A planet eaten from the inside is something out of science fiction, but researchers claim it might be reality. New research indicates dark matter can collapse within giant planets and produce small black holes that devour them.
How would exoplanets trap dark matter?
Superheavy dark matter particles, the study says, might get trapped within giant planets like Jupiter. The particles would lose energy over time and sink towards the center of the planet. After enormous spans of time, the particles might accumulate and collapse, creating a black hole that consumes the planet.
But this concept relies on the nature of dark matter itself. If dark matter particles annihilate one another when they touch, as some theories suggest, they would never accumulate in the huge numbers needed. Researchers are mystified because dark matter comprises 85 percent of the universe but doesn't respond to light. That is to say, it can't be regular matter such as electrons, protons or neutrons, and is invisible to telescopes.
Why can't all particles create these black holes?
For this theory to be valid, dark matter particles should be very heavy and should not annihilate. That rules out popular candidates like axions, which are predicted to have very tiny masses. "If the dark matter particles are heavy enough and don't annihilate, they may eventually collapse into a tiny black hole," said Mehrdad Phoroutan Mehr of the University of California, Riverside.
Currently, the smallest black holes we have confirmed are called stellar mass black holes, formed when giant stars die. They usually range from three to one hundred times the Sun’s mass. By contrast, these planetary black holes would be far smaller, because they would form from the mass of a planet like Jupiter, which has only one-thousandth the mass of the Sun.
The existence of such light black holes would challenge current limits, such as the Chandrasekhar limit that sets the threshold for white dwarfs and the Tolman–Oppenheimer–Volkoff limit, which divides neutron stars from black holes. The lightest black hole observed so far is 3.8 solar masses, while the heaviest neutron star is around 2.4 solar masses. A planet-sized black hole would therefore open a new category altogether.
Could these black holes be detected?
The study suggests exoplanets could be fertile hunting grounds for such objects. "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.
The research team argues that finding a black hole with the mass of a planet would strongly support the idea of superheavy non-annihilating dark matter. With over 5,000 exoplanets already confirmed, these worlds may become valuable tools in solving the mystery of dark matter.
What signals should astronomers look for?
Dark matter collecting in planets could heat them or even make them emit high-energy radiation. Similar processes have been suggested for neutron stars, where dark matter might gather and annihilate. Observing an old and cold neutron star could therefore disprove some dark matter models.
At present, existing instruments are not sensitive enough to detect these signals. Future telescopes, however, may be able to catch such faint emissions. "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," Phoroutan Mehr said.
The findings were published on 20 August in Physical Review D.
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