Imagine the Universe!

Satellite Showcase

XMM - New European Space Agency Satellite Launches in December 1999

The Mission

Artist's Conception of XMM
Credit: NASA
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 these objects.

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.

The Instrumentation

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.

image of the wafer-thin mirrors
Credit: NASA
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 hair.

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 black hole.

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

Additional References

  • About XMM (more technical) (
  • The GSFC XMM Guest Observer Facility XMM page (
  • ESA's XMM page (

Imagine the Universe is a service of the High Energy Astrophysics Science Archive Research Center (HEASARC), Dr. Alan Smale (Director), within the Astrophysics Science Division (ASD) at NASA's Goddard Space Flight Center.

The Imagine Team
Acting Project Leader: Dr. Barbara Mattson
All material on this site has been created and updated between 1997-2012.

DVD Table of Contents
Educator's Index