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Largest Spiral Galaxy in the Universe Confirmed --Five Times Size of the Milky Way





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.

"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. 

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.

"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.

Computer simulations of the collision between NGC 6872 and IC 4970 reproduce the basic features of the galaxies as we see them today. They indicate that IC 4970's closest encounter occurred 130 million years ago and that the smaller galaxy followed a path (dashed curve) close to the plane of the spiral's disk and in the same direction it rotates. 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.




The researchers studied the galaxy across the spectrum using archival data from the European Southern Observatory's Very Large Telescope, the Two Micron All Sky Survey, and NASA's Spitzer Space Telescope, as well as GALEX. By analyzing the distribution of energy by wavelength, the team uncovered a distinct pattern of stellar age along the galaxy's two prominent spiral arms. The youngest stars appear in the far end of the northwestern arm, within the tidal dwarf candidate, and stellar ages skew progressively older toward the galaxy's center. The southwestern arm displays the same pattern, which is likely connected to waves of star formation triggered by the galactic encounter.

A 2007 study by Cathy Horellou at Onsala Space Observatory in Sweden and Baerbel Koribalski of the Australia National Telescope Facility developed computer simulations of the collision that reproduced the overall appearance of the system as we see it today. According to the closest match, IC 4970 made its closest approach about 130 million years ago and followed a path that took it nearly along the plane of the spiral's disk in the same direction it rotates. The current study is consistent with this picture.

As in all barred spirals, NGC 6872 contains a stellar bar component that transitions between the spiral arms and the galaxy's central regions. Measuring about 26,000 light-years in radius, or about twice the average length found in nearby barred spirals, it is a bar that befits a giant galaxy. The team found no sign of recent star formation along the bar, which indicates it formed at least a few billion years ago. Its aged stars provide a fossil record of the galaxy's stellar population before the encounter with IC 4970 stirred things up.

"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.




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If there are other habitable worlds in these amazing galaxies (100 billion+ and counting) I can only imagine the beautiful worlds they must contain. Planets with multiple suns, multiple moons. Think about the amazing variety of landscapes here on this single planet, in this single galaxy. There must be such wondrous sights to behold out there among the stars. If i could jump 1000 years into humanities future just to witness the amazing sights they will experience i would. We live in a universe full of such amazing beauty.

How can you confirm that it is the "Biggest (whatever) in the UNIVERSE." Shouldn't you write: Biggest (whatever) in the KNOWN universe? Speaking purely on the articles title..

We have only begun our observations of the know, It is a simple mistake to say the biggest.

Sensationalistic titles such as this should be illegal, and the writers who come up with them whilst claiming to report "science" should have their hands forcibly removed. It is quite telling about the capability of the writing staff, the understanding of science which they carry (or utter lack thereof), and the sad, sad state of scientific journalism, for the editors of such a site to allow such things. That, or the editorial staff is completely incapable of judging things such as stupid titles that are obviously created to attempt to draw attention to an that if simply titled what for what it really is, say, "Gigantic Spiral Galaxy - 5 Times the Size of Milky Way," it would draw plenty of attention on its own. They don't even realize that in insulting their readers with such poor taste, they insult themselves, for in pandering to the lowest common denominator of demographics, they bring themselves down to the lowest common level. Readers of subjects such as scientific news and blogs are looking for REAL, tangible things to be amazed by, not pandering sensationalistic titles that have no bearing on reality.

"Largest Spiral Galaxy in the Universe Confirmed?" Sounds more like a silly, childish species on a backwater planet thinks itself so grand as to be able to see and measure the entire universe from their little mud-puddle. What arrogant little creatures. They even think they can confirm things about a Universe they've yet to experience. They obviously need a few more lessons in humility, which is quite sad, seeing all the lessons their history has already tried to give them. Must be a rather dense species on top of being arrogant.

I even told my friends to take a look at your blog and in fact your blog is already bookmarked on my computer. Hope to see more of this.

If i could jump 1000 years into humanities future just to witness the amazing sights they will experience i would. We live in a universe full of such amazing beauty.

@Matthew: Scientists pride themselves on thinking that their knowledge is absolute, even though the very essence of scientific understanding involves gaining new insights which correct wrong assumptions.

God love 'em, but scientists are some of the most unscientific people in existence when it comes to their proclamations of new understanding. Theories, by definition, are unproven - and are therefore non-provable due to a lack of evidence and/or understanding at a particular point in time. Scientific theories are proven wrong far more often than not, and yet scientists still have the conceit to make bold (and often extremely foolish) claims that their theories are hard, cold fact.

Fact is, science is still only a mere fraction of a fraction the way to explaining the existence of the universe & how it works.

I guess dealing with scientist's over-inflated, self-important egos is something that isn't going to be reined in anytime soon, no matter how many times scientists are smacked down by new discoveries that prove their theories were based on flawed science.

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