"At higher temperatures, the whole spectrum of emissions of events are displaced toward higher energy radiation, in particular X-ray," he said.

The XMM, as it would look in orbit

Quasars, black holes and supernova remnants -- typical targets of X-ray telescopes -- are thought to be the sites of major cosmological birth and death events. Hot gases are whacked with intense energy fluxes and heat that can only be seen as X-rays.

Like NASA's Chandra, XMM's heart is a set of nested, curved mirrors capable of collecting some of the most energetic and powerful "light" or electromagnetic radiation in the universe, the stuff that heats up to temperatures above a million degrees and shows up supernovas, active galactic centers, galaxy clusters and black holes -- basically anywhere that new matter is being created or destroyed.

For the first time in the 35-year history of X-ray telescopes, Chandra and now hopefully XMM can return data that helps scientists learn what most of the universe is made of and the violent explosions that create it.

Along with its three X-ray detectors, XMM includes a visible light telescope which is key to helping scientists correlate energy bursts with other data.

"In principle, you can do a correlation between X-ray observations in space with visible optics on the ground, but in practice it has proven fairly difficult and unhandy," Kletzkine said. "Scientists are banking a lot on this."

Claude Canizares, a Massachusetts Institute of Technology scientist who helped develop Chandra and has used it for experiments, said he has been granted time next sprint to use XMM to address the same question he has used Chandra for: where is the universe's "normal matter"?

The stars and gas that we can see with visible light telescopes only account for a tenth of the total mass of the universe. Most of the rest of that mass, probably comprised of gases between galaxies, is called normal matter. Yet scientists know practically nothing about it.

Canizares wants to use XMM to look at a particular quasar several billion light years away from Earth (a light year is equivalent to about 6 trillion miles) to study how hot gases interact with nearby light and radiation. He hopes that will help him stumble upon the properties of normal matter.

"Normally, people talk about where is the 'dark matter,'" Canizares said. "The funny thing is, we don't even know where the normal matter is."

Chandra and XMM will complement each other, he said, just like a photographer might choose to use fast film for pictures taken in dim settings and a slow film for high quality images taken in bright light.

"For some problems, you're willing to give up fine details, just collecting a lot of signal is what you need to do," he said. "For those XMM is better. If you want fine details in image or spectrum, then Chandra is better."

On top of Chandra and XMM, the Japanese are expected to launch an X-ray observatory next year, called Astro-E.

"For years we've been limping along," Canizares said, "and then all of a sudden we've got three limousines coming up carrying us."