This is what our galaxy is believed to now look like. There are billions of galaxies in the Universe.
[img]http://www.newscientist.com/data/images/ns/cms/dn7854/dn7854-1_600.jpg[/img]
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Bar at Milky Way's heart revealed
18:03 16 August 2005
NewScientist.com news service
The Milky Way is not a perfect spiral galaxy but instead sports a long bar through its centre, according to new infrared observations from NASA's Spitzer Space Telescope.
Galaxies come in a wide variety of shapes usually thought to be produced by gravitational interactions with nearby objects. Some spiral galaxies look like pinwheels, with their arms curving out from a central bulge, while others have a straight bar at their centres.
Radio telescopes detected gas that hinted at a bar at the heart of the Milky Way in the late 1980s. A decade later, observations with the near infrared survey 2MASS bolstered the case for a bar, but dust in the centre of the galaxy obscured the observations.
Now, astronomers have used Spitzer to peer through that dust at slightly longer wavelengths, observing 30 million stars in the galactic plane in the region around the centre of the galaxy.
They found that the central bar was much longer than previous observations had suggested - reaching about half the distance between the galaxy's centre and our Sun. The bar is estimated to stretch a total of about 27,000 light years from end to end.
"It is a major component of our galaxy and has basically remained hidden until now," says team member Ed Churchwell, an astronomer at the University of Wisconsin in Madison, US. "The fact that it's large means it's going to have a major effect on the dynamics of the inner part of our galaxy."
Bar food
Stars in the spiral arms circle the galaxy in roughly circular orbits. But the old, red stars in the bar appear to be on more elliptical paths that take them more directly towards and away from the galaxy's core, where a colossal black hole is thought to lurk.
"This bar probably does carry matter into the centre of the galaxy and feeds the black hole," Churchwell told New Scientist.
But it is still not clear what the discovery reveals about the Milky Way's past. "I don't think anybody really fully understands how bars are formed," says Churchwell. "What we do know is that it appears there are so many barred galaxies they must be rather stable. Astronomers have to come up with some kind of model that can explain the stability of these structures."
The team will publish its results in an upcoming issue of Astrophysical Journal Letters and has requested more time on Spitzer to study the innermost part of the Milky Way.
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http://www.newscientist.com/article.ns?id=dn7854
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Milky Way’s Central Structure Seen with Fresh Clarity
By Robert Roy Britt
Senior Science Writer
posted: 16 August, 2005
10:00 am ET
A new infrared survey that claims to be the most comprehensive structural analysis of our galaxy confirms previous evidence for a central bar of stars.
The bar is embedded in the center of the galaxy's spiral arms and cuts across the heart of it all where a supermassive black hole resides. The survey found that the bar is longer than thought and sits at a sharp angle to the galaxy's main plane.
"This is the best evidence ever for this long central bar in our galaxy," said Ed Churchwell, a University of Wisconsin-Madison professor of astronomy.
The challenge
If you've ever been fortunate enough to see the Milky Way in the night sky, then you can appreciate the frustration astronomers face trying to probe the galaxy's center.
The milky swath of stars visible under a dark, rural, summertime sky represents a fraction of the millions upon millions of stars that crowd the center of the galaxy. We sit on the outskirts, looking in. Seeing through the glow to determine the galaxy's structure is hard.
Even more challenging is peering through all the dust between here there.
The survey was done with NASA's Spitzer Space Telescope, which records infrared light. All objects that emit any heat can be seen in infrared, and this wavelength penetrates dust, so the new survey revealed light from tens of millions of stars hidden to optical telescopes.
Bigger than expected
The bar is made of relatively old and red stars, the survey shows. It is about 27,000 light-years long, or roughly 7,000 light-years longer than previously thought. Churchwell's team also found that the bar is oriented at about a 45-degree angle relative to the main plane of the galaxy, in which the Sun and the other spiral-arm stars orbit.
A light-year is the distance light travels in a year, about 6 trillion miles (10 trillion kilometers).
Other stars exist outside the galaxy's main plane. The Milky Way, like many galaxies, is surrounded by a sparsely populated spherical halo of stars. The main galactic disk is about 100,000 light-years wide, and the Sun sits about 26,000 light-years from the center.
Bars are fairly common in large spiral galaxies, but some do not have them. Astronomers had glimpsed ours and were not sure if it was in fact a bar or perhaps an ellipse.
The results will be published in the Astrophysical Journal Letters.
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