The universe we can 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 have 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 analyzed 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 color. Credit: A. Bluck.
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, 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 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. Big bulges mean big black holes and these can put an end to star formation,” Asa said.
Published in Monthly Notices of the Royal Astronomical Society.
- PHYSICAL SCIENCES
- EARTH SCIENCES
- LIFE SCIENCES
- SOCIAL SCIENCES
Subscribe to the newsletter
Stay in touch with the scientific world!
Know Science And Want To Write?
- World Did NOT End On 29th July! AWFUL "Silly Season" Story - Journalists Please Be More Responsible
- Why An Extra Planet Can't Be Hidden Behind The Sun Or Above The South Pole
- My Applied National Security Paper. Being President Isn't For Idiots.
- Mind The (Risk Perception) Gap On BPA
- Why Do Consumers Participate In 'green' Programs?
- SYRINA: A Trojan Horse For Endocrine Disrupting Chemicals?
- Hugh Hefner's Wife Was Not Poisoned By Breast Implants
- "Hi mr walker glad were still here apparently that one yesterday wasent anything to do with nibiru..."
- "It's a bit smaller. Chicxulub was probably about 10 km in diameter, while 1950 DA is 1.1 km in..."
- "You forgot something there donaldtrump2, the most important US Constitutional right: buy more guns..."
- "Is 1950 DA bigger than chicxclub meteor sorry that I butchered the word ..."
- "I don't think iran wants nuclear weapons.and they are signatories of NPT.if they desire nuclear..."
- Tracking how HIV disrupts immune system informs vaccine development
- Green monkeys acquired Staphylococcus aureus from humans
- Researchers find molecular switch that triggers bacterial pathogenicity
- Scientists identify immunological profiles of people who make powerful HIV antibodies
- Breastfeeding associated with better brain development and neurocognitive outcomes