By viewing energetic galaxies called quasars through a high-tech equivalent of polarised sunglasses, astronomers have clinched the case that they are fuelled by discs of hot matter swirling onto huge black holes. The trick could allow them to better understand why the environs of a black hole can shine with the light of a trillion Suns.
"After many years of controversy, we finally have very convincing evidence that the expected disc is truly there," says Makoto Kishimoto from the Max Planck Institute for Radio Astronomy in Bonn, Germany.
Quasars are the brilliant cores of galaxies that have supermassive black holes at their hearts. Somehow they manage to radiate as much light as a large galaxy of stars, but from a region only about the size of our solar system.
For decades, physicists have theorised that the radiation comes from a hot "accretion disc" around the black hole. The black hole's gravity pulls in surrounding gas and dust, which swirls into a disc and heats up to hundreds of thousands of degrees.
A key prediction of this theory is that infrared light from the outermost, coolest region of the disc should show a very distinctive spectrum. It had never been possible to test this prediction because infrared light from dust clouds outside the disc completely swamps the disc's faint glow.
"The emission from hot dust grains in the surroundings is so strong that it buries emission from the accretion disc, so we just couldn't see it," Kishimoto told New Scientist.
However, there was some evidence that light emerging from the accretion disc is slightly polarised, just as light scattering from an ocean surface becomes polarised. So Kishimoto's team reasoned that by looking at just the polarised part of a quasar's infrared light, they could measure the glow of the disc alone.
The team used the United Kingdom Infra-Red Telescope in Hawaii and the European Very Large Telescope in Chile to look at the faint polarised component of infrared light from six different quasars at an average distance of 5 billion light years. Sure enough, all showed the telltale spectrum predicted for an accretion disc.
"It looks like the standard picture is correct, which really moves the field of quasars forward," says Kishimoto.
Now that astronomers have polarised specs that can home in on the outer portions of accretion discs, they hope to answer long-standing questions about their anatomy, including how large the discs are, and how matter falls onto them – whether smoothly or in sudden bursts.
Journal reference: Nature (vol 454, p 492)
By Phlegm
Thu Jul 24 03:05:52 BST 2008
[edited]By Anonymous
Thu Jul 24 10:46:01 BST 2008
"For the first time astronomers have seen discs of hot matter swirling onto huge black holes."By Anon
Thu Jul 24 12:40:01 BST 2008
Its not an artowkr its an image viewed through polarised light filters which removes the non-polarised light leaving only the polarized light behind.By Matt
Thu Jul 24 12:48:20 BST 2008
After reading your rant (including capitalised words for emphasis - always the sign of a rant), I really can't understand what your problem is.By Popoid
Thu Jul 24 17:06:05 BST 2008
Do you even understand what a quasar is? Obviouly you are VERY =) confused about it.By Jtankers
Thu Jul 24 11:59:12 BST 2008
I would be very interested in the math behind the growth rates of black holes. I understand that the larger the black hole the slower the growth.By Tony
Thu Jul 24 13:02:19 BST 2008
You mean mathS.....which is short for mathamaticSBy Matt
Thu Jul 24 13:32:47 BST 2008
Not so. In many countries, including the US, mathematics is shortened simply to 'math'. As in "do the math".By Acoyauh
Thu Jul 24 17:22:17 BST 2008
Your, possessive, not you're as in you are.All comments should respect the New Scientist House Rules. If you think a particular comment breaks these rules then please use the "Report" link in that comment to report it to us.
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18:53 05 September 2008
