For the first time, starlight from quasar galaxies has been detected at the dawn of the universe

For the first time, starlight has been detected in galaxies that burn brightly with the fury of fueling black holes in the first billion years of the Universe’s existence.

It stands to reason that these active supermassive black holes known as quasars would have galaxies around them. But spanning such vast distances, any starlight within them was previously impossible to detect, leaving astronomers to wonder how such monstrous objects form and grow in such a short amount of time.

Now, with combined data from the Subaru Telescope in Hawaii and the James Webb Space Telescope, a large international team has been able to probe two quasar galaxies in the early Universe to learn more about this mysterious moment in the history of everything.

The research was led by astrophysicists Xuheng Ding and John Silverman of the Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU) in Japan and Masafusa Onoue of the Kavli Institute for Astronomy and Astrophysics in China.

“This is the first time we have seen host galaxies from such an early age in the Universe. It is only possible thanks to deep imaging from JWST, which allows us to shape and subtract light from the quasar to reveal the host galaxy.” explains astronomer Chien-Hsiu Lee of the WM Keck Observatory.

“We’ve seen quasars of this age before, but they were so bright that it was impossible to subtract their light to reveal the host galaxy.”

An illustration of a quasar from the early Universe. (ESO/M. Kornmesser)

Black holes themselves don’t emit any light that we can currently detect. They’re famous for that, in fact.

But an active black hole is a slightly different matter. Well, not the black hole; it’s still as dark as dark gets. It is what is happening in the surrounding space. An active black hole is one that has enough material in its vicinity to feed itself. That material swirls around the black hole, heated to millions of degrees by friction and gravity, then glows across the electromagnetic spectrum.

There is so much material swirling in a quasar that it blazes positively through the eons of space-time. This is how we can see them shining in the Cosmic Dawn, the period covering the first billion years after the Big Bang. Even there, they are still relatively weak; you’d never see a Cosmic Dawn quasar with the naked eye or a backyard telescope, but in recent years our powerful telescopes have found them in increasing numbers.

This has raised all sorts of questions, such as: How can we get supermassive black holes this big, so soon after the Big Bang? What are their galactic environments like? We’re still a bit lost on the first question, but we’re finally getting answers on the second.

The two quasar galaxies in question are called HSC J2236+0032 and HSC J2255+0251, and we are observing them about 860 million years after the Big Bang. They were found in a survey done using Subaru, with JWST called in to study them in more detail.

The supermassive black holes at the center of these two quasar galaxies are 1.4 billion and 200 million times the mass of the Sun, respectively. This allows for constraints on the amount of light generated by the black hole’s activity, since there is a limit to the speed with which a black hole can feed.

The researchers subtracted this light from the JWST observations, which left them with the light generated by their host galaxies: the light of their stars, shining.

Even more than that, however, the light from the galaxies allowed the researchers to calculate the galaxies’ masses of 130 billion and 30 billion solar masses, respectively.

This is important because it tells us something we didn’t know about galaxies in the early Universe. The masses of supermassive black holes and their galaxies in the nearby Universe are connected. If you know the mass of a black hole, you can predict the mass of a galaxy around it, and vice versa, even for small galaxies.

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We’re not sure why, whether it’s a black hole property that limits the growth of galaxies beyond a certain point, or whether galaxies and supermassive black holes grow together, but finding black holes in the early Universe could give us some clues.

J2236+0032 and J2255+0251 were both consistent with this mass relationship between a supermassive black hole and its galaxy. This suggests that this relationship was already in place when the first supermassive black holes were born. And it gives astronomers a new data point to work with when modeling the evolution of the early universe to understand how things unfolded during the cosmic dawn.

Whether or not this is true for all galaxies in the early Universe remains to be investigated. Two galaxies aren’t a terribly large sample, so researchers will go back to find out more. They’ve booked more observing time with JWST and hope to learn more about how the first galaxies formed.

“The ongoing JWST observations will give us a significantly larger sample,” they write in their paper, “allowing us to better constrain models for the mutual evolution of black hole and stellar populations in galaxies.”

The research was published in Nature.

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