In an unprecedented new view of the cosmos, NASA's Chandra X-ray Observatory has taken a long hard look into the dark and spied a "treasure trove" of ancient black holes. This unique image shows the X-rays being radiated mainly from supermassive black holes in the cores of galaxies billions of light-years distant, some of which date back to the dawn of the universe.
Without context, it might be hard to see the profundity of this image. Chandra was commanded to stare into the same portion of the sky for a total of 7 million seconds, or eleven and a half weeks. This amount of time was needed to capture enough of the weak X-ray photons traveling over billions of light-years to reach the space telescope's lens to "see" the faintest (and therefore most distant) objects. And - like the Hubble's Space Telescope's famous "Deep Field" revealed an apparently empty region of space is in fact chock-full of thousands of undiscovered galaxies - Chandra's deep field observation of the X-ray universe has revealed a cosmos chock-full of black hole behemoths.
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Astronomers think, with the help of this new X-ray view of the cosmos, that as many as 5,000 X-ray emitting objects can be found in an area of the sky around the size of a full moon. They estimate a billion such objects cover the entire sky.
Each dot represents some kind of powerful X-ray emission, 70 percent of which are active black holes ranging in size from 100,000 to billions of times the mass of our sun. By lining up the X-ray view of the cosmos with Hubble observations of the same region of sky, the researchers were able to confirm that these powerful black hole emissions were indeed being generated inside the cores of galaxies.
These are black holes that are pulling in huge amounts of matter, causing superheated plasma near to the black holes' event horizons to form accretion disks and blast out powerful X-rays. The most distant X-ray sources, coming from galaxies 12.5 billion light-years away, are likely caused by huge collections of stellar-mass black holes (ranging between 5 to several dozen times the mass of our sun) actively consuming galactic gases.
As X-ray emitting black holes can be seen at all cosmic ages, astronomers can now study how these massive objects evolve with time, starting only two billion years after the Big Bang to the modern universe.
"With this one amazing picture, we can explore the earliest days of black holes in the Universe and see how they change over billions of years," said Niel Brandt, of Pennsylvania State University in University Park, Pa., and team leader of the astronomers who are currently studying this historic cosmic view. This work is being presented at the 229th meeting of the American Astronomical Society meeting in Grapevine, Texas.
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"It can be very difficult to detect black holes in the early Universe because they are so far away and they only produce radiation if they're actively pulling in matter," added collaborator Bin Luo, of Nanjing University in China. "But by staring long enough with Chandra, we can find and study large numbers of growing black holes, some of which appear not long after the Big Bang."
Although this observation of the deep X-ray universe will keep astronomers occupied for years to come, it seems some early discoveries have already been made. Although with know supermassive black holes occupy the cores of most galaxies, very little is known about how they form and how they get to be so massive. By measuring the distance of each of this Chandra dots, astronomers have worked out how old the black holes they represent are. Interestingly, in the earliest epoch of the universe, two billion years after the Big Bang, these black holes didn't gain pass steadily, they seemed to go through dramatic growth spurts.
"By detecting X-rays from such distant galaxies, we're learning more about the formation and evolution of stellar-mass and supermassive black holes in the early Universe," said Fabio Vito, also of Penn State. "We're looking back to times when black holes were in crucial phases of growth, similar to hungry infants and adolescents."
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