November 4th, 2011
03:44 PM ET

Hubble observes black hole's accretion disc

What does a black hole look like? Scientists have, for the first time, directly observed the disc that surrounds this area of tremendous gravitational pull, from which no light can escape.

Black holes power quasars, which are thought to be the extremely bright centers of certain galaxies surrounding supermassive black holes. Scientists believe that large amounts of energy are released when matter falls into a black hole, producing the light of the quasar. Around a black hole is an accretion disk, made of dust and gas.

The thing about quasars, though, is that they're so far from Earth that even at a typical size of 100 billion kilometers across, they appear so small to us that there will probably never be a telescope powerful enough to see their structures directly. That in turn means that most of our knowledge of quasars' inner structure is theoretical – not based on direct observations.

In order to learn more about the nature of these still-largely-mysterious objects, then, astronomers had to devise a new way to study quasars. That's exactly what they've done with the Hubble Space Telescope: They used the stars in a galaxy as a scanning microscope. The gravitational lensing of these stars amplifies the light from different parts of the quasar itself, resulting in detailed color information for a line through the accretion disc.

By combining several images produced using this technique, astronomers were able to see subtle color differences over the observation times, which translates to a full color profile across the black hole's accretion disc. The color profile in turn allowed the team to determine that the disc is between 100 to 300 billion kilometers across – a wide range, to be sure, but still incredibly accurate given the incredible distance between the relatively small quasar and Earth.

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Filed under: Discoveries • In Space • News
November 4th, 2011
10:45 AM ET


Every Friday, @CNNLightYears will suggest interesting and exciting space and science Twitter accounts to follow.

Today, @CNNLightYears is giving a #FollowFriday to a couple Twitter accounts that tweet about asteroids.

An asteroid the size of an aircraft carrier is heading toward Earth and it will pass closer to our planet than the moon, according to NASA’s Near Earth Object Program. Near-Earth asteroid 2005 YU55 will pass the Earth at a distance of 201,700 miles on Tuesday, November 8. NASA says the passing is safe.


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Filed under: FollowFriday • Voices


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