Friday, October 05, 2007

Einstein Ring

This photo illustration shows the foreground lensing source removed. The tiny reconstruceted galaxy 6 billion light-years away SDSS J0737+3216, is smaller than any galaxy ever seen at that distance.

Astronomers discovered this distant galaxy through a phenomenon called gravitational lensing. This phenomenon occurs when a massive galaxy in the foreground bends the light rays from a distant galaxy behind it in much the same way as a magnifying glass does. When both galaxies are exactly lined up, the light forms a bull's-eye pattern, called an "Einstein ring," around the foreground galaxy.

This ring can be seen in the hubblesite illustration. Einstein rings are named for physicist Albert Einstein, who predicted the phenomenon. By focusing the light rays, this gravitational lensing effect increases the observed brightness and size of the background galaxy by more than 10 times.

The illustration is based on images taken in infrared light from the W. M. Keck Telescope and visible-light images from NASA's Hubble Space Telescope. The Hubble and Keck data reveal information about the early years of the infant galaxy, namely that it is seen just after it formed most of its stars.

This galaxy is about half the size, and approximately one-tenth the "weight" of the smallest distant galaxies typically observed. Weighing only 1/100 as much as our Milky Way Galaxy, the dwarf is much smaller than anything studied before in any detail at this distance.

"Even though this galaxy is more than six billion light years away, the reconstructed image is as sharp as the ordinary ground-based images of the nearest structure of galaxies, the Virgo cluster, which is 100 times closer to us," said lead author Phil Marshall, a postdoctoral fellow at UCSB.
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"If the galaxy is representative of a larger population, it could be one of the building blocks of today's spiral galaxies, or a progenitor of modern dwarf galaxies," said Tommaso Treu from UC Santa Barbara. "It does look remarkably similar to the smallest galaxies in the Virgo cluster, but is almost half the way across the universe."

"We believe we may have identified the progenitors of local dwarf galaxies," says Tommaso Treu. "We see them as clearly as we would see dwarfs in the Virgo cluster using ground-based telescopes."

The mass estimate for the galaxy, and the inference that many of its stars have only recently formed, is made possible by the combination of optical and near infrared images from the Hubble Space Telescope with longer wavelength images obtained with the Keck Telescope.

The sharp view of NASA's Hubble Space Telescope, and the laser guide stars adaptive optics system on the W.M. Keck Telescope, were aimed at a natural lens in space, called a gravitational lens, to study the dwarf.

Adaptive optics systems use bright stars in the field of view to measure the Earth's atmospheric blurring and correct for it in real time. This technique relies on having a bright star in the image as well, so it is limited to a small fraction of the night sky.

The Keck Telescope uses a powerful laser to illuminate the layer of sodium atoms that exist in the Earth's atmosphere, explained Jason Melbourne, a team member from the Center for Adaptive Optics at the University of California, Santa Cruz.

The laser image acts as an artificial star, bright enough to perform adaptive optics correction at an arbitrary position in the sky, thus enabling much sharper imaging over most of the sky.

Scientists 'Weigh' Tiny Galaxy Halfway Across Universe UCSB Press Release
Seeing the Universe with Einstein's glasses from Space dotcom

New Image of the Central Region of the Active Galaxy M87
Fifty Times sharper than Hubble from the Max Planck Institute

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