Longer Cosmic Ruler Based On Black Holes - Science News: The brightness of an active nucleus is tightly related to the radius of a region of hot gases surrounding the central black hole. When scientists determine that radius, they can predict how intrinsically bright the nucleus should be — and compare that value to how bright it appears, which depends on distance...
A technique called reverberation mapping measures how long it takes photons being kicked out of the black hole’s immediate neighborhood to reappear after they’ve traversed the hot, gassy maelstrom surrounding the black hole. Because light travels at a constant speed, astronomers can determine the gassy region’s radius. Then, the luminosity of the active galactic nucleus can be calculated.
Showing posts with label active galactic nucleus. Show all posts
Showing posts with label active galactic nucleus. Show all posts
Friday, September 30, 2011
Monday, September 26, 2011
Astronomers Discover New Standard Candle - Technology Review
Astronomers Discover New Standard Candle - Technology Review: Active galactic nuclei are galaxies with a central supermassive black hole that emits intense radiation. When this radiation hits nearby gas clouds, it ionises them causing them to emit a characteristic light of their own.
In recent years, astronomers have found that they can see both the emissions from the supermassive black hole as well as the emissions from the gas clouds. These are obviously related but the time it takes for radiation to reach the cloud means that changes here lag those in the supermassive black hole.
This delay, which can be measured with a technique called reverberation mapping, is then clear measure of the radius of the cloud.
But since the flux of the radiation from the black hole drops as an inverse square law, the brightness of these clouds also depends on their radius.
So a good measure of their radius also gives an indication of their intrinsic brightness.
Now Watson and co have used this technique to measure the distance to 38 active galactic nuclei at distances of up to z=4. That's significantly further than is possible with type 1a supernova, whose distance cannot be accurately measured beyond z=1.7.
In recent years, astronomers have found that they can see both the emissions from the supermassive black hole as well as the emissions from the gas clouds. These are obviously related but the time it takes for radiation to reach the cloud means that changes here lag those in the supermassive black hole.
This delay, which can be measured with a technique called reverberation mapping, is then clear measure of the radius of the cloud.
But since the flux of the radiation from the black hole drops as an inverse square law, the brightness of these clouds also depends on their radius.
So a good measure of their radius also gives an indication of their intrinsic brightness.
Now Watson and co have used this technique to measure the distance to 38 active galactic nuclei at distances of up to z=4. That's significantly further than is possible with type 1a supernova, whose distance cannot be accurately measured beyond z=1.7.
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