An Insight into Celestial Vacuum Cleaners: Black Holes
Until the emblematic picture of the phenomenon that stood fiery-ringed at the heart of the M87 galaxy, black holes were simply another myth that were destined to transcend generations of astrophysicists. Katie Bouman’s 5 petabyte image was a revolution in science as a whole and a milestone for humanity, headlining newspapers and magazines alike. So what exactly is a black hole?
A black hole is the densest naturally occurring phenomenon in the universe, with the neutron star being a not-so-close second. It is a region that exists in and warps the very fabric of space-time. A black hole consists of a singularity (a point of infinite density) at its very core, which is enveloped by an event horizon, infamously nicknamed “the point of no return”. This owes to the fact that nothing- not even light (the fastest thing in the universe) can escape from the gravitational pull of the singularity. How are these nightmarish phenomena formed?
Black holes are dead stars. Coincidentally, so are humans, and every other piece of matter in the known universe. When a star’s mass exceeds the Chandrasekhar Limit (of approximately 1.4 solar masses), its energy due to nuclear fusion and electron degeneracy pressure (the pressure caused by fast moving electrons with high energy states) is unable to counteract the immense gravity that is exerted inwards. The star then implodes, in what we call a supernova. As this happens, most of its matter is blasted outward at an extremely high speed, leaving behind a superdense ball of matter. If this ball’s mass is greater than 3 solar masses, it becomes a black hole. If it is less, it becomes what we know as a neutron star.
Despite the popular notion that black holes are only capable of pulling things in, a certain Professor Stephen Hawking theorised the existence of Hawking radiation, a phenomenon where black holes seemingly emit particles. Upon closer inspection by Hawking, this isn’t quite the case though. So where do these particles come from?
When a particle-antiparticle pair (coupled particles with the same mass, but the energy sum of which is zero, e.g. an electron and a positron) pops into existence, they almost always annihilate each other almost instantaneously and disappear, never to be seen. However, in the instance that a particle-antiparticle pair appears near the event horizon of a black hole, there is a chance that one of the particles falls into the black hole while the other escapes, hence seemingly being “emitted” by the black hole itself. The theory of Hawking radiation follows the second law of thermodynamics, which states that the entropy (the degree of disorder) of a system will only increase with time. Without going into too much detail, this law is accounted by the fact that one particle of the pair, (i.e. the particle that escapes) has positive energy, while the other (that falls in) has negative energy (which is why they can add up to zero and disappear), hence decreasing the mass of the black hole to decrease ever so slightly as it falls in. This is the process by which black holes evaporate or decay, but it would take over 10 to the power 64 years for a black hole of 1 solar mass to evaporate, i.e. 10000000000000000000000000000000000000000000000000000000000000000 years.
This might seem like a wild guess, but I don’t reckon our generation will live to see it happen.
Hawking, S. (2018). A Brief History of Time. Random House US.Staff, S. (n.d.).