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?
- Could A Star Orbit A Planet? - Just For Fun
- Supertranslations And Eternal Ghosts: Black Holes No Closer To Being Understood
- Bel's Temple in Palmyra Is No More
- Blade Runner: The Science In The Fiction
- If Happy Meal Law Passes, NYC Kids Will Frown
- Highlights From ICNFP 2015
- Innate GMO Potato Deregulated By USDA
- "Could the Run 251244 Event 204117665 pp -> ZZ -> 2e2mu = 4L event be due to a Higgs mass state..."
- "There doesn't appear to be a particularly notable degree of collegiality here. Science isn't a..."
- "It is hard to admit it, but the suffering and death of civilians in Syria and elsewhere usually..."
- "We are living 21 century, everybody are thinking invention new technology. In this situation this..."
- "I wrote an article about this just today - why I think AI should not have emotions - and only very..."
- Not All Expensive Drugs Are Equal
- Conundrum Confronts DCIS Breast Cancer Patients
- Germany Rightly Skewered for GMO Nonsense; Kudos for WSJ
- Expect Only Frowns if Silly Happy Meal Law Passes
- “Shock Therapy” – Not a Cuckoo’s Nest, a Valid Depression Rx
- Innate: Simplot genetically engineered potato gets USDA nod for deregulation
- Relativistic Heavy Ion Collider confirms tiny drops of early universe 'perfect' fluid
- Magnetic fields provide a new way to communicate wirelessly
- With tobacco, what you don't know can kill you sooner
- Isthminia panamensis: New species of ancient river dolphin discovered
- Smoking prevalence stays the same but people who want to quit are up