Cold Quasar Defines New Stage in Galaxy Evolution

Jan 22, 2021 | AAS, Daily Space, Quasar

IMAGE: A cold quasar (illustrated) is a galaxy going through one last gasp of star formation as its central supermassive black hole wakes up. Within a few hundred million years, astronomers think that black hole will blow dust and gas out of the galaxy, shutting down star formation. CREDIT: NASA, Daniel Rutter

Last week, I told you about a galaxy that was dying because of a collision. This time, we have a galaxy whose supermassive black hole is just starting to consume and accrete the stars nearest it. It’s part of a new family of galaxies called “cold quasars” where there is an active black hole emitting high energy X-rays as well as colder gas shining dimly in infrared light.

This work was presented at last week’s AAS meeting, and co-author Kevin Cooke explained: When you see a black hole actively accreting material, you expect that star formation has already shut down. But cold quasars are in a weird time when the black hole in the center has just begun to feed.

Cold gas can still collapse and form stars. With a quasar, the black hole and its ferocious appetite heat up what unused gas is left in the galaxy to the point where it cannot coalesce and some is even blown away by the higher energy particles. But now, we’ve about two dozen of these cold quasars, and the researchers were able to observe one of them, CQ 4479, using the SOFIA airborne observatory. SOFIA does observations in the infrared, which is perfect for finding all that cold gas.

As a result of the new observations, the team found that CQ 4479 has about 20 billion times the mass of the sun in its stars, and its rate of star formation is essentially the same as the black hole’s rate of growth. This stage in the evolution of galaxies changes our theories on galaxy evolution. As co-author Allison Kirkpatrick noted: You should have all your stars finish growing first, and then your black hole grows. This [galaxy] shows there’s a period that they actually do grow together.

They estimate that CQ 4479’s black hole will go passive in about half a billion years. I doubt we will be covering that event when it happens, but I’m sure the team will find other examples and piece together a timeline for these cold quasars.

More Information

Science News article

Dying of the Light: Cold Quasars & The Shutdown of Galaxy Growth,” K.C. Cooke et al., 2021 January 11, American Astronomical Society Meeting


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