At the edge of time, a litter of galactic puppies

Dennis Overbye, The New York Times

Posted at Oct 05 2020 07:08 AM

At the edge of time, a litter of galactic puppies 1
In an image provided by Borisova et al./ESO, eighteen quasars observed by the European Southern Observatory’s Very Large Telescope, one of several telescopes around the world that contributed to the discovery of SDSS J1030+0524 and its cluster or proto-galaxies. The discovery of a black hole surrounded by protogalaxies provides astronomers with a rare glimpse of the web of matter permeating the cosmos. Borisova et al./ESO via The New York Times

(Out There)

Astronomers announced on Thursday that they had discovered a giant black hole surrounded by a litter of young protogalaxies that date to the early universe — the beginning of time.

The black hole, which powers a quasar known as SDSS J1030+0524, weighed in at a billion solar masses when the universe was only 900 million years old. It and its brood, the astronomers said, represented the infant core of what became a vast cluster of galaxies millions of light years across and encompassing a trillion suns worth of matter.

The discovery should help astronomers understand the origins of galactic clusters— the largest structures in the universe — and how supermassive black holes could have grown so quickly in the early universe. And it provides a rare glimpse of the cosmic web, a network of filaments spanning the cosmos that determine the large-scale distribution of matter in the universe.

“This research was mainly driven by the desire to understand some of the most challenging astronomical objects — supermassive black holes in the early universe,” said Marco Mignoli, an astronomer at the National Institute for Astrophysics in Bologna, Italy, in a statement. “These are extreme systems, and to date we have had no good explanation for their existence.”

Mignoli was the lead author of a paper published Thursday in Astronomy & Astrophysics summarizing a decadelong observation campaign that used some of the biggest and most powerful telescopes in the world, including the Hubble Space Telescope, the European Southern Observatory’s Very Large Telescope in Chile, the Keck II Telescope on Mauna Kea in Hawaii and the Large Binocular Telescope on Mount Graham in Arizona.

Astronomers have long thought that black holes and massive galaxies should appear earliest and grow fastest at the dense nodes where these filaments cross, where there is abundant gas to feed them. The new results suggest this is true, said team member Colin Norman of Johns Hopkins University, in an email.

Although the idea of the cosmic web is widely accepted, Alan Dressler of the Carnegie Observatories, who was not part of this work, said in an email that the web has not been “mapped” in the usual sense of the word. “Only a few places, near galaxies (like this one, the big one with the black hole) where it is sufficiently ‘lit up,’” he said. “And even then, it took a big telescope, a remarkable instrument, and a lot of time to see this structure.”

Mignoli and an international team of astronomers have been searching for signs of over-density around very distant, very early quasars.

Astronomers measure cosmic time and distance in the expanding universe by the degree to which light from receding objects has been lengthened, or redshifted, in wavelength, by the same phenomenon that makes a retreating siren drop in pitch.

The quasar SDSS J1030+0524 clocked in with a redshift of 6.31, meaning that light waves from it — indeed, the size of the whole universe — have been stretched by a factor of 7.31 since the time of the quasar. That corresponds to when the universe was 900 million years old, according to conventional cosmological calculations. That means it took 12.9 billion years for the light from that quasar to reach Earth, making it one of the most distant quasars ever discovered.

In images from the Hubble and other telescopes, the quasar was surrounded by myriad faint objects. The astronomers proceeded to track them down and make spectroscopic measurements.

“These objects are actually star-forming galaxies,” said Roberto Gilli, another team member. The objects were selected for further study based partly on their very red colors and other spectral characteristics, he said. Six had similar redshifts — between 6.129 and 6.355 — over a volume in space of about 27 billion cubic light-years.

Within that volume, the authors determined, were about a trillion solar masses of material, about as much material as is contained in a giant cluster of galaxies today, making that region twice as dense as regular space.

“This is the first spectroscopic identification of a galaxy overdensity around a supermassive black hole in the first billion years of the universe,” the astronomers wrote in their paper. The finding, they added, lent support to the idea that the most distant and massive black holes formed and grew within massive halos of dark matter in large-scale structures, “and that the absence of earlier detections of such systems is likely due to observational limitations.”

But those limitations will not last forever, Dressler noted. One of the primary goals for the next generation of “super telescopes,” like the Giant Magellan Telescope and the European Extremely Large Telescope, both now being built in Chile, and the Thirty Meter Telescope proposed for Hawaii’s Mauna Kea, is to map out this web with greater fidelity.

“The added light-gathering power of the next generation will allow us to use faint young galaxies to serve as the back lights” illuminating the faint filaments of atomic matter, Dressler said. Until now, what is known about the web has come from using quasars as back lights. But faint galaxies are 10 to 100 times more plentiful on the sky, Dressler said, “so you can start making a good ‘picture’ of the web.”

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