Hubble Spots Double Quasars in Merging Galaxies

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Double Quasars

This simulation shows the brilliant, flickering light from a pair of quasars. Astronomers in a recent study deduced that the blinking light is a telltale sign of the presence of two quasars and not a single object. Credit: NASA, ESA, and J. Olmsted (STScI)

Seeing Dual Quasars Is Like Finding a Needle in a Haystack

Inhabitants of our Milky Way galaxy living several billion years from now will have a markedly different-looking sky overhead. Two brilliant objects, each as bright as the full Moon or brighter, will drown out the stars with their radiance. These giant blazing light bulbs are a pair of quasars, brought to life by the collision of our Milky Way with the neighboring Andromeda galaxy.

Quasars are ignited by monster black holes voraciously feeding on infalling matter, unleashing a torrent of radiation. The Milky Way and Andromeda have such black holes at their hearts, which are now sleeping giants. That is, until the big bang-up. The duo will be as deadly then as it is dazzling. Blistering radiation from the quasar pair might sterilize the surfaces of planets, wiping out innumerable extraterrestrial civilizations.

This tale of “death star” dueling quasars looming in the sky might seem like a scene out of a science fiction movie. But the real universe is stranger than fiction. This is actually a story that played out between two pairs of galaxies that existed long ago and far away. The four galaxies, each containing a central, bright quasar, are in the process of merging. As the two galaxies in each quasar pair move closer together, so do their quasars. Hubble caught the action, photographing two quasar pairs that existed 10 billion years ago, during the peak epoch of galaxy close encounters. The discovery offers a unique way to probe collisions among galaxies in the early universe that might otherwise have gone undetected. Ancient quasars are scattered all across the heavens, so finding these dynamic duos is fortuitous. Astronomers estimate only one in a thousand quasars are really double quasars.

Double Quasars

These two Hubble Space Telescope images reveal two pairs of quasars that existed 10 billion years ago and reside at the hearts of merging galaxies. Each of the four quasars resides in a host galaxy. These galaxies, however, cannot be seen because they are too faint, even for Hubble. The quasars within each pair are only about 10,000 light-years apart—the closest ever seen at this cosmic epoch. Credit: NASA, ESA, H. Hwang and N. Zakamska (Johns Hopkins University), and Y. Shen (University of Illinois, Urbana-Champaign)

NASA’s Hubble Space Telescope is “seeing double.” Peering back 10 billion years into the universe’s past, Hubble astronomers found a pair of quasars that are so close to each other they look like a single object in ground-based telescopic photos, but not in Hubble’s crisp view.

The researchers believe the quasars are very close to each other because they reside in the cores of two merging galaxies. The team went on to win the “daily double” by finding yet another quasar pair in another colliding galaxy duo.

A quasar is a brilliant beacon of intense light from the center of a distant galaxy that can outshine the entire galaxy. It is powered by a supermassive black hole voraciously feeding on inflating matter, unleashing a torrent of radiation.

“We estimate that in the distant universe, for every 1,000 quasars, there is one double quasar. So finding these double quasars is like finding a needle in a haystack,” said lead researcher Yue Shen of the University of Illinois at Urbana-Champaign.

The discovery of these four quasars offers a new way to probe collisions among galaxies and the merging of supermassive black holes in the early universe, researchers say.

Quasars are scattered all across the sky and were most abundant 10 billion years ago. There were a lot of galaxy mergers back then feeding the black holes. Therefore, astronomers theorize there should have been many dual quasars during that time.

“This truly is the first sample of dual quasars at the peak epoch of galaxy formation with which we can use to probe ideas about how supermassive black holes come together to eventually form a binary,” said research team member Nadia Zakamska of Johns Hopkins University in Baltimore, Maryland.

The team’s results appeared in the April 1 online issue of the journal Nature Astronomy.

Double Quasars Illustration

This artist’s conception shows the brilliant light of two quasars residing in the cores of two galaxies that are in the chaotic process of merging. The gravitational tug-of-war between the two galaxies stretches them, forming long tidal tails and igniting a firestorm of starbirth. Quasars are brilliant beacons of intense light from the centers of distant galaxies. They are powered by supermassive black holes voraciously feeding on infalling matter. This feeding frenzy unleashes a torrent of radiation that can outshine the collective light of billions of stars in the host galaxy.
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