JWST finds plenty of low mass black holes in the early universe

Black holes played a critical role in the formation of the early universe. However, astronomers have been debating for a long time just how critical, as the information we had about early black holes, which exist at high red-shifts, was relatively limited.

A new paper from a group of researchers led by Sophia Geris at the University of Cambridge combined several spectra from the James Webb Space Telescope (JWST) to add some context to the formation of black holes early in the universe, and found that there are plenty of smaller ones lurking around, and lending credence to the idea that black holes of all sizes contributed to the formation of our modern universe. The study is published on the arXiv preprint server.

JWST has been operating for a few years now, and has had several data releases for its various instruments. The one used for the analysis in the paper was the third data release from the JWST Advanced Deep Extragalactic Survey (JADES), which included 4000 additional, never before seen spectra with 2375 objects in its dataset having defined redshifts, meaning scientists know how far away they are in space and time.

This particular study looked at 600 galaxies that were very far away, and removed the ones with known Active Galactic Nuclei (AGNs), which are active black holes eating gas and dust at the center of galaxies. Most of the known AGNs were very bright, and since the intent of this paper was to find faint AGNs that would otherwise be overlooked in a traditional survey, they needed to be removed.

After the known bright ones were removed, they stacked a series of images captured using different spectra to enhance the brightness of any faint AGNs still in the dataset. The authors also grouped the galaxies together by certain criteria, such as how bright the galaxies themselves were or how many stars they had.

After they had stacked the spectra together and got a series of AGNs that were now bright enough to be noticeable, they looked for a particular type of light called broad Hα. That light specifically indicates a black hole is actively eating material, though it could also be from other sources like supernovae or winds blowing out of the target galaxy.

Eliminating those possibilities left the dataset with a series of faint AGNs at the center of many galaxies at high red-shift that were otherwise thought not to have any active black holes at all. Importantly, many of these black holes are much smaller than those traditionally thought of when considering black holes in the early universe. They were only around 1,000,000 times the mass of our sun, and much less active than previously found AGNs at the same red-shift.

That also helped explain a previous puzzle in the sizing of black holes in the early universe. Many of the larger AGNs found in previous studies had seemed to be too big for their galaxies, while the black holes found in this study fit the more generally accepted size parameters for the galaxies they inhabited. This could indicate that, instead of a “black-hole first” view of galaxy evolution, these smaller black holes indicate there could be many galaxies where the galaxy itself forms before the black hole at its center gets large enough to be noticeable with astronomical observations.

Either way, studies like this are exactly what JWST was designed for—searching back to the early universe for pathways of galaxy creation and searching out the massive structure that defined much of how the universe evolved. It’s also just getting started, with many more data releases upcoming, some of which will undoubtedly shed more light on this early population of low-mass black holes, now that they have been definitively proved for the first time.