SUBSCRIBE NOW TO SPACE TODAY PLUS PREMIUM, ONLY R$29.00 PER MONTH, LESS THAN 1 REAL PER DAY!!! In a hypothetical scenario, small primordial black holes could be captured by newly formed stars. An international team, led by researchers from the Max Institute…
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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, has now modeled the evolution of these so-called “Hawking stars” and discovered that they can have surprisingly long lifetimes, resembling normal stars in many ways. The work is published in The Astrophysical Journal.
Asteroseismology could help identify such stars, which in turn could test the existence of primordial black holes and their role as a component of dark matter.
Let’s do a scientific exercise: if we assume that a large number of very small black holes were created shortly after the Big Bang (the so-called primordial black holes), some of them could be captured during the formation of new stars. How would this affect the star during his lifetime?
“Scientists sometimes ask crazy questions 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 if such primordial black holes exist, but we can still do an interesting thought experiment.”
Primordial black holes would have formed in the early universe with a wide range of masses, from ones as small as an asteroid to thousands of solar masses. They could constitute an important component of dark matter, as well as being the seeds of supermassive black holes at the center of today’s galaxies.
With very small probability, a newly formed star could capture a black hole with the mass of an asteroid or a small moon, which would then occupy the center of the star. This star is called the “Hawking star,” named after Stephen Hawking, who first proposed this idea in a paper in the 1970s.
The black hole at the center of a Hawking star would grow only slowly, as the inflow of gas to feed the black hole is hampered by the outflow of luminosity. An international team of scientists has now modeled the evolution of this star with various initial masses for the black hole and with different accretion models for the stellar center. Their surprising result: When the black hole’s mass is small, the star is essentially indistinguishable from a normal star.
“Stars that harbor a black hole at their center can live a surprisingly long time,” says Earl Patrick Bellinger, an MPA postdoctoral fellow and now an assistant professor at Yale University who led the study. “Our Sun may even have a black hole as massive as the planet Mercury at its center without us realizing it.”
The main difference between a Hawking star and a normal star would be near the core, which would become convective due to accretion into the black hole. It would not alter the properties of the star on its surface and would escape current detection capabilities. However, it could be detectable using the relatively new field of asteroseismology, where astronomers use acoustic oscillations to probe a star’s interior.
Also in its later evolution, in the red giant phase, the black hole can lead to characteristic signatures. With future projects, such as PLATO, such objects may be discovered. However, more simulations are needed to determine the implications of placing a black hole in stars of various masses and metallicities.
If primordial black holes really did form shortly after the Big Bang, looking for Hawking stars could be one way to find them.
“Even if the Sun is used as an exercise, there is good reason to think that Hawking stars would be common in globular clusters and ultrafaint dwarf galaxies,” points out Professor Matt Caplan of Illinois State University, co-author of the study.
“This means that Hawking stars could be a tool for testing the existence of primordial black holes and their possible role as dark matter.”
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2023-12-25 16:26:28
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