Astronomers at the University of California have found outflowing galactic winds with velocities up to 2,500 km per second that they detected in 29 massive galaxies to be powered by intense bursts of star formation.
Matter blasts out of the starburst galaxy M82 in this composite image (X-ray: NASA / CXC / JHU / D.Strickland; optical: NASA / ESA / STScI / AURA / the Hubble Heritage Team; IR: NASA / JPL-Caltech / Univ. of AZ / C. Engelbracht)
Galactic superwinds powered by a burst of star formation may blow gas right out of massive galaxies, shutting down their ability to make new stars.
“They’re nearly blowing themselves apart,” said Dr Aleksandar Diamond-Stanic of the University of California’s Southern California Center for Galaxy Evolution, who led the study published in the Astrophysical Journal Letters (arXiv.org version).
“Most galactic winds are more like fountains; the outflowing gas will fall back onto the galaxies. With the high-velocity winds we have observed the outflowing gas will escape the galaxy and never return.”
The objects they observed are young, bright and compact galaxies with outflowing winds of 500 to 2,500 km per second, located a few billion light years away. Initially the astronomers thought the winds might be coming from quasars, but a closer look revealed these winds emanate from entire galaxies.
These massive galaxies are in the midst of or just completing a period of star formation as intense as anyone has ever observed.
“These galactic-scale crazy-fast winds are probably driven by the really massive stars exploding and pushing out the gas around them,” said co-author Prof Alison Coil of the University of California’s Center for Astrophysics and Space Sciences. “There’s just such a high density of those stars it’s like all these bombs went off near each other at the same time. Each bomb evacuates the area around it, then the next can push gas out further until they’re evacuating gas on the scale of the whole galaxy.”
Galaxies with fast winds are also quite rare, opening up the question of whether these are unusual events or part of a common phase in the evolution of massive galaxies that is seldom observed because it is so brief.
Images show compact nuclei in three of the 29 observed massive galaxies (Diamond-Stanic et al)
Astrophysicists still lack an explanation for how and why starmaking ends. Theorists who model the evolution of galaxies often invoke supermassive black holes called active galactic nuclei, which can also generate savage winds, to explain how gas needed to form stars can be depleted.
These new observations demonstrate that black holes may not be neccesary to account for how these kinds galaxies run out of gas.
“The winds seem to be powered by the starburst,” Dr Diamond-Stanic said. “The central supermassive black hole is apparently just a spectator for these massive stellar fireworks.”
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Bibliographic information: Aleksandar M. Diamond-Stanic et al. 2012. High-velocity Outflows without AGN Feedback: Eddington-limited Star Formation in Compact Massive Galaxies. ApJ 755, L26; doi: 10.1088/2041-8205/755/2/L26
