Cosmic Log : Galaxy revealed in high-res

Cosmic Log : Galaxy revealed in high-res


The Hubble Space Telescope has sent back the best view yet of a picture-perfect galaxy known as M81 or Bode's Galaxy, resolving single points of starlight as well as star clusters and glowing regions of fluorescent gas.
"The amazing detail in this image took our breath away," Andreas Zezas, an astronomer at the Harvard-Smithsonian Center for Astrophysics, said in a news release unveiling the image. "We can see individual stars like tiny grains of sand."
M81, which lies 11.6 million light-years away in the northern constellation Ursa Major, is a popular target for astronomers and amateur stargazers. It can be seen in clear, dark skies with binoculars or a small telescope.(Check out the star chart on this Web page to find it.) Over the years, many space telescopes have taken turns looking at M81, ranging from the Astro-1 ultraviolet imager and Japan's Akari sky-surveying satellite to NASA's Spitzer Space Telescope and Galaxy Evolution Explorer.
But Hubble's image, presented Monday at the American Astronomical Society's spring meeting in Honolulu, is in a class of its own. It took the equivalent of two and a half days of observing time - parceled out over two years - for Hubble's Advanced Camera for Surveys to collect the visible-light and infrared data that went into this picture.
Although the view is aesthetically stunning, there's also a higher scientific purpose behind the picture: Like our own Milky Way, M81 is a "grand design" galaxy, noted for its symmetrical, cyclonic shape. Only about 10 percent of the galaxies we see fit this category. What's more, M81 is in the midst of a surge in star formation, perhaps sparked hundreds of millions of years ago by a close encounter with M82, an irregular-shaped starburst galaxy nearby.
In an e-mail, Zezas told me that an up-close and personal look at M81 could tell astronomers a lot about how galaxies are put together:
"The goal of the project is to map the star-formation history of this galaxy. By this I mean, [to] learn when and where the different populations of stars were formed. Studies of this type on spiral galaxies are difficult because they require large amounts of observing time, and they usually tend to focus on individual regions. The advantage of these data is that we map with the maximum detail possible the whole galaxy so we can study individual stars over the whole of M81.
"We know from previous studies that M81 had periods of enhanced star-formation in the past few hundred million years. The new data will show which regions of the galaxy were more active and will reveal new episodes of star formation.
"This work will tell us how spiral galaxies form and how galaxy interactions affect their stellar populations (M81 is in a group of interacting galaxies, which is the nearest analog of our own local group).
"Also, by comparing with observations in the X-ray band with the Chandra X-ray Observatory, we will study the populations of black holes and neutron stars, which will give us more information on stellar evolution and its endpoints. This in turn will help us to better understand the X-ray emission from more distant galaxies."
In the Hubble image, Zezas and his colleagues could track streams of bluish hot stars that formed in the past few million years, as well as somewhat older stars from an earlier episode of star formation. Lanes of dust wind their way down to M81's center. "The presence of dust lanes shows that star formation is happening all the way down to the nucleus," Zezas said.
Like our Milky Way, M81's nucleus appears to be anchored by a supermassive black hole - although at the equivalent of 70 million solar masses, M81's black hole is about 15 times as massive as the Milky Way's.
NASA / ESA / CfA / JPL-Caltech
This image of M81 combines data from the Hubble Space Telescope, the Spitzer Space Telescope and the Galaxy Evolution Explorer missions.
The Hubble project is part of a larger investigation of M81 that also draws upon the data from Spitzer and the Galaxy Evolution Explorer. In fact, the most sparkling view of M81 is an image that combines the data from all three space telescopes.
"It's absolutely amazing to be able to study star formation in this galaxy with three superb space telescopes in ways we could never achieve from the ground," said John Huchra, another astronomer at the Center for Astrophysics who is working with Zezas on the survey.
The bottom line is that by studying a galaxy far, far away, we get a better understanding of galaxies like our own. In a way, M81 is holding up a mirror to our own celestial face.
"The view we have of M81 is similar to what an astronomer in Andromeda would see if they looked at the Milky Way," Zezas explained.
For closer looks at the mirror, including zoomable images and videos, check out the Space Telescope Science Institute's Hubblesite as well as the European Space Agency's Hubble Information Center. And for a cornucopia of celestial pictures, visit our own Space Gallery.



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