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Prof. Im and Lee Find Quasars Beyond Milky Way

Jan 10, 2007

Professor Myung-shin Im and In-duk Lee of the Department of Astronomy of Seoul National University have discovered quasars in large numbers by looking through the Milky Way, the dense galaxy of which our planet is part of.

They found 40 quasars, including 13 bright quasars, beyond the Milky Way.

A quasar is a highly intense star-like source of light and radio waves that exists thousands of millions of light years outside of our galaxy. Energy is released by gases and stars accreted onto the super massive black hole located at the quasar’s center.

Astronomers have observed few quasars through the Milky Way because foreground stars and dust clouds block light coming from objects that lie beyond it. The part of the night sky that is obscured by the Milky Way is referred to as the zone of avoidance.

Scientists have found more than 100,000 quasars since 1963, when American astronomers discovered them for the first time, but only 10 of them have been found in the zone of avoidance and they had more than a magnitude of 18.

Im’s team discovered a total of 40, including 13 bright quasars. They were as far away as 700 million to 3 billion light years from the Earth.

``The discovery is significant, as finding a bright quasar in the zone of avoidance is like finding a person in a large stadium packed with people. There are simply too many stars that look like quasars,’’ Im said.

The professor said his team combined two existing methods of distinguishing quasars clearly from stars in the Milky Way _ catching radio waves from objects and using near infrared rays to select quasars among them.

The scientists used a long-slit spectrograph on the 1.8-meter telescope at the Bohyunsan Optical Astronomy Observatory in North Kyongsang Province.

They specifically targeted quasars that lie beyond the zone of avoidance, in contrast to chance discoveries in the past.

The discovery was reported at the 209th meeting of the American Astronomical Society, which began Jan. 5 in Seattle.

``This demonstrates that the zone of avoidance is no longer a place to avoid when searching for bright quasars,’’ Im said.

Dec. 9, 2006
SNU PR Office