A team of astronomers from the United States, Chile and Brazil have declared the spiral galaxy known as NGC 6872 to be the largest-known spiral in the universe. The word came down from NASA yesterday and was published today in the Monthly Notices of the Royal Astronomical Society.
If it helps to appreciate the enormity of NGC 6872, that spiral galaxy from end to end is more than five times the size of our galaxy, the Milky Way, and spans more than 522,000 light-years.
NASA is crediting their ability to measure NGC 6872 based on data gathered from their Galaxy Evolution Explorer (GALEX) mission.
"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.
Eufrasio presented the findings yesterday at the American Astronomical Society meeting in Long Beach, Calif.
According to NASA, 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 believe that large galaxies like our own, grew through mergers and acquisitions and assembled over billions of years by absorbing numerous smaller systems.
Interestingly enough, the gravitational interaction of NGC 6872 and IC 4970 may have done the opposite, spawning what may develop into a new small galaxy.
"The northeastern arm of NGC 6872 is the most disturbed and is rippling with star formation, but at its far end, visible only in the ultraviolet, is an object that appears to be a tidal dwarf galaxy similar to those seen in other interacting systems," said team member Duilia de Mello, a professor of astronomy at Catholic University.
The tidal dwarf candidate is brighter in the ultraviolet than other regions of the galaxy, a sign it bears a rich supply of hot young stars less than 200 million years old.
GALEX was developed under NASA's Explorers Program managed by NASA's Goddard Space Flight Center.
For more on NGC 6872, see the video accompanying this article.
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