An International Research Team Explores the Possibility of Black Holes at the Center of Stars
In a hypothetical scenario, small, primordial black holes could be captured by newly forming stars. An international team, led by researchers at the Max Planck Institute for Astrophysics, has now modeled the evolution of these so-called “Hawking stars” and found that they can have surprisingly long lifetimes, resembling normal stars in many aspects. The work is published in The Astrophysical Journal.
“Scientist sometimes ask crazy questions in order to learn more,” says Selma de Mink, director of the stellar department at the Max Planck Institute for Astrophysics (MPA). “We don’t even know whether such primordial black holes exist, but we can still do an interesting thought experiment.”
Primordial black holes would have formed in the very early universe with a wide range of masses, from some as small as an asteroid up to thousands of solar masses. They could constitute an important component of dark matter, as well as being the seeds for the supermassive black holes at the center of present-day galaxies.
With a very small probability, a newly forming star could capture a black hole with the mass of an asteroid or a small moon, which would then occupy the star’s center. Such a star is called a “Hawking star,” named after Stephen Hawking, who first proposed this idea in a paper in the 1970s.
The black hole at the center of such a Hawking star would grow only slowly, as the infall of gas to feed the black hole is hampered by the outflowing luminosity. An international team of scientists has now modeled the evolution of such a star with various initial masses for the black hole and with different accretions models for the stellar center. Their astonishing result: when the black hole mass is small, the star is essentially indistinguishable from a normal star.
“Stars harboring a black hole at their center can live surprisingly long,” says Earl Patrick Bellinger, MPA Postdoc and now Assistant Professor at Yale University, who led the study. “Our sun could even have a black hole as massive at the planet Mercury at its center without us noticing.”
If primordial black holes were indeed formed soon after the Big Bang, looking for Hawking stars could be one way to find them.
“Even though the sun is used an exercise, there are good reasons to think that Hawking stars would be common in globular clusters and ultra-faint dwarf galaxies,” points out Professor Matt Caplan at Illinois State University, co-author of the study.
The research offers an interesting insight into the possibility of black holes at the center of stars and the potential implications for the understanding of dark matter. Further simulations and research will be needed to explore this fascinating concept.