A team of radio astronomers led by Professor Barney Rickett of UCSD’s
Jacobs School of Engineering has explained wild fluctuations in radio waves
in one of the cosmos’ most energetic, mysterious, and puzzling of objects,
a distant quasar located about 10 billion light years from earth.

In the process, Rickett and team are also shedding new light on the
topography of our astronomical neighborhood, having located a layer of
interstellar material starting about 70 light years from earth, perhaps a
remnant of a super nova explosion.

The research, to be published December 10 in the Astrophysics Journal,
attributes the rapid variations in radio density from quasar PKS 0405-385
to interactions with this thin layer of material. The detected
scintillations match precisely the pattern to be expected from such
interference.

Initial explanations assumed the fluctuations were due to rapid intrinsic
changes in the quasars themselves, and led some astronomers to construct
exotic theories, which are now no longer needed.

Rickett and team believe that the quasar appears to scintillate because
radio waves it emits interact with the interstellar medium, or ISM,
composed of ionized gas particles in the Milky Way, in much the same way
starlight is made to twinkle by turbulence in earth’s atmosphere. Rickett
and team’s conclusions are similar to those reached by two other
astronomers examining the other quasar observed with a rapidly fluctuating
energy signature, J1819+3845, west of the Northern Hemisphere star Vega.
Last summer, Ger De Bruyn of the Netherlands Foundation for Research in
Astronomy and Jane Dennett-Thorpe of the University of Amsterdam reported
that this quasar’s observed pattern is due to interactions with the
interstellar medium. The research on both of the objects has also led to a
re-evaluation of their temperatures and sizes now consistent with the
prevailing theory that the energetic jets radiated by quasars are powered
by matter falling into massive black holes at the core of distant galaxies.

Rickett, who discovered the phenomena of interstellar scintillation in
1969, is professor of Electrical and Computer Engineering at the Jacobs
School. His team included Lucyna Kedziora-Chudczer and David L. Jauncey,
both of the Australia National (telescope) Facility. Kedziora-Chudczer and
Jauncey recorded the fluctuations from PKS 0405-385 in 1996, at the Compact
Array of the Australia Telescope in Northern New South Wales. The data
sparked a controversy that threatened to turn quasar theory on its head.
Kedziora-Chudczer was shocked to find that the object brightened and faded
by 50 percent in less than an hour, much faster than any known quasar.

By focusing on the rapid (intra-day) fluctuations of the radio waves from
PKS 0405-385, Rickett and team were able to come up with a better estimate
of its size viewed from earth, finding it no greater than 30 micro arc
seconds. This angular size is 50 times smaller than can be resolved by the
biggest of earth’s radio telescopes and implies a linear size at origin of
only one light year across.

With this information, Rickett was able to back out a new estimate for the
quasar’s radiation temperature about 2×10^13 degrees Kelvin, or about three
billion times hotter than the sun. That falls just within the bounds that
current physics would predict for a quasar but is 10 to 100 times cooler
than had been deduced by previous methods.

Another intriguing outcome of research are details about our own region in
space. The fluctuations from PKS 0405 385 indicate that there is a
turbulent layer of gas starting about 70 light years from earth, perhaps
providing evidence to support a theory that the sun rests in “cavity”
carved out by a super nova. If this theory is correct, the material
disturbing PKS 0405 385’s radio signals marks the edge of a “bubble” of
particles expelled by the super nova.