Astronomers using NASA's Hubble Space Telescope and Chandra X-ray Observatory have uncovered young, massive and compact galaxies that are dying earlier than expected.
The researchers said that the firestorm of star birth has blasted out most of the remaining gaseous fuel needed to make future generations of stars and are on track to possibly becoming so-called "red and dead galaxies," composed only of aging stars.
Scientists had earlier believed that powerful monster black holes lurking at the centers of the galaxies triggered the gaseous outflows and shut down star birth by blowing out any remaining fuel, but the recent study shows that the stars themselves are turning out the lights on their own star-making party, which happened when the universe was half its current age of 13.7 billion years.
Paul Sell of Texas Tech University in Lubbock, lead author of a science paper, said that the common belief was that stars cannot drive high-velocity outflows in galaxies; only more powerful supermassive black holes can do that but it was found that the stars can actually produce the velocities of the outflows alone without needing to invoke the black hole.
Team member Christy Tremonti of the University of Wisconsin-Madison first identified the galaxies from the Sloan Digital Sky Survey as post-starburst objects spouting high-speed gaseous fountains. The sharp visible-light views from Hubble's Wide Field Camera 3 show that the outflows are arising from the most compact galaxies yet found. These galaxies contain as much mass as our Milky Way galaxy, but packed into a much smaller area. The smallest galaxies are about 650 light-years across.
One reason for the stellar shutdown is that the gas rapidly heats up, becoming too hot to contract under gravity to form new stars. Another possibility is that the star-birthing frenzy blasts out most of the star-making gas via powerful stellar winds.
The researchers said that the biggest surprise from Hubble was the realization that the newly formed stars were born so close together and the extreme physical conditions at the centers of these galaxies explain how they can expel gas at millions of miles per hour.
They found that it was the powerful stellar winds from the most massive and short-lived stars at the end of their lives, combined with their explosive deaths as supernovae.
Based on their analysis of the Hubble and Chandra data, team members suggest that the "party begins" when two gas-rich galaxies collide, funneling a torrent of cold gas into the merging galaxies' compact center. The large amount of gas compressed into the small space ignites the birth of numerous stars. The energy from the stellar firestorm then blows out the leftover gas, quenching further star formation.
The study was published in the Royal Astronomical Society.
