Balls of gas with a black hole at their centre could glow like a star

Shutterstock / Nazarii_Neshcherenskyi

The early universe appears to be littered with enormous star-like balls of gas powered by a black hole at their core, a finding that has taken astronomers by surprise and might solve one of the biggest mysteries thrown up by the discoveries of the James Webb Space Telescope (JWST).

When JWST first started looking back to the universe’s first billion years, astronomers found a group of what looked like extremely compact, red and very bright galaxies that are unlike any we can see in our local universe. The most popular explanations for these so-called little red dots (LRDs) proposed they were either supermassive black holes with dust swirling around them, or galaxies very densely packed full of stars – but neither explanation fully made sense of the light that JWST was detecting.

Earlier this year, astronomers proposed instead that LRDs were dense spheres of gas with a black hole at their centre, called black hole stars. “When material falls into the black hole, a lot of gravitational energy is released, and this could make the whole ball of gas around it glow like a star,” says Anna de Graaff at Harvard University. Although the energy doesn’t come from nuclear fusion, as in a regular star, the end effect is a similar glowing ball of dense gas, just on a far bigger scale, billions of times brighter than our sun, says de Graaff.

However, while there were some promising LRDs that supported this interpretation, it was still controversial.

Now, de Graaff and her colleagues have analysed the widest sample of LRDs since JWST began its observations, including more than a hundred galaxies, and concluded that they are best explained by star-like objects, or black hole stars. “The name black hole star is, for sure, still controversial, but I do think that there is now a decent consensus in the community that we are looking at an accreting black hole that’s enshrouded in dense gas,” says de Graaff.

When the team looked at the brightness of light at different frequencies, called a spectrum, coming from the LRDs, the patterns best matched light coming from a single, relatively smooth surface, called a blackbody. This is also how stars appear, in contrast to the more complicated and spiky spectra seen from galaxies, which produce their light from a combination of stars, dust, gas and a central black hole.

“The black hole star model has been around for a while but was thought to be so weird and out there, but it actually does seem to work and make the most sense,” says at the American Museum of Natural History in New York.