By Katie McKissick
National Aeronautics and Space Administration
Dark matter is very mysterious. It makes up 27 percent of our whole universe, but we know very little about it. We can’t measure it directly. It doesn’t give off light or absorb it. We do know it has gravity, though, because we can see its pull on things like stars and galaxies.
Black holes are also very mysterious. A black hole is an area of such immense gravity that nothing — not even light — can escape from it. Black holes can form at the end of some stars’ lives. The gravity holding the star together overwhelms the pressure of the hot gas, and it collapses in on itself producing a magnificent explosion. Some of the material from the star escapes in the explosion, while the rest, many times the mass of our sun, falls into an infinitely small point but keeps the same amount of gravity.
Scientists want to know more about dark matter and black holes, but they’re very hard to study. But in a strange twist, the best way to learn about dark matter and black holes may be watching both of them at the same time.
Scientists think that dark matter is probably made of tiny things called weakly interacting massive particles, which some call WIMPS for short. They hardly ever run into each other in wide-open outer space. But things get crowded around the gravitational pull of a black hole. There, it’s much more likely that WIMPS could smash into each other. This is called annihilation. When it happens, WIMPS can release a burst of energy in the form of gamma rays. These are extremely high-energy rays, a thousand times more powerful than X-rays. Some of those gamma rays could escape the area around the black hole. They could make it all the way to us, and we could see them with our telescopes.
Right now, this is an idea based on computer simulations and lots of math. But if it turns out we can watch black holes and dark matter interact, we could learn a lot about both of these mysterious astronomical oddities. Who would have ever thought that combining two mysteries could lead to new answers?
This image shows the gamma-ray signal from the computer simulation of annihilations of dark matter particles. Lighter colors show higher energies. The highest-energy gamma rays come from the center of the crescent shape on the left, closest to the black hole’s equator and event horizon. The gamma rays with the greatest chances of escape are on the side of the black hole that spins toward us. Such lopsided emission is typical for a rotating black hole. Credit: NASA Goddard/Jeremy Schnittman
