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Hubble sees double in the young universe

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Going back ten billion years in the universe’s past, Hubble came across two pairs of quasars that were very close to each other. Astronomers conjure up two needles in a cosmic haystack.

A quasar is a very energetic galaxy with a very voracious supermassive black hole at its center. The object, which ingests a lot of matter, then emits an insane amount of energy in the form of electromagnetic radiation and in fact appears very bright. Quasars are thus presented as brightest objects in the universe.

Sometimes it happens that two of these cosmic ogres meet during a galaxy merger, thus forming a “double-quasars”. These galactic mergers having been more frequent several billion years ago, researchers are pointing their telescopes this far in an attempt to apprehend them. However, this is no small feat.

We believe that in the distant universe there is a double-quasars for a thousand quasars“, Specifies Yue Shen, of the University of Illinois at Urbana-Champaign. “Finding these double quasars is like falling on a needle in a haystack“.

Two old pairs of quasars detected

And precisely, a team recently fell on one of these hands… then on a second. In fact, it was Hubble who spotted them, more than 10 billion light years. On the ground, these two pairs of quasars appeared as two simple points of light.

So far, astronomers have already identified a hundred of these double objects in molten galaxies. However, none of them are as old as these two new discoveries.

This study, the results of which are published in the journal Nature astronomy, will allow researchers to better understand the collisions between galaxies and the fusion of their black holes in the early universe.

This is the first sample of double-quasars evolving during the peak period of galaxy formation that we can draw on to probe how supermassive black holes come together to form binaries.“Said Nadia Zakamska of Johns Hopkins University in Baltimore, Maryland.

In turn, these mergers shape the structure of galaxies. As two nearby galaxies begin to warp by gravity, their interaction channels matter into their respective black holes, then igniting their quasars.

Over time, the radiation from these giant “bulbs” propels powerful winds that sweep the surrounding gas. Deprived of matter, star formation ceases and galaxies evolve into elliptical galaxies.

The two pairs of quasars identified at the heart of molten galaxies. Credits: NASA, ESA, H. Hwang and N. Zakamska, and Y. Shen

Although astronomers are convinced of these results, it is still possible that these Hubble snapshots are actually duplicate images of the same quasars.

If so, they would be the work of gravitational lenses. As a reminder, these phenomena occur when the gravity of a massive foreground galaxy divides and amplifies the light of an object located in the background (here quasars) into two mirror images.

However, researchers believe this scenario is highly improbable, because Hubble did not detect any prominent galaxies near the two pairs of quasars.


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