Astronomers have stumbled
across the largest known spiral galaxy -- five times the size
of our own Milky Way galaxy.
The barred spiral galaxy NGC 6872, located some 212 million light-years from Earth, has been known to be among the largest stellar systems for over two decades. The full extent of its span was only discovered when a team of astronomers from Brazil, Chile and the US examined data from Nasa's Galaxy Evolution Explorer (Galex) telescope while looking for new star-forming regions.
When the team looked at the ultraviolet readings taken by Galex, they noticed a collection of hot young stars habiting a tidal dwarf galaxy on the northeastern arm of NGC 6872. From tip-to-tip of its spiral arms, NGC 6872 spans more than 522,000 light-years.
"Without Galex's ability to detect the ultraviolet light of the youngest, hottest stars, we would never have recognised the full extent of this intriguing system," said lead scientist Rafael Eufrasio, a research assistant at NASA's Goddard Space Flight Centre.
The team's findings, presented on 10 January at the American Astronomical Society meeting in California, indicate that the unusually large shape and size of NGC 6872 is caused by an interaction with a neighbouring disk galaxy, IC 4970.
A simulation run, by Cathy Horellou at Onsala Space Observatory in Sweden and Bäerbel Koribalski
of the Australia National Telescope Facility, indicates that the smaller disk galaxy IC 4970 "collided" with NGC 6872 some 130 million years ago.
This collision resulted in the formation of new stars, extending down the arms of NGC 6872 and
resulting in its massive span. "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, Washington DC.
The newly discovered tidal dwarf found by Galex contains ultraviolet readings that indicate it bears a rich supply of young stars less than 200 million years old.
The finding aids astronomers in their understanding of how the Universe has evolved. Large galaxies such as the Milky Way are thought to have grown by a process of small stellar systems merging over billions of years. Rather than merging together, the interaction of NGC 6872 and IC 4970 seems to have resulted in forming a new dwarf galaxy -- an altogether different evolutionary process.
"Understanding the structure and dynamics of nearby interacting systems like this one brings us a step closer to placing these events into their proper cosmological context, paving the way to decoding what we find in younger, more distant systems," said team member and Goddard astrophysicist Eli Dwek.
------------------------- *Leave a comments, questions or even a suggestions below this post. Your expressions are always welcomed.
The barred spiral galaxy NGC 6872, located some 212 million light-years from Earth, has been known to be among the largest stellar systems for over two decades. The full extent of its span was only discovered when a team of astronomers from Brazil, Chile and the US examined data from Nasa's Galaxy Evolution Explorer (Galex) telescope while looking for new star-forming regions.
When the team looked at the ultraviolet readings taken by Galex, they noticed a collection of hot young stars habiting a tidal dwarf galaxy on the northeastern arm of NGC 6872. From tip-to-tip of its spiral arms, NGC 6872 spans more than 522,000 light-years.
"Without Galex's ability to detect the ultraviolet light of the youngest, hottest stars, we would never have recognised the full extent of this intriguing system," said lead scientist Rafael Eufrasio, a research assistant at NASA's Goddard Space Flight Centre.
The team's findings, presented on 10 January at the American Astronomical Society meeting in California, indicate that the unusually large shape and size of NGC 6872 is caused by an interaction with a neighbouring disk galaxy, IC 4970.
A simulation run, by Cathy Horellou at Onsala Space Observatory in Sweden and Bäerbel Koribalski
of the Australia National Telescope Facility, indicates that the smaller disk galaxy IC 4970 "collided" with NGC 6872 some 130 million years ago.
This collision resulted in the formation of new stars, extending down the arms of NGC 6872 and
resulting in its massive span. "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, Washington DC.
The newly discovered tidal dwarf found by Galex contains ultraviolet readings that indicate it bears a rich supply of young stars less than 200 million years old.
The finding aids astronomers in their understanding of how the Universe has evolved. Large galaxies such as the Milky Way are thought to have grown by a process of small stellar systems merging over billions of years. Rather than merging together, the interaction of NGC 6872 and IC 4970 seems to have resulted in forming a new dwarf galaxy -- an altogether different evolutionary process.
"Understanding the structure and dynamics of nearby interacting systems like this one brings us a step closer to placing these events into their proper cosmological context, paving the way to decoding what we find in younger, more distant systems," said team member and Goddard astrophysicist Eli Dwek.
------------------------- *Leave a comments, questions or even a suggestions below this post. Your expressions are always welcomed.
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