We know that gravity is the forceful rope by which a small body, such as earth, is tethered to a massive body, like the Sun.
However, in the late 1960s, in the constellation Cygnus,
astronomers found a star revolving around
Nothing. They were convinced that they had just discovered a Black Hole.
Black holes are one of the few natural phenomena that were mathematically predicted first and only observed later. They were first predicted in the 1780s
by natural philosopher Jon Michell
Who suggested that the gravity of a sufficiently dense star could be so great that even light emitted
by it would be unable to escape its pull.
The discovery in Cygnus relieved astronomers
or else they would have been labeled as crazy to believe in an object so massive that it was actually invisible.
Because Michelle's star doesn't emit any light it wouldn't look like this, but perhaps something, like this.
This is why they're called black holes, because that's what they are: a black void in space.
To understand why a star would become so withdrawn, we must look at its rough childhood.
A star is born when gravity forces a huge volume of mostly hydrogen gas to collapse in on itself.
This compression increases the temperature of the gas, causing its atoms to violently collide with each other.
These collisions further heat the gas until the hydrogen atoms don't collide in ricochet, but instead coalesce to form helium atoms.
The mass of a helium atom is less than the combined mass of two hydrogen atoms. The remaining
mass is released as energy, the magnitude of which is given by einstein's famous e equals mc-squared equation.
The energy released might be small for two coalescing atoms, but for billions and billions of them, the cumulative release is tremendous.
This, same principle that makes a star shine is replicated inside a devastating hydrogen bomb, albeit in a more controlled manner.
To survive, the star's expansion driven
by the explosion must neutralize the compression driven
by its gravity. Eventually, however, the star will run out of fuel.
All the hydrogen has fused to form helium, all of which then fuse to form carbon and so on until iron is finally synthesized.
Iron refuses to fuse any further, so the star is now jammed packed with heavy elements.
With no more fuel to burn, the star begins to cool, and with no heat to combat the compression, it begins to contract.
In 1928, during his voyage from India to England,
Chandrashekhar realized that a star could survive if the gravity's contraction were counteracted, by the repulsive forces between its clustered matter.
We now call such stars "White Dwarfs".
These stars are hundreds of tons per cubic inch dense, as all the mass is packed in the sphere of just one thousand miles in diameter.
However, if the star were any denser, its gravity
would overcome even the repulsion forces between the electron. He calculated that a cold star
1.5 times the mass of the sun would undergo further contraction.
Yet, it could hold on to life by neutralizing gravity's pressure with it repulsive forces between its neutrons and protons.
Such a star is thus known as a "Neutron Star".
These are millions of tons per cubic-inch dense, as all the masses packed into a sphere nearly twenty miles in diameter!
However, what would happen if a star were to be even denser?
After arriving in England when Chandrashekhar showed his results to Arthur Eddington, the astronomer couldn’t believe that a star could become infinitely dense.
He refused to believe that a star, like the Sun, could collapse to a single point!
The 1960s, Stephen Hawking
and Roger Penrose predicted that an even denser star would contract into a point of infinite density and thus spacetime
curvature, a point where all known laws of physics break down.
This point is called a Singularity.
The star becomes a “black hole” because a singularity distorts the spacetime around it so severely that
any light falling into the pit is held captive…forever.
Nothing escapes it. The boundary where the pit begins is known as the black hole’s event horizon.
It is imperative to understand that black holes don’t suck everything up like a galactic vacuum cleaner.
If a massive or supermassive black hole the mass of the Sun were to replace it, we’d continue revolving undisturbed.
Survival, however, would not be guaranteed.
So, we developed a mathematically rigorous model of a black hole, but how is one supposed to find evidence of its existence?
How is one supposed to find, as Hawking asks, a black cat in a dark room?
Then we pointed our telescope towards the constellation Cygnus.
Cygnus X-1 is one of the strongest sources of X-rays visible from Earth.
Astronomers realized that matter from the rotating star was being blown off into orbit around its
invisible companion. The rotation caused it to heat so greatly that it gave off X-rays.
The unseen thing, however, didn’t necessarily have to be a black hole; it was equally likely to be a
massive star that was simply too faint to be visible.
However, with the knowledge of the dynamics of the star’s orbit,
astronomers determined the object’s mass to be six times that of the Sun.... The object was far too massive to be a
white dwarf or a neutron star.
While we lack any explicit evidence due to its withdrawn
nature, we have a multitude of indirect evidence suggesting that Cygnus X-1 is definitely a black hole.
Stephen Hawking believed that the Universe is replete with such black holes.
He audaciously speculated that the number of black holes is greater than the number of visible stars in the sky.
Surely, millions of stars have exhausted their fuel during the billions of years that this Universe has existed.
Supermassive black holes, billions of times the
mass of the Sun, are believed to exist at the center of our Milky Way galaxy, and probably every galaxy there is.
What’s more astonishing is that Hawking, who went on to occupy the prestigious Lucasian
Chair at Cambridge once held by Newton, showed that black holes aren’t so black after all.
He found that they emit very tiny amounts of radiation that we now call Hawking radiation!
A black hole radiates particles and eventually vanishes, but it takes billions and billions of years for a black hole to completely evaporate.
Lastly, a singularity is the most notorious phenomenon in the Universe. No one knows
what mystery lies at the bottom of the pit, but it seems to combine the final two pieces of physics.
Its large-scale properties concern the classical General Relativity,
while its point size concerns the microscopic field of Quantum Mechanics. Together these combine to form the Theory of Everything.
For over 60 years, no one,
including Einstein, has been able to fully grasp the solution. It would combine every minute discovery that man has made throughout his quest
The Theory of Everything will undoubtedly be the greatest triumph of human reason.