THE STARS
our own Galaxy show that a very massive black hole is
present there.
It is hard to decide what happens inside a black hole,
because beyond the event horizon all the ordinary laws of
science break down, and we can really do little more than
speculate. All sorts of exotic theories have been proposed.
For instance, is it possible that material vanishing into a
black hole can reappear at a ‘white hole’ elsewhere in the
Galaxy, or in a completely different part of the universe?
Can a black hole provide a bridge between our universe
and another? Stephen Hawking has suggested that a black
hole may lose energy, and finally explode, but this again is
only a theory, and at present we have to confess that our
understanding of black holes is very far from complete.
At least we have the satisfaction of knowing that our
Sun will never produce a black hole. It is not nearly mas-
sive enough, and it will end its career much more gently,
passing through the white dwarf stage and coming to its
final state as a cold, dead globe.Impression of a black hole
(Paul Doherty). Material
can be drawn into the black
hole, but nothing – absolutely
nothing – can escape.
Therefore, a black hole can
only be detected by its
effects upon objects which
we can record.Black holes revealed in the
Great Observatories Origins
Deep Survey field. By
comparing visible light, X-ray
and infrared views, scientists
have pinpointed
supermassive black holes in
young galaxies. Top and
bottom left are combined
images from Hubble and
Chandra; at right are the
Spitzer Telescope’s infrared
views of the same portion. NGC 7742, a spiral galaxy
imaged in 1998 with the
Hubble Space Telescope.
This is a Seyfert active
galaxy, probably powered
by a black hole at its core.
The core of NGC 7742
is the large yellow ‘yolk’
in the centre of the image.
The thick, lumpy ring
round this core is an area
of active star birth. The ring
is about 3000 light-years
from the core. Tightly
wound spiral arms are
visible. Surrounding the
inner ring is a wispy band
of material, probably the
remains of a once very
active stellar breeding area.152-191 Atl of Univ Phil'05 7/6/05 1:25 pm Page 185