XMM-Newton is a satellite observatory that studies the universe in X rays as well as visible and ultraviolet light. XMM-Newton is named in honor of the English scientist Sir Isaac Newton. The abbreviation XMM stands for X-ray Multi-Mirror mission. XMM-Newton uses three X-ray telescopes, each with its own mirror, to gather as many X rays as possible. The European Space Agency (ESA) built the observatory, launching it in 1999. Since then, astronomers have used the craft to observe many different kinds of objects, from comets in the solar system to distant clusters of galaxies.
Each of XMM-Newton’s mirrors actually consists of 58 cylindrical, mirrored surfaces arranged one inside the next. The surfaces reflect X rays at a shallow angle, focusing them onto an image-producing detector called a charge-coupled device (CCD). The three telescopes work together to gather more X rays and to observe the same target in different ways. Angular resolution measures the ability of a telescope to distinguish faraway objects that appear close together. The XMM-Newton’s telescopes give an angular resolution of 1/600 of a degree, equivalent to enabling a viewer to distinguish between the two headlights of an automobile about 30 miles (50 kilometers) away. XMM-Newton produces images that cover an area of sky about the size of the full moon. The X-ray telescopes can also record the spectrum (range of wavelengths) of X rays that an object gives off.
To record a more detailed spectrum, XMM-Newton uses a device called a spectrometer. The craft’s X-ray spectrometer diverts X rays from two of the mirrors and passes them through a grating. The grating separates the various wavelengths into a spectrum in much the same way that a prism spreads white light to produce a rainbow. A special CCD records the spectrum.
In addition, XMM-Newton carries an optical and ultraviolet telescope. This instrument has a field of view nearly as large as that of the X-ray telescopes and can also record spectra.
XMM-Newton moves around Earth in a highly elliptical (oval-shaped) orbit. It ranges from 6,000 to 68,000 miles (10,000 to 110,000 kilometers) in altitude, completing one orbit every 48 hours.
In 2012, XMM-Newton detected X rays originating from near the center of our own galaxy, the Milky Way. Scientists believe the X rays are produced by low-energy cosmic rays colliding with atoms. Cosmic rays are electrically charged, fast-moving particles that travel through space. These particular cosmic rays are thought to be created by fast-moving stars near the galactic center. The discovery marks the first detection of low-energy cosmic rays originating outside the solar system.
See also Astronomy (X-ray astronomy).
