New research suggests that dark matter could gather over vast periods of time at the heart of Jupiter-sized planets, creating black holes that eat these worlds from within. This striking concept may mean extrasolar planets, or “exoplanets,” could be used to study the mystery of dark matter.
In this new model, superheavy dark matter particles could be trapped by exoplanets, losing energy and drifting toward that world’s core. Once there, these superheavy dark matter particles accumulate until they collapse, forming a black hole. This black hole then ravenously eats its way out of its host planet.
This new dark matter/black hole theory doesn’t work with all recipes of black holes, however. For instance, if dark matter particles meet and annihilate each other as some models suggest (as happens when electrons meet their antiparticles, positrons), then it wouldn’t be possible for them to gather in quantities needed to collapse and birth a black hole.
Dark matter is troubling to scientists because, despite the fact that it accounts for 85% of the “stuff” in the universe, we have no idea what it is. The fact that dark matter doesn’t interact with light means it can’t be made up the electrons, protons, and neutrons that form the atoms that compose everything we see around us: the universe’s ordinary matter — stars, planets, moons, living things, etc.. This lack of interaction with electromagnetic radiation also makes dark matter effectively invisible. This puzzle has led to scientists to suggest all types of different particles that might possibly account for dark matter, many of which have different properties.
But there’s another caveat to the dark matter recipe needed for this process to occur. The constituent particles would have to have very large masses. This rules out one of the most highly favored dark matter candidate particles, the axion, a hypothetical particle with a very small mass.
“If the dark matter particles are heavy enough and don’t annihilate, they may eventually collapse into a tiny black hole,” University of California, Riverside researcher Mehrdad Phoroutan Mehr said in a statement. “If the dark matter particles are heavy enough and don’t annihilate, they may eventually collapse into a tiny black hole.”
How are dark matter black holes born?
Currently, the lightest black holes we are aware of are so-called stellar mass black holes. These are thought to have masses between around 3 and 100 times the mass of the sun. The logic behind this is sound, as these black holes are born when massive stars run out of nuclear fuel at the end of their lives. As a supernova explosion ejects the outer layers of these stars, their stellar cores collapse.
That means the mass range of stellar mass black holes is set by the masses of the progenitor stars that created them. Furthermore, the lower mass is set by the fact that stars with less than 1.4 times the mass of the sun (a value known as the Chandrasekhar limit) can’t go supernova, so can’t birth a black hole or a neutron star. Instead, these stars leave behind a white dwarf.
There’s another mass limit to consider, too. The Tolman–Oppenheimer–Volkoff (TOV) limit divides stellar cores that create black holes and those that birth neutron stars. Though less well defined than the Chandrasekhar limit, the TOV limit suggests that after ejecting most of its matter, a stellar core needs to have at least 2.2 to 2.9 times the mass of the sun to form a black hole.
This limit is uncertain, as currently the lightest black hole we have detected and confirmed is around 3.8 times the mass of the sun, while the heaviest neutron star ever detected weighs in at 2.4 solar masses.
These planet-eating black holes would be much more diminutive than even the lightest stellar mass black hole if they adopt the mass of the planet they devour. The team proposes that this process could occur within planets with masses the same as Jupiter, which has around 0.001 times the mass of the sun.
“In gaseous exoplanets of various sizes, temperatures, and densities, black holes could form on observable timescales, potentially even generating multiple black holes in a single exoplanet’s lifetime,” Phoroutan-Mehr said. “These results show how exoplanet surveys could be used to hunt for superheavy dark matter particles, especially in regions hypothesized to be rich in dark matter like our Milky Way’s galactic center.”
Of course, other than watching a planet devoured from the inside out, the creation pathway of stellar mass black holes and the TOV limit means that detecting a black hole with a mass less than the sun could support the team’s theory.
“Discovering a black hole with the mass of a planet would be a major breakthrough,” Phoroutan-Mehr said. “If astronomers were to discover a population of planet-sized black holes, it could offer strong evidence in favor of the superheavy non-annihilating dark matter model.”
This new theory, combined with the growing catalog of exoplanets, with over 5,000 worlds beyond the solar system, means these planets can now be added to the celestial bodies that have been suggested as dark matter probes.
An example of that is the suggestion that certain dark matter candidates could become trapped in neutron stars, gathering and gradually annihilating each other thus heating these stellar remnants.
“So, if we were to observe an old and cold neutron star, it could rule out certain properties of dark matter, since dark matter is theoretically expected to heat them up,” Phoroutan-Mehr said.
Dark matter trapping within exoplanets could also cause heating within these worlds or it could cause them to emit high-energy radiation.
“Today’s instruments aren’t sensitive enough to detect these signals. Future telescopes and space missions may be able to pick them up,” Phoroutan-Mehr concluded. “As we continue to collect more data and examine individual planets in more detail, exoplanets may offer crucial insights into the nature of dark matter.”
The team’s research was published on Wednesday (Aug. 20) in the journal Physical Review D.
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