Michigan Telescopes
Help Give Astronomers Insights Into Blazars
(23 April 2008) For the first time,
astronomers have observed a blazar in action, substantiating a prevailing
theory about how these luminous and energetic galactic cores
work.
A paper on the observations is published in the April 24
issue of Nature. Two University of Michigan astronomers contributed to the
research, which was led by Alan Marscher of the Institute for Astrophysical
Research at Boston University.
Blazars, among the most energetic objects
in the universe, are fuelled by supermassive black holes at the core of certain
giant elliptical galaxies. Periodically, they emit jets of high-energy plasma
at almost the speed of light. Competing theoretical models sought to explain
how this phenomenon occurs.
One model predicted that the jets were
propelled by magnetic fields that were twisted by the gravity of the black hole
and the materials falling into it. This is the behaviour the astronomers
detected.
"What we've observed is the mechanism by which the
acceleration of relativistic particles in the emanating jets occurs. Knowing
that mechanism enhances our understand of the physics that goes into the
acceleration process," said Hugh Aller, a professor in the U-M Department of
Astronomy.
Relativistic particles are particles travelling close to the
speed of light.
"Often, we'd observe blazars, but they didn't do
anything. It's been difficult to catch these outbursts when they occur," he
added.
Scientists from across the globe aimed a variety of telescopes at
the blazar BL Lacertae, about 950 million light-years away from Earth. Optical,
X-ray and radio telescopes monitored the galaxy at different electromagnetic
wavelengths periodically for several years. U-M recorded radio light curves at
the Radio Astronomy Observatory at Peach Mountain in Dexter.
"This is
the first observational evidence that really fits with the picture that the
theoreticians have had," said Margo Aller, a research scientist and lecturer in
the U-M Department of Astronomy. "The reason we have this evidence is a very
fine sampling of a large number of instruments, including the Michigan radio
telescopes."
Scientists hope to get a closer look at blazar jets when
NASA launches its Gamma-ray Large Area Space Telescope (GLAST) satellite
observatory in May.
(source: University of Michigan)
