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Tuesday, 23 April, 2002, 11:06 GMT 12:06 UK
Cosmic ray mystery 'solved'
Nasa/HST/Timothy Hamilton
The galaxies were all found close to The Plough
Astronomers believe they may have identified the source of galactic cosmic rays, the highest-energy particles in the Universe.

The American space agency (Nasa) scientists think these fragments of matter come from "retired" quasars, galaxies containing supermassive black holes that once shone with astonishing brilliance.

The fact that these four giant elliptical galaxies are apparently inactive makes them viable candidates for generating ultra high-energy cosmic rays

Dr Elihu Boldt, Nasa scientist
The researchers came to their conclusions after studying several elliptical-shaped galaxies sited in the sky close to the handle of The Plough (Big Dipper).

"Each contains a central black hole of at least 100 million solar masses that, if spinning, could form a colossal battery sending atomic particles, like sparks, shooting off towards Earth at near-light speed," the agency reports.

Starting point

Cosmic rays are bits of matter: protons, electrons, and atomic nuclei which have been stripped of their electrons.

Although supernovae, gigantic exploding stars, have long been suspected as the source of most rays, the origin of the highest-energy rays has been more difficult to tie down.

The magnetic fields that pepper our galaxy and Solar System and surround the Earth distort their movements, making it very hard for scientists to trace back along a flight path to find a starting point.

However, researchers at Nasa and Princeton University have now identified four elliptical galaxies they think could be associated with high-energy cosmic ray production.

Viable candidates

These huge galaxies were probably once quasars, where enormous black holes swallowed up everything that came near them and blasted intense radiation out across the Universe.

"For the first time, we see the hint of a possible connection between the arrival directions of ultra-high energy cosmic rays and locations on the sky of nearby dormant galaxies hosting supermassive black holes," said Princeton's Dr Diego Torres.

The researchers believe that if these galaxies now have spinning, albeit more sedate, black holes they would possess just the right environment to generate and then accelerate cosmic rays across space.

"The very fact that these four giant elliptical galaxies are apparently inactive makes them viable candidates for generating ultra high-energy cosmic rays," said Dr Elihu Boldt, of Nasa's Goddard Space Flight Center.

Drenching radiation from an active quasar would dampen cosmic-ray acceleration, sapping most of their energy, he added.

See also:

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