X-raying the violent Universe

XMM is 10 metres long, just fitting on Ariane

By BBC News Online's Dr Damian Carrington

The most sensitive X-ray satellite ever is set for launch on 10 December and aims to reveal the most violent regions of the Universe in unprecedented detail.

Matter destroyed in black holes 'scream' out X-rays

It will probe black holes, where matter is being torn apart and the glowing remnants of supernovae. The latter could be the key to understanding the origin of the enigmatic cosmic rays that pervade the Universe.

Also captured will be images of 'vampire stars', which feed off their neighbours by dragging matter through space.

And the high-speed cameras aboard the European Space Agency's X-ray Multi-Mirror satellite (XMM) will allow X-ray pulses and flashes to be grabbed, possibly pinpointing the gigantic explosions of colliding black holes.

Most sensitive

The key to XMM is new technology which makes it many time more sensitive than even Nasa's recently launched Chandra X-ray observatory.

The conical mirrors are highly polished

Rob Laine, XMM's production manager explains: "XMM has been made possible by a big breakthrough in X-ray optics. Previous X-ray satellites used relatively thick optics - one to 2.5 centimetres - and that limited the capability of putting many mirrors inside a spacecraft, as each one was extremely heavy.

"For XMM, we have developed a technology where the mirrors are only less than one millimetre thick. Therefore we can pack many more mirrors in the same volume and therefore have much more collecting power than any other satellite before."

XMM has three barrel-shaped telescope modules. Packed inside each are 58 concentric, tube-shaped mirrors. This gives XMM a "gargantuan appetite" for X-rays, according to Esa.

The mirrors guide the X-rays to the detectors

The mirrors are made from gold on a nickel backing. Each one was shaped to an accuracy of a thousandth of a millimetre, and then polished to a smoothness a thousand times better still.

The mirrors guide the X-rays to focus on the detection equipment at the far end of the spacecraft. The total mirror surface is 120 square metres.

The detectors will not only record X-ray images but also measure the 'colour' or wavelength of the X-rays gathered to spot the presence of individual elements.

Each 'eye' contains 58 concentric mirrors

There is also a sensitive optical telescope on board, capturing visible and ultraviolet light, to give astronomers additional information about the X-ray emitting bodies they will study.

Highly eccentric orbit

XMM is the largest science satellite ever built in Europe and is due to be launched by an Ariane-5 rocket from the European Spaceport in Kourou, French Guiana.

After being released by the launcher, XMM will be placed in a highly eccentric 48-hour orbit. It will rise to a distance of 114,000 km from the Earth before swooping back to within 7,000 km of our planet.

Ariane 5 will carry XMM into orbit

This orbit offers the best possible contact with ground-tracking stations and allows the satellite to pass rapidly through the Earth's radiation belts, which could harm its delicate science instruments. Above all, it will offer astronomers the longest-possible observation periods.

X-rays from space cannot penetrate the Earth's atmosphere and were first measured in the 1950s, by instruments mounted on sounding rockets. Many astronomers consider the turn of the millennium a golden age for X-ray astronomy. XMM is set to fly, Nasa's Chandra Observatory is already in space and Japan is set for a fifth X-ray mission early next year.

And Europe is already planning a next generation X-ray astrophysics facility, called Xeus. This will use the International Space Station and will allow, for example, the study of the very first black holes.