Drakkith said:In order to fall into the black hole the mass must decrease it's orbital radius. To do this it is required that it shed momentum and energy, otherwise it's orbit would remain the same and it would not fall in. This is similar to spacecraft having to fire retrorockets in order to start reentry into Earths atmosphere. The infalling material is moving faster, but the total angular momentum is less. This is compensated by having the lost momentum transferred to material that doesn't fall in.
Aziza said:ohh right! But now why is it necessary for objects to actually fall in? Maybe they just spin around the hole without ever falling in, thus no need for angular momentum loss?
Drakkith said:It's not necessary. If it doesn't happen then nothing falls in. However when material such as a gas or dust cloud falls into the black hole, it's not all falling in at the same speed and radius and stuff. As it orbits around the black hole the material nearer to the black hole is moving faster, and the end result is lots of friction that transfers orbital energy into heat and radiation, with the particles that lose energy falling further towards the black hole.
Aziza said:So then why do we need models such as magnetorotational instability to explain loss of angular momentum? Cant we just attribute it to frictional energy loss/radiation? Also why do we say that the agn jets are possibly carrying away the angular momentum?
Drakkith said:I'd guess that friction in this manner isn't the ONLY way to lose angular momentum.
Black hole accretion is the process by which matter is pulled into a black hole's event horizon, increasing its mass and energy. This can occur through the gravitational pull of the black hole on surrounding matter, or through interactions with a companion star.
Angular momentum, or the rotational motion of matter, plays a crucial role in black hole accretion. If the matter being accreted has a high angular momentum, it can form a disk around the black hole, allowing for more efficient accretion. However, if the matter has low angular momentum, it can directly fall into the black hole without forming a disk.
In black hole accretion, angular momentum can be lost through various processes such as magnetic fields, turbulence, and gravitational interactions with other objects. This can alter the structure of the accretion disk and impact the rate of accretion onto the black hole.
Black hole accretion can release large amounts of energy and radiation, which can have significant effects on the surrounding environment. This can include heating up the surrounding gas and dust, triggering star formation, and influencing the growth of galaxies.
Yes, black hole accretion can be observed through various methods such as X-ray and radio telescopes. These observations provide valuable insights into the physics of black holes and their surrounding environments.