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Astrophysics: X-ray Astronomy
Overview
Faculty in this area of research:
Astrophysics Areas of Research
Overview
X-ray astronomy was born 30 years ago with the discovery, during
a brief sounding-rocket experiment, of a bright celestial X-ray
source over and above the diffuse X-ray background. Today, X-ray
astronomy has evolved into a mature science alongside optical and
radio astronomy. Some of the most recent satellites feature fully
imaging X-ray telescopes with arc-second angular resolution. Approximately
60,000 X-ray sources have already been catalogued, including examples
from nearly all known classes of astronomical objects. The X-ray
band typically serves as a "filter" to reveal astronomical
objects in which some of the most highly energetic processes in
the universe are taking place.
MIT astrophysicists have carried out pioneering investigations
of X-ray sources since the very inception of X-ray astronomy. Current
investigations include the study of close binary systems containing
a collapsed star (neutron star, black hole, or white dwarf). For
those systems in which X-ray pulsations are detected, it is often
possible to measure the mass of the neutron star; to determine the
properties and chemical composition of the companion's stellar wind
from studies of X-ray scattering and fluorescence; and to probe
tidal interactions in the binary system from changes in the orbital
period.
X-ray burst sources, which result from thermonuclear flashes of
accreted material on the surface of a neutron star, can be used
to probe the properties of the neutron star, including its mass
and radius. MIT astrophysicists also study other sources exhibiting
quasiperiodic oscillations in order to understand the source of
the oscillations and infer the rotation rate and magnetic field
strength of the underlying neutron star. Measured Doppler shifts
of companion stars in binary systems containing black hole candidates
provide crucial evidence in support of the black hole hypothesis.
On a larger scale, department astrophysicists study supernova remnants
with high-resolution X-ray spectrographs, thus yielding the plasma
properties of the shocked interstellar medium.
MIT also runs an ongoing program to identify the optical counterparts
of X-ray sources discovered in various surveys, including sources
found with the High Energy Astronomical Observatory, the HEAO-1
satellite, and those imaged in the Andromeda galaxy with the ROSAT
satellite. Active galactic nuclei (such as quasars, Seyfert galaxies,
and BL Lacertae objects) thought to contain massive black holes
have been investigated to learn about their temporal variability
and structure. Clusters of galaxies have been studied with imaging
and spectroscopic instruments to investigate the X-ray emission
from the very hot gas bound within the clusters of galaxies. Searches
for dark matter in clusters of galaxies are also underway.
The MIT X-ray astronomy group has used the SAS-3 X-ray Observatory
(whose entire scientific payload was developed at MIT); the Einstein
X-ray Observatory (which included a Bragg crystal x-ray spectrometer
built at MIT); the European satellites EXOSAT and XMM-Newton; the
Japanese satellites Tenma, Ginga, and ASCA (which included an imaging
X-ray CCD spectrometer provided by MIT), and the Dutch-Italian satellite
Beppo-Sax.
MIT plays a special role in three current satellites. The Rossi
X-Ray Timing Explorer (RXTE) is named for former MIT professor Bruno
Rossi and includes an all-sky monitor for detecting X-ray transients
that was developed by MIT. The High-Energy Transient Explorer (HETE-II),
which detects cosmic gamma-ray bursts, was developed at MIT. And
MIT provided a charge-coupled device (CCD) X-ray camera and transmission
grating X-ray spectrometer for the Chandra X-Ray Observatory, one
of NASA's great observatories in space.
Finally, MIT is leading the development of Micro-X, a new sounding rocket payload consisting of a high energy resolution imaging spectrometer at the focus of a grazing incidence X-ray optic. The microcalorimeter detector technology used in Micro-X is being considered for the proposed International X-ray Observatory. The science targets for Micro-X are diffuse X-ray objects including supernova remnants and clusters of galaxies.
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