Washington, July 24 : Astronomers have used a infrared filter with large telescopes to get a clean view of the scattered light coming from the disks surrounding black holes.
Supermassive black holes in the nuclei of galaxies are the subject of intense research in astronomy, but they are too far away from us to see any details even with the biggest telescopes on Earth.
Furthermore, such a black hole and its surrounding gas and dust clouds constitute a messy environment.
This has confused astronomers who tried to observe the spectrum of the black hole vicinity, as the strong emission from these clouds badly contaminates the spectrum.
Now, an international team of astronomers has found a way around this problem.
Some of the black holes feature a very small amount of scattered light, which turns out to be coming from the near vicinity of the black holes and not from the surrounding dust clouds.
Scattered light is polarized, which is how polaroid sunglasses help get rid of glare on car windshields, for example.
By using a polarizing filter with large telescopes to detect this small amount of scattered light and measure it with unprecedented accuracy, one could use the natural scattering mirror as a periscope and see the light from the immediate vicinity of the black hole.
To do this one needs a polarimeter.
The United Kingdom Infrared Telescope (UKIRT) on Mauna Kea in Hawaii offers just such an instrument to its users.
Built at the University of Hertfordshire (UK) and affectionately known as IRPOL (infrared polarimeter), this instrument offered the needed capability that is not often seen on large telescopes.
The dust cloud contamination has previously presented difficulties in identifying an expected disk prediction, a particular blue color of the disk in infrared light. The team has finally uncovered this blue color by eliminating the dust contamination using the polarizing filter.
Using similar techniques, the team has already reported the discovery of an important predicted spectral feature in the blue part of the spectrum, which could not be discovered in any other way.
Furthermore, this disk property is expected to originate in the outermost region of the disk, where important questions are yet to be answered: how and where the disk ends and how material is being supplied to the disk.
The team's new method may provide answers to these questions in the near future.