Quasars Tell The Story Of How Fast The Young Universe Expanded

Astronomers from the Sloan Digital Sky Survey Make the Most Precise Measurement Yet of the Expanding Universe

Astronomers from the Sloan Digital Sky Survey have used 140,000 distant quasars to measure the expansion rate of the Universe when it was only one-quarter of its present age. This is the best measurement yet of the expansion rate at any epoch in the last 13 billion years.

The Baryon Oscillation Spectroscopic Survey (BOSS), the largest component of the third Sloan Digital Sky Survey (SDSS-III), pioneered the technique of measuring the structure of the young Universe by using quasars to map the distribution of intergalactic hydrogen gas. Today, new BOSS observations of this structure were presented at the April 2014 meeting of the American Physical Society in Savannah, GA.

An artist's conception of how BOSS uses quasars to measure the distant universe. + MORE + Credit: Zosia Rostomian (Lawrence Berkeley National Laboratory) and Andreu Font-Ribera (BOSS Lyman-alpha team, Berkeley Lab.)

An artist’s conception of how BOSS uses quasars to measure the distant universe.
Credit: Zosia Rostomian (Lawrence Berkeley National Laboratory) and Andreu Font-Ribera (BOSS Lyman-alpha team, Berkeley Lab.)

These latest results combine two different methods of using quasars and intergalactic gas to measure the rate of expansion of the Universe. The first analysis, by Andreu Font-Ribera (Lawrence Berkeley National Laboratory) and collaborators, compares the distribution of quasars to the distribution of hydrogen gas to measure distances in the Universe. A second analysis team led by Timothée Delubac (École Polytechnique Fédérale de Lausanne, Switzerland) focused on the patterns in the hydrogen gas itself to measure the distribution of mass in the young Universe. Together the two BOSS analyses establish that 10.8 billion years ago, the Universe was expanding by one percent every 44 million years.

“If we look back to the Universe when galaxies were three times closer together than they are today, we’d see that a pair of galaxies separated by a million light-years would be drifting apart at a speed of 68 kilometers per second as the Universe expands,” says Font-Ribera.

Delubac explains that “we have measured the expansion rate in the young Universe with an unprecedented precision of 2 percent.” Measuring the expansion rate of the Universe over its entire history is key in determining the nature of the dark energy that is responsible for causing this expansion rate to increase during the past six billion years. “By probing the Universe when it was only a quarter of its present age, BOSS has placed a key anchor to compare to more recent expansion measurements as dark energy has taken hold,” says Delubac.

BOSS determines the expansion rate at a given time in the Universe by measuring the size of baryon acoustic oscillations (BAO), a signature imprinted in the way matter is distributed, resulting from sound waves in the early Universe. This imprint is visible in the distribution of galaxies, quasars, and intergalactic hydrogen throughout the cosmos.

An illustration of how astronomers used quasar light to trace the expansion of the universe. + MORE + Credit: Paul Hooper at Spirit Design, with Mat Pieri and Gongbo Zhao, ICG

An illustration of how astronomers used quasar light to trace the expansion of the universe. 
Credit: Paul Hooper at Spirit Design, with Mat Pieri and Gongbo Zhao, ICG

“Three years ago, BOSS used 14,000 quasars to demonstrate we could make the biggest 3-D maps of the Universe,” says David Schlegel (Lawrence Berkeley National Laboratory), principal investigator of BOSS. “Two years ago, with 48,000 quasars, we first detected baryon acoustic oscillations in these maps. Now, with more than 140,000 quasars, we’ve made extremely precise measures of BAO.”

As the light from a distant quasar passes through intervening hydrogen gas distributed throughout the Universe, patches of greater density absorb more light. Each absorbing patch absorbs light from the spectrum of the quasar at a characteristic wavelength of neutral hydrogen. As the Universe expands, the quasar spectrum is stretched out, and each subsequent patch leaves its absorption mark at a different relative wavelength. The quasar spectrum is finally observed on Earth by BOSS, and it contains the signatures of all the patches encountered by the quasar light. Astronomers then measure from the quasar spectrum how much the Universe has expanded since the light passed through each patch of hydrogen.

With enough good quasar spectra, close enough together, the position of the gas clouds can be mapped in three dimensions. BOSS determines the expansion rate by using these maps to measure the size of the BAO pattern at different epochs of cosmic time. These new measurements provide key data for astronomers seeking the nature of the dark energy postulated to be driving the increase in the expansion rate of the Universe.

David Schlegel remarks that when BOSS was first getting underway, precision measurements using quasars and the Lyman-alpha forest had been suggested, but “some of us were afraid it wouldn’t work. We were wrong. Our precision measurements are even better than we optimistically hoped for.”

Read more at http://www.sdss3.org/press/precise.php

Astronomers Discover Largest Structure in the Universe

It’s ten billion light years across and almost as far away but nobody had spotted it…until now

: 283 GRBs with observed redshift (blue) and the 31 GRBs (red) between redshift 1.6 and 2.

283 GRBs with observed redshift (blue) and the 31 GRBs (red) between redshift 1.6 and 2.

What’s the largest structure in the Universe? That’s a question that has intrigued scientists for centuries. Today, they get an answer thanks to astronomers who say they’ve discovered the largest structure ever observed and one that dwarfs the previous record-holder by billions of light years.

Astronomer’s ideas about the universe’s largest structures have changed dramatically in the last 100 years. At the beginning of the 20th century, they began to suspect that stars were clustered together to form “island universes” or galaxies which themselves were separated by vast distances.

The question was eventually settled in the 1920s by Edwin Hubble and others who measured the distance to different galaxies, thereby proving that they were much further away than stars . These galaxies, they thought, were the largest structures in the universe and distributed more or less uniformly throughout space.

It wasn’t until 1989 that astronomers found something even bigger. In the 1970s and 80s, they had begun to systematically measure the distances to large numbers of galaxies and this eventually allowed them to produce a 3D map of them.

To their surprise, the galaxies were not distributed evenly but instead formed filamentary structures with walls and voids. They called the largest of these “the Great Wall”, a structure that is 200 million light years away and some 500 million light years long.

That was puzzling at the time because these walls and voids were too large to have formed through gravitational interactions in the time since the birth of the universe. Of course, astronomers now know that this structure comes from variations in the density of the early universe soon after the Big Bang, caused by quantum fluctuations.

Since then, astronomers have found even larger structures as the technology to look further into the universe improved. In 2003, they discovered the Sloan Great Wall, another wall of galaxies some 1.4 billion light years long and about a billion light years from Earth.

Earlier this year, they spotted a larger structure in the constellation of Leo called the Huge-LQG (Large Quasar Group) . This consists of 73 quasars stretching over a distance of 4 billion light years.

Now I Horvath at the National University of Public Service in Budapest, Hungary, and a couple of pals say they’ve identified something even bigger. Their data is based on gamma-ray bursts, the most energetic events in the universe.

Astronomers think these bursts are emitted by stars as they collapse to form neutron stars or black holes. These bursts are incredibly bright—a typical burst releases about the same energy in a fraction of a second as the Sun will during its entire life time.

Astronomers measure the distance of gamma ray bursts by looking for the optical afterglow of the explosion when it is detected and measuring its redshift. Since 1997, when this technique was first used, they’ve measured the distance to 283 of these bursts and mapped their position within the universe.

Astronomers have always assumed that these explosions are distributed evenly throughout the universe. And for the most part, this looks to be the case.

But Horvath and co say they’ve found a significant irregularity. They say there are far more gamma ray bursts at a distance of about ten billion light years than would be expected if the distribution was uniform.

These gamma ray bursts form a structure that is some ten billion light years in size, significantly larger than even the Huge-LQG. So this thing, presumably another wall of even more distant galaxies, is the new largest structure in the universe.

Of course, there are caveats associated with this new work. The first is the small sample size of just 283 gamma ray bursts of which only 31 make up this new giant structure. Horvath and co say that, statistically, this number of gamma ray bursts should not be grouped together in this way if they are evenly distributed.

That’s a decent pointer that something interesting might be going on here but it is by no means an astronomical slamdunk; more data is desperately needed. “One or two years more of gamma burst observations will hopefully provide the statistics to confirm or disprove this discovery,” they say.

If this tale seems a little familiar, that’s because astronomers have regularly assumed that the objects they can see must be distributed uniformly around the universe. As history has shown time and again, this usually turns out to be wrong. The universe always seems to have structure at every scale.

That may have even more significance. One of the fundamental tenets of cosmology is the Cosmological principle—this holds that the distribution of matter in the universe will appear uniform if viewed from a large enough scale.

This is equivalent to the idea that the universe appears the same to all observers, wherever in the cosmos they may be.

But the evidence, as far as astronomers can gather it, does not back up this idea. At whatever scale they look, large scale structures always seem to emerge.

That doesn’t disprove the Cosmological principle. Indeed, cosmologists are quick to say that the key idea is that the laws of physics must be the same for all observers, not necessarily the large scale structure.

Nevertheless, the possibility that the Cosmological principle may sit on shaky ground will provide many theorists with some interesting food for thought.

Ref: http://arxiv.org/abs/1311.1104 : The Largest Structure Of The Universe, Defined By Gamma-Ray Bursts

Read more at https://medium.com/the-physics-arxiv-blog/267ddcb8057b

The quasar and its Fata Morgana

Multiple images of a quasar through a gas cloud of our Milky Way

Artist's diagram of the refraction event (not drawn to scale), showing how radio waves from the distant quasar jet are bent by a gas cloud in our own Galaxy, creating multiple images seen with the Very Long Baseline Array.  © Bill Saxton, NRAO/AUI/NSF

Artist’s diagram of the refraction event (not drawn to scale), showing how radio waves from the distant quasar jet are bent by a gas cloud in our own Galaxy, creating multiple images seen with the Very Long Baseline Array.
© Bill Saxton, NRAO/AUI/NSF

Bonn astronomers discover how the image of a distant quasar splits into multiple images by the effects of a cloud of ionized gas in our own Milky Way Galaxy. Such events were predicted as early as in the 1970s, but the first evidence for one now has come from observations performed with the telescope array VLBA and analysed in the Max Planck Institute for Radio Astronomy.

The scientists observed the quasar 2023+335, nearly 3 billion light-years from Earth, as part of a long-term study of ongoing changes in some three hundred quasars. When they examined a series of images of 2023+335, they noted dramatic differences. The differences, they said, are caused by the radio waves from the quasar being bent as they pass through the Milky Way gas cloud, which moved through our line of sight to the quasar. “So as we would see a spot of light get broader or even multiple behind a frosted glass, we see this quasar ‘dancing’ behind a gas cloud in our own Galaxy”, so Anton Zensus, Director at the Max Planck Institute for Radio Astronomy (MPIfR) in Bonn, Germany, and member of the international team who has discovered this effect. “This is similar to the fata morgana to be seen in the desert or to the Sun dogs caused by iced clouds with the image of our own star”, adds Zensus.

“This event, obviously rare, gives us a new way to learn some of the properties of the turbulent gas that makes up a significant part of our Galaxy,” said Alexander Pushkarev from the MPIfR in Bonn, Germany, and the Crimean Astrophysical Observatory, Ukraine, and leader of the international team.

New insights into turbulent galactic gas clouds become tangible
The scientists added 2023+335 to their list of observing targets in 2008. Their targets, in the framework of the MOJAVE project, are quasars and other galaxies with supermassive black holes at their cores. The gravitational energy of the black holes powers “jets” of material propelled to nearly the speed of light. The quasar 2023+335 initially showed a typical structure for such an object, with a bright core and a jet. In 2009, however, the object’s appearance changed significantly, showing what looked like a line of bright, new radio-emitting spots.

“We’ve never seen this type of behaviour before, either among the hundreds of quasars in our own observing program or among those observed in other studies,” adds Eduardo Ros from the MPIfR, also a team member in the discovery….
Read more at http://www.mpg.de/7515949/quasar-cloud-fata-morgana?filter_order=L&research_topic=

Most Quasars Live on Snacks, Not Large Meals

The galaxies in these four images have so much dust surrounding them that the brilliant light from their quasars cannot be seen in these Hubble Space Telescope images. Quasars are the brilliant beacons of light that are powered by black holes feasting on captured material, and in the process, heating some of the matter to millions of degrees. The images at top right, bottom left, and bottom right reveal three of the survey’s normal-looking galaxies that host quasars. Only one galaxy in the sample, at top left, shows evidence of an interaction with another galaxy. The two white blobs are the cores from both galaxies. A streamer of material, colored brown and blue, also lies below the merging galaxies.The galaxies existed roughly 8 billion to 12 billion years ago, during a peak epoch of black-hole growth. The galaxies’ masses are comparable to our Milky Way’s. The blue patches are star-forming regions. The brown areas are either dust or old stars. The images were taken by Hubble’s Wide Field Camera 3 between 2011 and 2012. Credit: NASA, ESA, and K. Schawinski (Yale University)

Read more: www.nasa.gov

Quasars Acting as Gravitational Lenses

Image Credit: NASA, ESA, and F. Courbin (EPFL, Switzerland)

Astronomers using NASA’s Hubble Space Telescope have found several examples of galaxies containing quasars, which act as gravitational lenses, amplifying and distorting images of galaxies aligned behind them.

Quasars are among the brightest objects in the universe, far outshining the total starlight of their host galaxies. Quasars are powered by supermassive black holes.
To find these rare cases of galaxy-quasar combinations acting as lenses, a team of astronomers led by Frederic Courbin at the Ecole Polytechnique Federale de Lausanne (EPFL, Switzerland) selected 23,000 quasar spectra in the Sloan Digital Sky Survey (SDSS). They looked for the spectral imprint of galaxies at much greater distances that happened to align with foreground galaxies. Once candidates were identified, Hubble’s sharp view was used to look for gravitational arcs and rings (which are indicated by the arrows in these three Hubble photos) that would be produced by gravitational lensing.

Quasar host galaxies are hard or even impossible to see because the central quasar far outshines the galaxy. Therefore, it is difficult to estimate the mass of a host galaxy based on the collective brightness of its stars. However, gravitational lensing candidates are invaluable for estimating the mass of a quasar’s host galaxy because the amount of distortion in the lens can be used to estimate a galaxy’s mass.

The next step for the team is to build a catalog of “quasar-lenses” that will allow them to determine masses for a statistically significant number of quasar host galaxies and to compare them with galaxies without quasars. With the numerous wide-field surveys that will start in the near future or that are already started, hundreds of thousands of quasars will be accessible for looking for lensing effects…..
Read more: nasa.gov

The origins of a torus in a galactic nucleus

An artist's conception of a quasar, with a Chandra X-ray Observatory image of the quasar GB1508+5714 inset. The data reveal a jet of high-energy particles that extends more than 100,000 light years from the supermassive black hole powering the quasar. A new study shows for the first time that a torus of gas and dust will naturally form around the nuclear black hole as material falls in toward the nucleus. Credit: NASA/Chandra

Quasars are among the most energetic objects in the universe, with some of them as luminous as ten thousand Milky Way galaxies. Quasars are thought to have massive black holes at their cores, and astronomers also think that the regions around the black holes actively accrete matter, a process that releases vast amounts of energy and often ejects a powerful, narrow jet of material. Because they are so bright, quasars can be seen even when they are very far away, and this combination of being both highly energetic and located at cosmological distances makes them appealing to astronomers trying to figure out the nature of galactic center black holes (our own Milky Way has one) and the conditions in the early universe that prompt these monsters to form.
Quasars, and other galaxies with less dramatic but still active nuclei, come in a variety of subgroups. Some, for example, contain hot gas moving at huge velocities, while others do not; some are seen with strong dust absorption features, but others are not. One problem in unraveling the mystery of quasars is that many (perhaps most) quasar nuclei seem to be surrounded by a torus of obscuring dust that makes them difficult to study. In fact, the standard model of these objects proposes that the various subgroups result from viewing the active nuclei at different angles with respect to its dusty torus. If the nucleus happens to be seen face-on, and if there is a jet present, the gas velocities are large and the dust is not apparent; if seen edge-on through the torus, the observed velocities are much smaller and the dust absorption features are dominant. But so far no one knows for sure how quasars form, how they develop in time, or how (or what) physical processes generate their stupendous energies.
The situation may be about to change. The violent activity around a black hole is very difficult to analyze with just pen and paper, and so for years researchers have tried to use computer simulations to identify what happens. But these simulations have faced a major challenge: tracing the detailed flow of material from galaxy-wide scales of hundreds of thousands of light-years down into the central tenth of a light-year around the black hole. It has just been too hard to keep track of everything at such a fine scale across such a large one.
CfA astronomers Chris Hayward and Lars Hernquist, together with ex-CfA member Phil Hopkins and a fourth colleague, have figured out a way to deal with the computational dilemma. They use a clever scheme of multi-scale “zoom-ins” which allows them to track and model, in a physically consistent way, selected parcels of gas as they move inward towards the torus. Their simulations lead them to reach two very significant conclusions. First, they show that a dusty torus is likely to be produced around the black hole – in the past it had been postulated in order to explain the various morphologies but had never been demonstrated, even in a simulation. Secondly, the scientists show that the torus is not just a passive screen: it plays an active role in feeding gas and dust into the accretion disk around the black hole itself.
Provided by Harvard-Smithsonian Center for Astrophysics
Read more: www.physorg.com

How fast black holes spin in quasars

Umberto Maio, Massimo Dotti, Margarita Petkova, Albino Perego, Marta Volonteri
Mass and spin are often referred to as the two `hairs’ of astrophysical black holes, as they are the only two parameters needed to completely characterize them in General Relativity. The interaction between black holes and their environment is where complexity lies, as the relevant physical processes occur over a large range of scales. This is particularly relevant in the case of super-massive black holes (SMBHs), hosted in galaxy centers and surrounded by swirling gas and various generations of stars, that compete with the SMBH for gas consumption, and affect the thermodynamics of the gas itself. How dynamics and thermodynamics in such fiery environment affect the angular momentum of the gas accreted onto SMBHs, and hence black hole spins is uncertain. We explore the interaction between SMBHs and their environment during active phases through simulations of circum-nuclear discs (CND) around black holes in quasars hosted in the remnants of galaxy mergers. These are the first 3D (sub-)parsec resolution simulations that study the evolution of the SMBH spin explicitly including the effects of star formation, stellar winds, supernova feedback, and radiative transfer. This approach is crucial to investigate the angular momentum of the material that is accreted by the hole. We find that maximally rotating black holes are slightly spun down, and slow-rotating holes are spun up, leading to upper-intermediate equilibrium values of the spin parameter (~0.7-0.9). Our results suggest that, when quasar activity is driven by mergers of galaxies of similar sizes, stellar feedback does not induce strong chaos in the gas inflow, and that most SMBHs at the end of the quasar epoch have substantial spins….
Read more: arxiv.org/pdfpdf