Black holes in the Galactic Center
center of the Milky Way there is a supermassive black hole about four
million times more massive than our own Sun. It was first detected as
a point like source in radio waves and named Sgr A*
then it has been detected in the submillimeter, infrared, and x-ray wavebands.
The most interesting and revealing discovery to date, however, has
been the motion of young stars around it. Just as the planets move
around the Sun, and the Moon around Earth, these stars trace out the
gravitational pull of the supermassive black hole revealing its mass
Surrounding Sgr A*
is also a cusp of millions
of stars and, we suspect, tens of thousands of smaller, stellar-mass
black holes. With Bence Kocsis and Avi Loeb, I determined how these
black holes should interact with each other and the stars to form such
a cusp if the black holes don't all have exactly the same mass. These
stars and black holes zoom by each other, sometimes
producing gravitational wave sources
as I showed with Avi Loeb, othertimes kicking out stars in to the rest
of the Milky Way as hypervelocity stars. Hypervelocity stars are
stars moving so fast, that they will escape from the gravitational
pull of the Milky Way and never return. Their discovery in 2005 by
Warren Brown and collaborators has opened a new window into the
galactic center, since they likely can only reach such high velocity
in the environment of a supermassive black hole like Sgr A*
either from stellar mass black holes or when a tight binary is tidally
disrupted by the supermassive black hole. Blake Sherwin, with Avi
Loeb and me, showed that we might even find hypervelocity stars
ejected from our neighbor, the Andromeda Galaxy.