Bright mutterings in the core of 3C273
The montage below shows new detailed measurements of the
core regions of a so-called quasar, in this case one of the
most famous, "3C273". Quasars display some of the most amazing
phenomena in astronomy, apparently able to spit out truly huge
amounts of energy from a central region no bigger than the solar
system. They are thought to be powered by black holes, which may
weigh as much as a billion times the Sun, into which gas and dust
are being dragged in dribs and drabs, resulting in spitting and
sputterings in the light as the gas is heated to enormous
temperatures. The environment is such that as much energy in
X-rays and gamma rays are emitted by the gas as in visible regions
of the spectrum; in fact, it was the discovery of this phenomenon
in the early darks of X-ray and gamma-ray satellites in space
which lead to our present ideas about quasars as physical systems.
Quasars invariably appear as very bright central points of
light at most wavelengths, from radio to gamma rays. The glare
from the central source may be so strong that detecting the
background galaxy is a considerable challenge; nevertheless,
researchers are interested to do so because the type of galaxy,
and the environment in which it finds itself, are vital clues in
tracking down the nature of these objects. Tuorla researchers have
compiled many such detailed
images of less fierce objects, termed "BL Lac galaxies".
In order to see the greatest details at the core of these very
distant objects, special techniques are required. One of these is
so-called VLBI, or Very Long Baseline Interferometry, in which the
power of several widely seperated radio telescopes are combined in
order to produce, using computers, a combined image of very much
greater resolution than a single telescope could produce.
Now, Tuomas Savolainen, Esko Valtaoja
and Kaj Wiik at Tuorla Observatory,
have used VLBI techniques using the VLBA
telescope array to obtain very detailed monitoring of
goings-on in the core of the quasar 3C273.
The central part of the montage shows the radio image of 3C273
as it appeared in February 2003; the resolution of these images is
remarkable -- detail on the scale of milliarcseconds is seen. To
get an idea of how small this is, an optical
image of 3C273 is typically an arcsecond in size; the VLBI
image has about 1000 times better resolution, and we are seeing
details of what is happening within a few hundred light years of
the core. This close, the core is seen to consist of several
components; what we are likely seeing is cosmic sputtering --
rather than a smooth outflow of hot gas from the very inner
regions, where the black hole lies, the gas is being spat out in
dribs and drabs.
The bursts seen here are at the very heart of the process which
produces 3C273's spectacular jet, seen at many wavelengths and
which extends to a few hundred thousand light years from the
center. Some spectacular images can be seen at the X-ray telescope
Chandra's
website.
The exciting aspect of the new data is that not only can the
individual outbursts from the central black hole be monitored, the
spectrum, or energy distribution of each can be measured as
well. Spectra are shown for seven different blobs in the central
image; they are quite different, some showing more energy at
higher wavelengths while others show the opposite. Detailed
studies of these preliminary spectra are underway, and promise to
reveal much about the physical processes taking place in quasar
cores.
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