They are the most mysterious objects in the comos. Ravenous
monters lurking in secret places, they are also the most terrifying. They
power the birth pangs of young galaxies, and may control the fate of the
whole Universe. They might even be gateways to other universes, quite seperate
from our own. But despite their bizarre properties no one, yet has ever
seen one. Black holes. The stuff of science fiction. To astronomers, though,
they are real - as real as the Sun, the Moon, and the stars - even though
they are invisible. We explore the secrets world of black holes, a twilight
zone at the very edge of space and time.
Black holes are aptly named. The "Black Hole of Calcutta"
was a room in 18th-century India used to hold three prisoners. Once, 46
were crammed in - and 24 died. Just as in its astronomical counterpart,
a large amount of matter was concentrated in a small space from which there
was no escape.
Black holes come in all sizes. The most common ones, which
future spacefares are bound to encounter, weigh the equivalent of about
10 Suns. These holes are the remains of supernovas - the explosion of massive
stars. Then there are supermassive black holes that lurk at the centres
of galaxies. Created in the early days of the Universe, they have had almost
15 billion years in which to devour anything that has come too close. The
biggest, weighing in at billions of Suns, drove the frenetic activity of
quasars when galaxies were young. Now , these supermassive black holes
lurk unseen at the heart of many apparently placid galaxies. And at the
other extreme, scientists believe there are countless mini black holes
the size of atoms. Created when the Universe was born, these holes have
been getting steadily smaller.
Black holes have been around since the beginning of time-but
we didn't know about them until astronomers developed new ways of looking
at the Universe. Instead of using just light, today's astronomers explore
space with other wavelengths. Radio waves, infrared, ultraviolet, X-rays,
gamma rays-these invisible radiations have brought information of previously
unknown and violent events taking place out there. Except for the very
smallest, black holes emit no detectable radiation, but their gravity can
have a dramatic effect on their surroundings.
| A false- colour image from a radio telescope shows a region 20 light years across at the heart of our Galaxy. It reveals a ring of hot gas circling what is probably a huge black hole. |
The star that became a black hole
This bleak scene shows the aftermath of a colossal supernova
that wreaked a star and destroyed its family of planets. The remains of
the star have become a black hole; its planets circle as fragments of debris.
If they orbit close to the black hole, gravity will ultimately drag them
in. Farther out, it is a different story. Although black holes have a reputation
for swallowing everything their gravitational strength drops off with distance.
You can still get reasonably close and stay safe.
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