 |
|
Accretion Discs Show Their True Colours
July 25, 2008Quasars are the brilliant cores of remote galaxies, at the hearts of which lie supermassive black holes that can generate enough power to outshine the Sun a trillion times. These mighty power sources are fuelled by interstellar gas, thought to be sucked into the hole from a surrounding 'accretion disc'. A paper in this week's issue of the journal Nature, partly based on observations collected with ESO's Very Large Telescope, verifies a long-standing prediction about the intensely luminous radiation emitted by these accretion discs.
"Astronomers were puzzled by the fact that the best models of these discs couldn't quite be reconciled with some of the observations, in particular, with the fact that these discs did not appear as blue as they should be," explains lead-author Makoto Kishimoto.
Such a discrepancy could be the signal that there was something very wrong with the models. With his colleagues, he investigated this discrepancy by studying the polarised light from six quasars. This enabled them to demonstrate that the disc spectrum is as blue as predicted.
"The crucial observational difficulty here has been that the disc is surrounded by a much larger torus containing hot dust, whose light partly outshines that of the disc," says Kishimoto. "Because the light coming from the disc is scattered in the disc vicinity and thus polarised, by observing only polarised light from the quasars, one can uncover the buried light from the disc."
In a similar way that a fisherman would wear polarised sunglasses to help get rid of the glare from the water surface and allow him to see more clearly under the water, the filter on the telescope allowed the astronomers to see beyond surrounding clouds of dust and gas to the blue colour of the disc in infrared light.
The observations were done with the FORS and ISAAC instruments on one of the 8.2-m Unit Telescopes of ESO's Very Large Telescope, located in the Atacama Desert, in Chile, as well as several other telescopes, including STFC's UKIRT.
The standard picture of the accretion disc is therefore vindicated. The authors believe that further measurements could eventually provide valuable insight into how and where the disc ends, and how material is being supplied to the disc.
ESO
"The crucial observational difficulty here has been that the disc is surrounded by a much larger torus containing hot dust, whose light partly outshines that of the disc," says Kishimoto. "Because the light coming from the disc is scattered in the disc vicinity and thus polarised, by observing only polarised light from the quasars, one can uncover the buried light from the disc."
In a similar way that a fisherman would wear polarised sunglasses to help get rid of the glare from the water surface and allow him to see more clearly under the water, the filter on the telescope allowed the astronomers to see beyond surrounding clouds of dust and gas to the blue colour of the disc in infrared light.
The observations were done with the FORS and ISAAC instruments on one of the 8.2-m Unit Telescopes of ESO's Very Large Telescope, located in the Atacama Desert, in Chile, as well as several other telescopes, including STFC's UKIRT.
The standard picture of the accretion disc is therefore vindicated. The authors believe that further measurements could eventually provide valuable insight into how and where the disc ends, and how material is being supplied to the disc.
ESO
Quasars Current Events and Quasars News RSSMilagro detects cosmic ray hot spots
The University of Maryland-led Milagro collaboration, comprised of scientists from 16 institutions across the United States, has discovered two nearby regions with an unexpected excess of cosmic rays.
Los Alamos Observatory Fingers Cosmic Ray 'Hot Spots'
A Los Alamos National Laboratory cosmic-ray observatory has seen for the first time two distinct hot spots that appear to be bombarding Earth with an excess of cosmic rays. The research calls into question nearly a century of understanding about galactic magnetic fields near our solar system.
Mystery of missing hydrogen
Something vital is missing in the far distant reaches of the Universe: hydrogen - the raw material for stars, planets and possible life.
Serendipitous observations reveal rare event in life of distant quasar
A bit of serendipity has given astronomers a surprise view of a never-before-observed event in the birth of a galaxy.
First detection of magnetic field in distant galaxy produces a surprise
Using a powerful radio telescope to peer into the early universe, a team of California astronomers has obtained the first direct measurement of a nascent galaxy's magnetic field as it appeared 6.5 billion years ago.
BOSS: the Baryon Oscillation Spectroscopic Survey
The Sloan Digital Sky Survey (SDSS) uses a 2.5-meter telescope with a wider field of view than any other large telescope, located on a mountaintop in New Mexico called Apache Point and devoted solely to mapping the universe.
'Cosmic ghost' discovered by volunteer astronomer
When Yale astrophysicist Kevin Schawinski and his colleagues at Oxford University enlisted public support in cataloguing galaxies, they never envisioned the strange object Hanny van Arkel found in archived images of the night sky.
Polarizing filter allows astronomers to see disks surrounding black holes
For the first time, a team of international researchers has found a way to view the accretion disks surrounding black holes and verify that their true electromagnetic spectra match what astronomers have long predicted they would be.
Radio Telescopes Reveal Unseen Galactic Cannibalism
Radio-telescope images have revealed previously-unseen galactic cannibalism -- a triggering event that leads to feeding frenzies by gigantic black holes at the cores of galaxies. Astronomers have long suspected that the extra-bright cores of spiral galaxies called Seyfert galaxies are powered by supermassive black holes consuming material. However, they could not see how the material is started on its journey toward the black hole.
Galaxies gone wild!
Interacting galaxies are found throughout the Universe, sometimes as dramatic collisions that trigger bursts of star formation, on other occasions as stealthy mergers that result in new galaxies.
More Quasars Current Events and Quasars News Articles
| © 2009 BrightSurf.com |