Image of the day

Captured by
Michael Scherman

The Moon and Some Sagittarius goodies

My Account

New to Astromart?

Register an account...

Need Help?

Eight New Einstein Rings and Eleven New "Gravitationally Lensed" Galaxies Discovered

11/19/2005 01:46AM

Eight New Einstein Rings and Eleven New "Gravitationally Lensed" Galaxies Discovered
Astronomers have combined two powerful astronomical assets, the Sloan Digital Sky Survey (SDSS) and NASA's Hubble Space Telescope to identify 19 new "gravitationally lensed" galaxies. Among these 19, they have found eight new so-called "Einstein rings", which are perhaps the most elegant manifestation of the lensing phenomenon. Only three such rings had previously been seen in visible light.

In gravitational lensing, light from distant galaxies is deflected on its way to Earth by the gravitational field of any massive object that lies in the way. Because of this light bending, the galaxy is distorted into an arc or multiple separate images. When both galaxies are exactly lined up, the light forms a bull's-eye pattern, called an Einstein ring, around the foreground galaxy.

Besides producing odd shapes, gravitational lensing gives astronomers the most direct probe of the distribution of dark matter in elliptical galaxies. Dark matter is an invisible and exotic form of matter that has not yet been directly observed. By searching for dark matter in galaxies, astronomers hope to gain insight into galaxy formation.

The newly discovered lenses come from an ongoing project called the Sloan Lens Survey (SLACS). A team of astronomers, led by Adam Bolton of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass. and Leon Koopmans of the Kapteyn Astronomical Institute in the Netherlands, selected the candidate lenses from among several hundred thousand optical spectra of elliptical galaxies in the Sloan Digital Sky Survey.

"Being able to study these and other gravitational lenses as far back in time as several billion years allows us to see directly whether the distribution of invisible and visible mass changes with cosmic time," says Koopmans. "With this information, we can test the commonly held idea that galaxies form from collision and mergers of smaller galaxies."


Click here for more about this subject. -Ed.