When clusters of galaxies collide, the hot gas that fills the space between the stars in those galaxies also collides and splatters in all directions with a motion akin to splashes of water. Dark matter makes up about 90% of the matter in galaxy clusters: Does it splatter like water as well? New research suggests that no, dark matter does not splatter when clusters of galaxies collide, and this finding limits the kinds of particles that can make up dark matter.
Dark matter may not be part of a “dark sector” of particles that mirrors regular matter, as some theories suggest, say scientists studying collisions of galaxy clusters. When clusters of galaxies collide, the hot gas that fills the space between the stars in those galaxies also collides and splatters in all directions with a motion akin to splashes of water. Dark matter makes up about 90% of the matter in galaxy clusters: Does it splatter like water as well?
Our galaxy contains hundreds of billions of stars, and there are hundreds of billions of galaxies in the observable universe. There’s also a lot of gas and dust between the stars and the galaxies. But all of those stars, galaxies, gas and dust make up only about 10% to 15% of the matter in the universe.
Scientists have tried to use these galaxy cluster crashes to study dark matter for decades, but improved techniques for observing the different components of those mergers has inspired a revival, he said. “We wanted to have a big statistical sample that tries to average over all these different merging scenarios, and try to get a statistical idea of what dark matter is doing during these cosmological crashes.”
However, in between the galaxies is a thick gas full of charged particles. When the galaxy clusters collide, the gas splatters in all directions, like water splashed from a puddle, Harvey said.
Dark matter doesn’t radiate or reflect light, but its gravitational pull can help scientists “see” it. Light that is passing near a very massive object will bend around it, in an effect called gravitational lensing. Scientists can see the bending of the light and use that to figure out where dark matter is present.
Some theories of dark matter posit that it is part of a “dark sector” that is sort of like a mirror of the regular universe — in other words, that it contains dark versions of regular matter particles, like dark photons and dark electrons. In some of those theories, dark matter might be made up of dark protons.
“Chances are that dark matter is not made up of dark protons interacting with dark protons, and chances are, there is not a mirror universe out there with these dark particles,” Harvey said. “The caveat is that theorists could change some of their parameters, so the field is still open to what [dark matter] could be, but we’re narrowing it down.” Read more…