July 1, 2013
Astronomers Discover New Way To Map Out Quasars
Lee Rannals for redOrbit.com - Your Universe Online
Astronomers said at a Royal Astronomical Society Meeting in St Andrews, Scotland on Monday that they have found a new way to map out quasars.Quasars are energetic and luminous central regions found in distant galaxies. When a star passes too close to a giant black hole, it is shredded by the gravitational field, producing a flare-up in the brightness of an otherwise normal looking galaxy. Astronomers observed this effect and found flare-ups with very different behavior than predicted.
The team found "normal" looking quasars that are fading over a timescale of years rather than months. They said the biggest surprise was that the quasars seem to be at the wrong distance.
Astronomers measure the shift in lines in the spectrum of quasars to find the speed at which they are moving away from Earth. This enables them to determine the distance of the object. The team determined the quasars are typically around eight billion light years away, whereas the galaxies that host them are 3.4 billion light years away. These numbers were so exaggerated that the team believes they were looking at a distant quasar through a foreground galaxy. This effect produces a gravitational lensing effect making the background quasar seem temporarily much brighter.
The astronomy observation method is widely used, helping scientists observe very distant objects. This lensing effect may also be the cause of low-level "flickering" seen in some quasars. The team said this is the first time it has been suggested to cause such giant brightening events.
Professor Andy Lawrence of the Royal Observatory Edinburgh suggests this latest observation may provide scientists with a new way to map out quasars in the sky.
"This could give us a way to map out the internal structure of quasars in a way that is otherwise impossible, because quasars are so small," Lawrence said. "As the star moves across the face of the distant quasar, it is like scanning a magnifying glass across it, revealing details that would otherwise simply be impossible to detect."
This research builds on what another group of scientists wrote in the journal Physical Review Letters last October. They said quasars could help scientists map out the spread and structure of the universe. This team was able to measure the redshift of a quasar to help them calculate the relative size of the universe when the light was emitted.
"It appears we may have a useful tool for mapping out the expansion history of the universe," Glenn Starkman, a physics professor at Case Western Reserve, said in a statement. "If we could measure the redshifts of millions of quasars, we could use them to map the structures in the universe out to a large redshift."
Image Below: Illustration of the effect of gravitational microlensing on a distant quasar. Credit : Jason Cowan, Astronomy Technology Centre; adapted from a figure made by NASA.