# What is Accretion: Definition and 75 Discussions

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. ### 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...
2. ### I Formation of jets with accretion disks at black holes

Dear all, I'm going to give a course about black holes at an astrophysics association. The public will consist mainly of lay persons, perhaps wit a little bit of physics background. My background in General Relativity is good, but my background in astrophysics at bit less. My question is if you...
3. ### 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...
4. ### Pebble accretion and the early Earth

It is being reported in the press that there is new evidence for pebble accretion models https://www.bbc.co.uk/news/science-environment-51295365 Normally when we think of the very early Earth we think of being formed violently . This model seems more gentle. I am wondering what that means for...
5. ### How Does Eddington Luminosity Limit Black Hole Mass Accretion Rates?

The Eddington luminosity gives a limit on the mass accretion rate of the black hole and therefore of the mass of the black hole. L_edd = 13*10^38 M/M_sun [erg s-1]. When I calculate from this I get that the maximum mass is M = 10^(-8)M_sun... which is impossible. Any ideas?
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. ### I Can I Simulate Planetary Accretion with Disksim?

Hi - having come up blank when searching, I figured I'd ask here: do you know of any (free, preferably open source) planetary accretion models/simulators available for download? I'm primarily looking for solar system formation / evolution rather than planetary geochemistry (although I'd have an...
9. ### I Accretion disc poloidal magnetic field, right or left hand rule?

If your fingers of one hand curl around the axis of rotation of the accretion disc of a massive black hole and your fingers point in the direction of the flow is the direction of the central twisted poloidal magnetic field given by a right hand rule, a left hand rule, no rule? Is there a simple...
10. ### Calculating the Feeding Rate of Supermassive Black Holes to Power Quasars

Homework Statement Quasars arise when supermassive black holes swallow nearby gas, or even entire stars. Their masses are typically 10&7 solar masses, and their luminosities are typically around 10&39 W. Hide the children! Roughly how many stars must one of these monsters eat per year, in order...
11. ### A Where can I find a text about heavy elements migration?

Let me be more specific: I'm needing some source that talks, in a more broad way, about how heavier elements tend to "sink into the core" during Earth's formation (when we're talking about siderophile elements, that readily combine with molten iron). Wikipedia's page about the Goldschmidt...
12. ### I Exploring the Eddington Limit: Deriving the Formulation of Accretion Processes

I am studyng accretion process on "Astrophysics in a nutshell" by Dan Maoz and I have some doubts about the derivation of the formula for the eddington limit. I understand what the edding limit is. The accretion rate cannot be arbitrarly large. The starting point is to consider an electron at a...
13. ### A Questions about Accretion disk

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...
14. ### I Models of accretion disc emissions contradicted by experiment

Ref: http://www.spaceref.com/news/viewpr.html?pid=51416 I would be very interested to see comments from knowledgeable people about this. My impression is that this is one more example of a need to remain at least somewhat skeptical about theoretical models that have not yet been validated by...
15. ### 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?
16. ### I Spherical Accretion Mass inflow Rate

Hello everyone I am a new user around here. I have been attempting to understand spherical accretion and create a simple model of that process but I am running into a problem. This is getting at the heart of the issue. So far I have come up with two concentric spheres, the outer sphere is the...
17. ### A Quantify the mass of polar jets

I would like a discussion to quantify just how much mass is ejected at the poles (including the mass equivalence of the photons) when jets form. In quasars the black hole presumably reaches over a Billion solar masses, where the mass is proportionate to the mass of the galaxy and is also related...
18. ### 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
19. ### Could accretion on a neutron star’s poles cause the jets?

Could accreting material on a neutron star’s poles impact with enough energy to initiate fusion reactions, some of which escapes the star as ultra-relativistic jets?
20. ### Does accretion reduce the magnetic field of a neutron star?

When a large amount of plasma radiates greatly while accreting on a magnetized neutron star, where does the radiation ultimately get its energy from, the magnetic field and/or gravitational field? Without doing the numbers, if the magnetic field does the work against the gravitational field, and...
21. ### Accretion Discs in Non-Rotating Black Holes: A Closer Look at Sagittarius A*

Does a non rotating BH have an accretion disc?
22. ### Black Hole Time Dilation And Observation Of Accretion

Hello. If time is infinitely dilated at the edge of the EH, how do we observe accretion?
23. ### Accretion for Gamma > 5/3 | Black Hole Solutions

Hello, I would like to know, what happen with accretion (cloud) when drop toward a black hole. In Bondi case and terminology. If I understand: 1) We describe the cloud falling to star (black hole) by EoS P(\rho)=K\rho^\Gamma . 2) This accretion is steady it means \dot{M}=4\pi r^2u\rho=const...
24. ### Non-Dimensional Accretion Rate λ: Overview and Questions

Hello, I have question about "so called" non-dimensional accretion rate, mostly known as λ. In Shapiro,Teukolsky 14.3. is made an overview but, λ is just defined, but I don't know why? Why do we need it? What is good for?
25. ### Accretion in Extreme Conditions: PBHs & More

Hello, I have an extreme question :) Let's assume that here are Primordial Black Holes (PBH) in range 10^15 - 10^24 g for example. What would happen if some of them get into the some other object(Sun, Planet or compact object) and settle in the center (ideal case). I have computed radius of...
26. ### Accretion to Primordial Black Hole (PBH): Exploring Extreme Conditions

Hello, I would like to examine or learn something about accretion to Primordial Black Hole (PBH) captured by some compact object (sitting in the center). How is this happening? What is happening to material, "blob", which is falling to PBH? How much is squeezed? Can you somebody let me know...
27. ### Black Holes: Accretion Disks /Increase/ Angular Momentum?

I've been reading Kip Thorne's "Black Holes and Time Warps," and it mentioned something rather counter-intuitive; apparently, when material forms an accretion disk and falls into a spinning black hole, it increases the angular momentum of it. Now, let's take a gas cloud, and put a spinning...
28. ### Solving Planetesimal Accretion: How Long Does It Take?

Kinda stumped. The question gives three equations and I don't know what to do with them, because given the equations there's always more than one unknown. Any assistance/tips would be appreciated! If a planetesimal has a cross-sectional area of πR2 (where R is the planetesimal's radius) and...
29. ### Planetesimal Accretion Time Estimation

Kinda stumped. The question gives three equations and I don't know what to do with them, because given the equations there's always more than one unknown. Any assistance/tips would be appreciated! If a planetesimal has a cross-sectional area of πR2 (where R is the planetesimal's radius) and...
30. ### Thermonuclear fusion in accretion disks?

I was wondering whether thermonuclear fusion could be achieved in accretion disks around black holes, or even neutron stars/white dwarfs. Seems like, in AGN at the very least, you would easily get the kind of temperatures and pressures necessary for thermonuclear fusion, perhaps even synthesis...
31. ### 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...
32. ### Calculating Accretion Rate and Luminosity of Black Holes

Homework Statement This is the original problem for part 1 A) Suppose that a black hole of mass M accretes mass at a rate ##\dot{M}##. Further suppose that accretion of mass Δm leads to the radiation of energy ##\Delta E= \eta Δmc^2##, for some effeciency of energy conversion, ##\eta##. What...
33. ### Black hole Accretion Luminosity

Homework Statement Suppose that a black hole of mass M accretes mass at a rate ##\dot{M}##. Further suppose that accretion of mass Δm leads to the radiation of energy ##\Delta E= \eta Δmc^2##, for some effeciency of energy conversion, ##\eta##. What is the luminosity of emitted radiation in...
34. ### Question regarding maximum accretion of black holes

So I've got a question that I can't seem to figure out. If the accretion efficiency of a black hole is L=εM(dot)c2 with ε=0.1 I have to set this to the Eddington luminosity which is Ledd = 4πcGMmp/σT to find the maximum rate at which a black hole can accrete by. I found that κ=mp/σT so I...
35. ### Black hole accretion disk/jet reference

I found this extremely handy reference on Black hole calculations and models to measure black hole accretion disk/jets. The article also covers several types of BH non rotating and rotating. Methodologies that can be used to distinquish between Neutron and black hole event horizons...
36. ### Accretion with galaxies (IMF)

Homework Statement I had a homework problem which was already due. I got the solutions for the homework and still don't understand where the solution is coming from. The question and solution are located here: http://ircamera.as.arizona.edu/Astr_540/PS3_soln.pdf The problem is #3. Homework...
37. ### 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
38. ### What is the Accretion Rate of Earth?

Homework Statement i) Estimate (in kg/yr) the rate of Earth accreting inter-planetary dust. Assume a particle number density of n=1e-8/m3, a particle mass density of 5 gm/cc, a particle radius 50 microns and a relative velocity equal to Earth's orbital velocity (so the dust particles are, on...
39. ### Black hole accretion: angular momentum loss

Why exactly is it necessary for angular momentum to be lost by a mass if it is to accrete around a black hole? the mass is decreasing its radius, so it speeds up: thus angular mometum is conserved. But everywhere it is saying that 99.99% of the angular momentum must be shed for accretion to...
40. ### 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...
41. ### 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...
42. ### 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...
43. ### Torque on the Accretion disc

http://www.maths.qmul.ac.uk/~rpn/ASTM735/lecture3.pdf The diagram on page 26 is the accretion disc. The torque acting on the inner edge of the ring (the one that has a thickness of dR in the diagram) is RFin = -2\piR3\nuƩ\frac{dΩ}{dR} The torque acting on the outer edge of the...
44. ### Hydrostatic Equilibrium in an Accretion Disc

This is regarding an accretion disc orbiting a star. In the z (vertical) direction there is a hydrostatic equilibrium. \frac{1}{ρ}\frac{∂P}{∂z} = -\frac{GMz}{(R^{2} + z^{2})^{3/2}} The right hand side of the expression is the Gravitational potential energy and the left side is the pressure...
45. ### Calculating luminosity given accretion power

Homework Statement I have a question regarding calculating luminosity given accretion power. I have accretion power given to me as Δm/Δt= 1.5 solar masses/yr, in order to solve for luminosity are we supposed to convert the accretion power into solar masses/seconds or is it just some kind of...
46. ### Planetary Formation Based on Matter Condensation and Accretion

The understanding of the origins of our planet (as well as the other planets in the Universe) has always remained a question to astronomers. Inherently, the application of Newton’s known concepts of gravity has granted us the ability to make educated assumptions concerning planetary formation...
47. ### Can Simple Mass Accretion Turn a Neutron Star Into a Black Hole?

Can simple mass accretion turn a neutron star into a Black Hole, or does a BH require temperatures and pressures from the collapsed massive star?
48. ### Black Hole Mass Accretion Temperature

Hey everyone, I have a quick question. I have to find out how hot a cloud of material falling into a black hole would become. I have a hint that it is due to the gain in kinetic energy the material experiences as it falls in, but I'm not sure how to relate the two. Also, I have to find the...
49. ### Accretion disc for a black hole

has the matter in the accretion discs for a black hole entered the BH or is it circling the actual BH?...
50. ### Celestial Mass Accretion Spectrum

Hello, Over the past few weeks I've been interested in the idea of developing a celestial mass accretion spectrum, or in other words, a spectrum that places celestial objects of a given mass as being part of a band of that spectrum. This spectrum would help give definitions on what a planet is...