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Colossal Winds of Change
2 November 2007 (All day)
For the first time, astronomers have observed titanic tornadoes emerging from a supermassive black hole. The intense winds--theoretical until now--blow with such force that they influence the shape of the surrounding galaxy. The find could contribute new insights to theories about the evolution of the early universe.
To make the observation, a team of astronomers from the Rochester Institute of Technology in New York state, along with colleagues at the University of Hertfordshire in the United Kingdom, studied polarized light emanating from the known active center of galaxy PG 1700+158, located about 3 billion light-years away. Black holes whip out superheated gas from their accretion disks--pulled together from material in surrounding space by their massive gravity--at such temperatures that the resulting light can outshine entire galaxies. Just as a good pair of sunglasses eliminates glare, interstellar dust can polarize the light. This allowed the astronomers to break down the light into its constituent colors, which revealed subtle shifts in its wavelengths. The team interpreted those shifts as the effect of cyclonic winds moving above and below the black hole at speeds of about 4000 kilometers per second, tens of thousands of times stronger than the most intense cyclones on Earth.
The influence of such winds extends well beyond the galaxy, says astronomer and lead author Stuart Young, who along with colleagues reports the findings in the 1 November issue of Nature. The winds may heat the surrounding intergalactic medium enough to prevent it from condensing, which halts the growth of the galaxy, he says. If so, then winds from black holes could have restricted the size of galaxies in the early universe. But astronomers will need to spot more such cyclones in order to be sure that they were common back then, Young says.
"This critical observation is the first time astronomers have been able to 'zoom in' on a black hole and watch the actual source of such power," says astronomer Kimberly Weaver of NASA's Goddard Space Flight Center in Greenbelt, Maryland. "It's amazing new proof that the technique of simply splitting white light into different colors can be used like puzzle pieces to reconstruct speeds, directions, and shapes of material surrounding black holes--places we still cannot photograph with our telescopes."