What is a black hole star (a black hole wrapped in gas that shines like a star)?

Images from the James Webb Space Telescope (JWST) showed many objects in the distant universe that look like small red dots. Such objects are called “little red dots.” A paper that came out in 2023 (Matthee et al.) put this name in its title and studied 20 objects found in JWST observations whose hydrogen light lines (light of one set color given off by hydrogen) are wide.

Light from distant objects reaches us shifted toward the red (longer wavelengths, where wavelength is the length of the light’s waves), because its waves are stretched as the universe expands. The size of this shift is called redshift, and the bigger the number, the farther away and further back in time the object is. For example, MoM-BH*-1, the main object on this page, has a redshift of about 7.76, and we see it as it was about 660 million years after the universe began.

When their light is split into colors (wavelengths), giving a spectrum, the lines of light given off by hydrogen are spread out wide. This has been taken as a sign of gas moving fast around a black hole. On the other hand, their X-rays are very weak or barely seen at all. Researchers have disagreed over whether they are growing black holes or galaxies tightly packed with stars.

A black hole itself gives off no light, because not even light can get out from inside it. What glows around a black hole is gas that hasn’t been swallowed yet. As it circles the black hole, the gas forms a hot, bright, flat disk (an accretion disk).

When gas falls into a supermassive black hole at the center of a galaxy (one with hundreds of thousands to billions of times the Sun’s mass) and shines very brightly, the object is called a quasar. Seen from far away, quasars looked like points of light, like stars, so they were named “quasi-stellar,” meaning star-like.

In the black hole star idea, this glowing disk is further wrapped in extremely dense, dust-free gas. The disk’s light is absorbed, scattered (bumped into new directions) and given off again in the gas before it gets out. What we see from outside is light that came through the gas, and it looks much like light that came through a star’s atmosphere (the layer of gas over its surface). The MoM-BH*-1 paper likens this gas to an “atmosphere” around the black hole and estimates that it spans about 10 to 100 times the Earth–Sun distance (about the size of the solar system).

The paper argues that the little red dots look red not because dust blocks their light but because gas absorbs it. It also says that because the gas is so thick, it blocks X-rays too, which may explain why their X-rays are weak.

The clue is a step in brightness seen when the light is split into colors like a rainbow (the spectrum): the Balmer break. A light’s color is set by the length of its waves (wavelength). Hydrogen atoms that have taken in a little energy (with the electron on the second level from the inside) soak up all light with wavelengths shorter than 364.6 nanometers (shorter even than violet: invisible ultraviolet). So light that has passed through a lot of such hydrogen gets dimmer only on the short side of this wavelength, making a step.

A star’s atmosphere (the layer of gas over its surface) has this kind of hydrogen too. In galaxies where new stars stopped forming a few hundred million years ago and the light of a kind of star called A-type stands out, this step is clear. But for groups of stars without dust, the short side doesn’t get that dim: the ratio of brightness across the step is usually at most about 3, and under 5 even in the extreme case of nothing but A-type stars.

In MoM-BH*-1, observed by JWST in December 2024 in an observing program called “Mirage or Miracle,” that ratio was about 7.7. It is one of the biggest steps ever found, near or far. Its split light also showed dark lines made where hydrogen absorbs light of set colors (absorption lines). For such absorption lines to form, the gas has to be extremely dense: at least a billion (10 to the 9th power) hydrogen atoms per cubic centimeter.

So the paper calculated a model in which the black hole’s glowing disk is wrapped in extremely dense gas, and explained the step and the absorption lines together. In the model, the gas has about 100 billion (10 to the 11th power) hydrogen atoms per cubic centimeter and churns violently at around 500 km per second. But the paper cautions that the model is very simple and that its detailed numbers shouldn’t be read too much into.

In March 2025, on the same day as the MoM-BH*-1 paper, another paper (de Graaff et al.) came out. It studied a bright little red dot at a redshift (a measure of distance: the bigger, the farther) of about 3.5, nicknamed “The Cliff” because the step in brightness in its split light is so big. The ratio of brightness across its step was about 6.9, about twice as strong as any distant object found before. Only MoM-BH*-1 matches it.

The researchers first tried to explain it with light from evolved stars (stars in a group that stopped making new stars some time ago). That would need stars totaling about 25 to 40 billion times the Sun’s mass packed into a small region with a radius of only about 130 light-years. That is more than 10 times more tightly packed than the densest known groups of stars. Stars would collide about 5 times a year. And even with dust acting more strongly than anything seen so far in observations or models, the shape around the step still didn’t fully fit.

On the other hand, if something shining brightly in the center is wrapped in dense, light-absorbing gas, both the step and the hydrogen absorption line could be explained with the least strain. The researchers consider this the most plausible explanation. But they write that the model and the observations still don’t match everywhere and that starlight mixed in can’t yet be ruled out, and they also raise the possibility that what is wrapped in the gas is not a black hole but very massive stars gathered at the galaxy’s center. This paper was published in the journal Astronomy & Astrophysics in 2025.

The mass of a distant black hole is usually worked out from the width of a light line (light of one set color) given off by the gas around it, and its brightness. Light from gas coming toward us shifts a little toward blue, and light from gas moving away shifts toward red, so the faster the gas moves, the more the line spreads out and the wider it gets. A heavier black hole is needed to make gas circle that fast, so the width tells the mass. This method was checked on black holes in the nearby universe.

Applying it to MoM-BH*-1 as is gives about 200 million times the Sun’s mass if dust is dimming it, or about 50 million if there is no dust. But in the black hole star idea, the light may bounce off particles and change direction many times in the dense gas (scattering), making the line look wider than it really is. Recalculating with that in mind gives about 1 million. The paper sums up the mass as about 1 to 10 million times the Sun’s and says the black hole masses of little red dots may be overestimated by a large factor. The black hole in The Cliff is estimated at about 10 million times the Sun’s mass, and it too may be overestimated.

In 2026, two studies on this question were published in Nature. A January study (Rusakov et al.) examined 12 objects in detail and concluded that in most of them, the light lines are widened because, in the dense gas, light hits electrons (one of the tiny particles that make up atoms) and changes direction as it travels. It put the black hole masses at 100,000 to 10 million times the Sun’s, about a hundredth of earlier estimates.

In contrast, a May study (Juodžbalis et al.) looked at a distant object called QSO1, which appears magnified because the gravity of something in front of it bends its light (gravitational lensing). Measuring the black hole’s mass directly from how fast the gas circles it gave about 50 million times the Sun’s mass. That agrees well with the roughly 40 million from the usual method. So it doesn’t seem that masses are overestimated for every object, and how to pin down the mass is still being studied.

There are other ideas about what the little red dots are. One is that they are galaxies tightly packed with a huge number of stars. Another is that they are active galactic nuclei (where gas falling into the black hole at a galaxy’s center glows brightly) that look red because they are wrapped in dust. The black hole star idea shares the black hole inside with the second idea, but differs in saying the red color comes from gas, not dust.

The MoM-BH*-1 paper first came out in March 2025 as a paper not yet checked by other researchers (peer review), and it was published in Nature, under a new title, on August 12, 2026. The researchers think other little red dots may also hold black hole stars inside brighter surrounding galaxies. They also write that MoM-BH*-1 is expected to merge with a heavier galaxy nearby within about 100 million years, and that the result would look like a little red dot.

Questions remain. How very heavy black holes grew so quickly in the early universe is still a puzzle. Theory predicts that a black hole wrapped in dense gas can grow faster than usual, and MoM-BH*-1 may be an example. Whether most little red dots are black hole stars, or whether other ideas fit some of them better, will be tested by future observations and research.