The black hole accounts for over two-thirds the mass of the object it inhabits.
The James Webb Space Telescope (JWST) was designed to give us the ability to look at one of the earliest periods in the evolution of the Universe, a time when some of the earliest stars were putting out enough light to ionize the hydrogen that accounted for almost all of the normal matter present at the time. There were lots of ideas about what we might see, but the Universe is full of surprises.
One of the first surprises was the existence of what picked up the moniker “little red dots,” which are exactly what their name suggests. After some initial arguments, it became clear that these were early versions of the supermassive black holes that presently sit at the center of almost every galaxy. Now, gravitational lensing has allowed astronomers to confirm that a little red dot is little more than a supermassive black hole without much in the way of a galaxy around it.
Making a little red dot bigger
The little red dot in question is called Abell 2744−QSO1, and gravitational lensing has both magnified it and caused it to appear three times in the vicinity of the galaxy cluster that did the lensing. Based on details in its spectrum, we’re looking at the object as it appeared just 700 million years after the Big Bang.
We’ve already known about QSO1 for a couple of years, and it has been the subject of intense study. One paper noted that the three lensed images of the object differ in some of their details. Since the light from each of those took different paths to Earth, and thus different amounts of time, this suggests there have been variations in QSO1’s emissions—consistent with a black hole feeding on different amounts of material over time. And, based on the luminosity of the object, people had estimated that the black hole itself was quite large for that early in the Universe’s history, at above 10 million times the mass of the Sun.
Other work revealed that most of the material around it was gas that had formed relatively few stars. And, just last month, a detailed look at the spectrum of QSO1 showed that there is very little other than hydrogen present, consistent with the object having produced very few stars by this point in its history.
The big uncertainty in all of this is the relationship between the luminosity of the object and the mass of the black hole. We derive that relationship from the recent Universe, where supermassive black holes are embedded in mature galaxies that provide some structure to the material that the black hole is feeding on. There’s no guarantee that this same relationship would hold this early in the Universe’s history.
Fortunately, thanks to the magnification of the gravitational lensing, QSO1 provides us a fantastic opportunity to find out how far back this relationship holds.
A “galaxy” with very few stars
To get a more detailed picture of what’s at the center of QSO1, a large international team constructed a detailed picture of the environment around it. These included the amount of light emitted by different areas, as well as how fast the material in those areas was moving relative to the Earth, as determined by the red- and blue-shifting of hydrogen emissions. (The data is nicely consistent, with one side of the object showing red shifting, and the opposite side blue.) They also looked at the velocity dispersion, which registers how much variation there is relative to the mean velocity.
With this data in hand, they built models to test which system best explained it. In every case, the best fit was a system with a massive point source at its center, and the rest of the material rotating around it. Attempts to build versions with a star cluster around the black hole similar to that seen in the Milky Way led to a much less accurate match to the real-world data.
These models placed the black hole’s mass at about 50 million times that of the Sun, which is in line with previous estimates. That suggests the rules governing black hole luminosity haven’t changed in at least 13 billion years.
Attempting to estimate the mass of any stars surrounding the black hole suggested there were very few. “The Keplerian rotation curve leaves little room for any stellar component,” the researchers conclude. Attempts to estimate the total stellar mass in the “galaxy” that the black hole sits in came up with an upper limit of 20 million solar masses—less than half of the mass of the black hole itself.
In other words, over two-thirds of the mass of QSO1 resides in the black hole, with the stars accounting for less than one-third. Which explains why the word ‘galaxy’ is in quotes above. “To our knowledge, this upper limit makes QSO1 the most ‘naked’ massive BH ever found,” the team concludes.
Making supermassives
A lot of the paper is dedicated to the consideration of how this particular black hole got so big so early in the Universe’s history. There are three leading ideas for it: primordial black holes formed in the immediate aftermath of the Big Bang; direct collapse of massive gas clouds that skip the formation of stars entirely; or runaway mergers of black holes formed in early, dense star clusters.
Here, the researchers argue that having a supermassive black hole with so few stars around suggests we can ignore option three. If there are no dense stellar clusters, you can’t form enough black holes to merge. This leaves two mechanisms that are entirely theoretical at this point.
That said, the discussion seems to suggest that many of the direct collapse models that currently work require a major source of ultraviolet radiation, and more mass around than we see in QSO1. That would seemingly favor a primordial black hole as the source, although that would likely require it to have grown by a factor of 10 in the 700 million years of its existence. That, in turn, would suggest there were mergers among this population early in the Universe’s history.
All of which makes for an interesting discussion that will certainly not be resolved until we have additional examples of this sort of naked supermassive black hole.
Nature, 2026. DOI: 10.1038/s41586-026-10579-4 (About DOIs).
John is Ars Technica's science editor. He has a Bachelor of Arts in Biochemistry from Columbia University, and a Ph.D. in Molecular and Cell Biology from the University of California, Berkeley. When physically separated from his keyboard, he tends to seek out a bicycle, or a scenic location for communing with his hiking boots.
