When blindingly bright ultraviolet light from the young galaxy NGC 6872 reached the Galaxy Evolution Explorer (GALEX) satellite, astronomers were startled to discover that the largest known spiral galaxy was actually bigger than we ever thought: four times larger than the Milky Way to be exact.
Located within the constellation Pavo 212 million light-years from Earth, NGC 6872 reportedly collided with the IC 4970 galaxy, igniting a tremendous growth spurt.
IC 4970 "splashed stars all over the place - 500,000 light-years away," says Catholic University of America scientist Rafael Eufrasio. "It shows the evolution of galaxies in the larger context of the Universe - how the large galaxies we had before we accreted from small clumps in the early universe."
Courtesy of collaboration with NASA's Goddard Space Flight Center, Eurfrasio and his team examined the ages of various stars within the faraway galaxy and found that the youngest were located on the spiral arms furthest from NGC 6872's center.
Eurfrasio adds, "We're just seeing one example of two interacting galaxies but in the past that happened much more often - that's how the big discs we have were probably formed. Putting that in a larger context, it's a very cool system."
The researchers specifically used the Spitzer space telescope and the European Southern Observatory's 'Very Large Telescope,' which is stationed in Northern Chile.
Fellow Catholic University Professor Dulia de Mello explains, "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."
Scientists have known about the galaxy for two decades, but never knew the extent of its true size until now.
The GALEX mission's principal investigator, Chris Martin, admits that "This mission was full of surprises and now more surprises are sure to come. It already has scanned a large fraction of the sky, improving our understanding of how galaxies grow and evolve. The astronomy community will continue those studies, in addition to spending more time on stars closer to home in our own galaxy."
The discovery was originally announced at the 221st American Astronomical Society meeting.
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