Astronomers Discover Two Very Distant Double Quasars
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The two newly-discovered pairs of quasars, J0749+2255 and J0841+4825, existed 10 billion years ago and resided in the cores of merging galaxies, according to a team of astronomers from the United States and Japan.

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. Image credit: NASA / ESA / J. Olmsted, STScI.

Quasars are highly luminous objects powered by black holes billions times the mass of our Sun.

They 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.

“Quasars make a profound impact on galaxy formation in the Universe,” said Dr. Nadia Zakamska, an astrophysicist in the Department of Physics and Astronomy at Johns Hopkins University.

“Finding dual quasars at this early epoch is important because we can now test our long-standing ideas of how black holes and their host galaxies evolve together.”

The images of J0749+2255 and J0841+4825 captured with the NASA/ESA Hubble Space Telescope show that individual quasars within the pairs are only about 10,000 light-years apart. By comparison, our Sun is 26,000 light-years from the supermassive black hole in the center of our Galaxy.

The pairs of host galaxies will eventually merge, and then the quasars also will coalesce, resulting in an even more massive, single solitary black hole.

These Hubble images show two pairs of quasars: J0749+2255 and J0841+4825. Image credit: NASA / ESA / Hubble / H. Hwang & N. Zakamska, Johns Hopkins University / Y. Shen, University of Illinois, Urbana-Champaign.

“The quasars aren’t moving through space in any measurable way, but instead their jiggle could be evidence of random fluctuations of light as each member of the quasar pair varies in brightness,” the researchers said.

“Quasars flicker in brightness on timescales of days to months, depending on their black hole’s feeding schedule.

“This alternating brightness between the quasar pair is similar to seeing a railroad crossing signal from a distance. As the lights on both sides of the stationary signal alternately flash, the sign gives the illusion of ‘jiggling’.”

“When the targets were observed with Hubble, its crisp vision revealed that they are two close pairs of quasars.”

The team also used data from ESA’s Gaia satellite and the ground-based Sloan Digital Sky Survey.

“The study is a proof of concept that really demonstrates that our targeted search for dual quasars is very efficient,” said Hsiang-Chih Hwang, a graduate student in the Department of Physics and Astronomy at Johns Hopkins University.

“It opens a new direction where we can accumulate a lot more interesting systems to follow up, which astronomers weren’t able to do with previous techniques or datasets.”

The discovery is described in a paper in the journal Nature Astronomy.

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Y. Shen et al. A hidden population of high-redshift double quasars unveiled by astrometry. Nat Astron, published online April 1, 2021; doi: 10.1038/s41550-021-01323-1

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