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Space astronomy zooms aloft in physics Hot Papers this
period, as technical descriptions of a unique X-ray observatory
grab places #2 and #3. The Wilkinson Microwave Anisotropy Probe
again takes pole position: #1 charts the cosmological implications
and is highly cited because it is the standard source document for
values of the fundamental parameters that describe our universe.
Papers #2 and #3 describe the Suzaku observatory and its imaging
spectrometer. Suzaku mission research scientists have already
produced 100 research papers in 2007-8, all of which cite #2 and
#3. Next on the grid is high flier #4 on the third Japanese solar
observatory, Hinode (sunrise), carrying three major telescopes, all
of which have made successful first light observations.
Suzaku is a joint Japanese-U.S. satellite for X-ray astronomy, and
it is the fifth such rocket-science mission from the Japanese space
agency in the past 25 years. As #2 and #3 explain, Suzaku has four
X-ray telescopes, each equipped with a focal plane low-energy X-ray
spectrometer and CCD. With this quartet, Suzaku has the best
spectral resolution of any cosmic X-ray instrument. Additionally,
the satellite carries a hard X-ray detector sensitive to the 10-600
keV band. This detector extends the bandpass of the Suzaku
observatory to gamma-ray energies, thus allowing broadband studies
of celestial objects.
The detector’s high sensitivity has opened up X-ray
variability studies, an important step towards understanding the
behavior of jets in sources such as Cyg X-1, a binary star
consisting of a blue supergiant, a black hole, and an accretion
disk. The detector can be used as a wide field monitor of bright
X-ray transients, gamma-ray bursts, and solar flares. The unique
capability of the satellite is its ability to cover an enormous
energy range simultaneously. That’s important because Suzaku
is capable of studying in detail both thermal and non-thermal
phenomena, a first in X-ray astronomy.
In September 2008 the Johns Hopkins University hosted a one-day
workshop to review the scientific advances made in the first three
years of operation. At the workshop, the U.S. Suzaku Project
Scientist Dr. Rob Petre (NASA Goddard Space Flight Center,
Greenbelt, Maryland) showcased three big questions for which Suzaku
is providing answers. What is the nature of spacetime near black
holes? What is dark energy? And how do cosmic accelerators work?
The strong gravitational field near a black hole can be probed by
this satellite through broadband spectroscopy of many X-ray sources
in our Galaxy. Galactic black holes and neutron stars are, in
effect, laboratories for research into general relativity. Suzaku
provides a handle on the size of the accreting object, and thus
flags up binaries containing a stellar mass black hole.
That’s because the time scale for flickering in the intensity
of X-rays is a direct measure of the light travel time across the
object.
Suzaku probes the interstellar medium and supernova remnants in its
quest to get a better grasp of the abundances of elements that are
created in supernova explosions. As an example of what can be
achieved by Suzaku, consider Type 1a supernova explosions, which
are of central importance to supernova cosmology. It is absolutely
imperative to improve our knowledge of the physics of these
explosions because they provide "standard candles" at great
distances where the acceleration of the universe is detectable.
Suzaku measurements of the abundances of rare elements in a
supernova remnant in our Galaxy show that the initial trigger was a
carbon explosion at the center of a star, followed by a slow burn,
or delayed detonation of material outside the central core. The
point being that a Type 1a supernova is a controlled explosion,
which is good for a standard candle, rather than a shattering
firework display with chaotic physics. Further contributions to
supernova physics come from Suzaku’s imaging of ejecta
distribution in supernova remnants in the Galaxy.
The satellite holds much promise for further discoveries in the
next few years of operation. Spectroscopy will be carried out of
all active galactic nuclei (AGNs) discovered by the Swift gamma-ray
observatory. Since AGNs trace the large scale structure of the
universe, the study will contribute towards solving the mystery of
dark matter. And the good news continues: a snapshot survey of 500
clusters of galaxies will shed fresh light on
dark energy.
Dr. Simon Mitton is an associate of the department for
History and Philosophy of Science at the University of Cambridge,
U.K.
Keywords: Suzaku, X-ray astronomy, Hinode, solar flares, black
holes, supernovae, dark matter, Rob Petre, X-ray spectrometry.