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The brightest quasar in the early universe has been discovered

Posted: 10 Jan 2019 04:15 AM PST

Astronomers have discovered the brightest gravitationally lensed object ever seen at a time when the universe was less than one billion years old. With the help of multiple, world-class telescopes in Hawaii – Gemini Observatory, James Clerk Maxwell Telescope (JCMT), United Kingdom Infra-Red Telescope  (UKIRT), and W. M. Keck Observatory on Maunakea, Hawaii Island, as well as the Panoramic Survey Telescope and Rapid Response System (Pan-STARRS1) operated by the University of Hawaii Institute for Astronomy on Haleakala, Maui – the researchers discovered that the brilliant beacon is a quasar, the core of a galaxy with a black hole ravenously eating material surrounding it.

The results are published recently in the The Astrophysical Journal Letters and were announced during a press conference at the 233rd Meeting of the American Astronomical Society in Seattle, Washington, United States.

Though the quasar is very far away – 12.8 billion light years – astronomers can detect it because a galaxy closer to Earth acts as a lens and makes the quasar look extra bright. The gravitational field of the closer galaxy warps space itself, bending and amplifying the distant quasar's light. This effect is called gravitational lensing.

Though researchers have searched for these very remote quasars for over 20 years, a rare and fortuitous celestial alignment made this one visible to them.

"We don't expect to find many quasars brighter than that in the whole observable universe," says lead investigator Xiaohui Fan, Regents' Professor of Astronomy at the University of Arizona's Steward Observatory.

The super-bright quasar, cataloged as J043947.08+163415.7, could hold the record of being the brightest lensed quasar in the early universe for some time, making it a unique object for follow-up studies.

Shining at an apparent brightness equivalent to 600 trillion Suns, the quasar is fuelled by a supermassive black hole at the heart of a young galaxy in the process of forming. An immense amount of energy is emitted as the black hole consumes material around it. The detection provides a rare opportunity to study a zoomed-in image of how such black holes accompanied star formation in the very early universe and influenced the assembly of galaxies.

The quasar existed at a transitional period in the universe's evolution, called reionisation, where light from young galaxies and quasars reheated the obscuring hydrogen that cooled off not long after the Big Bang. The quasar would have gone undetected if not for the power of gravitational lensing, which boosted its brightness by a factor of 50.

However, because very distant quasars are identified by their red colour (due to absorption by diffuse gas in intergalactic space), sometimes their light is "contaminated," and looks bluer because of the starlight of an intervening galaxy. As a result, they may be overlooked in quasar searches because their colour is diluted to resemble that of a normal galaxy. Fan proposes that many other remote quasars have been missed due to this light contamination.

His team got lucky with finding J043947.08+163415.7, because the quasar is so bright it drowns out the starlight from the especially faint foreground lensing galaxy. "Without this high level of magnification, it would make it impossible for us to see the galaxy," says co-author Feige Wang, a physics postdoctoral scholar at the University of California, Santa Barbara, United States. "We can even look for gas around the black hole and what the black hole may be influencing in the galaxy."

"This detection is a surprising and major discovery; for decades we thought that these lensed quasars in the early universe should be very common, but this is the first of its kind that we have found," says Fabio Pacucci, a postdoctoral associate at Yale University who observed J043947.08+163415.7 with Fan at Keck Observatory. "It gives us a clue on how to search for 'phantom quasars' – sources that are out there, but cannot be really detected yet."

Pacucci is the lead author of a follow-up paper with Harvard University's Astronomy Department Chair, Abraham (Avi) Loeb, on the theoretical implications of Fan's discovery, which is published in the same issue of The Astrophysical Journal Letters as Fan's paper.

"Our theoretical study predicts that we might be missing a substantial fraction of the population of these 'phantom quasars.' If they are indeed numerous, it would revolutionise our idea of what happened right after the Big Bang, and even change our view of how these cosmic monsters grew up in mass," says Pacucci.

A Hubble Space Telescope image of a very distant quasar (right) that has been magnified and split into three images by the effects of the gravitational field of a foreground galaxy (left). The crosses mark the centres of each quasar image. Image credit: NASA/ESA/X. Fan (University of Arizona)

"The puzzling growth of extremely bright quasars within less than a billion years after the Big Bang might be partly a mirage. After removing the magnification by gravitational lensing, the inferred black holes would be less massive and could originate more naturally in the infant universe," adds Loeb.

Fan's team selected J043947.08+163415.7 as a very distant quasar candidate based on its colour by combining photometric data from the UKIRT Hemisphere Survey in the near-infrared, Pan-STARRS1 survey at optical wavelengths, and NASA's Wide-field Infrared Survey Explorer archive in the mid-infrared.

Follow-up spectroscopic observations at the University of Arizona's Multi-Mirror Telescope confirmed that the candidate was in fact a high-redshift, ultra-distant quasar.

The team then analysed the quasar in greater detail using Keck Observatory's Low Resolution Imaging Spectrometer (LRIS) to obtain a sensitive spectrum in optical light.

"I have been observing at Keck since I was a graduate student more than 20 years ago," says Fan. "The combination of Keck's large collecting area, powerful instruments, and unparalleled observing conditions on Maunakea allows us to study objects at literally the edge of the observable universe and constantly expand our cosmic horizon."

Another Maunakea Observatory, Gemini North, collected an infrared spectrum, which determined the distance of the quasar and the mass of its powerful black hole.

All the data combined revealed the signature of a very faint foreground galaxy directly between the quasar and Earth that is magnifying the quasar image.

However, the foreground lensing galaxy and the quasar are so close in the sky that it is impossible to separate them with images taken from the ground due to blurring of Earth's atmosphere. It took the exquisitely sharp images by NASA's Hubble Space Telescope to finally reveal that the quasar image is split into three components by a faint lensing galaxy.

"It's a hard system to photograph because it turns out to be so compact, which requires the sharpest view from Hubble," Fan says.

Besides being bright in visible and infrared wavelengths, the lensed quasar is also bright in submillimeter wavelengths, where it was observed with the JCMT. This is due to hot dust heated by intense star formation in the galaxy hosting the lensed quasar. The formation rate is estimated to be up to 10,000 stars per year (by comparison, our Milky Way galaxy makes one star per year).

"Clearly, this black hole is not only accreting gas, but has a lot of star formation around it," says co-author Jinyi Yang, a postdoctoral fellow at the University of Arizona. "However, because of the boosting effect of gravitational lensing, the actual rate of star formation could be much lower than the observed brightness suggests," she adds.

The quasar is ripe for future scrutiny. Fan's team is analysing a detailed 20-hour spectrum from the European Southern Observatory's Very Large Telescope, which would show gas absorption features to identify chemical composition and temperatures of intergalactic gas in the early universe.

Astronomers also will use the Atacama Large Millimeter/submillimeter Array, and eventually NASA's James Webb Space Telescope, to look within 150 light-years of the black hole to directly detect the influence of the black hole's gravity on gas motion and star formation in its vicinity.

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Unusual radio signals have been found coming from deep space

Posted: 10 Jan 2019 01:35 AM PST

Fast radio bursts (FRBs) are short bursts of radio emissions from the sky lasting only few milliseconds. Image credit: Jingchuan Yu/Beijing Planetarium

A Canadian-led team of scientists has found the second repeating fast radio burst (FRB) ever recorded. FRBs are short bursts of radio waves coming from far outside our Milky Way galaxy. Scientists believe FRBs emanate from powerful astrophysical phenomena billions of light years away.

The discovery of the extragalactic signal is among the first, eagerly awaited results from the Canadian Hydrogen Intensity Mapping Experiment (CHIME), a revolutionary radio telescope inaugurated in late 2017 by a collaboration of scientists from Canadian institutions such as University of British Columbia, McGill University, University of Toronto, Perimeter Institute for Theoretical Physics, and the National Research Council of Canada.

In a resounding endorsement of the novel telescope's capabilities, the repeating FRB was one of a total of 13 bursts detected over a period of just three weeks during the summer of 2018, while CHIME was in its pre-commissioning phase and running at only a fraction of its full capacity. Additional bursts from the repeating FRB were detected in following weeks by the telescope, which is located in British Columbia's Okanagan Valley.

Of the more than 60 FRBs observed to date, repeating bursts from a single source had been found only once before – a discovery made by the Arecibo radio telescope in Puerto Rico in 2015.

"Until now, there was only one known repeating FRB. Knowing that there is another suggests that there could be more out there. And with more repeaters and more sources available for study, we may be able to understand these cosmic puzzles—where they're from and what causes them," says Ingrid Stairs, a member of the CHIME team and an astrophysicist at UBC.

Before CHIME began to gather data, some scientists wondered if the range of radio frequencies the telescope had been designed to detect would be too low to pick up fast radio bursts. Most of the FRBs previously detected had been found at frequencies near 1400 MHz, well above the Canadian telescope's range of 400 MHz to 800 MHz.

The CHIME team's results – published on 9 January 2019 in two papers in Nature and presented the same day at the American Astronomical Society meeting in Seattle, Washington, United States – settled these doubts, with the majority of the 13 bursts being recorded well down to the lowest frequencies in CHIME's range. In some of the 13 cases, the signal at the lower end of the band was so bright that it seems likely other FRBs will be detected at frequencies even lower than CHIME's minimum of 400 MHz.

The Canadian Hydrogen Intensity Mapping Experiment (CHIME) radio telescope began detected a total of 13 FRBs over the summer of 2018. Image credit: CHIME

The majority of the 13 FRBs detected showed signs of "scattering," a phenomenon that reveals information about the environment surrounding a source of radio waves. The amount of scattering observed by the CHIME team led them to conclude that the sources of FRBs are powerful astrophysical objects more likely to be in locations with special characteristics.

"That could mean in some sort of dense clump like a supernova remnant," says team member Cherry Ng, an astronomer at the University of Toronto. "Or near the central black hole in a galaxy. But it has to be in some special place to give us all the scattering that we see."

Ever since FRBs were first detected, scientists have been piecing together the signals' observed characteristics to come up with models that might explain the sources of the mysterious bursts and provide some idea of the environments in which they occur. The detection by CHIME of FRBs at lower frequencies means some of these theories will need to be reconsidered.

"Whatever the source of these radio waves is, it's interesting to see how wide a range of frequencies it can produce. There are some models where intrinsically the source can't produce anything below a certain frequency," says team member Arun Naidu of McGill University.

"[We now know] the sources can produce low-frequency radio waves and those low-frequency waves can escape their environment, and are not too scattered to be detected by the time they reach the Earth. That tells us something about the environments and the sources. We haven't solved the problem, but it's several more pieces in the puzzle," says Tom Landecker, a CHIME team member from the National Research Council of Canada.

CHIME is a revolutionary new telescope, designed and built by Canadian astronomers. "CHIME reconstructs the image of the overhead sky by processing the radio signals recorded by thousands of antennas with a large signal processing system," explains Perimeter Institute's Kendrick Smith. "CHIME's signal processing system is the largest of any telescope on Earth, allowing it to search huge regions of the sky simultaneously.”

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Curtains close on the Dark Energy Survey

Posted: 09 Jan 2019 05:29 AM PST

The final day of data-taking for the Dark Energy Survey is 9 January 2019. Image credit: Fermilab

Scientists' effort to map a portion of the sky in unprecedented detail is coming to an end, but their work to learn more about the expansion of the universe has just begun. After scanning in depth about a quarter of the southern skies for six years and cataloguing hundreds of millions of distant galaxies, the Dark Energy Survey (DES) will finish taking data tomorrow, on 9 January 2019.

The survey is an international collaboration that began mapping a 5,000-square-degree area of the sky on 31 August 2013, in a quest to understand the nature of dark energy, the mysterious force that is accelerating the expansion of the universe. Using the Dark Energy Camera, a 520-megapixel digital camera funded by the U.S. Department of Energy Office of Science and mounted on the Blanco four-metre (13-foot) telescope at the National Science Foundation's Cerro Tololo Inter-American Observatory in Chile, scientists on DES took data on 758 nights over six years.

Over those nights, they recorded data from more than 300 million distant galaxies. More than 400 scientists from over 25 institutions around the world have been involved in the project, which is hosted by the U.S. Department of Energy's Fermi National Accelerator Laboratory. The collaboration has already produced about 200 academic papers, with more to come.

According to DES Director Rich Kron, a Fermilab and University of Chicago scientist, those results and the scientists who made them possible are where much of the real accomplishment of DES lies.

"First generations of students and postdoctoral researchers on DES are now becoming faculty at research institutions and are involved in upcoming sky surveys," Kron says. "The number of publications and people involved are a true testament to this experiment. Helping to launch so many careers has always been part of the plan, and it's been very successful."

DES remains one of the most sensitive and comprehensive surveys of distant galaxies ever performed. The Dark Energy Camera is capable of seeing light from galaxies billions of light years away and capturing it in unprecedented quality.

According to Alistair Walker of the National Optical Astronomy Observatory, a DES team member and the DECam instrument scientist, equipping the telescope with the Dark Energy Camera transformed it into a state-of-the-art survey machine.

"DECam was needed to carry out DES, but it also created a new tool for discovery, from the Solar System to the distant universe," Walker says. "For example, 12 new moons of Jupiter were recently discovered with DECam, and the detection of distant star-forming galaxies in the early universe, when the universe was only a few percent of its present age, has yielded new insights into the end of the cosmic dark ages."

The survey generated 50 terabytes (that's 50 million megabytes) of data over its six observation seasons. That data is stored and analysed at the National Center for Supercomputing Applications (NCSA) at the University of Illinois at Urbana-Champaign, United States.

"Even after observations are ended, NCSA will continue to support the scientific productivity of the collaboration by making refined data releases and serving the data well into the 2020s," says Don Petravick, senior project manager for the Dark Energy Survey at NCSA.

Now the job of analysing that data takes centre stage. DES has already released a full range of papers based on its first year of data, and scientists are now diving into the rich seam of catalogued images from the first several years of data, looking for clues to the nature of dark energy.

The first step in that process, according to Fermilab and University of Chicago scientist Josh Frieman, former director of DES, is to find the signal in all the noise.

"We're trying to tease out the signal of dark energy against a background of all sorts of noncosmological stuff that gets imprinted on the data," Frieman says. "It's a massive ongoing effort from many different people around the world."

The Dark Energy Camera is mounted on the four-metre (13-foot) Blanco telescope at the Cerro Tololo Inter-American Observatory in Chile. Image credit: Fermilab

The DES collaboration continues to release scientific results from their storehouse of data, and scientists will discuss recent results at a special session at the American Astronomical Society winter meeting in Seattle, Washington, United States, on the 8 January 2019. Highlights from the previous years include:

  • the most precise measurement of dark matter structure in the universe, which, when compared with cosmic microwave background results, allows scientists to trace the evolution of the cosmos.
  • the discovery of many more dwarf satellite galaxies orbiting our Milky Way, which provide tests of theories of dark matter.
  • the creation of the most accurate dark matter map of the universe.
  • the spotting of the most distant supernova ever detected.
  • the public release of the survey's first three years of data, enabling astronomers around the world to make additional discoveries.

DES scientists also spotted the first visible counterpart of gravitational waves ever detected, a collision of two neutron stars that occurred 130 million years ago. DES was one of several sky surveys that detected this gravitational wave source, opening the door to a new kind of astronomy.

Recently DES issued its first cosmology results based on supernovae (207 of them taken from the first three years of DES data) using a method that provided the first evidence for cosmic acceleration 20 years ago. More comprehensive results on dark energy are expected within the next few years.

The task of amassing such a comprehensive survey was no small feat. Over the course of the survey, hundreds of scientists were called on to work the camera in nightly shifts supported by the staff of the observatory. To organise that effort, DES adopted some of the principles of high-energy physics experiments, in which everyone working on the experiment is involved in its operation in some way.

"This mode of operation also afforded DES an educational opportunity," says Fermilab scientist Tom Diehl, who managed the DES operations. "Senior DES scientists were paired with inexperienced ones for training and, in time, would pass that knowledge on to more junior observers."

The organisational structure of DES was also designed to give early-career scientists valuable opportunities for advancement, from workshops on writing research proposals to mentors who helped review and edit grant and job applications.

Antonella Palmese, a postdoctoral researcher associate at Fermilab, arrived at Cerro Tololo as a graduate student from University College London in 2015. She quickly came up to speed and returned in 2017 and 2018 as an experienced observer. She also served as a representative for early-career scientists, helping to assist those first making their mark with DES.

"Working with DES has put me in contact with many remarkable scientists from all over the world," Palmese says. "It's a special collaboration because you always feel like you are a necessary part of the experiment. There is always something useful you can do for the collaboration and for your own research."

The Dark Energy Camera will remain mounted on the Blanco telescope at Cerro Tololo for another five to 10 years and will continue to be a useful instrument for scientific collaborations around the world. Cerro Tololo Inter-American Observatory Director Steve Heathcote foresees a bright future for DECam.

"Although the data-taking for DES is coming to an end, DECam will continue its exploration of the universe from the Blanco telescope and is expected remain a front-line 'engine of discovery' for many years," Heathcote says.

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