Astronomers have found Quasar pairs in distant merging galaxies which can provide more information about the early universe

Credit: International Gemini Observatory/NOIRLab/NSF/AURA/J. da Silva

Two pairs of quasars have been found by the Hubble space telescope and Gaia spacecraft.

Well, what are Quasars? They are intensely bright celestial objects, which can also be the cores of galaxies, and a supermassive black hole is thought to be present in their center, that powers them. They are theorized to affect galaxy formation and evolution. And observing quasar pairs in the early universe let us investigate the evolution of merging galaxies and also research the formation of binary supermassive black holes.

The special thing about these pair is that they are closer together than any pair of quasars found by us, which inclines on the evidence of the existence of supermassive black hole pairs as well as crucial insight into galaxy mergers in the early universe.

The quasars in each of the pairs are separated by 10,000 light-years, which suggests that they belong to two merging galaxies. And we are seeing these quasar pairs as they existed 10 billion years ago.

Quasars pairs are very rare and also hard to identify, so the astronomers found the two quasars pairs by combining data from several space-based and ground-based telescopes, including Gemini Observatory.  Quasar pairs at such large distances can only be resolved by sharp-eyed telescopes such as Hubble or Gemini. And to focus their search the researchers first identified 15 quasars using the Sloan Digital Sky Survey, a three-dimensional map of objects in the night sky, from that they used observations from the Gaia spacecraft to identify four potential quasar pairs. When these candidates were images by the Hubble space telescope, which visually resolved two quasar pairs. After which they used GMOS (Gemini Multi-object Spectrograph) on Gemini North in Hawai to very this discovery and also investigate one of the quasar pairs.

Credit: International Gemini Observatory/NOIRLab/NSF/AURA/J. da Silva

This provided the team with independent measurements of the distance of the quasars and their composition, as well as confirming that the two quasars are indeed a pair rather than a chance alignment of a single quasar with a foreground star. And this was possible only because of Gemini observations, as the GMOS is very sensitive, and also resolved spectra to yield redshifts and spectroscopic confirmations simultaneously for both quasars.

While the team members are confident in their findings, there is a small possibility that they have observed double images of a single quasar, this could have been formed by gravitational lensing which occurs when an intervening massive galaxy distorts and splits the light from distant objects, which can result in multiple images of a single object. But researchers say that they could not detect any foreground galaxies in their observations, which makes it highly unlikely that this could have been due to gravitational lensing. 

Now the researchers are planning to search for more quasars pairs, building a census of double quasars in the early universe, which can let us know more about galaxy formation in the early universe and also open up a lot of insights into nature of the early universe.

Source - DOI: 10.1038/s41550-021-01323-1