[Music]
Narrator: Dark matter makes up about 27 percent
of the cosmos, but so far no one knows what it is.
Dark matter neither emits nor absorbs light and it
interacts with the rest of the universe primarily through gravity.
In fact, it's thought dark matter traced the initial framework of the
cosmos, attracting normal matter that formed stars and galaxies.
Black holes are astronomical objects famed for their
extreme gravity. Jeremy Schnittman, an astrophysicist at
NASA's Goddard Space Flight Center, wondered if they could serve as a kind of
laboratory for exploring different dark matter models. [Dr. Schnittman]: The leading
particle physics model for dark matter is called weakly
interacting massive particles, or also known as WIMPS. These guys just
fly through the universe without even bumping into anything
or each other. The idea of two WIMPS coming together,
annihilating, and forming gamma rays, is kind of like two bullets hitting
head-on in a crossfire--it's very rare. But when you
go to the area around a supermassive black hole, we expect the
density to be much higher so the probability of annihilation is much higher
and thus detection with a gamma-ray telescope.
Narrator: In Schnittman's computer simulation, a population
of dark matter particles orbits a rapidly spinning black hole.
Close in, at the brink of the black hole's event horizon, the particles
are orbiting at nearly the speed of light. The lightly shaded region
farther out is the ergosphere, a zone where all particles are forced
to move in the same direction as the black hole's spin.
The concentrated dark matter collides and makes gamma rays,
but not all of this light can escape the ergosphere. The gamma rays
most likely to make it out come from the left side, where the black hole spins
toward us. The result is an asymmetric glow.
The highest energy gamma rays come from the center of this region,
corresponding to the black hole's equator. Schnittman's work has
uncovered previously overlooked orbits that can produced extremely energetic
gamma rays, and has shown that the peak energy attainable for this escaping light
is a strong function of the black hole's rotation.
So far, the initial work is focusing on setting upper limits on dark matter
annihilation rates by looking at otherwise quiescent galaxies. But Schnittman's
ultimate ambition is nothing short of an unambiguous detection of dark matter
annihilation around supermassive black holes. [Dr. Schnittman]: To me,
dark matter, black holes, two of the most elusive things in the
universe coming together to help explain each other
is quite poetic. [Music]
[Beeping]