An object lurking in the foggy dawn of the Universe has just given astronomers a big surprise.
Observations collected through the James Webb Space Telescope have revealed an active supermassive black hole 10 million times the mass of the Sun – one that is actively growing as it slurps up matter from the space around it.
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| Visualization of an active black hole. (NASA’s Goddard Space Flight Center/Jeremy Schnittman) |
The black hole was found inside one of the earliest galaxies ever detected, previously known as EGSY8p7 though since renamed CEERS_1019. Its discovery could help with one of the biggest head-scratchers of the early Universe: how the black holes in the Cosmic Dawn grew to such large sizes in such a short amount of time.
A paper detailing the discovery led by astrophysicist Rebecca Larson of the University of Texas at Austin has been submitted to The Astrophysical Journal, and is available on preprint server arXiv.
"We found the most distant active galactic nucleus (AGN) and the most distant, earliest black hole we've ever found," Larson tells ScienceAlert.
Larson was initially looking at CEERS_1019 as part of her work investigating light produced by star formation in the very early Universe. This light, called Lyman-alpha emission, is thought to be generated by the ionization of neutral hydrogen by star formation activity. The early Universe was filled with a fog of neutral hydrogen, which prevented light from propagating; it was only after this hydrogen was ionized that light could stream freely.
This Epoch of Reionization, as it is known, is not fully understood. We know it took place in the first billion years after the Big Bang 13.8 billion years ago, but seeing that far into the early Universe is really hard. CEERS_1019 and a handful of other super-early galaxies are excellent targets for this research, because they're relatively bright.
The galaxy was identified in Hubble data in 2015, and at the time, was the earliest, most distant galaxy observed. Subsequent observations confirmed its existence, but more detailed information remained elusive: the earliest light in the Universe has shifted so far into the infrared part of the spectrum due to the Universe's expansion that a powerful, dedicated infrared instrument like JWST is necessary to probe them.
So, when JWST came along, CEERS_1019 – the brightest of the Hubble galaxies from this epoch – was an obvious target. The telescope stared at the galaxy for just one hour, with all four of its instruments, but returned a wealth of data.
"In the moment I was kind of like, wow look at everything we can see with JWST, we've seen this whole portion of the spectrum of this galaxy – and any galaxies early on in the Universe – we've never seen before," Larson tells ScienceAlert. "I was just overwhelmed by the amount of information."
But then she noticed something she wasn't quite expecting. In addition to the light of star formation, there was a broad emission feature usually associated with AGN. And when she mentioned it to some AGN researchers, things started to get interesting.
Typically a galaxy in the early Universe emits either light from an AGN or light from star formation. To see both in the same galaxy was extremely unexpected.
"I was just as surprised as everyone," Larson says. "We had this whole argument for weeks, as to which one it should be, it should be one or the other. And it turns out, it is both. There is some impact that the black hole is having on the emission lines that we're seeing, but most of the light we see in our images is still dominated by the star-forming part of the galaxy."
That a supermassive black hole existed more than 13.2 billion years ago, and was seen growing, is not as surprising as you might think. Much larger black holes have been detected in the early Universe; J1342+0928, a quasar galaxy detected 690 million years after the Big Bang, has a supermassive black hole clocking in at 800 million Suns. The black hole in J0313-1806, 670 million years post-Big Bang, was measured at 1.6 billion Suns.
Both of these quasars are dominated by AGN emission. What CEERS_1019 seems to represent, Larson and her colleagues believe, is an intermediate step: a point between the later, larger, AGN-dominated galaxies, and how those galaxies and their black holes started forming in the first place.
"We did not know and still do not know how the black holes in those galaxies got to be so massive, that early on in the Universe," Larson explains.
"So what we found is what we think could be the progenitor or the thing that grew into these incredibly massive quasars."
Looking at the supermassive black hole in CEERS_1019, the researchers think the object formed from the collapse of a massive object, such as one of the first stars in the Universe. These stars were much, much bigger than the stars we have around today, so the black hole from such a collapse would have had a head-start on its path to becoming supermassive.
But it would still need a bit of a boost. This could have come in the form of periodic super-Eddington accretion. The Eddington limit is the maximum sustainable rate at which black holes can grow. Material swirls around a black hole in a disk, feeding into the black hole like water down a drain. Over the Eddington limit, the material is moving so fast that, rather than circling the black hole, it flies off into space. Super-Eddington accretion is only possible for short periods; but, according to the team's modeling, it could be possible in bursts that helped grow the black hole at the center of CEERS_1019.
But the best way to learn more about them is to find more intermediate galaxies, and this is looking extremely achievable. As Larson points out, the results came from just one hour of observations. The truly deep observations are expected to reveal more distant, and even fainter galaxies that finally help us understand how the Universe was born and how it grew.
"I don't think my record will stand for long," Larson says. "And I hope it doesn't, because I think that that's more exciting, that we're starting to answer these questions."
The research has been submitted to The Astrophysical Journal, and is available on arXiv.