A LOOK AT BLACK HOLES AND THEIR COUNTERPARTS
For as long as the Earth has been around, humans have looked up in awe at the night sky and
wondered about the intricate pieces that make up what is our universe. For most of Earth’s
history, the universe only encompassed what was visible to the naked eye. In 1609, however,
everything changed when telescopes were invented and the realm of the universe opened to
unveil new and mysterious aspects never before seen. Interestingly enough, though technology
has grown to gigantic proportions, there is still a lot we don’t know about the universe, and black
holes, white holes, and wormholes are just a few of the aspects we still have much to learn about.
At this point in time, astronomists have yet to actually see a black hole. So how do they know
that black holes do in fact exist? And how can they deduce that related beings like white holes
and wormholes do (or do not) exist? Through careful deduction and intensive examination,
scientists like Einstein, Stephen Hawking, and many others have been able to give insight into
the deep, enigmatic universe and exactly what these mysterious beings are all about.
Einstein’s general theory of relativity describes gravity as a curvature of space time caused by
the presence of matter. If the curvature is fairly weak, Newton’s laws of gravity can explain most
of what is observed, for example, the regular motions of the planets. Very massive or dense
objects generate much stronger gravity. The most compact objects imaginable are predicted by
General Relativity to have such strong gravity that nothing, not even light, can escape their grip.
Scientists today call such an object a black hole. Why black? Though the history of the term is
interesting, the main reason is that no light can escape from inside a black hole: it has, in effect,
disappeared from the visible universe.
By definition a black hole is a region where matter collapses to infinite density and where, as a
result, the curvature of spacetime is extreme. Moreover, the intense gravitational field of the
black hole prevents any light or other electromagnetic radiation from escaping. But where lies
the “point of no return” at which any matter or energy is doomed to disappear from the visible
universe? How does such a thing come into existence? Black holes are thought to form from
stars or other massive objects if and when they collapse from their own gravity to form an object
whose density is infinite: in other words, a singularity. The singularity is where matter is crushed
to infinite density, the pull of gravity is infinitely strong, and spacetime has infinite curvature.
Here it’s no longer meaningful to speak of space and time, much less spacetime. Jumbled up at
the singularity, space and time cease to exist as we know them. As a stars lifetime goes on,
nuclear fusion in the core generates electromagnetic radiation, including the particles of light
known as photons. This radiation exerts an outward pressure that exactly balances the inward
pull of gravity caused by the star’s mass. As the nuclear fuel is exhausted, the outward forces of
radiation diminish, allowing the gravitation to compress the star inward. The contraction of the
core causes its temperature to rise and allows remaining nuclear material to be used as fuel. The
star is saved from further collapse — but only for
a while. Eventually, all possible nuclear fuel is used up and the core collapses. How far it
collapses, into what kind of object, and at what rate, is determined by the star’s final mass and the
remaining outward pressure that the burnt-up nuclear residue (largely iron) can muster. If the star
is sufficiently massive or compressible, it may collapse to a black hole.
The first person to discuss black holes was a Cambridge man by the name of John Mitchell.
Mitchell argued that it was possible to have a star that was sufficiently massive and sufficiently
small in size that its escape velocity would be greater than the velocity of light (Hawking 117).
Such a star would obviously not be visible on Earth because its light would never reach us, but
Mitchell argued that it might be possible to detect the presence of that star by the effect that its
gravitational field would have on nearby matter (Hawking 117). The idea being implied was that
light could actually be slowed by a strong enough force of gravity. According to the theory of
general relativity, space and time together can be regarded as forming a four-dimensional space
called spacetime (Hawking 118). This space is not flat but rather distorted and curved by the
matter and energy within it. The curvature of spacetime can be observed in the bending of the
light or even radio waves that travel close to a strong gravitational field. This field would be so
strong around and within a black hole that not even light could escape. The boundary of a black
hole is formed by an area called the event horizon, which is formed by light that fails to escape
from the black hole but stays hovering around its edges.
