Researchers have spotted young galaxies that have stopped star production prematurely.
An unusually violent star-making process has used up all of the fuel needed to make a future generation of stars, and now these depleted galaxies are on their way to becoming what has been referred to as "red and dead galaxies," which are made up of only elderly stars, the Space Telescope Science Institute (STScI) reported. The findings were made using NASA's Hubble Wide Field Camera 3.
For decades researchers have wondered what triggered galaxies to stop forming stars, and mysterious geysers of gas have seemed to hold the answer. Researchers thought these features suggest massive black holes at the center of the galaxies trigger a gaseous outflow, resulting in a permanent halt in star production.
A recent analysis looked at 12 merging galaxies at the tail end of their star birth and observed that they actually shut themselves off.
"Before our study, the common belief was that stars cannot drive high-velocity outflows in galaxies; only more powerful supermassive black holes can do that," said Paul Sell of Texas Tech University in Lubbock, lead author of a science paper describing the study's results. "Through our analysis we found that if you have a compact enough starburst, which Hubble showed was the case with these galaxies, you can actually produce the velocities of the outflows we observed from the stars alone without needing to invoke the black hole."
Researchers observed outflows from some of the most compact galaxies, which form about a hundred suns a year for what is predicted to be only a few tens of millions of years. After that stellar shutdown occurs because gas rapidly heats up, becoming too hot to form new stars under the state of gravity.
"The biggest surprise from Hubble was the realization that the newly formed stars were born so close together," said team member Aleks Diamond-Stanic of the University of Wisconsin-Madison. "The extreme physical conditions at the centers of these galaxies explain how they can expel gas at millions of miles per hour."
Through observations of the Hubble data and that from the Chandra X-ray Observatory the researchers pinpointed powerful stellar winds from star deaths combined with supernovae as the source of the outflows rather than black holes.The findings suggest that when two gas-rich galaxies collide a funnel of cold gas occurs at the galaxy's center, which spurs a massive star birth. This gas can then blow over, putting an abrupt halt to the star birth.
"If you stop the flow of cold gas to form stars, that's it," Sell said. "The stars stop forming, and the galaxy rapidly evolves and may eventually become a red, dead elliptical galaxy. These extreme starbursts are quite rare, however, so they may not grow into the typical giant elliptical galaxies seen in our nearby galactic neighborhood. They may, instead, be more compact."
