Accretion Disks

[Racoon]

After reading one of the latest articles, about Neutron Stars producing jets of matter,

I am a little stumped by these Accretion Disks...:eek_big:

 

Can anyone explain in layman terms what exactly is their significance?

Or provide any links?

I'm getting to understand slow and steady like.

 

Thank you in advance esteemed Cosmologers :)

[Jay-qu]

hmm I think it means as matter is sucked towards star(or black hole), if it is rotating then it accretes into a disk around the axis of rotation..

[Michaelangelica]

Sinificance to what?

 

here is alink about them

Ask an Astrophysicis

thttp://imagine.gsfc.nasa.gov/docs/ask_astro/answers/001106a.html

 

 

The Question

(Submitted November 06, 2000)

 

Could you tell me the basics of accretion discs?

 

The Answer

Accretion disks arise when material (usually gas) is being transferred from one celestial object to another. "accretion" means collecting of additional material. Two major places where astronomers see accretion disks are in binary star systems (two stars orbiting each other) and active galactic nuclei.

 

I will discuss an accretion disk in a binary star system, but the basic ideas are the same for all cases. If one star in a binary system is a compact object such as a very dense white dwarf star and the other star is a normal star like the sun, the white dwarf can pull gas off the normal star and accrete it onto itself. Since the stars are revolving around each other and since angular momentum must be conserved, this gas cannot fall directly onto the white dwarf, but instead spirals in to the white dwarf much like water spirals down a bathtub drain. Thus material flowing from the normal star to the white dwarf piles up in a dense spinning accretion disk orbiting the white dwarf. The gas in the disk becomes very hot due to friction and being tugged on by the white dwarf and eventually loses angular momentum and falls onto the white dwarf. Since this hot gas is being accelerated it radiates energy, usually in x rays which astronomers detect and use to identify and study accretion disks.

 

You can find some more basic information at: http://imagine.gsfc.nasa.gov/docs/features/exhibit/asca_agndisk.html and more at http://antwrp.gsfc.nasa.gov/apod/ap991219.html (part of Astronomy Picture of the Day).

[CraigD]

Can anyone explain in layman terms what exactly is their [accretion disks’] significance?

I’d say the main significance of accretion disks (or flattened clouds, to use, possibly, a more intuitively accurate phrase) is that they are often hot, and radiate a lot of energy in the form of photons.

 

This is why objects like black holes – which, possible having the capability of capturing photons, one might reasonably expect to radiate no photons, are often, perhaps almost always, intense radiation sources, typically in the radio and x-ray spectrum. The black hole itself may be effectively invisible, but the super-hot cloud of swirling and infalling matter around it is not.

[Eclogite]

Two major places where astronomers see accretion disks are in binary star systems (two stars orbiting each other) and active galactic nuclei.

You have overlooked the rather important proto-planetary discs that surround young stars and from which planetary systems form. These are governed by many of the same processes as those you have mentioned and certianly qualify as accretion discs.

[Harry Costas]

Hello All

 

There is little that I can add to what has been said.

 

 

See links for more info.

 

http://www.stsci.edu/stsci/meetings/shst2/ballyj.html

 

http://observe.arc.nasa.gov/nasa/space/stellardeath/stellardeath_4.html

 

http://www.astro.umd.edu/~miller/nstar.html

[Racoon]

So its like the swirl in a toilet bowl flush... :)

 

All matter getting sucked in, and the swirly pop is the accretion disk?

 

thanks for the responses. I appreciate the help. :D

[Racoon]

plus lots of radiating energy..

 

That sounds pretty important... where does that energy go to?

[ronthepon]

plus lots of radiating energy..

 

That sounds pretty important... where does that energy go to?

The radiant energy just keeps moving away from it's source until it reaches some barrier. Think of it as the same thing that happens to the energy emmitted by stars.