In a cosmic
game of pinball, black holes
fling high-energy protons into space, where they zigzag around at near
light-speeds before smashing into low-energy protons, finds a new study.
Then the
collisions send bursts of gamma
rays flying out from the center of our galaxy, which explains for the first
time the mechanism for the high-energy jets first spotted in 2004.
This proton-slinging
could explain more than this cataclysmic light show deep in our galaxy. The scientists suggest other
black holes in the universe could
rely on the pinball mechanism to produce enormous jets of light.
"Our
galaxy's central supermassive object has been a constant source of surprise
ever since its discovery some 30 years ago," said study team member Fulvio
Melia, an astrophysicist at the University of Arizona (UA).
"Slowly
but surely it has become the best-studied and most compelling black hole in the
universe," Melia said. "Now we're even finding that its apparent quietness over
much of the spectrum belies the real power it generates a mere breath above its
event horizon--the point of no return."
Rockin'
rays
In recent
years, astronomers have tried to get at the secrets of this gamma-ray
light show, which originates from our galactic middle in the neighborhood
of a supermassive
black hole called Sagittarius
A* and boasting 3 million solar
masses.
Like all black holes, Sagittarius
A* is veiled in a whirlpool of churning spacetime, the outer border of
which is called the event
horizon. Nothing, not even light, can escape the black hole's immense
gravitation once it passes this perimeter, so astronomers have had a difficult
time figuring out what exactly goes on around a black hole.
And also
like many black holes, Sagittarius
A* emits X-rays as it devours matter crossing the event
horizon.
Based on years
of theoretical sleuthing, Melia and his colleagues have suggested that chaotic
magnetic fields near this event horizon accelerate protons and other particles
to high energies.
Play
pinball
To put the
theory to an Earthly test, Melia and David Ballantyne, also of UA, created a
computer model that tracked the trajectories of more than 200,000 protons
floating freely in a superheated gas called plasma.
The model
found that gravity from Sagittarius
A* hurls protons from the magnetized
plasma to near light-speeds with energies as high as 100 trillion electron volts.
As if shot from a pinball machine's flippers--the black hole in this case--the
particles zigzag along random paths [image]
so that it takes thousands of years for each to make it beyond 10 light-years
of the black hole.
Once in
interstellar space, the protons smash into low-energy protons to form pions.
These particles of matter immediately decay into high-energy gamma
rays that shoot in all directions.
"So a very
high-energy proton can dump its energy into radiation through that mechanism," Ballantyne
told SPACE.com.
The
discovery could explain how the most powerful black
holes in the universe produce their jets extending over intergalactic
proportions, the scientists suggest.
"The same
particle slinging almost certainly occurs in all black-hole systems, though
with much greater power earlier in the universe," Melia said.
The
findings are detailed in the current issue of Astrophysical Journal Letters.
advertisement
