Accretion Definition and 75 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.

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  1. I

    What is Accretion Induced Collapse and its Relationship with Type IA Supernovae?

    Hi all, I recently came across one of the proposed mechanisms by which black hole could be formed as stated above.Can someone please explain me what is it all about? Also what's their relationship with type IA supernovae? I always thought that, a black hole is formed only when a main sequence...
  2. Q

    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...
  3. L

    How Do You Estimate the Mass Accretion Rate for a Quasar?

    Homework Statement A typical quasar luminosity is about 1012 L, where L = 3:83 1033 erg s1 is the luminosity of the Sun. If the energy is released by mass falling into a SMBH, estimate the mass accretion rate. (Convenient units are solar masses per year.) B)If the mass accretion rate is...
  4. D

    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?
  5. S

    Accretion discs - Orbital angular momentum

    Homework Statement There is a binary system accreting via Rcohe lobe overflow, where mass is transferred fromthe donor to the accretor and then lost in an isotropic wind. State an expression for the orbital angular momentum of the accretor, J1 and then use keplers third law to find an...
  6. N

    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...
  7. F

    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...
  8. V

    How Do Accretion Disks Around Black Holes Form and Function?

    How is it formed? How do particles move on it?
  9. I

    Mass uncertainties and the calculation of accretion disks

    I'm currently writing an extended essay about black holes in binary systems and accretion disks, and I wonder how I should proceed when calculating the size of the accretion disk. Take, for instance, the binary system A 0620-00 where the mass of the black hole is said to be 5-10 solar masses...
  10. G

    Astrophysics - Accretion of Space Dust

    Homework Statement Imagine a planetesimal sweeping up small particles from a dust cloud. Suppose the planetesimal, of mass M and radius R, is moving through the cloud at a velocity v. There are nd dust particles per m3, each of mass md (a) Derive an expression for the number of collisions per...
  11. tiny-tim

    How Is the Inner Radius of an Accretion Disc Determined?

    What is the inner radius of an accretion disc? Is it simply the radius of the smallest possible orbit of a massive particle (the marginally stable radius), 6M ?
  12. Z

    Dilution and Accretion Problem - Diff. Eq.

    Homework Statement A tank initially contains 100 gal of brine whose salt concentration is 1/2 lb/gal. Bine whose salt concentration is 2 lb/gal flows into the tank at the rate of 3 gal/min. The mixture flows out at the rate of 2 gal/min. Find the salt content of the brine and its concentration...
  13. S

    How long does it take for a white dwarf to go supernova through accretion?

    Hi, Let's say we have a white dwarf accreting material from a giant partner. How long would it typically take for the white dwarf to go supernova? Is it of the order of a thousand years? A million? Any references would be much appreciated. Thanks, San
  14. marcus

    Observing Quasar Accretion Disks: Scientists See Standard Cosmology at Work

    Nice picture of quasar accretion disk---pat on back for standard cosmology in Nature The 24 July issue of Nature reports some beautiful observational work, using a polarized light filter. Actually able to SEE the hot blue accretion disk whirling around a supermassive black hole at the center of...
  15. B

    Accretion disk/black hole/gas jets

    I have a few questions regarding these phenomena. 1. I don't quite understand what is going on in the picture. Obviously there is a spin on the black hole but why doesn't the gases get sucked straight towards the black hole. I know this is a simulated picture but I don't see how this would...
  16. J

    Accretion of specific minerals from seawater

    I understand the process of electro-accretion of limestone from seawater. I was wondering if anyone had any links to information regarding the accretion of specific minerals from seawater...such as gold or silicon. I remember reading something a long time ago that you could modify the...
  17. Z

    Detecting Black Hole accretion disc

    How might one detect the plane of an accretion disc of a Black Hole? Might it just be assumed, by the orbital plane of a BH binary system? http://en.wikipedia.org/wiki/Accretion_disc"
  18. Abel Cavaşi

    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...
  19. V

    How Do Accretion Discs and Black Holes Emit High-Velocity Charged Particles?

    The gravity of black holes is the same as the gravity of other objects at large distances.Are black holes really just the same as everything else? When an atomic nucleus forms from protons and neutrons energy is released, because, if it is not,then energy would not have to be put into the...
  20. P

    Calculating Earth's Accretion Time: Solving the Formulas for Astronomy Homework

    My Astronomy homework has a problem asking to find the accretion time of Earth. The forumula's the professor gave (since the book doens't have ANY) are: \frac{dm}{dt}=\pi s^2\frac{\sigma \omega}{2} And \frac{ds}{dt}=\frac{\sigma \omega}{8 \rho} (1+ \frac{V_{esc}^2}{V_{relative}^2}) Where...
  21. S

    What is the role of accretion discs in proving the existence of black holes?

    I'm doing a project on accretion disks, and I was wondering if anyone could suggest something interesting relating to their observation that I could talk about. One thing I remember reading was that accretion discs are one of the most compelling means of proving the existence of black holes...
  22. G

    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...
  23. -Job-

    Does Gravity Play a Significant Role in Accretion?

    The phnenomenon of accretion doesn't really seem to need the effect of gravity, as long as particles have different speeds, sizes and intersecting trajectories, then they'll eventually form bigger and bigger clumps of matter. These clumps don't really need gravity to remain together either, if...
  24. F

    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...
  25. 2

    Analogous Hawking Radiation from Astrophysical Black Hole Accretion

    Hi everyone Im trying to understand a paper(title of the thread) arxiv.org/abs/astro-ph/0404482 Just woundering what an acoustic black hole and acoustic event horizon would actually be? Is the Analogous Hawking Radiation just ascoustic osccilations in the Accretion matter? like the...
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