X-ray Observatory captures black holes

Hopkins, Penn State findings may change star, galaxy theories

March 14, 2001|By Frank D. Roylance | Frank D. Roylance,SUN STAFF

WASHINGTON - Black holes, it turns out, are like cockroaches. You can't see them, but there are more out there than you can possibly imagine.

Peering patiently through two seemingly empty gaps in the night sky with NASA's orbiting Chandra X-ray Observatory, astronomers at Johns Hopkins and Penn State universities have discovered the gaps are filled with swarms of objects glowing faintly in X-rays.

Observers aiming powerful ground-based telescopes at the same places then confirmed that most of these feeble beacons are so far away that they had to be powered by massive black holes at the cores of distant galaxies. Some were so far away their X-rays began their journey to Earth as much as 9 billion years ago.

If human eyes could see the X-rays, scientists said, the night sky would be filled with more than 200 million points of X-ray light, each one marking a black hole. And there are probably many more.

"It's back holes and more black holes, dominating the scene as we look back further and further into the universe," said Alan Bunner, a NASA science director.

Black holes are concentrations of matter so dense that neither matter nor radiation can escape their powerful gravity. Massive or "supermassive" black holes - millions or billions of times as massive as the sun - are believed to lurk at the centers of most, if not all, galaxies, including our own Milky Way.

Without nearby matter to feed on, black holes are quiet, and invisible. But when clouds of gas and dust, or whole stars are drawn close, the matter heats up violently just before vanishing into the black hole. Intense gushers of matter and energy - including X-rays - spew out across the universe, revealing the black holes' presence.

Some of the black holes spied by Chandra were veiled in dust and gas, the first time that long-theorized phenomenon has been seen.

The Chandra findings - the longest, most detailed observation of the sky ever made in X-ray wavelengths - are expected to have an impact on current theories for the early evolution of stars, galaxies and black holes. And they'll raise many new questions, such as how so many black holes could form so soon after the Big Bang, some 15 billion years ago.

For decades, astronomers have detected a diffuse X-ray glow, called the "X-ray background," coming from all parts of the sky. They suspected the radiation might come from vast numbers of distant individual sources.

With this new data from Chandra, "90 percent of this background is resolved as individual sources," said Riccardo Giacconi, a research professor at Johns Hopkins, who was the first to detect the X-ray background in 1962 and led Chandra's survey of the southern "Deep Field."

To capture enough of the faint X-rays to record an image, Giacconi had to aim the Chandra observatory for more than 11 days at an empty patch of sky one-quarter the size of a full moon, located in the southern constellation Fornax.

Another team at Penn State made similar observations with Chandra aimed at a spot in the northern skies, near the Big Dipper, with similar results.

"It is like seeing galaxies similar to our own Milky Way at much earlier times in their lives," said Ann Hornschemeier, a member of the Penn State team.

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