# What is Accretion disk: Definition + 25 Threads

An accretion disk is a structure (often a circumstellar disk) formed by diffuse material in orbital motion around a massive central body. The central body is typically a star. Friction, uneven irradiance, magnetohydrodynamic effects, and other forces induce instabilities causing orbiting material in the disk to spiral inward towards the central body. Gravitational and frictional forces compress and raise the temperature of the material, causing the emission of electromagnetic radiation. The frequency range of that radiation depends on the central object's mass. Accretion disks of young stars and protostars radiate in the infrared; those around neutron stars and black holes in the X-ray part of the spectrum. The study of oscillation modes in accretion disks is referred to as diskoseismology.

View More On Wikipedia.org
1. ### I Can there be slowly-falling accretion disks in black holes?

Black holes accrete mass around them and it falls gradually up to the even horizon where mass is trapped by the black hole forever. However, the rate of mass falling from the accretion disk to the black hole ranges from being very fast to very long-lived, depending on various conditions...
2. ### I Radiatively efficient accretion onto BHs

It is said that accretion disk around compact objects like black hole can convert up to 40% of the mass of an infalling material into energy. This means, to my understanding, that if we throw 1kg of matter onto a BH through an accretion disk, during the accretion 0.4kg worth of energy in the...
3. ### Density of a patch of an accretion disk

In the frame of the patch ##-(1/\rho) \nabla p = - \nabla \phi##, and putting ##\nabla p = (\partial p/\partial \rho) \nabla \rho = c_s^2 \nabla \rho## and taking the ##z## component gives\begin{align*} -\frac{c_s^2}{\rho} \frac{\partial \rho}{\partial z} = -c_s^2...
4. ### A Life supported by radiation from the accretion disk of a black hole

For a planet to be able to support life, it needs to have a source of energy. In our case this energy comes from the sun. But in this paper, the author argues that a rogue planet (a planet that has been ejected from its stellar system and no longer orbits any star and is wandering in...
5. ### I Black hole image: What are those "lobes"? [M87 10April2019]

Lobes Did anyone hear an explanation of the appearance of the lobes visible in the published image? I only caught part of the Q&A. (Visible most prominently at at eleven o'clock and four o'clock positions, and to lesser degree at three and nine) Do these type of observations generate "lense...
6. ### A Dark Matter Accretion Disk for Black Hole (Neutron Star)

Hello! Dark Matter (if exists)(if it is in form of particles - collisionless) could also be attracted by Black Holes (or Neutron Stars) and form accretion disk. I would like to discuss possible properties of such hypothetical object. DM particles could be trapped and settled in around...
7. ### Accretion rate onto a WD over time (relation)

Hi all, I was wondering if there is a correlation between the accretion rate and time. I think it should decrease as time increases, but I can't find the right correlation
8. ### A Why Are These Accretion Disk Concepts Challenging?

I was studying about Accretion disks and found some difficulties regarding some concepts. My questions are 1. For an accretion disk, ## v_r<<c_s ## Why? 2. The conservation of mass equation is derived as, The mass in an annulus of radius ##\Delta r## is ##2\pi r \Delta r\Sigma ## and it is...
9. J

### B Black holes cause neutron fusion in neutron stars

I read an article today stating that the possible explanation for the near total absence of heavier elements such as gold and uranium in many galaxies may be due to those galaxies not forming around a central black hole that has in absorbing one or more neutron stars causing fusion of neutrons...
10. A

### A Exploring the Standard Accretion Disk Model: Stationarity and Limitations

hi I'm an astronomy student and i was studying the standard accretion disk model and I've got some questions related to it.! why do we consider the accretion disk to be stationary in standard accretion disk model? and what are the limitations of standard disk model? and i just read somewhere...
11. ### B Is fusion in an accretion disk of a black hole possible?

I know that the accretion disk of a black hole gets hot enough for powerful emission of x-rays, but does that disk get hot enough for certain elements to fuse?
12. ### Does this neutron star have an accretion disk?

Does this neutron star have an accretion disk?: https://en.wikipedia.org/wiki/IGR_J11014-6103#/media/File:Lighthouse_nebula.jpg
13. ### Mass: Accretion Disk vs. Black Hole

I asked a question recently about orbiting black holes. Thanks for the answers. So if I'm correct in my thinking, long before the event horizons of orbiting black holes become close to each other, the two accretion disks get mightily disrupted and much of the mass of the two disks would fall...
14. ### Formation of accretion disk / frame drag

came across the concept of Frame dragging. i cannot find if this phenomena also aids in addition to the conversation of angular momentum the formation of an accretion disk around neutron stars/black holes. cheers
15. ### About accretion disk of a binary system

In an X-ray binary system, in which one of the two objects is black hole candidate, there are several ways to exchange mass. A paper states that" their host systems are mass-exchange binaries containing a nondegenerate star that supplies gas to the black hole via a stellar wind or via...
16. ### Angular Velocity of a Nebula Accretion Disk

[SOLVED]Angular Velocity of a Nebula Accretion Disk [SOLVED] According to astronomy our solar system was created about 4.5 billion years ago when the nebula of an exploded supernova accreted to form a stellar mass known as our sun. They say that this "accretion disk" or mass of clumping...
17. ### Accretion disk around galaxy NGC 4261

Hello, When you look at the accretion disk around NGC 4261 (see here), you can read that the dark, dusty disk represents a cold outer region which extends inwards to an ultra-hot accretion disk with a few hundred million miles from the suspected black hole. So, from the outside, you have...
18. ### Is Fusion possible at the accretion disk of a Black Hole?

So if we have a supermassive black hole or a regular black hole with gas swirling around it. Can this gas get hot enough to fuse with other gas molecules around it? It seems like there would be enough energy to do this, maybe not. This question seems non-trivial and I think it needs some...
19. ### Accretion Disk Density & Fusion: What You Need to Know

Can an accretion disk get dense enough to start fusion? How dense does something have to be in order to start fusion? Does it depend on the material? is there a way of measuring the density of accretion disks?
20. ### How Can I Simulate an Accretion Disk Using the Naviar-Strokes Equations?

I've recently been messing around with the ol' Naviar-Strokes equations, creating a fluid simulator with the help of Mr. Jos Stam. I added vorticity confinement, which made for some really beautiful visual effects. I noticed these appeared similar to an accretion disk. I'd like to model an...
21. ### Null geodesics of light from a black hole accretion disk

Sorry I don't know latex so this may look a little messy. Homework Statement I'm trying to solve the equation for null geodesics of light traveling from a rotating black hole accretion disk to an observer at r = infinity. The point of emission for each photon is given by co-ordinates r, phi...
22. ### How Do Accretion Disks Around Black Holes Form and Function?

How is it formed? How do particles move on it?
23. ### Saturn's hexagon and his accretion disk jets

Hi! What do you know about Saturn's Nord Pole hexagon? Is sure than the Saturn's hexagon is owed to nothing else but his convection. Then we ask ourselves what fact makes the convection from the Saturn's North Pole. There are two possibilities: 1). the convection is due to a temperature...
24. ### Nuclear reactions in AGN accretion disk

As I understand it, it's all atomic material in the accretion disk of a big black hole, with very high orbital velocities and high density. However, the the disk is quite flat, and cooler than one would think with the velocities involved, because the material is swirling in smoothly, with...
25. ### Accretion disk model: Hydrodynamical or collisional N-Body?

Right now I'm playing around with DynGen, a routine which uses a hydrodynamical approach to simulate a dusty torus and a planet orbiting within it. It uses laroche limits, etc. to model what happens with the resonant trapping as this planet orbits - the parameters are planet mass and disk...