Featured Research

from universities, journals, and other organizations

Red stars and big bulges: How black holes shape galaxies

Date:
April 22, 2014
Source:
Royal Astronomical Society (RAS)
Summary:
The universe we can see is made up of thousands of millions 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 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.

Images of a small fraction of the galaxies analysed in the new study. The galaxies are ordered by total mass of stars (rising from bottom to top) and by ‘bulge to total stellar mass ratio’ (rising 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 colour.
Credit: A. Bluck

The universe we can see is made up of thousands of millions 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 have found a (relatively) simple relationship between the colour of a galaxy and the size of its bulge: the more massive the bulge the redder the galaxy.

The researchers publish their results in the Oxford University Press journal Monthly Notices of the Royal Astronomical Society.

Asa and his team used data from the Sloan Digital Sky Survey to group together over half a million galaxies of all different colours, shapes, and masses. They then used pattern recognition software to measure the shape of each one, to 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 colour 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 centres. 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.

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


Story Source:

The above story is based on materials provided by Royal Astronomical Society (RAS). Note: Materials may be edited for content and length.


Journal Reference:

  1. Asa F. L. Bluck, J. Trevor Mendel, Sara L. Ellison, Jorge Moreno, Luc Simard, David R. Patton, Else Starkenburg. Bulge mass is king: The dominant role of the bulge in determining the fraction of passive galaxies in the Sloan Digital Sky Survey. Monthly Notices of the Royal Astronomical Society, 2014 [link]

Cite This Page:

Royal Astronomical Society (RAS). "Red stars and big bulges: How black holes shape galaxies." ScienceDaily. ScienceDaily, 22 April 2014. <www.sciencedaily.com/releases/2014/04/140422084655.htm>.
Royal Astronomical Society (RAS). (2014, April 22). Red stars and big bulges: How black holes shape galaxies. ScienceDaily. Retrieved October 20, 2014 from www.sciencedaily.com/releases/2014/04/140422084655.htm
Royal Astronomical Society (RAS). "Red stars and big bulges: How black holes shape galaxies." ScienceDaily. www.sciencedaily.com/releases/2014/04/140422084655.htm (accessed October 20, 2014).

Share This



More Space & Time News

Monday, October 20, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Latin America Launches Communications Satellite

Latin America Launches Communications Satellite

AFP (Oct. 17, 2014) Argentina launches a home-built satellite, a first for Latin America. It will ride a French-made Ariane 5 rocket into orbit, and will provide cell phone, digital TV, Internet and data services to the lower half of South America. Duration: 00:41 Video provided by AFP
Powered by NewsLook.com
This Week @ NASA, October 17, 2014

This Week @ NASA, October 17, 2014

NASA (Oct. 17, 2014) Power spacewalk, MAVEN’s “First Light”, Hubble finds extremely distant galaxy and more... Video provided by NASA
Powered by NewsLook.com
Saturn's 'Death Star' Moon Might Have A Hidden Ocean

Saturn's 'Death Star' Moon Might Have A Hidden Ocean

Newsy (Oct. 17, 2014) The smallest of Saturn's main moons, Mimas, wobbles as it orbits. Research reveals it might be due to a global ocean underneath its icy surface. Video provided by Newsy
Powered by NewsLook.com
Comet Set for Rare Close Shave With Mars

Comet Set for Rare Close Shave With Mars

AFP (Oct. 16, 2014) A fast-moving comet is about to shave by Mars for a once-in-a-million-years encounter that a flurry of spacecraft around the Red Planet hope to capture and photograph, NASA said. Video provided by AFP
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:

Breaking News:

Strange & Offbeat Stories


Space & Time

Matter & Energy

Computers & Math

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile: iPhone Android Web
Follow: Facebook Twitter Google+
Subscribe: RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins