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  • richardmitnick 9:57 am on March 14, 2017 Permalink | Reply
    Tags: , , , , , Quasars   

    From phys.org: “Astronomers discover 16 new high-redshift quasars” 

    physdotorg
    phys.org

    March 14, 2017
    Tomasz Nowakowski

    1
    The color track of quasar at z = 5 to 6 (red dots and line) with a step of ∆z = 0.1, generated by calculating the mean colors of simulated quasars at each redshift bin. The contours show the locus of M dwarfs, from early type to late type. The cyan contours denote M1-M3 dwarfs, the orange contours denote M4-M6 dwarfs and the purple contours denote M7-M9 dwarfs. Clearly, z ∼ 5.5 quasars are serious contaminated by late type M dwarfs. Credit: Yang et al., 2017.

    Using a new color selection technique, astronomers have detected 16 new luminous, high-redshift quasars. The discovery could be very important for understanding of the early universe, as such high-redshift, quasi-stellar objects provide essential clues on the evolution of the intergalactic medium, quasar evolution and early super-massive black hole growth. The findings were presented in a paper published Mar. 10 on the arXiv pre-print repository.

    High-redshift quasars (at redshift higher than 5.0) are very difficult to find using conventional color selections. This is due to their low spatial density and high contaminants from cool dwarfs. Among more than 300,000 quasars discovered to date, only 290 of them are at redshift higher than 5.0. The scientific community is especially interested in high-redshift quasars at redshift between 5.3 and 5.7, due to their optical colors, which are similar to those of late-type stars. Only about 30 such objects have been found so far.

    With the aim of filling this gap of known quasars at redshift ranging from 5.3 to 5.7, a team of astronomers led by Jinyi Yang of the Peking University in Beijing, China, has developed a new optical/infrared color selection technique. The method is based on optical, near-infrared and mid-infrared photometric data from Sloan Digital Sky Survey (SDSS), UKIRT InfraRed Deep Sky Surveys – Large Area Survey (ULAS), VISTA Hemisphere Survey (VHS) and NASA’s Wide field Infrared Survey Explorer (WISE).


    SDSS Telescope at Apache Point Observatory, NM, USA


    UKIRT, located on Mauna Kea, Hawai’i, USA as part of Mauna Kea Observatory


    NASA/WISE Telescope

    The method has proved its worth as the researchers were able to find 16 new luminous, high-redshift quasars at redshift within the desired range. The observations were carried out between October 2014 and November 2015.

    “In this paper, we report initial results from a new search that focuses on the selection of z ~ 5.5 quasars,” the team wrote.

    Among the newly discovered quasi-stellar objects, J113414.23+082853.3 is the one with the highest redshift – at 5.69. This quasar also showcases strong Lyman-alpha emission and strong intergalactic medium absorption blueward of Lyman-alpha line.

    Another interesting new quasar found by the researchers is J152712.86+064121.9 (at 5.57). It is a weak line quasar with a very weak Lyman-alpha emission line and no other obvious emission features. However, the team revealed that its redshift was measured by matching the continuum to template; thus, its redshift uncertainty is a little larger than others.

    The scientists underline the importance of their research, noting that it could help us better understand the evolution of quasars at redshift from 5.0 to 6.0, over the post-reionization epoch.

    “The physical conditions of the post-reionization intergalactic medium, at z ~ 5-6, provides the basic boundary conditions of models of reionization, such as the evolution of intergalactic temperature, photon mean free path, metallicity and the impact of helium reionization. They place strong constraints on reionization topology as well as on the sources of reionization and chemical feedback by early galaxy population,” the paper reads.

    The team now plans to publish another paper in which a broader sample of high-redshift quasars will be presented. This study will also include the data from the UKIRT Hemisphere Survey (UHS), Pan-STARRS PS1 Survey and the VLT Survey Telescope (VST) ATLAS.


    Pan-STARRS1 located on Haleakala, Maui, HI, USA


    ESO VST telescope, at ESO’s Paranal Observatory

    See the full article here .

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  • richardmitnick 1:26 pm on March 10, 2017 Permalink | Reply
    Tags: , , , , Kavli Institute for Cosmology Cambridge, Quasars   

    From Kavli: “Will a New Discovery Fast-track Our Understanding of the Origins of Galaxies and Gargantuan Black Holes?” 

    KavliFoundation

    The Kavli Foundation

    Kavli Institute for Cosmology, Cambridge

    Mar 10, 2017
    Adam Hadhazy

    Thanks to a record haul of new, ultra-distant quasars—powerhouses of light from the farthest reaches of the universe—astrophysicists can now piece together the rise of mighty objects in the early cosmos.

    THE DISCOVERY OF MORE THAN 60 QUASARS—stupendously bright regions in the cores of galaxies, powered by gargantuan black holes—is a windfall for astrophysicists probing the early universe. At more than 13 billion light-years away, these quasars rank among the farthest objects ever glimpsed by humans.

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    An artist’s iconic impression of an extremely bright quasar. (Credit: ESO/M. Kornmesser)

    That’s important because they take us way back in time, to the first billion years after the Big Bang, and may help explain how the first galaxies and supermassive black holes arose. Guided by their light, astrophysicist hope to understand how the universe transitioned from a dark, featureless expanse into a rich, starry realm loaded with luminous galaxies.

    The Kavli Foundation recently spoke with three astrophysicists about how this haul of ultra-distant quasars will transform what we know about the early universe.

    The participants were:

    ROBERTO MAIOLINO – is a professor of experimental astrophysics at the Cavendish Laboratory of the University of Cambridge and director of the Kavli Institute for Cosmology, Cambridge (KICC). He studies distant quasars to learn about how galaxies and black holes have evolved together throughout cosmic history.
    LINHUA JIANG – is the Youth Qianren Research Professor at the Kavli Institute for Astronomy and Astrophysics (KIAA) at Peking University. An author of two recent studies that discovered dozens of new and extremely distant quasars, Jiang is interested in how the first galaxies changed the universe hundreds of millions of years after the Big Bang.
    MARTA VOLONTERI – is research director at the Institut d’Astrophysique de Paris. A theorist, she is the principal investigator of the BLACK project, which investigates how supermassive black holes formed and influenced their host galaxies, especially as quasars, in the early universe.

    The following is an edited transcript of their roundtable discussion. The participants have been provided the opportunity to amend or edit their remarks.

    THE KAVLI FOUNDATION: Before we talk about the new discovery, what is a quasar and why do you find them so fascinating?

    ROBERTO MAIOLINO: Quasars are the cores of galaxies powered by supermassive black holes gobbling up matter at a high rate. These black holes have masses typically exceeding one million times that of our Sun. The process of consuming matter radiates a lot of energy as light. In fact, most quasars are so bright, they outshine their host galaxy by a large factor. Most quasars are also very far away, and the ones we are particularly interested in are those that developed when the universe was young—less than a billion years old.

    You can think of quasars as lighthouses in the dark of the early universe. Just as a lighthouse’s beam might shine on nearby land forms, making them visible from far away, quasars enable us to investigate the very distant universe and understand the physics of primordial galaxies. We think that quasars indicate special regions in the early universe where matter is particularly dense. As the cosmos developed, these so-called overdense regions probably ended up being populated by a large number of galaxies. So quasars help us to learn about these sites of galaxy formation. We also believe that quasars are tightly connected with the evolution of their young, host galaxies.

    MARTA VOLONTERI: I’m interested in whether quasars can illuminate the origins of supermassive black holes, which can possess less than a million to several billions of times the mass of the Sun. Black holes exist in the center of most galaxies, including the Milky Way, but we don’t know how they got there.

    LINHUA JIANG: What makes distant quasars so interesting to me, as an observational astronomer, is that they are very difficult to find.

    TKF: And we now have twice as many of these lighthouses in deep space to observe. Why is that important?

    MAIOLINO: Until now, we have only had a chance to study a few ultra-distant quasars. What those can teach us about the nature of quasars, and more broadly about the general state of the cosmos long ago, is highly limited. With the newly discovered quasars, we will be able to gauge the variety of these monstrously powerful objects in the universe and how they affect their host galaxies.

    JIANG: Echoing what Roberto just said, now that we have a much larger sample of quasars than ever before, roughly 200, we can study them to learn about their individual variation and how they collectively influenced the primordial cosmos.

    TKF: The more quasars, the merrier, right?

    MAIOLINO: Exactly.

    TKF: Quasars were identified in the early 1960s, and yet the tally remains pretty small compared to the hundreds of billions of galaxies known to exist in our universe. Why are quasars so difficult to find?

    MAIOLINO: Quasars are typically so far away, we generally only see them as point-like sources of light through our telescopes—the same as we see stars. That’s how these objects got their name—“quasars,” for “quasi-stars.” We didn’t know these objects were inside other galaxies, and not just stars, until we measured the light coming from them, which showed they were very far away. The identification of quasars, especially the very distant ones, generally require extensive observing campaigns with large telescopes. Luminous distant quasars are also very rare, hence finding them among the plethora of other celestial objects is often a difficult process.

    TKF: So finding quasars depends heavily on building increasingly powerful and sensitive telescopes?

    JIANG: Yes. To find the most distant quasars, which are not as bright as closer quasars, you really need telescope surveys that take images across a very large part of the sky. My colleagues and I used both the Sloan Digital Sky Survey and the Pan-STARRS survey to find the quasars that we recently reported. Before those surveys began, we really knew very little about distant quasars.


    DSS Telescope at Apache Point Observatory, NM, USA


    Pan-STARRS1 located on Haleakala, Maui, HI, USA

    TKF: And while quasars have been hard to find in the past, do you expect this to change?

    JIANG: Yes. With the next generation of telescopes, we should find many more quasars.

    VOLONTERI: We are probably seeing just the tip of the iceberg. We know that small objects are more common in the universe than big things. We see this when it comes galaxies, stars, planets . . . really everything else! We would therefore expect there to be a lot more quasars out there that are smaller and fainter. Also, the luminosity of the quasars we’ve detected is extremely high, so we are probably only seeing the brightest outliers. That means we are studying quasars with a very limited range of properties.

    TKF: Roberto, you mentioned earlier that quasars outshine their host galaxies. How does all this energy affect their host galaxies?

    MAIOLINO: Quasars can “kill” themselves and their galaxies by completely cleaning out a galaxy’s gas content. This happens because they drive some of the most powerful outflows of gas in the universe that we’ve ever seen, and when they do, they remove the fuel available for star formation.

    VOLONTERI: Right. A quasar dumps so much energy into a host galaxy that it can influence how often stars form.

    TKF: As for black holes, what do quasars reveal about them, and why is this important?

    VOLONTERI: Knowing more about the black holes powering quasars will allow us to know more about how galaxies develop, and knowing about the evolution of galaxies allows us to trace the universe’s history overall. That’s why finding more quasars to study is so fundamental.

    MAIOLINO: Observations have shown us that a significant fraction of these primordial black holes is extremely massive. In the local universe, black holes typically have masses of only one-thousandth of their host galaxy. But in the distant, early universe, we now know some black holes can reach masses close to 10 percent of that of their host galaxy. That’s amazing and this tells us that in the early universe, black holes overtake galaxies in terms of forming and growing. Only later in the universe’s history do the galaxies catch up. So observations are already giving us some indications about the early evolutionary path of our universe.

    JIANG: A mystery, though, is that there does not seem to have been enough time for the universe to have grown these supermassive black holes, given how early in cosmic history we begin to see them as quasars. So for a supermassive black hole formation scenario to be right, it has to account for that rapid growth.

    TKF: Shifting gears here, let’s talk about a period in the history of the universe when it literally went from dark to light. Linhua, what role do we think the earliest quasars had in this transformation?

    JIANG: The idea is still controversial, but quasars may have provided the energy that fueled a change in the gas between the galaxies, allowing light to pass through it. That turning point, when the universe was roughly a billion years old, is known as the “epoch of reionization.” It happened when neutral atoms of hydrogen gas became ionized, which is how they had originally been when the universe began in a hot, dense state. The question is, how and why did this happen? Ionization takes a lot of energy. What were the cosmic sources of the high-energy light that drew the universe out of the so-called dark ages, the era before the first stars and galaxies formed? Could quasars be the answer? At the moment, that seems unlikely because there are so few quasars known. But, as Marta said earlier, we are probably seeing only the tip of the quasar iceberg. There could be a lot more that we haven’t seen yet.

    VOLONTERI: We have recently made a theoretical breakthrough that will help us figure out how much of a role quasars played in the epoch of reionization. We can now accurately monitor radiation inside of our computer simulations as galaxies evolve. We should soon be able to count how many light particles can leave a galaxy and start ionizing extragalactic gas, which I think is really awesome.

    TKF: Looking ahead, what are some of the projects and missions that could help us find even more quasars and better characterize them?

    MAIOLINO: I expect that the Large Synoptic Survey Telescope, or LSST, will greatly expand our numbers of distant quasars using visible light, when it opens in 2022.



    LSST/Camera, built at SLAC


    LSST telescope, currently under construction at Cerro Pachón Chile, a 2,682-meter-high mountain in Coquimbo Region, in northern Chile, alongside the existing Gemini South and Southern Astrophysical Research Telescopes.

    If we want to look even further back on time, before the epoch of reionization, then we need to use infrared light. The prime surveys for doing that will both be space-based. One is called EUCLID, launching in 2020, and the other is WFIRST, launching in the mid 2020s.


    ESA/Euclid spacecraft


    NASA/WFIRST

    I’d expect these missions to deliver very distant galaxies and quasars and to help detect quasars hidden by cosmic dust.

    JIANG: Once we find new candidates, we have to confirm them as quasars by looking for chemical signatures in the light observations using a method called spectroscopy. It is very costly to allocate the time on telescopes to take the long observations we need to do spectroscopy. But we will do it, because it allows us to learn a lot about the properties of quasars.

    MAIOLINO: Right. We will want to investigate the physical properties of distant quasars even better than we can do now. The James Webb Space Telescope, the successor to the Hubble Space Telescope, and a few other next-generation facilities, like the Thirty Meter Telescope, the Giant Magellan Telescope, and the European Extremely Large Telescope will enable us to scrutinize what’s happening in the quasars’ host galaxies and with their supermassive black holes.


    NASA/ESA/CSA Webb Telescope annotated


    TMT-Thirty Meter Telescope, proposed for Mauna Kea, Hawaii, USA


    Giant Magellan Telescope, Las Campanas Observatory, to be built some 115 km (71 mi) north-northeast of La Serena, Chile


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

    TKF: What mysteries about quasars do you still hope to answer?

    MAIOLINO: Observations of the earliest quasars show that their host galaxies are already enriched with huge amounts of heavy elements, such as iron, as well as cosmic dust, small particles that are ejected into space when the stars die. This enrichment process takes time—many hundreds of millions of years.

    Yet, we see these distant galaxies, illuminated by quasars, when the age of the universe was less than one billion years. That suggests that everything in these early galaxies with quasars seems to be going on at a much faster rate than any other galaxies that we know of in the universe, and we don’t know why.

    I’m confident that upcoming observations will shed a lot of light on these amazing objects.

    JIANG: Studying distant quasars will help us gauge the “clumpiness” of gas in the spaces between the galaxies. We’ll learn more about the early history of galaxies and how the cosmos got its shape, so to speak.

    VOLONTERI: As we’ve said, 200 distant quasars is only the tip of the iceberg. We still don’t know about the broader population of quasars and how they can explain the growth of black holes in galaxies, so we need more data.

    See the full article here .

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    The Foundation’s mission is implemented through an international program of research institutes, professorships, and symposia in the fields of astrophysics, nanoscience, neuroscience, and theoretical physics as well as prizes in the fields of astrophysics, nanoscience, and neuroscience.

     
  • richardmitnick 9:05 am on March 10, 2017 Permalink | Reply
    Tags: , , , How long do quasars shine?, Quasars   

    From astrobites: “How long do quasars shine?” 

    Astrobites bloc

    Astrobites

    Title: Statistical detection of the He II transverse proximity effect: evidence for sustained quasar activity for > 25 million years
    Authors: Tobias M. Schmidt, Gabor Worseck, Joseph F. Hennawi, J. Xavier Prochaska, Neil H. M. Crighton
    First Author’s Institution: MPIA, Heidelberg, Germany
    1
    Status: Submitted to ApJ, open access

    In the deep center of every massive galaxy, extremely massive but invisible black holes reign supreme. How these supermassive black holes (SMBHs) grew to boast of their 107-109 Msun masses still eludes us today. These massive beasts are awakened when surrounding matter spirals in and falls into them, creating active galactic nuclei (AGN) as luminous as our Milky Way.

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    UCSB

    In this state, they spew out radiation from the radio to the X-rays. When the accretion of matter is particularly high, the AGN becomes very luminous and is called a quasar. (Here is a handy guide on AGN taxonomy.)

    We believe that part of the reason SMBHs grow so massive is that they are fed by a voluminous amount of accreting material during the bright quasar phase. Even if some SMBHs appear dormant (i.e. no accretion of matter), it is believed that they must have gone through at least one quasar period in the past. Thus the quasar lifetime can shed light on the growth and evolution of SMBHs. Current estimates of the quasar lifetime are not very tight — they span a couple of orders of magnitudes from 106 to 108 years. These assume that black holes go through the quasar phase once, although it is possible that a black hole undergoes multiple quasar outbursts. Multiple episodic lifetimes would then sum up to the net quasar lifetime.

    This paper examines the episodic lifetime of quasars using singly-ionized helium (He II) as the probe. At redshift z~3, most of the Helium in the Universe is singly-ionized. The last electron in He II can be knocked free by the powerful radiation from quasars. As a quasar ionizes its surrounding He II, one can imagine a sphere of ionized He II around the quasar that expands outward with the ionizing radiation. The longer the quasar shines, the larger this sphere becomes.

    What happens when there is a foreground quasar at almost the same redshift close to a background quasar? In this case, when light from the background quasar passes through the ionized He II sphere of the foreground quasar, it will not be absorbed by the He II near the foreground quasar, since the He II would already be ionized (by the foreground quasar). On Earth we see an increased flux transmission in the spectrum of the background quasar, at the ionization wavelength of He II. This is known as the proximity effect. We’re particularly interested in the transverse proximity effect, which is the proximity effect across the plane of the sky.

    To find this, the authors carried out an intensive imaging and spectroscopic campaign in the vicinity of 22 background quasars at z~3 with 4m- and 8m-class telescopes including the Large Binocular Telescope (LBT), the Very Large Telescope (VLT), and the New Technology Telescope (NTT).


    Large Binocular Telescope, Mount Graham, Arizona, USA


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


    ESO/NTT at Cerro La Silla, Chile

    They ended up with a final sample of 66 foreground quasars, the largest that has ever been used in such studies. There were multiple foreground quasars near any one background quasar. The authors first searched for the proximity effect in individual background quasars (an example is shown in Figure 1), but failed to detect any signal. But don’t lose heart, as stacking the spectra can reveal the hidden signal.

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    Fig. 1 – Spectra of four background quasars in this study, where the stars mark the locations of the foreground quasars. Values on top indicate the rate at which the foreground quasars emit ionizing photons. The spectra had been truncated to only focus on foreground quasars with high ionizing radiation. The transverse proximity effect appears as a spike at the location of the stars relative to the continuum. Except for the lower right panel, none of the spectrum here and in the rest of the sample indicates strong proximity effect. [Figure 6 in paper]

    The authors stacked their spectra at the positions of foreground quasars whose ionizing radiation passes a certain cut — this gives them an average He II transmission profile, as shown in Figure 2. The stacked profile shows a clear transmission spike with 3σ significance. In order to ionize the He II gas, the quasar had to shine for at least the transverse light-crossing-time between the foreground and background quasar. The authors stacked quasar spectra for a range of transverse separations from the background quasar. The maximum separation where the proximity effect persists gives a lower limit on the quasar lifetime. The proximity effect is found to persist up to > 25 mega light years for their sample, translating to a minimum 25 Myr for the quasar lifetime.

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    Fig. 2 – Stacked spectra of foreground quasars whose ionizing radiation passes a certain cut (indicated top left). The red line indicates the position of the foreground quasars, where an increase in He II transmission can be seen. The thin black line is an estimate of the mean He II spectrum in the intergalactic medium, while the bottom panel shows the number of foreground quasars that are used in the stacking process. [Figure 7 in paper]

    Since the authors ran out of foreground quasars at larger separations and implemented a cut on the quasar ionizing radiation, the intrinsic quasar lifetime could actually be longer than 25 Myr. To probe longer lifetimes, one would need a larger sample of foreground and background quasars. More sophisticated modeling would also provide richer interpretation of the data beyond a simple lifetime constraint. In any case, this study is the first to be able to detect the proximity effect in any ion (previous studies have detected the proximity effect in neutral Hydrogen). It also places stronger constraints on the episodic lifetime of quasars than any past studies of the same nature.

    See the full article here .

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  • richardmitnick 1:20 pm on February 5, 2017 Permalink | Reply
    Tags: , , , , Maarten Schmidt, Quasars, quasi-stellar radio source 3C273,   

    From EarthSky: “Today in science: Quasar mystery solved” A Fascinating Look Back to February 5, 1963 

    1

    EarthSky

    February 5, 2017
    Deborah Byrd

    1
    Maarten Schmidt via CalTech

    February 5, 1963. On this date, Caltech astronomer Maarten Schmidt solved a puzzle about the quasi-stellar radio source 3C273 that changed the way we think about our universe.

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    X-ray image of 3C273 and its jet. Today, this quasar is known to lie at the center of a giant elliptical galaxy. Image via Chandra X-ray Observatory.

    This object appeared starlike, like a point of light, with a mysterious jet. But its spectrum – the range of wavelengths of its light – looked odd. Astronomers routinely use spectra to learn the composition of distant objects. But, in 1963, emission lines in the spectrum of 3C273 didn’t appear to match any known chemical elements. Schmidt had a sudden realization that 3C273 contained the very ordinary element hydrogen. He realized that the spectral lines of hydrogen appeared strange because they were highly shifted toward the red end of the spectrum. Such a large red shift could occur if 3C273 were very distant, about three billion light-years away.

    Dr. Schmidt told EarthSky that he recognized immediately the implications of his revelation. He said:

    “This realization came immediately: my wife still remembers that I was pacing up and down much of the evening”

    The implications were just this. To be so far away and still visible, 3C273 must be intrinsically very bright and very powerful. It’s now thought to shine with the light of two trillion stars like our sun. That’s hundreds of times the light of our entire Milky Way galaxy. Yet 3C273 appears to be less than a light-year across, in contrast to 100,000 light-years for our Milky Way.

    So 3C273 is not only distant. It is also exceedingly luminous, implying powerful energy-producing processes unknown in 1963. Schmidt announced his revelation about quasars in the journal Nature on March 16, 1963.

    Today, hundreds of thousands of quasars are known, and many are more distant and more powerful than 3C273. It’s no exaggeration to say they turned the science of astronomy on its ear. Why, for example, are these powerful quasars located so far away in space? Because light travels at a finite speed (186,000 miles per second), we are seeing distant objects in space in the distant past. In other words, quasars existed in early universe. They do not exist in our time. Why?

    In the 1960s, 3C273 and other quasars like it were strong evidence against the Fred Hoyle’s Steady State theory, which suggested that matter is continuously being created as the universe expands, leading to a universe that is the same everywhere. The quasars showed the universe is not the same everywhere and thus helped usher in Big Bang cosmology.

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    Timeline of the universe. A representation of the evolution of the universe over 13.77 billion years. The far left depicts the earliest moment we can now probe, when a period of “inflation” produced a burst of exponential growth in the universe. (Size is depicted by the vertical extent of the grid in this graphic.) For the next several billion years, the expansion of the universe gradually slowed down as the matter in the universe pulled on itself via gravity. More recently, the expansion has begun to speed up again as the repulsive effects of dark energy have come to dominate the expansion of the universe. The afterglow light seen by WMAP was emitted about 375,000 years after inflation and has traversed the universe largely unimpeded since then. The conditions of earlier times are imprinted on this light; it also forms a backlight for later developments of the universe.
    Date circa 2006
    Author NASA/WMAP Science Team

    ESA/Planck supercedes WMAP
    3
    21 March 2013
    ESA’s Planck satellite has delivered its first all-sky image of the Cosmic Microwave Background (CMB), bringing with it new challenges about our understanding of the origin and evolution of the cosmos. The image has provided the most precise picture of the early Universe so far.

    But Steady State theory had been losing ground, even before 1963. The biggest change caused by Maarten Schmidt’s revelation about the quasar 3C273 was in the way we think about our universe.

    In other words, the idea that 3C273 was extremely luminous, and yet occupied such a relatively small space, suggested powerful energies that astronomers had not contemplated before. 3C273 gave astronomers one of their first hints that we live in a universe of colossal explosive events – and extreme temperatures and luminosities – a place where mysterious black holes abound and play a major role.

    According to a March 2013 email from Caltech:

    In 1963, Schmidt’s discovery gave us an unprecedented look at how the universe behaved at a much younger period in its history – billions of years before the birth of the sun and its planets. Later, Schmidt, along with his colleague Donald Lynden-Bell, discovered that quasars are galaxies harboring supermassive black holes billions of light-years away – not stars in our own galaxy, as was once believed. His seminal work dramatically increased the scale of the observable universe and advanced our present view on the violent nature of the universe in which massive black holes play a dominant role.

    What are quasars? Astronomers today believe that a quasar is a compact region in the center of a galaxy in the early universe. The compact region is thought to surround a central supermassive black hole, much like the black hole thought to reside in the center of our own Milky Way galaxy and many (or most) other galaxies. The powerful luminosity of a quasar is thought to be the result of processes taking place in an accretion disk, or disk of material surrounding the black hole, as these supermassive black holes consume stars that pass too near.

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    ULAS J1120+0641, farthest quasar known as of 2011. The quasar appears as a faint red dot close to the center. Composite image created from the Sloan Digital Sky Survey and the UKIRT Infrared Deep Sky Survey, via Wikimedia Commons.

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

    UKIRT, located on Mauna Kea, Hawaii, USA as part of Mauna Kea Observatory
    UKIRT interior
    UKIRT, located on Mauna Kea, Hawaii, USA as part of Mauna Kea Observatory

    The Chinese-born U.S. astrophysicist Hong-Yee Chiu coined the name quasar in May 1964, in the publication Physics Today. He wrote:

    So far, the clumsily long name ‘quasi-stellar radio sources’ is used to describe these objects. Because the nature of these objects is entirely unknown, it is hard to prepare a short, appropriate nomenclature for them so that their essential properties are obvious from their name. For convenience, the abbreviated form ‘quasar’ will be used throughout this paper.

    Today, the farthest known quasar is ULAS J1120+0641. Its co-moving distance is 28.85 billion light-years.

    Bottom line: On February 5 1963, astronomer Maarten Schmidt’s flash of inspiration led to the understanding that quasi-stellar radio sources, or quasars, exist in the very distant universe. Quasars became the most distant, and most luminous, objects known. They changed the way we think about the universe.

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  • richardmitnick 9:00 am on September 12, 2016 Permalink | Reply
    Tags: , , , Quasars   

    From Carnegie: “Discovery nearly doubles known quasars from the ancient universe” 

    Carnegie Institution for Science
    Carnegie Institution for Science

    1
    An artist’s rendering of a very distant quasar courtesy of ESO/M. Kornmesser.

    Quasars are supermassive black holes that sit at the center of enormous galaxies, accreting matter. They shine so brightly that they are often referred to as beacons and are among the most-distant objects in the universe that we can currently study. New work from a team led by Carnegie’s Eduardo Bañados has discovered 63 new quasars from when the universe was only a billion years old. (It’s about 14 billion years old today.)

    This is the largest sample of such distant quasars presented in a single scientific article, almost doubling the number of ancient quasars previously known. The findings will be published by The Astrophysical Journal Supplement Series.

    “Quasars are among the brightest objects and they literally illuminate our knowledge of the early universe,” Bañados said.

    But until now, the population of known ancient quasars was fairly small, so scientists’ ability to glean information from them was limited. One of the main challenges is finding these distant quasars, which are extremely rare. Scientists have searched for them for decades, but the effort is comparable to finding a needle in a haystack.

    The quasars discovered by Bañados and his team will provide valuable information from the first billion years after the Big Bang, which is a period of great interest to astronomers.

    Why?

    The universe was created in the Big Bang and hot matter exploded everywhere. But then it cooled off enough for the first protons and electrons to form and then to coalesce into hydrogen atoms, which resulted in a dark universe for a long time. It wasn’t until these atomic nuclei formed larger structures that light was able to shine once again in the universe. This happened when gravity condensed the matter and eventually formed the first sources of illumination, which might have included quasars.

    There is still a lot about this era when the universe’s lights were turned back on that science doesn’t understand. But having more examples of ancient quasars will help experts to figure out what happened in those first billion years after the Big Bang.

    “The formation and evolution of the earliest light sources and structures in the universe is one of the greatest mysteries in astronomy,” Bañados said. “Very bright quasars such as the 63 discovered in this study are the best tools for helping us probe the early universe. But until now, conclusive results have been limited by the very small sample size of ancient quasars.”

    The coming years will see a great improvement in what we know about the early universe thanks to these discoveries.

    This work was funded by a Carnegie-Princeton Fellowship, the European Research Council, the National Science Foundation, and a NASA Hubble Fellowship

    This work include data obtained from the following facilities: PS1 (GPC1), VLT:Antu (FORS2), NTT (EFOSC2), LBT (MODS), Max Planck:2.2m (GROND), Magellan:Baade (FIRE), Magellan:Clay (LDSS3), Keck:I (LRIS), Hale (DBSP), CAO:3.5m (Omega2000), CAO:2.2m (CAFOS), MMT (SWIRC), Du Pont (Retrocam).

    Pann-STARRS1 Telescope, on Haleakala, Maui, Hawaii, USA
    Pann-STARRS1 Telescope, on Haleakala, Maui, Hawaii

    ESO VLT new laser
    ESO VLT, Cerro Paranal, Chile, with new laser for guide stars

    1
    ESO NTT at Cerro La Silla, Chile

    Large Binocular Telescope,  Mount Graham,  Arizona, USA
    Large Binocular Telescope, Mount Graham, Arizona, USA

    MPG/ESO 2.2 meter telescope at La Silla, Chile
    MPG/ESO 2.2 meter telescope at La Silla, Chile

    Carnegie 6.5 meter Magellan Telescopes located at Carnegie’s Las Campanas Observatory, Chile.
    Carnegie 6.5 meter Baade and Clay Magellan Telescopes located at Carnegie’s Las Campanas Observatory, Chile

    Keck Observatory, Mauna Kea, Hawaii, USA
    Keck Observatory, Mauna Kea, Hawaii, USA

    Caltech Palomar 200 inch Hale Telescope, at Mt Wilson, CA, USA
    Caltech Palomar 200 inch Hale Telescope, at Mt Wilson, CA, USA

    MMT Telescope at the summit of Mount Hopkins near Tucson, Arizona, USA
    MMT Telescope at the summit of Mount Hopkins near Tucson, Arizona, USA

    Carnegie Las Campanas Dupont telescope exterior,Atacama Desert, Chile
    Carnegie Las Campanas Dupont telescope, Atacama Desert, Chile

    See the full article here .

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    Carnegie Institution of Washington Bldg

    Andrew Carnegie established a unique organization dedicated to scientific discovery “to encourage, in the broadest and most liberal manner, investigation, research, and discovery and the application of knowledge to the improvement of mankind…” The philosophy was and is to devote the institution’s resources to “exceptional” individuals so that they can explore the most intriguing scientific questions in an atmosphere of complete freedom. Carnegie and his trustees realized that flexibility and freedom were essential to the institution’s success and that tradition is the foundation of the institution today as it supports research in the Earth, space, and life sciences.

    6.5 meter Magellan Telescopes located at Carnegie’s Las Campanas Observatory, Chile.
    6.5 meter Magellan Telescopes located at Carnegie’s Las Campanas Observatory, Chile

     
  • richardmitnick 7:28 pm on March 23, 2016 Permalink | Reply
    Tags: , , , Quasars   

    From Hopkins: “Far fewer stars are born due to intense radiation from quasars, researchers say” 

    Johns Hopkins
    Johns Hopkins University

    3.23.16
    Arthur Hirsch

    Quasar. ESO/M. Kornmesser
    Quasar. ESO/M. Kornmesser

    Research led by Johns Hopkins University scientists has found new, persuasive evidence that could help solve a long-standing mystery in astrophysics: why did the pace of star formation in the universe slow down some 11 billion years ago?

    Scientists have puzzled for years over the question of why galaxies slowed their star-making pace to what astronomers estimate is now 30 times slower than their peak pace 11 billion years ago. The chief suspect has been the feedback process from quasars within galaxies, where stars are born. A paper published in the Monthly Notices of the Royal Astronomical Society presents evidence that intense radiation and galaxy-scale winds emitted by the quasars—the most luminous objects in the universe—heats clouds of dust and gas, preventing them from cooling to form more dense clouds and eventually stars.

    “I would argue that this is the first convincing observational evidence of the presence of quasar feedback when the universe was only a quarter of its present age, when the cosmic star formation was most vigorous,” said Tobias Marriage, an assistant professor in the university’s Henry A. Rowland Department of Physics & Astronomy. While the findings are not conclusive, Marriage said, the evidence is very compelling and has scientists excited. “It’s like finding a smoking gun with fingerprints near the body but not finding the bullet to match the gun.”

    Investigators looked at information on 17,468 galaxies and found a tracer of energy known as the Sunyaev-Zel’dovich Effect. The phenomenon, named for the two Russian physicists who predicted it nearly 50 years ago, appears when high-energy electrons disturb the Cosmic Microwave Background, or CMB.

    Cosmic Microwave Background per Planck
    Cosmic Microwave Background per ESA/Planck

    ESA/Planck
    ESA/Planck

    The CMB is a pervasive sea of microwave radiation, a remnant from the superheated birth of the universe roughly 13.7 billion years ago.

    Devin Crichton, a Johns Hopkins graduate student and the paper’s lead author, said the thermal energy levels were analyzed to see if they rise above predictions for what it would take to stop star formation. A large number of galaxies were studied to give the study statistical heft, he said.

    “For feedback to turn off star formation, it must be occurring broadly,” said Crichton, one of five Johns Hopkins scientists who led the work conducted by a total of 23 investigators from 18 institutions.

    To take the temperature measurements that would show the SZ Effect, the scientists used information gathered by two ground-based telescopes and one receiver mounted on a space observatory. Using several instruments with different strengths in search of the SZ Effect is relatively new, Marriage said.

    “It’s a pretty wild sort of thermometer,” Marriage said.

    Information gathered in the Sloan Digital Sky Survey [SDSS] by an optical telescope at the Apache Point Observatory in New Mexico was used to find the quasars.

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

    Thermal energy and evidence of the SZ Effect were found using information from the Atacama Cosmology Telescope [ACT], an instrument designed to study the CMB that stands in the Atacama Desert in northern Chile.

    Princeton Atacama Cosmology Telescope
    Princeton Atacama Cosmology Telescope

    To focus on the dust, investigators used data from the SPIRE, or Spectral and Photometric Imaging Receiver, mounted on the [ESA]Herschel Space Observatory.

    ESA/Herschel SPIRE
    ESA/Herschel SPIRE

    ESA/Herschel
    ESA/Herschel

    Nadia Zakamska, an assistant professor in the Department of Physics & Astronomy at Johns Hopkins and one of the report’s co-authors, said it is only in the last few years that evidence of this phenomenon from direct observation has been compiled. The SZ Effect, she said, is a novel approach to the subject, making more clear the full effect of galactic wind on the surrounding galaxy.

    “Unlike all other methods that are probing small clumps within the wind, the Sunyaev-Zeldovich Effect is sensitive to the bulk of the wind, the extremely hot plasma that’s filling the volume of the wind, and is completely undetectable using any other technique,” she said.

    See the full article here .

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    Johns Hopkins Campus

    The Johns Hopkins University opened in 1876, with the inauguration of its first president, Daniel Coit Gilman. “What are we aiming at?” Gilman asked in his installation address. “The encouragement of research … and the advancement of individual scholars, who by their excellence will advance the sciences they pursue, and the society where they dwell.”

    The mission laid out by Gilman remains the university’s mission today, summed up in a simple but powerful restatement of Gilman’s own words: “Knowledge for the world.”

    What Gilman created was a research university, dedicated to advancing both students’ knowledge and the state of human knowledge through research and scholarship. Gilman believed that teaching and research are interdependent, that success in one depends on success in the other. A modern university, he believed, must do both well. The realization of Gilman’s philosophy at Johns Hopkins, and at other institutions that later attracted Johns Hopkins-trained scholars, revolutionized higher education in America, leading to the research university system as it exists today.

     
  • richardmitnick 9:38 am on January 20, 2016 Permalink | Reply
    Tags: , , , Quasars   

    From New Scientist: “Ancient quasars in distant galaxies caught switching on suddenly” 

    NewScientist

    New Scientist

    20 January 2016
    Shannon Hall

    Quasar
    ESO/M. Kornmesser

    Most cosmic events happen on huge timescales. Not so for quasars – the bright centres of galaxies that are powered by supermassive black holes gobbling down gas and dust. We have just seen them ignite in a matter of years.

    Astronomers expect quasars to use up their fuel and settle down into quiet galaxies – a process that should take hundreds of thousands of years. So last year, when a dozen quasars were spotted shutting down in just hundreds of days, it was a shock.

    Chelsea MacLeod of the University of Edinburgh, UK, and her colleagues wondered if these objects might turn on again. The team compared images of galaxies from the Sloan Digital Sky Survey (SDSS) with images of the same objects from the Pan-STARRS survey, taken 10 years later.

    SDSS Telescope
    SDSS telescope, Apache Point, NM, USA

    Pann-STARSR1 Telescope
    Pan-STARRS telescope

    After flagging 1000 objects that varied in brightness from one survey to the next, the team pinpointed five galaxies that appeared to shape-shift into quasars.

    Fast work

    What’s more, one quasar appeared to turn on several years after turning off. But it’s not clear if the other four are turning on for the first time, or if they are also flickering.

    The real surprise is the timescale. Previously, astronomers thought it should take thousands to millions of years to funnel enough gas on to a supermassive black hole for it to spawn a quasar. It definitely shouldn’t take less than 10.

    “This is a bit of an embarrassing moment for black hole and quasar scientists,” says Eric Morganson of Harvard University. “The conventional wisdom was found to be dramatically wrong.”

    Now the big question is how these beasts ignite in the first place. The most common explanation has two galaxies colliding, sending gas and dust swirling into the merged supermassive black hole. But the SDSS galaxy images show no sign of recent collisions, so something else must be acting as a funnel for the gas.

    Some kind of instability in the galaxy itself, such as a central bar or spiral arms that push stars out of their circular orbits, could provide the funnel, suggests Mike Eracleous of Pennsylvania State University. But according to models this happens on much longer timescales than decades.

    Future studies will hopefully shed light on such a rapid process, which in turn affects how galaxies, like the Milky Way, form and evolve. “Understanding how [quasars] work is really part of the puzzle of how we went from the big bang to galaxies to stars to planets,” Morganson says.

    Journal reference: arxiv.org/abs/1509.08393

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  • richardmitnick 10:34 am on January 15, 2016 Permalink | Reply
    Tags: , , , Chaotic Turbulence Roiling 'Most Luminous Galaxy' in the Universe, Quasars   

    From ALMA: “Chaotic Turbulence Roiling ‘Most Luminous Galaxy’ in the Universe” 

    ESO ALMA Array
    ALMA

    15 January 2016
    Tanio Díaz Santos
    Núcleo de Astronomía, Facultad de Ingeniería
    Universidad Diego Portales, Santiago, Chile
    Tel: +56 2 2213 0480
    Email: tanio.diaz@mail.udp.cl

    Valeria Foncea

    Education and Public Outreach Officer

    Joint ALMA Observatory

    Santiago, Chile

    Tel: +56 2 467 6258

    Cell: +56 9 75871963
    Email: vfoncea@alma.cl

    Charles E. Blue
    Public Information Officer
    National Radio Astronomy Observatory
    Charlottesville, Virginia, USA
    Tel: +1 434 296 0314
    Cell: +1 434.242.9559
    E-mail: cblue@nrao.edu

    Richard Hook
    Public Information Officer, ESO

    Garching bei München, Germany

    Tel: +49 89 3200 6655

    Cell: +49 151 1537 3591
    Email: rhook@eso.org

    Masaaki Hiramatsu

    Education and Public Outreach Officer, NAOJ Chile
    Observatory
Tokyo, Japan

    Tel: +81 422 34 3630

    E-mail: hiramatsu.masaaki@nao.ac.jp

    Temp 1
    Artist impression of W2246-0526, a single galaxy glowing in infrared light as intensely as approximately 350 trillion suns. It is so violently turbulent that it may eventually jettison its entire supply of star-forming gas, according to new observations with ALMA. Credit: NRAO/AUI/NSF; Dana Berry / SkyWorks; ALMA (ESO/NAOJ/NRAO).

    The most luminous galaxy in the Universe –a so-called obscured quasar 12.4 billion light-years away – is so violently turbulent that it may eventually jettison its entire supply of star-forming gas, according to new observations with the Atacama Large Millimeter/submillimeter Array (ALMA).

    A team of researchers used ALMA to trace, for the first time, the actual motion of the galaxy’s interstellar medium – the gas and dust between the stars. What they found, according to Tanio Díaz-Santos of the Universidad Diego Portales in Santiago, Chile, and lead author of this study, is a galaxy “so chaotic that it is ripping itself apart.”

    Previous studies with NASA’s Wide-field Infrared Survey Explorer (WISE) spacecraft reveal that the galaxy, dubbed W2246-0526, is glowing in infrared light as intensely as approximately 350 trillion suns.

    NASA Wise Telescope
    NASA/WISE

    Evidence strongly suggests that this galaxy is actually an obscured quasar, a very distant galaxy [whi h] contains a voraciously feeding supermassive black hole at its center that is completely obscured behind a thick blanket of dust.

    This galaxy’s startling brightness is powered by a tiny, yet incredibly energetic disk of gas that is being superheated as it spirals in on the supermassive black hole. The light from this blazingly bright accretion disk is then absorbed by the surrounding dust, which re-emits the energy as infrared light.

    “These properties make this object a beast in the infrared,” said Roberto Assef, an astronomer with the Universidad Diego Portales and leader of the ALMA observing team. “The powerful infrared energy emitted by the dust then has a direct and violent impact on the entire galaxy, producing extreme turbulence throughout the interstellar medium.”

    The astronomers compare this turbulent action to a pot of boiling water. If these conditions continue, they say, the galaxy’s intense infrared radiation would boil away all of its interstellar gas.

    This galaxy belongs to a very unusual type of quasar known as Hot, Dust-Obscured Galaxies or Hot DOGs These objects are very rare; only 1 out of every 3,000 quasars observed by WISE belong to this class.

    The research team used ALMA to precisely map the motion of ionized carbon atoms throughout the entire galaxy. These atoms, which are tracers for interstellar gas, naturally emit infrared light, which becomes shifted to millimeter wavelengths as it travels the vast cosmic distances to Earth due to the expansion of the Universe.

    “Large amounts of ionized carbon were found in an extremely turbulent dynamic state throughout the galaxy,” Díaz-Santos describes. The data reveal that this interstellar material is careening anywhere from 500 to 600 kilometers per second across the entire galaxy.

    The astronomers believe that this turbulence is primarily due to the fact that the region around the black hole is at least 100 times more luminous than the rest of the host galaxy combined; in other quasars, the proportion is much more modest. This intense yet localized radiation exerts tremendous pressure on the entire galaxy, to potentially devastating effect.

    “We suspected that this galaxy was in a transformative stage of its life because of the enormous amount of infrared energy discovered with WISE,” said Peter Eisenhardt with NASA’s Jet Propulsion Laboratory in Pasadena, California, and scientific leader of the WISE mission. “Now ALMA has shown us that the raging furnace in this galaxy is making the pot boil over.”

    Current models of galactic dynamics combined with the ALMA data indicate that this galaxy is unstable and its interstellar gas is being blown away in all directions. This means that the galaxy’s Hot DOG days are numbered as it matures into a more traditional unobscured quasar.

    “If this pattern continues, it is possible that in the future W2246 ends up shedding a large part of the gas and dust it contains,” concludes Manuel Aravena also from the Universidad Diego Portales, and co-author of the study. “Only ALMA, with its unparalleled resolution, can allow us to see this object in high definition and fathom such an important episode in the life of this galaxy.”

    This article, The Strikingly Uniform, Highly Turbulent Interstellar Medium of The Most Luminous Galaxy in the Universe, will be published in the Astrophysical Journal Letters.

    From ESO article:

    This research was presented in a paper “The Strikingly Uniform, Highly Turbulent Interstellar Medium of The Most Luminous Galaxy in the Universe”, by T. Díaz-Santos et al., and will be published in the journal Astrophysical Journal Letters.

    The team is composed of T. Díaz-Santos (Universidad Diego Portales, Santiago, Chile), R. J. Assef (Universidad Diego Portales, Santiago, Chile), A. W. Blain (University of Leicester, UK) , C.-W. Tsai (Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, USA) , M. Aravena (Universidad Diego Portales, Santiago, Chile), P. Eisenhardt (Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, USA), J. Wu (University of California Los Angeles, California, USA), D. Stern (Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, USA) and C. Bridge (Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, USA).

    See the full article here .

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    The Atacama Large Millimeter/submillimeter Array (ALMA), an international astronomy facility, is a partnership of Europe, North America and East Asia in cooperation with the Republic of Chile. ALMA is funded in Europe by the European Organization for Astronomical Research in the Southern Hemisphere (ESO), in North America by the U.S. National Science Foundation (NSF) in cooperation with the National Research Council of Canada (NRC) and the National Science Council of Taiwan (NSC) and in East Asia by the National Institutes of Natural Sciences (NINS) of Japan in cooperation with the Academia Sinica (AS) in Taiwan.

    ALMA construction and operations are led on behalf of Europe by ESO, on behalf of North America by the National Radio Astronomy Observatory (NRAO), which is managed by Associated Universities, Inc. (AUI) and on behalf of East Asia by the National Astronomical Observatory of Japan (NAOJ). The Joint ALMA Observatory (JAO) provides the unified leadership and management of the construction, commissioning and operation of ALMA.

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    ESO 50

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  • richardmitnick 2:25 pm on January 11, 2016 Permalink | Reply
    Tags: , , , Quasars,   

    From AAAS: “The quasar that switched off the light” 

    AAAS

    AAAS

    8 January 2016
    Daniel Clery

    Temp 1
    An artist’s impression of a quasar, showing the characteristic quasar spectrum of J1011 taken by the Sloan Digital Sky Survey. Dana Berry/SkyWorks Digital Inc.; SDSS collaboration

    In 2003, astronomers took a snap of quasar—the superbright core of a distant galaxy—called SDSS J1011+5442. A year ago, they took another look at it and found to their astonishment that it had all but disappeared. Its bright beacon—a supermassive black hole that is heating the gas around it to millions of degrees—seemed to have switched off, leaving J1011 looking like just any other galaxy.

    The observers, using the Sloan Digital Sky Survey (SDSS), a 2.5-meter telescope at Apache Point, New Mexico, sought out observations by other telescopes and found that the abrupt change had taken place over the course of just a few years after 2010.

    SDSS Telescope
    SDSS

    Over the past year, the team has found a dozen other quasars that similarly blinked out, earning them the name “changing-look” quasars. “These are classified by eye. You can see it happen,” says team leader Jessie Runnoe of Pennsylvania State University, University Park.

    Fellow astronomer and team member John Ruan of the University of Washington, Seattle, told the American Astronomical Society meeting here today that he had previously assumed changes to something as big as a quasar would take tens of thousands if not hundreds of thousands of years. Ruan and his colleagues considered a number of possible causes for the abrupt change. First, a dust cloud could have moved in the way and blocked the light. But this would have taken much longer than a few years for something as big as a quasar. They also thought that in 2003 the galaxy could have emitted a brief flare as it tore apart a star and swallowed it up, but other observations showed the quasar was still bright for years after 2003. So they finally concluded that J1011 simply ran out of fuel.

    The black holes at the heart of quasars have disks of gas and dust orbiting around them, and it’s the innermost part of the disk that burns brightest just before it is sucked in. J1011 simply consumed its entire inner disk, leaving a signal that looks just like a normal galaxy. “If you drain the inner part of the disk, it shuts everything down,” Runnoe says.

    “It’s definitely an interesting result. It adds to a picture of quasars being highly variable systems on a range of timescales,” says astronomer Kevin Schawinski of the Swiss Federal Institute of Technology in Zurich, who is not involved in the work. Recent theoretical and observational work has suggested that quasars “flicker” on scales of a few hundred thousand years. “What this work shows is that quasars can change pretty dramatically on even shorter timescales of a few years.”

    The SDSS team is now keeping its eyes peeled, just in case the inner disk of one of their changing-look quasars fuels up and turns the lights back on again.

    Posted in Space

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  • richardmitnick 3:04 pm on November 28, 2015 Permalink | Reply
    Tags: , , Quasars,   

    From Ethan Siegel: “How Do Black Holes Make Such Bright Quasars?” 

    Starts with a bang
    Starts with a Bang

    11.28.15
    Ethan Siegel

    1
    Image credit: ESO/M. Kornmesser.

    If they eat everything they come in contact with, how do quasars shine so bright?

    “Twinkle, twinkle quasi-star.
    Biggest puzzle from afar.
    How unlike the other ones.
    Brighter than a billion suns.
    Twinkle, twinkle, quasi-star.
    How I wonder what you are.” –George Gamow

    Black holes are the enigmas of the Universe: regions of space where so much mass is collected into such a tiny volume that nothing can escape its gravitational pull, not even light. No matter how much energy or how much speed an object within a black hole’s event horizon acquires, it can never get out and affect the Universe beyond.

    2
    Image credit: Ute Kraus, Physics education group Kraus, Universität Hildesheim; background: Axel Mellinger.

    Which is what makes our reader Rik’s question for this week’s Ask Ethan so interesting:

    How is it possible that super-massive black holes emit quasars when they ‘eat’ too much, too fast? You would expect that all matter is simply sucked in.

    This is one of the strangest phenomena imaginable: that black holes, an object from which nothing can escape, gives rise to the brightest class of objects ever observed.

    3
    Image credit: NASA, ESA, and G. Canalizo (University of California, Riverside).

    A quasar is an incredibly interesting object, so interesting that when we first saw them, we had no idea what they actually were. With the advent of radio astronomy, we started to discover these incredibly bright sources in radio frequencies.

    7
    The NRAO/Very Large Array, a radio interferometer in New Mexico, USA

    And yet, when we looked in other wavelengths of light — visible, X-ray, ultraviolet, infrared, microwave — we saw absolutely nothing. For some reason, there were these radio sources, these point-like, concentrated radio sources, that exhibited no other signals at all. We named them Quasi-Stellar Radio Sources (QSRS), or quasars.

    4
    Images credit: John Bahcall (Institute for Advanced Study, Princeton), Mike Disney (University of Wales), and NASA.

    Over time, we began to discover a number of interesting properties about these objects:

    Almost all of them were located extremely far away, at colossal redshifts far exceeding the other modern limits of what was observable.
    The brightness in the radio indicated that something more energetic was happening than anything else thus far seen in the Universe.
    And finally, these objects appeared somewhat different depending on how they were oriented with respect to us.

    Eventually, our observational toolkit improved enough that we started to discover similarities between quasars and a few other classes of objects: active galactic nuclei (AGNs), blazars, and magnetars.

    5
    Image credit: © 2014 Ángel R. López-Sánchez, via http://oldweb.aao.gov.au/local/www/alopez/multiwave.html.

    What we came to realize was that the same generic thing was happening in all of these objects: a supermassive black hole at the center of a galaxy was somehow feeding on matter, and ejecting a tremendous amount of material, energy, and (radio) light out into space. Finally, our observations improved enough that we were able to detect the host galaxies for these quasars as well, even the ones located many billions of light years away.

    But how does this occur? How do these supermassive black holes actually emit so much energy? Shouldn’t they be absorbing, or sucking all the matter-and-energy in instead? After all, that’s the one thing we all learn about black holes: that they suck everything in, and there’s no escape.


    download mp4 video here.

    Well, it’s true that there’s no escape, but as far as “sucking everything in” goes? It’s a lie. The illustrations and visualizations you’ve seen to that effect — including the video made by NASA , above — are outright wrong. Instead, if you’re outside the event horizon, being near a black hole is no different than being near any other source of gravity. If the Sun were surreptitiously replaced by a black hole of the exact same mass — 1.99 × 10³⁰ kg — the Earth and all the planets would continue in their orbits in exactly the same fashion they’re moving right now.

    The reason quasars do what they do, so to speak, is because these incredibly large masses can accelerate matter near them to very rapid speeds.

    6
    Image credit: C. Carilli at NRAO, of Cygnus A in four different radio bands.

    The matter itself forms an accretion disk around the black hole, where it gets accelerated to speeds so great that they give off radiation of many different frequencies, including in the radio. We also see two “lobes” perpendicular to the accretion disk, which are jets of accelerated matter getting ejected at relativistic speeds. The sources we call blazars happen to be oriented with one of the lobes/jets pointed right towards us, while other active galaxies tend to be oriented otherwise.

    7
    Image credit: Aurore Simonnet, / NASA/Fermi — GLAST telescope

    NASA Fermi Telescope
    NASA/Fermi

    Quasars shine as brightly as they do because the things they devour get stretched apart, torn into bits, and accelerated by the irresistible force of gravity. They put out so much energy because that matter interacts with other bits of matter, heats up and has no choice but to emit radiation. And they’re visible from such great distances because these are black holes hundreds of millions or even billions of times the mass of our Sun, devouring millions of solar masses worth of matter but not devouring tens or hundreds of millions more.

    Black holes aren’t the vacuum cleaners of the cosmos; they’re the cookie monsters of the cosmos, missing their “mouths” with practically all of their potential food.


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

     
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