The question “Is travelling to distant galaxies
possible?” has fascinated many teenage minds. I confess I was one of them when
I first read about fictional, intergalactic travel. I was mesmerised by the sheer
magnitudes Space Science encompasses; the farthest of stars, the most violent
of events, the brightest of explosions and the densest of objects. I have been
fascinated by Black Holes ever since
I saw a documentary in 6th grade. What followed was a sudden and
determinedly incessant reading up session comprising several encyclopaediae. It
is for this reason that I’ve decided to write about the most mysterious objects
in the universe. Here’s hoping that you find them as fascinating as I did and
still do. Happy reading!
Introduction:
With the advent of quantum mechanics, we now know that really both
theories are correct.
Under the theory that light is made up of waves, it was not clear
how it would respond to gravity. But if one accepts that light is composed of
particles, then one might expect these particles to be affected by gravity in
the same way as any matter is affected. That said, it is possible to
extrapolate this idea to a star that is sufficiently massive to have a
gravitational field so strong that even light can’t escape from it.
The light from such a star would be pulled back inside before it got
very far. This obviously means that we will not be able to see the star. This
is exactly what a black hole is; a black void in space that is invisible and
which can only be “felt” by means of gravitational attraction. The term black hole was coined by John Wheeler,
an American scientist, in the year 1969.
Death of a Star
We know that there are three possible results when a stellar death
occurs. One, the star shrinks into a
white dwarf. Two, the star shrinks into a neutron
star and three, it collapses
under its own gravity and explodes into a supernova thereby forming a black
hole. This is governed by the Chandrasekhar limit (which is a mass equal to 1.4
times the mass of the Sun) of the star. A star having mass more than this limit
explodes into a supernova. A supernova is a cataclysmic explosion in space
whose brightness outshines even supergiants (a category of stars) sometimes.
The magnitude of this explosion can’t be imagined by the human mind. The energy
released in a supernova explosion far exceeds the energy that will be emitted
by our sun in its entire lifetime.
White dwarves and neutron stars are incredibly dense objects found
in space. A cubic centimetre of matter from a neutron star would have a mass
equivalent to several football stadiums.
However, it’s the third category of stellar death that is of
paramount importance to us. The Chandrasekhar limit determines whether a star
would eventually collapse into a black hole. This limit is merely a mass which
was calculated by Dr. Chandrasekhar to be 1.4 times the mass of our sun. (So
no, our sun will not form a black
hole when its fuel runs out.)
Thus, a black hole is a region of space with
a gravity field so strong that nothing, including light, can escape from it,
i.e. it has an escape velocity greater than the speed of light.
A black hole is thought to be
a result of the gravitational collapse of a massive star at the end of its
life. Black holes may also be created in the
centres of young galaxies.
Imagine a star in space as a ball on a rubber
sheet. A massive object like a star will “bend” space and anything close to it
will fall in towards it. If the ball were so heavy that the sheet stretched
into a long, deep tube, the result would be a black hole.
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