A quasar has been spotted 13 billion light years away from us. It’s the farthest one we’ve ever seen, and it already existed 690 million years after the birth of the universe. Finding a quasar – a supermassive black hole with a bright disc of material circling it – from so long ago indicates that huge black holes must have formed quickly in the universe’s youth. The quasar’s strange light could also help us understand how the cosmos evolved.
at the Observatories of the Carnegie Institution for Science in Pasadena, California, and his colleagues searched through telescope data from three surveys that have looked at nearly the entire sky, and then confirmed possible instances of distant quasars with new observations.
Considering how few of these distant objects we think there are, it was a long shot. Based on estimates from nearer quasars “there should be between 5 and 100 of these very distant and bright quasars in the universe, and the universe is very big”, says Bañados.
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Giant seeds
The quasar 13 billion light years away is one of the most distant objects we’ve ever seen, and the fact we can see it despite its distance means it is one of the brightest objects anyone has spotted in the universe.
It is more than 800 million times the mass of the sun, which presents a problem. Theory tells us that it should take billions of years for such a huge object to form, but it already existed just 690 million years after the universe formed.
“They have to start out at about masses about 1000 times that of the sun,” says at Pennsylvania State University. “Otherwise they wouldn’t be able to grow to the sizes that we see today.”
These seeds could have been an early generation of enormous stars, or huge gas clouds thousands or millions of times the mass of the sun that collapsed and formed enormous black holes. Eracleous says the newly found distant quasar might effectively rule out the first of these ideas because it was formed too early in the universe’s history to allow stars to grow large enough.
Universal transformation
The galaxy that hosts the quasar is full of bright dust, stars and metals that also needed time to form, which is more evidence for a fast evolution of the early universe.
“It is possible that this galaxy already has a third of the mass of stars that our Milky Way has, but the Milky Way had 13 billion years to form all the stars – this galaxy only had 690 million years,” says team member at the Max Planck Institute for Astrophysics in Heidelberg, Germany.
Bañados and his colleagues also spotted something strange about the quasar’s light: on its way to us, some of the light was absorbed by hydrogen that wasn’t ionised, even though most of the gas in interstellar space today is ionised.
That means the quasar must have lived during the universe’s early epoch of reionisation, when stars and galaxies began to form and remove electrons from the hydrogen gas that pervades space. Only after reionisation did the universe start to resemble the one we live in today. We’re still not sure exactly when this transformation occurred, but this is a clue that it was still ongoing around 690 million years after the big bang.
“Reionisation was sort of the last transition that the whole universe made together – and this object was sitting right there,” says Bañados. “We are seeing the peak of the action there. If we can find more objects like this, we will be able to start figuring out how exactly this process happened.”
Read more: Ancient quasars in distant galaxies caught switching on suddenly
Nature
Astrophysical Journal Letters
