A tiny blob of red light spotted at the beginning of the Universe could represent the first direct evidence for a supermassive black hole formation pathway.
In a dazzling new paper, a large international team led by astrophysicist Ignas Juodžbalis of the University of Cambridge in the UK has directly measured the mass of one of the mysterious ‘Little Red Dots’ (LRDs) spotted by JWST in the Epoch of Reionization, just 600 million years after the Big Bang.
The team’s results suggest that the mysterious glow named QSO1 is a black hole with a mass equivalent to 50 million Suns. If validated – and that’s not a small if – this could be evidence of primordial black holes that formed in the very first moments after the Big Bang.
Related: Earliest Black Hole Ever Confirmed Could Explain Mysterious Red Dots
“Regardless of the specific model, the high mass in such a remote cosmic epoch, the extremely high black hole to stellar mass ratio, together with the near-pristine environment, indicate that QSO1 is a massive black hole seed caught in the earliest phases of accretion,” the researchers write in a preprint uploaded to arXiv ahead of peer review.
We always expected that JWST, the most powerful space telescope ever built, would reveal things about the mysterious first billion years after the Big Bang that we didn’t even know we didn’t know.
The LRDs are one such thing. As the name suggests, they are small pinpricks of extremely redshifted light in the Epoch of Reionization; the billion-year process whereby light from the first stars and galaxies is thought to have cleared the opaque fog that filled the early Universe, allowing light to stream freely.
Because this period of the Universe is so far away from us across space-time, and so foggy, it’s difficult to see past its boundary. Scientists have some pretty good explanations for how the first stars, galaxies, and black holes came together out of primordial darkness, but finding observational support has been a little bit harder.
Light from objects during the early Universe has become stretched towards the red end of the electromagnetic spectrum, or redshifted, thanks to the ongoing expansion of the Universe. JWST is designed to see light in these wavelengths, making it the best tool we have for trying to understand how everything began.
The telescope has found hundreds of LRDs, and scientists aren’t quite sure what they are. They could be early black holes, but black holes are usually accompanied by X-ray light, of which the skies around the LRDs are curiously devoid. Another school of thought proposes they might be clusters of stars.
Juodžbalis and his colleagues selected QSO1 as a candidate for studying these blobs in greater detail. That’s because QSO1 forms part of a curious, random cosmological arrangement known as a gravitational lens. Space-time is bending around a massive galaxy cluster between us and QSO1 in such a way that it magnifies light behind it, including the glow of QSO1. This strong lensing effect means that scientists can see QSO1 much more clearly than other LRDs.
By carefully teasing apart and analyzing the lensed light, they were able to calculate the rotation curve of the object – a measurement that, for galaxies, reveals the mass of the galaxy in question and the black hole at its center.
Their results, the researchers say, are incompatible with the star cluster interpretation of LRDs. Rather, the rotation curve of QSO1 is neatly consistent with a galaxy rotating around a mass of about 50 million solar masses – an interpretation that also fits estimates from the black hole’s mass obtained from hydrogen lines in the object’s spectrum.
But the galaxy around the black hole is tiny, much smaller than expected for the black hole’s mass, making the black hole the most naked massive black hole ever spotted. This could be a clue about how galaxies came together in the early Universe, suggesting that the black holes came first, and the galaxies assembled around them.
“The only scenarios that can account for such a system are those invoking ‘heavy seeds’, such as direct collapse black holes (DCBHs, resulting from the direct collapse of massive pristine clouds), or primordial black holes (PBHs, formed in the first second after the Big Bang),” the researchers write in their paper.
Both scenarios would need further investigation. On the one hand, DCBHs would be accompanied by ultraviolet light not seen in QSO1. On the other hand, PBHs are considerably smaller than 50 million solar masses. It is possible, however, that the object is the product of rapid growth, both through accretion and collisional processes – making QSO1, potentially, the first direct evidence for the existence of primordial black holes.
The paper remains to be peer reviewed, and it is quite an extraordinary claim, so we’ll be waiting to see how this line of enquiry develops. Whatever the outcome, though, we’re sure that LRDs are going to tell us something really fascinating about the birth of the Universe.
The team’s paper can be found on arXiv.