Physics - Classical Mechanics - Black Holes and Schwarzschild Radius

in StemSocial5 months ago

[Image1 - First Image of a Black Hole - Messier 87]


Hey it's a me again @drifter1!

In this article we will continue with Physics, and more specifically the branch of "Classical Mechanics". Today's topic are Black Holes and the so called Schwarzschild Radius.

So, without further ado, let's get straight into it!

Black Holes

First of all, Black holes aren't actually holes. Black holes are stars that have collapsed gravitationally, so much that not even light can escape. Stars achieve a certain balance between the crushing force of gravity and the push of the incredibly hot gases. This balance exists, because there is fuel to burn in the fusion process within the star. When the fuel runs out then gravity collapses the star, and the more massive the star, the more intense the collapse.

Small Stars become White Dwarfs

Stars about the size of the Sun collapse into something called a white dwarf. After their fuel runs out, gravity produces enough pressure for electrons and nuclei to be packed tightly together. The result is an object about the size of the Earth.

Large Stars become Neutron Stars

Stars in the range of six to eight times the size of the Sun undergo a catastrophic explosion known as a supernova. The force of gravity jams the electrons together into the nuclei creating a neutron star, with a small diameter of some Kms. The neutron star stage is the final combination and the forces between the neutrons prevent further collapse.

Massive Stars turn into Black Holes

Stars that are ten or more times larger then the sun collapse even the neutron core, thus forming a black hole. The repulsion that prevented the neutron star to collapse cannot withstand the gravity force of about two to three solar masses. Gravity near a black hole is so strong that not even light can escape it. And matter or radiation inside the sphere of influence of the black hole, known as the event horizon, falls inward and cannot escape. A black hole with ten times the mass of the sun, has an event horizon of about 30 Km.

Types of Black Holes

Massive stars of about 10-100 times the size of the Sun turn into galactic black holes. In the center of galaxies roam supermassive black holes - *insert Muse song* - that can range up to billions of solar masses in size.

How to See Them

From their definition black holes are invisible. Its possible to identify stellar black holes by observing light that disappears in a binary star system, where one of the stars is a black hole. Black holes also emit X-rays and larger ones even form a swirling gas disk around the event horizon.

Schwarzschild Radius

The Schwarzschild Radius (or gravitational radius), is the radius below which the gravitational attraction between the particles of a body forces it to undergo an irreversible gravitational collapse. Its the radius below which massive stars turn into black holes. The radius was investigated in the early 20th Century by German astronomer and physist Karl Schwarzschild.

Mathematically, this radius can be calculated as follows:


  • G : the gravitational constant (6.674 × 10-11 Nm2/kg2)
  • M : the mass of the object (in Kg)
  • c : the speed of light (~3 × 108 m/s)

One Solar mass

For the sun, with a mass of about 1.989 × 1030 Kg, to become a black hole, it must be compressed into a radius of:

Three Solar Masses

An object of three solar masses needs to be compressed to at least:


What needs to be the radius of the Earth, mass of 6 × 1024 Kg, for it to turn into a black hole?

The Earth needs to be compressed into a 8.89 mm radius, which is extremely small. Only some bits larger then the thickness of a strand of hair, which is in the range of 0.04 to 0.1mm!


Lastly, Can a human also become a black hole?

The answer is of course Yes, but what is the Schwarzschild Radius for a let's say 60 Kg Human being?

Alright that's infinitesimal small. An atom is in the scale of picometers (pm) 10 -12 m, meaning that a human has to become smaller then an atom, which is basically impossible.






Mathematical equations used in this article, where made using quicklatex.

Previous articles of the series

Rectlinear motion

Plane motion

Newton's laws and Applications

Work and Energy

Momentum and Impulse

Angular Motion

Equilibrium and Elasticity


Final words | Next up

And this is actually it for today's post!

Next time we will get into a new chapter of Classical Mechanics: "Periodic Motion".

See ya!

Keep on drifting!

@tipu curate 2

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