# How Do Black Holes Swallow Matter?

Rev. Green | 12:52 Fri 04th Jan 2019 | Science
How do Black Holes swallow matter? They have high gravity, but almost every object that approaches them should go into orbit in the same way that almost everything in the Solar System orbits the Sun. Even a missile fired from Earth directly towards the Sun will continue to orbit. Is the angular momentum of an object near a Black Hole destroyed by tidal effects?

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I was going to give a detailed answer but it maybe takes too long to prepare. The gist of it, though, is that you also have to consider the energy of the object in orbit, as well as its angular momentum. Objects that come near a black hole tend to have very low energies, and, as a result, don't form closed orbits, instead wanting to come close to the black hole and then...
18:11 Fri 04th Jan 2019
Question Author
IJKLM says that gravitational force transfers angular momentum from a body to the black hole. I understand that gravity can change (linear) momentum, but how can it affect angular momentum?
There is angular momentum in the orbit of one body around another, as well as in the rotation of the body around its own axis.

The earth has angular momentum with respect to the sun both through its 24-hour rotational period and its 365-day orbital period.

The AM of the orbital motion is far greater than that of thre daily rotation.

Angular momentum of the earth due to the 24-hour period is around 7.1 x 10^33 kg m^2 s^-1

Angular momentum of the earth due to the orbit around the sun is around 2.7 x 10^40 kg m^2 s^-1 (around 5 million times greater)

https://www.vanderbilt.edu/AnS/physics/astrocourses/ast201/angular_momentum.html

If the falling body transitions from largely linear motion to elliptical/hyperbolic motion (orbiting), the body gains angular momentum.

Where does that comes from?

The large massive body transfers some of its AM to the smaller body.

That can be seen through the orbital slingshot of a spacecraft, in which the spacecraft accelerates, at the expense of (a very small part of) the rotational momentum of the planet around which it slingshots.

Hope it helps
Question Author
Thanks IJKLM. Can I check that I've (partly) understood?
We can forget angular momentum from spinning objects: the Earth's spin slows due to tidal effects, but that doesn't concern us.
A spacecraft passing a planet can have its angular momentum around the Sun greatly increased, and the planet's angular momentum around the Sun will decrease by the same amount, which is a tiny proportion of the planet's angular momentum.
For an object to fall into a black hole its angular momentum must reduce. The black hole's gravity exerts a pull directly towards the black hole and cannot alter the angular momentum of any orbiting matter. Are you saying that other orbiting objects will provide the slingshot effect?
This topic appears to be spiraling out of control.

Perhaps orbital decay would help explain how black holes eat.

https://en.wikipedia.org/wiki/Orbital_decay#Tidal_effects

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