ALBUQUERQUE, N.M. - On June 18, 1962, a rocket outfitted with a Geiger counter soared above Earth and collected about five minutes worth of rather primitive data, nonetheless discovering the first source of X-rays outside our solar system, an object called Scorpius X-1.

Forty years later, astronomers are blessed with four space-based X-ray observatories. Unlike a simple Geiger counter, these powerful instruments "see" like real telescopes, and they have peeled back a skin of the universe to photograph previously invisible objects and phenomena.

Just like light, radio waves or infrared radiation, X-rays offer a unique view of the universe.

These emissions are all part of the same electromagnetic spectrum, as it is called. But X-rays are produced only by the most energetic processes. They penetrate the universe largely unscathed and undeterred. They therefore provide insight into what's going on around a black hole or a neutron star, for example. These dense objects are known to generate X-rays when matter from a companion star, called a binary, is siphoned inward, accelerated to nearly the speed of light and superheated. Very hot gas emits X-rays, and only an X-ray telescope can see them.

Scorpius X-1, that first X-ray source ever detected from beyond the solar system, is now known to be one of these binary systems, and astronomers have since found them all over our galaxy and beyond. They are still finding them, filling gaps in their understanding of how stars live and die.

One new study, based on data from the European Space Agency's XMM-Newton satellite, found more than 100 previously unknown X-ray sources in the Milky Way's nearest large neighbor, the Andromeda galaxy.

The X-ray sources are thought to be binary star systems similar to Scorpius X-1.

Importantly, the binaries are not concentrated near the center of Andromeda, where most of the previous X-ray sources had been found.

"With earlier surveys we were able to study the X-ray capital of the galaxy, its center," said Konstantin Borozdin of the Los Alamos National Laboratory. "Now, with data from the most sensitive survey ever performed [on Andromeda] using X-rays, we can see dimmer lights from the galactic countryside."

Some of the sources were found to fluctuate in intensity. One powered down and re-appeared every 2.8 hours. The cause, the researchers think, is the inflowing gas passing in front of a black hole or neutron star as the gas and the companion star orbit the central object. That process allows the researchers to calculate just how close the two objects are.

"This binary system is so compact that it can be easily hidden inside a Sun-like star," said Los Alamos' Sergey Trudolyubov.

X-rays are also employed in the search for truly invisible material. So called "dark matter" is thought to fill much of the universe. Scientists say it must be there because when they examine our galaxy and others, the visible matter they find is not enough to keep the collections of stars from flying apart.

Previous research has yielded an estimate for dark matter that is widely accepted. Some 90 percent of the matter in the universe is thought to be dark.

But this estimate derives in part from X-ray studies of huge clusters of many galaxies, which are relatively rare.

A new study led by John Mulchaey of the Carnegie Observatories yielded a similar estimate for the amount of dark matter in a smaller structure, a group of just a handful of galaxies that is thought to be a far more common configuration.

The researchers used XXM-Newton to measure the temperature of a cloud of hot gas that surrounds the galactic gathering. The temperature revealed that the cloud should have dispersed into space. Since it has not, it must be held together by an unseen mass that Mulchaey and his colleagues were able to estimate.

They found that there must be a combined mass in the system of 20 trillion Suns, but visible observations only reveal 2 trillion Suns worth of stuff. The result confirms the broader estimates of dark matter.

Using two space-based observatories and a novel estimation technique, another research team claims to have found distant galaxies that are 10 times fainter than anything previously detected in X-rays.

The new galaxies are not among the most distant known. But they are very dim. In some cases, each galaxy's X-rays probably come from several binary stars -- similar to Scorpius X-1 -- generating a combined effect that is detectable, explained Richard Griffiths, a Carnegie Mellon University professor of astrophysics who led the new research.

In other galaxies, mid-sized black holes produce the X-rays. Griffiths said his team may be witnessing a building-block process that would lead to a supermassive black hole, a gravity well that could contain the mass of billions of Suns and anchor an entire galaxy.

Griffiths and his colleagues combined data from XMM-Newton and NASA's Chandra X-ray Observatory.

Studies like these are becoming almost routine as the field of X-ray astronomy matures. Its practitioners have instruments to work with that make the 1962 Geiger counter -- a marvel of technology in its day -- look quaint.

"The faint galaxies now being detected in X-rays using large X-ray telescopes in space are about 10 billion times fainter" than Scorpius X-1, Griffiths pointed out.