New measurements reveal that some of the earliest galaxies in the universe produced winds so forceful and persistent that they blew material from one galaxy to another.
By redistributing some 20 percent of the ordinary, visible matter when the universe was just 2 billion years old, these superwinds may have profoundly influenced the evolution of future generations of galaxies, says Kurt L. Adelberger of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass. The winds could also help solve several persistent puzzles posed by the leading theory of galaxy formation.
Adelberger presented the findings last week in Cozumel, Mexico, at a conference on galaxy evolution. He and his colleagues Charles C. Steidel and Alice E. Shapley of the California Institute of Technology in Pasadena and Max Pettini of the University of Cambridge in England base their view on the spectra of light emitted and absorbed by galaxies that date from a time when the universe was less than one-fifth its current age.
Previous studies by Steidel, who pioneered an efficient technique to find distant galaxies (SN: 2/7/98, p. 92), had identified some 1,000 galaxies from the early universe. Two years ago, the research team established that many of these galaxies harbored strong winds. But whether the winds had enough oomph to escape the galaxies and push around intergalactic material remained an open question.
Several lines of evidence now indicate the winds were indeed that powerful. The team’s analysis of starlight absorbed by gas within the galaxies shows that the gas was flowing outward at some 600 kilometers per second.
About a dozen of the early galaxies are pierced by the beacons of background quasars, enabling the researchers to measure the abundance of atomic hydrogen just outside the galaxies. Within 1.5 million light-years of the galaxies, they found significantly less atomic hydrogen than the cosmic average.
Adelberger’s team argues that a succession of some 100 billion supernovas exploding in each of the galaxies–the aftermath of intense waves of starbirth–created powerful winds that may have lasted for 100 million years.
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Such winds would have zoomed out of their home galaxies, blowing hydrogen from the immediate neighborhood.
The researchers found an excess of hydrogen at distances some 3 to 15 million light-years from clusters of the galaxies. The astronomers suggest that the winds peter out at these distances and deposit their hydrogen cargo.
Forged inside stars, carbon is also carried outward by supernova winds. The new data reveal an abundance of carbon in the same regions where the winds have unloaded their hydrogen.
Before superwinds, says Adelberger, visible matter was virtually imprisoned by the gravity of dark matter–the invisible material thought to account for more than 90 percent of the mass of the cosmos. Wherever dark matter clumped, visible matter followed.
Dark matter reacts only to gravity. Unlike visible matter, it can’t be pushed by winds. The superwinds could therefore have temporarily separated visible matter from dark matter, adding both complexity and diversity to the process of galaxy formation. For instance, Adelberger says, by driving visible matter out beyond dark matter’s grip, the winds may solve a long-standing problem–the surprisingly large size of spiral galaxies.
The new data provide the first direct observations that galactic winds interacted with the early intergalactic medium, notes Timothy M. Heckman of Johns Hopkins University in Baltimore.