Webb Looks at One of the Best Gravitationally Lensed Quasars Ever Discovered
By Carolyn Collins Petersen
It looks like a distant ring with three sparkly jewels, but the Webb telescope’s (JWST) most recent image is really the view of a distant quasar lensed by a nearby elliptical galaxy. The telescope’s Mid-Infrared Instrument (MIRI) looked at the faint apparition during a study of dark matter and its distribution in the Universe.
We get to see this ghostly vision thanks to the gravitational lensing of the quasar. Such lensing creates one of the great natural telescopes in nature. It uses the gravitational effect of matter to warp space. All matter does this, but bigger conglomerations of it do it more. So, for example, a galaxy cluster and its aggregate stars, planets, gas clouds, black holes—and dark matter—warps space quite a bit. So does an individual galaxy.
When that happens, the path of light from more distant objects around (or through) the lens also gets warped. The lens magnifies the view of those distant objects between us and the lensing mass. So, thanks to gravitational lensing, astronomers often get intriguing views of objects otherwise too dim or far away for detailed study.
A Lensed View of a Distant Quasar
The distant quasar RX J1131-1231 that JWST imaged for this view lies about six billion light-years away from Earth. Astronomers know there’s a supermassive black hole at the galaxy’s heart. It emits high-energy X-rays, which Chandra X-ray Observatory and the XMM-Newton orbiting telescope detected. Hubble Space Telescope has also viewed this eerie-looking object.
Those X-rays tell astronomers that something very energetic is happening in the galaxy—that’s why it’s also often called a quasar. The X-ray emissions get produced by a superheated accretion disk and eventually bounce off the inner edge of the disk. Astronomers can take a spectrum of that reflected X-ray emission—but they have to account for the fact that it’s affected by the strong gravitational pull of the black hole. The larger the change in the spectrum, the closer the disk’s inner edge lies to the black hole. In this case, the emissions come from a region that lies only three times the event horizon’s radius. That suggests the black hole is spinning very, very fast—at half the speed of light.
JWST’s mid-infrared observation of the lensed quasar allows astronomers to probe the region around the its heart. They should be able to tease out details of matter distribution in the region, which should help them understand the distribution of dark matter there.
Mapping the Black Hole’s History
The central supermassive black hole at the heart of quasar RX J1131-1231 has its own tale to tell. Those X-ray emissions from its accretion disk provide clues to how fast that black hole grew over time and how it formed. There are a couple of main theories about the growth of black holes. We know that stellar-mass ones come from the deaths of supermassive stars. They explode as supernovae. What’s left collapses and that creates the black hole.
However, the supermassive ones at the hearts of galaxies probably form in one of two ways. They could come from the accumulation of material over a long time during collisions and mergers between galaxies. If that happens, a growing black hole gathers material in a stable disk. If it has a steady diet of new material from the disk, that should lead to a rapidly spinning black hole. On the other hand, if the black hole grows due to many small accretion episodes, its diet would come from random directions and its spin rate would be slower.
So, what’s the story of the bright, supermassive monster at the heart of RX J1131-1231? All the observations to date show a rapidly spinning black hole. That means it likely grew via mergers and collisions. Further observations of its high-energy activity should help astronomers as they probe deeper into the Universe and see objects at earlier and earlier epochs of cosmic time. JWST’s contribution helps them use gravitational lenses to spot these things. At the same time, they get to map the distribution of dark matter that helps the Universe create those natural magnifying glasses.
For More Information
Webb Admires Bejeweled Ring
Distant Quasar RX J1131
RX J1131-1231: Chandra & XMM-Newton Provide Direct Measurement of Distant Black Hole Spin
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July 7, 2024 at 04:10AM
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