The spectacular barred spiral galaxy NGC 6872 has ranked among the biggest
stellar systems for decades. Now a team of astronomers from the United States,
Chile and Brazil has crowned it the largest-known spiral, based on archival data
from NASA's Galaxy Evolution Explorer (GALEX) mission, which has since been
loaned to the California Institute of Technology, Pasadena, Calif.
Measuring tip-to-tip across its two outsized spiral arms, NGC 6872 spans
more than 522,000 light-years, making it more than five times the size of our
Milky Way galaxy.
"Without GALEX's ability to detect the ultraviolet
light of the youngest, hottest stars, we would never have recognized the full
extent of this intriguing system," said lead scientist Rafael Eufrasio, a
research assistant at NASA's Goddard Space Flight Center in Greenbelt, Md., and
a doctoral student at Catholic University of America in Washington. He presented
the findings Thursday at the American Astronomical Society meeting in Long
Beach, Calif.
The galaxy's unusual size and appearance stem from its
interaction with a much smaller disk galaxy named IC 4970, which has only about
one-fifth the mass of NGC 6872. The odd couple is located 212 million
light-years from Earth in the southern constellation Pavo.
Astronomers
think large galaxies, including our own, grew through mergers and acquisitions
-- assembling over billions of years by absorbing numerous smaller systems.
Intriguingly, the gravitational interaction of NGC 6872 and IC 4970 may
have done the opposite, spawning what may develop into a new small galaxy.
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