Tonight's Sky
Sun
Sun
Moon
Moon
Mercury
Mercury
Venus
Venus
Mars
Mars
Jupiter
Jupiter
Saturn
Saturn

Tonight's Sky — Change location

OR

Searching...

Tonight's Sky — Select location

Tonight's Sky — Enter coordinates

° '
° '

How black holes shape galaxies

A group of astronomers has found a relatively simple relationship between the color of a galaxy and the size of its bulge — the more massive the bulge, the redder the galaxy.
RELATED TOPICS: GALAXIES | BLACK HOLES
Galaxies
Images of a small fraction of the galaxies analyzed in the new study. The galaxies are ordered by total mass of stars (from bottom to top) and by "bulge to total stellar mass ratio" (from left to right). Galaxies that appear redder have high values for both of these measurements, meaning that the mass of the bulge — and central black hole — determines their color.
A. Bluck
The universe we see is made up of billions of galaxies, each containing anywhere from hundreds of thousands to hundreds of billions of stars. Large numbers of galaxies are elliptical in shape, red, and mostly made up of old stars. Another, more familiar type is the spiral where arms wind out in a blue thin disk from a central red bulge. On average, stars in spiral galaxies tend to be much younger than those in ellipticals.

Now a group of astronomers led by Asa Bluck of the University of Victoria in Canada has found a relatively simple relationship between the color of a galaxy and the size of its bulge — the more massive the bulge, the redder the galaxy.

Asa and his team used data from the Sloan Digital Sky Survey to group together over half a million galaxies of all different colors, shapes, and masses. They then used pattern-recognition software to measure the shape of each one and see how the proportion of red stars in a galaxy varies with its other properties.

They found that the mass in the central bulge — regardless of how big the disk surrounding it may be — is the key to knowing the color of the whole galaxy. Above a given bulge mass, galaxies are red and have no new young stars.

Almost all galaxies have supermassive black holes at their centers. The mass of the bulge is closely related to the mass of the black hole — the more massive the black hole, the more energy is released into the surrounding galaxy in the form of powerful jets and X-ray emission. This can blow away and heat up gas, stopping new stars from forming.

“A relatively simple result, that large galaxy bulges mean red galaxies, has profound consequences,” said Asa. “Big bulges mean big black holes, and these can put an end to star formation.”
0

JOIN THE DISCUSSION

Read and share your comments on this article
Comment on this article
Want to leave a comment?
Only registered members of Astronomy.com are allowed to comment on this article. Registration is FREE and only takes a couple minutes.

Login or Register now.
0 comments
ADVERTISEMENT

FREE EMAIL NEWSLETTER

Receive news, sky-event information, observing tips, and more from Astronomy's weekly email newsletter.

ADVERTISEMENT
ADVERTISEMENT
BoxProductcovernov

Click here to receive a FREE e-Guide exclusively from Astronomy magazine.

Find us on Facebook

Loading...