In a hypothetical scenario, small primordial black holes could be captured by newly formed stars. An international team led by researchers from the Max Planck Institute for Astrophysics modeled the evolution of these stars, called “Hawking stars,” and found that they can have surprisingly long lifetimes, similar in many ways to ordinary stars. The study was published on: Astrophysical Journal.

Astroseismology can help identify such stars, which can test the existence of primordial black holes and their role as a component of dark matter. Let’s do a scientific study: Assuming that a large number of very small black holes (also known as primordial black holes) were formed immediately after the Big Bang, some of them may have been captured during the formation of new stars. How will this affect the star over its lifetime?

“Scientists sometimes ask crazy questions to find out more,” says Selma de Minck, director of the star division at the Max Planck Institute for Astrophysics (MPA). “We don’t even know if such primitive black holes exist, but we can still make an interesting thought experiment.”

Primordial black holes must have formed in the very early universe, with a wide range of masses from as small as an asteroid to thousands of solar masses. They may constitute an important component of dark matter and may also be the seeds of supermassive black holes at the centers of modern galaxies.

There is a very small chance that a newly formed star may capture a black hole the mass of an asteroid or a small moon, and this black hole may then occupy the center of the star. Such a star is called a “Hawking star” in memory of Stephen Hawking, who first proposed the idea in a paper in the 1970s.

A black hole at the center of such a Hawking star grows slowly because the flow of gas powering the black hole interferes with the original brightness. Now, an international team of scientists has modeled the evolution of such a star, with different initial masses for the black hole and different accretion patterns for the star center. The striking result: When the mass of the black hole is small, the star is almost indistinguishable from an ordinary star.

“Stars with black holes at their centers can live surprisingly long,” says Earl Patrick Bellinger, an MPA postdoctoral researcher who led the study and now an associate professor at Yale University. “Our Sun may even have a black hole of similar size at the center of the planet Mercury without us noticing.”

The main difference between such a Hawking star and an ordinary star is that it will be close to the core, which will become convective due to accretion onto the black hole. This does not change the features of the star on its surface and eliminates current detection capabilities. However, it can be detected by asteroseismology, a relatively new field in which astronomers use acoustic vibrations to probe the interior of a star.

Also in their late evolution, during the red giant stage, a black hole can give rise to characteristic features. Such objects may be discovered with future projects such as PLATO. However, more simulations are needed to determine the consequences of placing black holes in stars of different masses and metallicities. If primordial black holes formed shortly after the Big Bang, one way to find them might be to look for Hawking stars.

“Although using the Sun as an exercise, there is good reason to believe that Hawking stars are often found in globular clusters and extremely faint dwarf galaxies,” said University of Illinois Professor Matt Kaplan, one of the study’s authors.

“This means that Hawking stars could be a tool to test both the existence of primordial black holes and their possible role as dark matter.”