Did experts just found a needle in a haystack? A team of astronomers discovered two double quasars closer to each other than any other pair found in the distant universe to date. They are nearby since they are located in a couple of merging galaxies.
Quasars are very bright nuclei of distant galaxies that are fed by supermassive black holes within and emit a stream of radiation.
The Hubble Space Telescope and Gaia Space Probe discovered the two pairs of quasars. At the same time, the Gemini North telescope in the United States performed in-depth research.
Congratulations—it’s TWINS! Astronomers scored a double bonus by uncovering not one, but two sets of twin quasars with the Hubble Space Telescope. The host galaxies cannot be seen because they are too faint, even for Hubble. (1/6) pic.twitter.com/ORaZQFImF5
— Hubble Space Telescope (@HubbleTelescope) April 6, 2021
Double Trouble Quasars?
The American National Research Laboratory on Optical-Infrared Astronomy (NOIRLab) explains that the quasars are separated by just 10,000 light-years in each pair. This made them smaller than any other double quasar identified so far. They belong to two merging galaxies.
Scientists are interested in double quasars because they can provide essential details about the merger of galaxies in the early universe, but they are also scarce.
"We estimate that in the distant universe, for every thousand quasars, there is one that is double. So finding these double quasars is like finding a needle in a haystack," said Yue Shen, an astronomer at the University of Illinois. Shen is the lead author of the study, titled "A Hidden Population of High-Redshift Double Quasars Unveiled by Astrometry."
While the team is confident in their findings, they acknowledge that there is a small possibility that the Hubble snapshots captured two images of the same quasar due to gravitational lensing. This effect occurs when a large foreground galaxy's gravity separates and amplifies the light from a background quasar into two mirror images. Hubble did not find any foreground galaxies near the two quasar pairs, so the researchers say this possibility is improbable.
Galactic Mergers Still Common Today
While galactic mergers were more common billions of years ago, Phys.org said a few are still taking place today. NGC 6240, a nearby merging galaxies system with two, probably three supermassive black holes, is one example.
Our Milky Way galaxy will collide with the neighboring Andromeda galaxy in a few billion years, resulting in an even near galactic merger. The galactic squabble would most likely fuel the supermassive black holes at each galaxy's center, igniting them as quasars.
Since quasar pairs are the only way to research galaxy fusions and are a natural laboratory for studying the processes that lead to the creation of binary supermassive black holes, observations by quasar pairs in the early universe are the only way to examine the evolution of galaxy fusions.
Researchers are now looking for more pairs of quasars to compile a list of such objects in the early universe. The quasars' host galaxies will be studied by NASA's James Webb Space Telescope, an infrared observatory set to launch later this year. Webb can show galactic merger signatures such as starlight distribution and long streamers of gas pulled from interacting galaxies.
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