Astronomers have  debated for decades how massive galaxies rapidly evolve from active  star-forming machines to star-starved graveyards. Previous observations  of these galaxies reveal geysers of gas shooting into space at up to 2  million miles an hour. Astronomers have suspected 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.     

   Now an analysis of 12 merging  galaxies at the end of their star-birthing frenzy is showing that the  stars themselves are turning out the lights on their own star-making  party. This happened when the universe was half its current age of 13.7  billion years.      

   "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," explained 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."      

   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.      

   In such  small regions of space, these galaxies are forming a few hundred suns a  year. (By comparison, the Milky Way makes only about one sun a year.)  This makes for a rowdy party that wears itself out quickly, in only a  few tens of millions of years. 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.      

  For a little more insight into the project see this：  

http://hubblesite.org/newscenter/archive/releases/2014/48/full/