XMM - New European Space Agency Satellite Launches in
XMM (short for X-ray
Multi-Mirror Mission) will be a prime tool for astronomers
studying black holes, star formation and much more. XMM was built largely
by the European Space Agency (ESA) and was launched December 10, 1999.
From its incarnation, XMM was designed to complement the recently launched
Chandra Observatory. For
example, Chandra's sensitive cameras produce sharp images of newborn stars
and supernova remnants. XMM's huge collecting area, in turn, captures
enough X-ray photons to reveal the temperature and velocity of the gas in
X-ray photons enter the telescopes and bounce off the mirrors at a shallow
angle towards instruments several meters away at the other end of the
satellite. For two of the telescopes, half of the incoming photons are
directed to cameras similar to the ones installed on Chandra. In this
way, XMM will generate images of the X-ray sources it observes.
The other half of the incoming photons (and all of the photons on the
third telescope) go directly to a device that analyzes the "colors" of the
X-rays, producing X-ray spectra of the objects observed by the telescope.
In total, XMM has two telescopes that produce X-ray images and spectra
(called the European Photon Imaging Cameras), one telescope dedicated
completely to spectra (the Reflection Grating Spectrometer) and one
optical-UV telescope (the Optical Monitor).
XMM's three advanced X-ray telescopes, each with 58
high-precision nested mirrors, gives XMM a total X-ray collecting
area of nearly the size of a tennis court - yet the
telescopes themselves are only 30 centimeters wide. Sound impossible?
The secret is in the design.
Each sleek, barrel-shaped telescope has 58 wafer-thin mirrors curved into
cylinders and nested within each other like Russian dolls. Each mirror
sits 25 microns from its neighbor, about a quarter the width of a human
The large collecting area offered by
these three telescopes combined will allow observations of millions of
X-ray sources. But what excites astronomers most is the
capacity (due to the spacecraft's highly eccentric orbit) to make long and
uninterrupted observations with unprecedented
sensitivity. With XMM astronomers will be able to peer into deep space
and observe detail of very hot objects created when
the Universe was very young.
XMM's Optical Monitor is like a scaled-down
version of the Hubble Space Telescope. The telescope has a 30-centimeter
aperture, which means the viewing area is 30-cm wide. But because it's
above the atmosphere, the telescope has the power of a 4-meter-wide
earth-bound telescope. This telescope is handy for viewing the optical and
UV counterparts of X-ray sources. For example, the gas and miscellaneous
star-stuff that spirals into a black hole can glow in X-rays as well
as optical and UV light. XMM can view this simultaneously
across wavelengths, learning more about the bizarre physics behind a
The Science Results
Astronomers around the world are so excited about XMM because the
satellite observes so many different types of objects and events.
These include cosmic background X-ray radiation, elliptical galaxies and
clusters of galaxies, normal and starburst galaxies, active galactic
nuclei and quasars, stellar black holes, neutron stars, pulsars, supernova
remnants, and even comets.
For more information on XMM's science objectives, please visit