A team of researchers from Russia and Greece has shown a way to determine the origins and nature of quasar light by its polarization.
Active galactic nuclei, also known as quasars, are massive black holes with matter orbiting around them. They emit two oppositely directed jets of plasma traveling out into space at close to the speed of light. The team distinguished between the light coming from different parts of quasars — their disks and jets — by discerning its distinct polarizations.
Yuri Kovalev, from the Moscow Institute of Physics and Technology, said: “The fact that jet radiation was polarized was known. We combined the data obtained by radio and optical telescopes and showed that the polarization is directed along the jet. The conclusion from this is that hot plasma must be moving in a magnetic field that is coiled like a spring.”
Any massive black hole has matter orbiting around it, slowly falling toward it and emitting light. This matter forms what is known as an accretion disk. Part of the matter approaching the black hole makes an escape. It is accelerated to tremendous velocities and expelled along the black hole’s axis of rotation in the form of two symmetric jets of hot plasma. When a quasar is observed, the radiation picked up by a telescope comes from the jets, the accretion disk, and also from the stars, dust, and gas in the host galaxy.
Optical telescopes don’t have the resolution to tell which part of the quasar the light comes from or in which direction the jet points. All an optical telescope can do is measure the polarization of light, which has been shown to contain clues about the origins of that radiation.
Radio telescopes offer a much better resolution and produce an image that reveals the direction of the jet. However, these telescopes pick up no radiation from the most interesting central region, which includes the accretion disk.
The astrophysicists combined the strengths of both types. Co-author of the study, published in Monthly Notices of the Royal Astronomical Society, MIPT’s Alexander Plavin said. “This is analogous to how 3D glasses enable each eye to see a different picture. There is no other way to obtain such information about the disk and jet with an optical telescope.”