption flare ASASSN-14li’ published in the journal Science on 26/11/2015. A copy of the paper is available upon request. ​

    See the full article here .

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    ICRAR is an equal joint venture between Curtin University and The University of Western Australia with funding support from the State Government of Western Australia. The Centre’s headquarters are located at UWA, with research nodes at both UWA and the Curtin Institute for Radio Astronomy (CIRA).
    ICRAR has strong support from the government of Australia and is working closely with industry and the astronomy community, including CSIRO and the Australian Telescope National Facility, iVEC, and the international SKA Project Office (SPO), based in the UK.

    ICRAR is:

    Playing a key role in the international Square Kilometre Array (SKA) project, the world’s biggest ground-based telescope array.

    SKA Square Kilometer Array
    Attracting some of the world’s leading researchers in radio astronomy, who will also contribute to national and international scientific and technical programs for SKA and ASKAP.
    Creating a collaborative environment for scientists and engineers to engage and work with industry to produce studies, prototypes and systems linked to the overall scientific success of the SKA, MWA and ASKAP.

    SKA Murchison Widefield Array
    A Small part of the Murchison Widefield Array

    Enhancing Australia’s position in the international SKA program by contributing to the development process for the SKA in scientific, technological and operational areas.
    Promoting scientific, technical, commercial and educational opportunities through public outreach, educational material, training students and collaborative developments with national and international educational organisations.
    Establishing and maintaining a pool of emerging and top-level scientists and technologists in the disciplines related to radio astronomy through appointments and training.
    Making world-class contributions to SKA science, with emphasis on the signature science themes associated with surveys for neutral hydrogen and variable (transient) radio sources.
    Making world-class contributions to SKA capability with respect to developments in the areas of Data Intensive Science and support for the Murchison Radio-astronomy Observatory.

     
  • richardmitnick 2:17 pm on November 20, 2015 Permalink | Reply
    Tags: , , , , Supermassive Black Holes   

    From Nautilus: “This Is Why It’s Hard to Recognize a Black Hole” 

    Nautilus

    Nautilus

    Nov 18, 2015
    Summer Ash

    1
    Black Beauty: The supermassive black hole at the center of this galaxy, around 11 million light years away toward the constellation Centaurus, is currently classified as a quasar. It is roughly 55 million times more massive than our Sun. Its collimated jets, in blue, surpass the diameter of the entire galaxy, extending up to 13,000 light years. The Milky Way, by comparison, is roughly ten times this length. NASA/CXC/CfA/R.Kraft et al.; MPIfR/ESO/APEX/A.Weiss et al.; ESO/WFI.

    Astronomers can sometimes be literal to a fault. We like to call things as we see them. For example, if it’s red and it’s huge: Red Giant. White and small: White Dwarf. Massive explosion: Big Bang. Dark and sucks everything in: Black Hole. Most of the time, classifying objects this way works fine—either it’s new, or it’s something we already know of. But sometimes, as with Pluto, we make new observations that force us to question the name, reassess the object, and identify it differently. You might think this never happens with something as clearly defined as a black hole, but you’d be wrong.

    Though we can’t observe them directly, we can see how the two types of black holes—stellar mass and supermassive—affect their surroundings. Stellar mass black holes, the product of a dying star going supernova and collapsing on itself, are the more familiar, predicted nearly a century ago by [Albert] Einstein’s theory of general relativity; They usually only affect the behavior of the nearest star or two. Supermassive black holes, on the other hand, are over a million times more massive. We still don’t know how these form, but we believe they exist at the center of almost every galaxy, sometimes having the power to alter the appearance of their entire galaxy.

    This capacity for mass distortion makes characterizing supermassive black holes particularly tricky.

    As the stars, gas, and dust in the center of a galaxy get closer and closer to a supermassive black hole, they get packed tighter and tighter into a smaller and smaller space, heating up until, at a critical distance, everything is ripped apart, reduced to atomic particles. When we spot supermassive black holes, it’s this heat radiating away from the orbiting debris—known as an accretion disk—that we actually see, not the black hole itself. Some supermassive black holes “eat” more than others and, in the process, give off significantly more light than their less active brethren. These active galactic nuclei, or AGN for short, are some of the most powerful, most energetic forces in the Universe. Not only do they give off heat, they also often eject material in the form of collimated (beamed) jets, perpendicular to the plane of the disk, which blast their way out of the galaxy’s core—dwarfing in size not just the accretion disk, but also the galaxy itself. What’s more, some AGN have a dusty torus, the geometric equivalent of a donut, in the same plane as their accretion disk, but much, much bigger and thicker. So thick, in fact, that if you looked at them from the side, you wouldn’t see the disk at all, much less the black hole in the center (as seen in the image above).

    Despite having this standard model of an AGN—a supermassive black hole surrounded by an accretion disk with jets streaming out in opposite directions, all encompassed by a dusty torus—making sense of our observations is still a challenge: The light we see doesn’t always paint the same picture. Sometimes we see jets, sometimes we don’t. Sometimes we see the torus, sometimes we don’t. Sometimes we see light so concentrated and bright that we can’t even tell if there’s a galaxy there at all. We label these sightings accordingly: AGN at great distances with cores so bright, they outshine all their stars in optical light, are called quasars (for “quasi-stellar”), like the one pictured above; AGN that glow strongly in the infrared are called Seyferts, after the astronomer Carl Seyfert, who first identified them in 1943; And AGN, with cores and jets whose emitted light dominates in the radio spectrum, are called radio galaxies.

    3
    Resembling a swirling witch’s cauldron of glowing vapors, the black hole-powered core of a nearby active galaxy appears in this colorful NASA Hubble Space Telescope image. The galaxy lies 13 million light-years away in the southern constellation Circinus.
    This galaxy is designated a type 2 Seyfert, a class of mostly spiral galaxies that have compact centers and are believed to contain massive black holes. Seyfert galaxies are themselves part of a larger class of objects called Active Galactic Nuclei or AGN. AGN have the ability to remove gas from the centers of their galaxies by blowing it out into space at phenomenal speeds. Astronomers studying the Circinus galaxy are seeing evidence of a powerful AGN at the center of this galaxy as well.
    Much of the gas in the disk of the Circinus spiral is concentrated in two specific rings — a larger one of diameter 1,300 light-years, which has already been observed by ground-based telescopes, and a previously unseen ring of diameter 260 light-years.
    In the Hubble image, the smaller inner ring is located on the inside of the green disk. The larger outer ring extends off the image and is in the plane of the galaxy’s disk. Both rings are home to large amounts of gas and dust as well as areas of major “starburst” activity, where new stars are rapidly forming on timescales of 40 – 150 million years, much shorter than the age of the entire galaxy.
    At the center of the starburst rings is the Seyfert nucleus, the believed signature of a supermassive black hole that is accreting surrounding gas and dust. The black hole and its accretion disk are expelling gas out of the galaxy’s disk and into its halo (the region above and below the disk). The detailed structure of this gas is seen as magenta-colored streamers extending towards the top of the image.
    In the center of the galaxy and within the inner starburst ring is a V-shaped structure of gas. The structure appears whitish-pink in this composite image, made up of four filters. Two filters capture the narrow lines from atomic transitions in oxygen and hydrogen; two wider filters detect green and near-infrared light. In the narrow-band filters, the V-shaped structure is very pronounced. This region, which is the projection of a three-dimensional cone extending from the nucleus to the galaxy’s halo, contains gas that has been heated by radiation emitted by the accreting black hole. A “counter-cone,” believed to be present, is obscured from view by dust in the galaxy’s disk. Ultraviolet radiation emerging from the central source excites nearby gas causing it to glow. The excited gas is beamed into the oppositely directed cones like two giant searchlights.
    Located near the plane of our own Milky Way Galaxy, the Circinus galaxy is partially hidden by intervening dust along our line of sight. As a result, the galaxy went unnoticed until about 25 years ago. This Hubble image was taken on April 10, 1999 with the Wide Field Planetary Camera 2.
    The research team, led by Andrew S. Wilson of the University of Maryland, is using these visible light images along with near-infrared data to further understand the dynamics of this powerful galaxy.
    Date 10 April 1999

    If they are all fueled by supermassive black holes, why don’t all AGN look the same? One reason could be our point of view. The theory of AGN unification posits that all AGN have the same basic building blocks (accretion disk, jets, torus); The striking differences we observe, according to this theory, are all due to their orientation in space.

    Here on Earth, we only have one vantage point from which to observe the cosmos. We see galaxies randomly distributed around us, some of them edge-on, some of them face-on, and the rest at all the angles in-between. We cannot fly around to look at these galaxies from any other angle than the one they present to us. But with the advent of supercomputers, we can now simulate these galaxies better than ever before and virtually fly around them as much as we like, enjoying the sights from any angle. We can take an AGN and turn it so we’re looking straight down one of the jets, towards the galactic core, making it resemble a blazar, sort of a blazing quasar. Start tilting the AGN until the jet is rotated ninety degrees away from us, and it appears to morph from a blazar to a quasar to, finally, a Seyfert.

    Yet AGN unification is far from a settled problem in astrophysics. There could be other factors at play than just our point of view, like physical processes in and around black holes we don’t fully understand or measurements we haven’t thought to take. As we build better telescopes and amass new data, we can only hope that we’ll see these active galactic nuclei for what they really are. Otherwise, we might need a lot more names.

    See the full article here .

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

     
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