Dark matter may not be part of a "dark sector" of particles that mirrors regular matter, as some theories suggest, according to 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 percent of the matter in galaxy clusters: Does it splatter like water as well?
New research suggests that it doesn't, and this finding limits the kinds of particles that can make up dark matter. Specifically, the authors of the newly published research say it's unlikely that dark matter is part of an entire "dark sector" — a mirror version of the visible universe. [Infographic: Dark Matter Mystery Explained]
David Harvey, a postdoctoral researcher at the Swiss Federal Institute of Technology Lausanne, is one of many scientists currently trying to figure out what dark matter is made of. There are lots of ways to go about this, and Harvey decided to see what happens when dark matter collides with itself.
To do this, Harvey and his colleagues at the University of Edinburgh, where Harvey did his Ph.D. work, looked at collisions involving entire clusters of galaxies, where as much as 90 percent of the mass involved in the collision is dark matter.
The researchers gathered data on 30 galaxy-cluster collisions, drawn from observations by the Hubble Space Telescope and Chandra X-ray Observatory. They traced the movement of dark matter by looking for gravitational lensing effects. That's how they determined that the dark matter didn't splatter. [Chandra Observatory's X-ray Universe in Photos]
The findings tell scientists something about what dark matter might be made of — or more precisely, what it's probably not made of. "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.