High-velocity stars in the galactic halo

One of the nearest 45 stars, called Kapteyn’s star, is an example of a high-velocity star moving in the space near our sun.

Our sun is a star . . .

And there are billions of other stars in our Milky Way galaxy. These are the same stars we see at night when we look in a clear dark sky. Over the scale of many human lifetimes, these stars look as if they’re standing still. But they’re really moving. All stars in our Milky Way galaxy are moving in orbit around the galaxy’s center.

Rosemary Wyse is an astronomer at Johns Hopkins University in Baltimore. She studies a component of the motion of stars called their radial velocity. That’s just their motion toward us or away from us.

Rosemary Wyse: So although we’re sitting here, orbiting the sun … and we’re going around with the sun around the galactic center, there are all these other stars that are on very high-velocity, we call them, orbits, with respect to the sun.

These high-velocity stars, as Wyse called them, tend not to reside in the disk of the galaxy, as our sun does. Instead, they’re found in what astronomers call the halo of the galaxy, like a huge cloud of stars surrounding the galactic center. Though speedy relative to the sun and other disk stars, these halo stars aren’t going fast enough to escape the gravity of the Milky Way.

Wyse told EarthSky that her work is to clock the speed of high-velocity stars. She hopes to use these measurements to find out just how much the Milky Way galaxy weighs.

Our thanks to Research Corporation, a foundation for the advancement of science.

Our thanks to:
Rosemary Wyse
Johns Hopkins University