A European space project hopes to prove conclusively the existence of black holes,
writes Tim Furniss
Telescope to take a look back in time
A EUROPEAN space telescope to be launched next year could return the first pictures of matter being sucked into a black hole, writes Tim Furniss.
Astronomers hope the European Space Agency (ESA) x-ray multi-mirror telescope (XMM) will provide conclusive evidence of the existence of black holes, believed to be remnants of exploded stars created shortly after the Big Bang.
They emit no radiation, making them virtually invisible. However, their enormous gravitational force, which absorbs gas and dust, betrays their existence.
Before matter drops into the abyss, where it is lost forever, it revolves around the black hole at almost the speed of light. The frictional forces among these accelerated gas particles generate temperatures of several million degrees, emitting x-rays that can be detected.
XMM, which will be launched by an Ariane 5 in August 1999, is equipped with three x-ray imaging cameras, two high-resolution x-ray spectrometers and a 300mm-diameter optical monitoring telescope that will for the first time enable simultaneous observations in the visible and near-infrared wavelength, as well as x-ray.
XMM is more than 30ft long and weighs almost four tons. The telescope will be put into an orbit 71,250 miles by 4,300 miles and will take 48 hours to go around the Earth once, enabling the craft to be far outside the Earth's interfering radiation belts for as long as possible.
Data will be transmitted in real time to ESA's control centre at Darmstadt, Germany, and Leicester University, which is the XMM science survey centre. The telescope will also be used to photograph neutron stars, supernova remnants, the centre of the Milky Way and cores of distant galaxies.
X-ray satellites have been launched before, but XMM will be the most sensitive and, ESA claims, be able to look back halfway into the history of the universe, with the ability to detect millions of x-ray sources, compared with the 300 detected by a Nasa satellite, Uhuru, in the 1970s and the 120,000 by the US-UK-German Rosat spacecraft launched in 1990.
The XMM will be five times more sensitive than Nasa's advanced x-ray astrophysics facility (Axaf) telescope, to be launched by the space shuttle Columbia next January.
Although the telescope itself was built by the prime contractor, Daimler Benz Aerospace Space Systems in Germany, the XMM's altitude and orbit-control system (AOCS) has been built by Matra Marconi Space (MMS) in Bristol and its propellant tanks by Dowty UK.
According to Mike Backler, the XMM project manager at MMS Bristol, the AOCS will enable XMM to remain pointing perfectly at a specific target for up to 40 hours.
"The XMM is accurate enough to detect perfectly the position of four small melons perched on the top of St Paul's Cathedral in London from a distance the equivalent of Bristol," says Backler.
The less a spacecraft "jitters" or vibrates, like a wobbly pair of hand-held binoculars pointing at the night sky, the better the images.
The AOCS is made up of a computer, electronics, failure-detection and correction systems, reaction wheels, star tracker, fine sun sensors, inertial measurement unit, a device that keeps the telescope on course by detecting the position of the sun, and an attitude anomaly detector. The XMM has a nominal mission life of 2 1/2 years but ESA hopes that it will continue to operate for at least 10 years. To save costs, ESA plans to use the XMM service module design for other spacecraft, including the Integral gamma-ray observatory, to be launched in 2001.
Even before XMM has been launched, ESA is also already looking to the next x-ray telescope, called Xeus, which will be so sensitive it will be able to reach 80% back into the history of the universe - even before the birth of galaxies.