"Dark matter asteroids" could be spotted colliding with stars
Although it should be extremely common in the universe, dark matter has proven tricky to detect. Now researchers have proposed an intriguing new method to spot it – looking for shock waves as dark matter “asteroids” collide with stars.
Dark matter earns its somewhat spooky name because it doesn’t reflect, absorb or emit light, which of course makes it difficult to observe. But scientists are pretty sure it’s there because it does interact with light and regular matter through its immense gravitational influence. This affects the movements of stars and other astronomical objects, and from this it was calculated that there should be five times more dark matter in the universe than regular matter.
In a new study, researchers from the SLAC National Accelerator Laboratory and Université Paris Saclay propose a brand new way to potentially detect dark matter out in the cosmos. The team says that as dark matter passes through stars, it would create unique signals that could be picked up by telescopes.
Part of the challenge of detecting dark matter is that many of its properties remain unknown, including the mass of the particles that make it up. For this study, the team focused on clumps that would have the equivalent mass of an asteroid.
"Most experiments have searched for dark matter made of separate particles, each about as heavy as an atomic nucleus, or clumps about as massive as planets or stars," said Kevin Zhou, an author of the study, in an interview with Phys.org. "We were interested in the intermediate case of asteroid-sized dark matter, which had been thought to be hard to test experimentally, since dark asteroids would be too rare to impact Earth, but too small to see in space.”
If they exist, these dark matter asteroids would be expected to pass through astronomical objects occasionally, and that might be how they ultimately reveal themselves. The team says that as a dark matter asteroid hurtles through a star at supersonic speeds, it would create shock waves. When these waves reach the star’s surface, it would produce a short-lived signal of optical, ultraviolet and X-ray light, which could be detected by telescopes.
One problem is that these signals would resemble flares that stars naturally give off, but the team says that this could be accounted for by focusing the search on stars with low UV emissions, such as orange dwarfs, and those located in dense globular clusters where there’s a higher concentration of dark matter. This would make it easier to see a spike in signals above the expected background that flares would produce.
The team says that existing and upcoming telescopes could be capable of picking up these signals, and they wouldn’t even need to be hunting for them specifically – astronomers could pick them out of other data.
In a way, this intriguing new idea is like a scaled-up version of the types of experiments already searching for dark matter here on Earth. Many of these experiments use huge tanks of exotic fluids stored in quiet, calm conditions, with the idea that if a dark matter particle happens to pass through it could bump the nucleus of an atom in a tank, creating a flash of light that can be detected by instruments. This new technique works in a similar way, but swaps atoms for stars, and dark matter particles for asteroid-sized clumps.
Other studies have proposed other ways to potentially spot signs of dark matter out in the cosmos, including unexplained X-ray bursts in galaxies, flashes of light around neutron stars, or even clouds of dark matter dragging on black holes and slowing their spins.
With the search for dark matter encompassing so many very different ideas, there’s a chance that we might get some intriguing new clues in the near future that could unravel one of the most puzzling cosmic mysteries of all time.
The new study was published in the journal Physical Review Letters.