The hypotheses about the existence of black holes are true, the detection of gravitational waves 100 years after Einstein predicted them confirms it. Black hole is the strangest and the most powerful object in the Universe. It is in fact, a space-time region with the gravitational pull so strong that no particle and radiation can escape it.
Mostly, a black hole is formed when a dying star collapses. Some black holes after their formation will keep on absorbing other stars or even combining with other black holes to form a supermassive black hole (SMBH). Such black holes are thought to exist at the centers of the most galaxies.
For example our galaxy, the Milky Way itself has a supermassive black hole of about 4.3 million solar mass at its center.
Black hole is detected only when it interacts with matter or visible light. When matter falls into the black hole, gravitational and frictional forces cause the compression of matter.
The compression of matter causes the temperature to rise which results in emission of electromagnetic radiation and thus the formation of an Accretion Disk, resulting in the formation of some of the brightest objects (Quasars) in the universe.
Given below are 10 mind-bending facts about the black holes, backed by its brief cosmological history:
1. Karl Schwarzschild First Discovered the Existence of Black Holes
Einstein’s theory of general relativity did predict the formation of black holes, but it was Karl Schwarzschild, who first discovered its existence.
While working on his relativity theory, Einstein had to deal with tensor calculus, which took him almost ten years to formulate the theory. Despite his endeavour and forbearance, Einstein could only approximate the solutions to his own equation.
However, Karl Schwarzschild, a German Astrophysicist, was the first individual to give rigidly accurate solution to the field equations in Albert Einstein’s theory of general relativity.
He revealed that black holes could indeed form. He accomplished this theory in 1915, the same year Einstein’s articles on general relativity were published.
In his theory, Schwarzschild explained about singularity being surrounded by a spherical gravitational boundary around a black hole, which no light or other radiation can even escape, known as the Event Horizon.
To enable calculation of the size of event horizon, Schwarzschild introduced a formula known as the Schwarzschild radius – the critical radius or a measurement at which any object if collapsed or compressed indefinitely can create a black hole.
If the Sun had to be compressed to a singularity, the Event Horizon would occur three kilometres above its surface. Similarly, if Earth had to be compressed, its Event Horizon would be about the size of marble.
So in theory, you can create a black hole out of anything if you compressed it to an infinitely small space. As you compress the object, the object becomes more and more dense, giving the object a stronger gravitational pull similar to that of a black hole.
Schwarzschild radius differs from object to object, so different objects has to be shrunk down to different sizes in order to create a black hole.
2. You Cannot Directly See A Black Hole
Contrary to popular belief, black holes are not really holes and are not empty. In fact, they are filled with matter stuffed into the least space of any object in the universe so densely that they have gravity so strong which not even light can escape.
No matter what kind of instrument or any electromagnetic radiation device you use, you cannot directly see a black hole.
Even if there were a brightest star shining next to the black hole, instead of reflecting the light like any other objects would, the black hole would swallow the starlight forever. If the star gets closure, it would get swallowed and ripped it to shreds. You might want to check out what it is like when it explodes.
Some theoretical physicists would attempt to say black holes do not really explode. As a matter of fact they actually do. They have an outburst of energy which rips them apart.
Too bad for them, outburst is referred to as explosions and new theory suggests quantum bounce could make black holes explode.
3. Black Holes Can be Used as an Energy Source
Black hole behaves like an electric dynamo. When it spins, it pumps out a huge amount of energy through cable-like magnetic field lines into a huge mass of gas spinning around it.
So when the gas spins, the magnetic fields slow down the spin creating a friction. And, this friction heats the region around black hole to even higher temperature.
As the surrounding areas heat up, the high temperature transforms 10% of mass from the spinning gas into a form of energy once it is in thermodynamic equilibrium with its environment, giving out an electromagnetic radiation known as blackbody radiation.
Our nuclear fusion can convert only about 0.7% of mass into energy. But the condition around black holes gives a huge amount of energy that could power future starships.
Theoretically, as Stephen Hawking showed in 1970, black holes should emit energy from their rotating boundaries, but in the form of radiation produced by quantum fluctuations of empty space itself. Therefore, the energy should be accessible since the rotation is imposed on the space outside the black hole and extractable.
But in practice, based on the current technologies, extracting energy from a black hole is impossible. Also, Hawking Radiation is not that powerful enough.
The best possible explanation regarding this can be found on Kip Thorne’s Black Holes and Time Warps.
4. The Biggest Confirmed Black Hole Lies at the Core of Galaxy Messier 87 (M87)
Messier 87, also known as Virgo A or NGC 4486 is a giant elliptical galaxy in the constellation Virgo. At the core of this galaxy, there lies a largest black hole which is about 6.6 billion times the mass of the Sun. It spans a diameter of about 40 billion kilometers and the disk around it spins at roughly around 1000 km/sec.
Observation suggests that the black hole in the galaxy M87 could be displaced by a distance of 7.75763329 × 10^14 kilometers away from the center. Scientists believe displacement happened likely during the merger of two supermassive black holes (SMBH).
5. Information in the Black Hole May Not be Lost, But May Be Preserved Forever
Physicists previously believed that information, once sent into a black hole, would be lost forever. And this information loss paradox had been fiddling around with physics for almost 40 years. However, a new study claimed that information is not lost once it enters a black hole. But, it can reveal information about what lies within by how the particles emitted by the black hole interact.
Since they have claimed that black holes do not erase information, what happens when the black hole disappears? Information are preserved in it, so they should disappear along with the black hole – which is a violation of quantum mechanics. According to quantum mechanics, every information should be conserved.
Also, according to Stephen Hawking, energy would be lost as the black hole continues to emit particles. As it continues emitting particles, the black hole would eventually shrink and then disappear completely. Moreover, the emitted particles would provide no clues if the information stored in it would be completed gone with the black hole.
However, he later claimed that the information could escape from the black hole. His claim is made clear in the study, Radiation from a Collapsing Object is Manifestly Unitary,” but, there is still no possible explanation of how the information from the black hole can be recovered.
6. Black Holes Could Create New Universes
Theoretical physicists suggest our universe may just be a bubble and we live in a Multiverse. It is no surprising that when a star collapses into a black hole – it crushes down to infinite density to the point where time stops, which then again bounces back and finally begins expansion – which marks the birth of a new universe.
Time stops inside a black hole and it again starts with a bang, so-called Big Bang, in a new universe.
The theory behind black holes spawning into universe is still an active field of research as of now. According to theory, black holes could create new universes. Well, if so many stars collapse, we should not be dazzled when someone talks about multiverse.
Also another theory suggests that a black hole in a higher dimensional universe could have a three-dimensional event horizon and it could spawn a whole new universe as it forms. This criticizes the big bang theory and proposes that our universe was never inside the singularity.
7. Time Slows Down As You Approach Black Hole Event Horizons
As you reach the black hole event horizons – point of no return, time starts to slow down. This is in accordance with Theory of General Relativity which states that when you travel at an extreme velocity nearly at the speed of light, time will slow down.
For example, if you were travelling towards the black hole and your friend was watching you from a great distance, your friend would see your watch to be going slower and slower as you approach the event horizon. And you would see your watch to be ticking at a perfectly normal rate.
Also from a great distance, you would see that your friend’s watch ticks at a much faster rate, while he would see his own watch ticking at a normal rate.
In fact, both your watch and that of your friend’s tick at a normal rate. It is just a special relativity. So, if you were to return once after being outside the black hole to see your friend, you would find that your friend had aged more.
Black holes greatly influence space–time continuum, to the point where even light cannot escape. This phenomenon is best explained in Stephen Hawking’s Into a Black Hole.
8. If You Fall Into a Black Hole, You May Live as a Hologram
A recent research in theoretical physics has shown that anything falling into a black hole would become a hologram, a near-perfect copy of itself.
Complementarity hypothesis requires that hologram created by a black hole should exactly look the same as the original, however this new fuzzball-firewall debate concluded strict complementarity is impossible. Therefore, perfect hologram cannot form on the surface of black hole.
So if the world gets sucked by a black hole, the world would become a hologram – an imperfect hologram which we would not even know. The study challenges the so claimed – anything that falls into a black hole would be immediately destroyed once it hits the firewall.
9. Black Holes Will Not Suck Up Everything in the Universe
First of all, black holes are not cosmic vacuums that suck up everything in the universe. They only suck up what crosses the Event Horizon – the point of no return. So if something goes pass beyond the horizon, it would eventually hit the singularity.
The gravitational field around the black hole is same as the field that surrounds any other object of the same mass.
Secondly, it is estimated that our universe has 10^24 stars and most stars in our universe are not massive enough to become a black hole at the end of their lives. They either end up as neutron stars or white dwarfs. However, if Edwin Hubble is right about the Universe expanding, then our universe may end up as a cosmic graveyard one day.
10. The Sun Can Never Become a Black Hole
The Sun is just an average sized star, it is not massive enough to become a black hole. Only stars with considerable large masses end their lives as black holes. So even if the Sun had to run out of nuclear fuel in its core four billion years from now, it would enter a red giant phase.
During the red giant phase, the scary part is that it would eventually swallow up Mercury and Venus. The oceans in the Earth would start boiling and atmosphere would escape, and finally the Sun would become a white dwarf star. Any stars should be 20 times the Sun’s mass in order to form a black hole at the end of their lives.
If the Sun became a black hole due to some reason, the Earth and surrounding planets would not get sucked into it and its Event Horizon would be only about 3 kilometers. Every planet would be in their respective orbits, but there would not be light, and as a result there would be extreme cold weather.
[Image: AlphaSpace via DeviantArt]