Evidence suggests all radio-loud quasars may be blazars
UNIVERSITY OF TEXAS AT AUSTIN NEWS RELEASE
Posted: June 15, 2001
Researchers at The University of Texas at Austin have found new evidence to suggest that all radio-loud quasars may be blazars -- and the differences between them may be related to the angle from which they are viewed. Quasars are quasi-stellar objects found in distant reaches of the universe and blazars are much brighter types of quasars.
After a spectroscopic survey of 62 quasars using the Harlan J. Smith Telescope at UT Austin's McDonald Observatory, astronomers Dr. Feng Ma and Dr. Beverley Wills say there is new ultraviolet evidence suggesting that radio-loud quasars are simply blazars seen from the side. Their work will be published Friday in the journal Science.
"A blazar is a special type of quasar that beams an intense jet of radiation in our direction. It's as if we're looking into a searchlight beam," said Wills, a McDonald Observatory research scientist.
A quasar is a star-like object that emits more energy than 100 giant galaxies combined and is among the most distant objects found so far in the universe. The brilliance of a quasar is believed to originate from swirling gas and stars in the process of falling into a gigantic black hole at the quasar's center.
About ten percent of all quasars catalogued by astronomers are referred to as radio-loud quasars because they are more luminous (or louder) at radio wavelengths than optical wavelengths. The strong radio emission of a radio-loud quasar results from two jets of energetic particles shooting away from the center of the quasar in opposite directions.
Wills explained that some of the radio-loud quasars are much more luminous than other quasars "and randomly change their brightness, even from hour to hour. These are classified as blazars."
Ma, a graduate research assistant in the Microelectronics Research Center in the UT Austin College of Engineering, said the blazar's powerful radiation also could be compared to a flashlight beam. "For most quasars, we are looking from the side, not directly into the beam, so we don't really see the jets. But some have their beams pointing at us and we call them blazars," Ma said.
Wills said the scientists found evidence from spectra of several quasars suggesting that the unseen jets "heat up the gas swirling around the center and we see this glowing gas. This is like seeing light from a searchlight beam as the beam pierces a cloud, even though the searchlight may not be pointing in our direction. This is new, direct evidence from ultraviolet light that every radio-loud quasar has jets."
Ma said this phenomenon was predicted in the Astrophysical Journal Letters in a paper titled "Does Every Quasar Harbor a Blazar?" that he and Wills published in 1998 before observations were completed.
"Our work will also have an influence on a method astronomers use to study cosmology," Ma added. "Because blazars are highly variable, radio-loud quasars should all be excluded when using (the brightness of) quasars to measure distances in the universe."