How do binary star systems form?

  • 6 Replies
  • 5843 Views

0 Members and 1 Guest are viewing this topic.

*

Offline chris

  • Neilep Level Member
  • ******
  • 5425
  • The Naked Scientist
    • View Profile
    • The Naked Scientists
How do binary star systems form?
« on: 18/09/2008 18:02:31 »
An interesting fact is that about 50% of the stars in the night sky are binary systems comprising two stars twirling around each other.

But how did this configuration arise in the first place, given our current model of star and planetary formation?

Chris
I never forget a face, but in your case I'll make an exception - Groucho Marx

*

Offline Evie

  • Sr. Member
  • ****
  • 200
  • "Back off man...I'm a Scientist."
    • View Profile
    • My Website
How do binary star systems form?
« Reply #1 on: 18/09/2008 18:51:14 »
This is a debated topic. There are basically four different ideas:

1)One star captures another

2)Fission - one star splits into two.

*3)Star forming cloud splits into two (or more) parts, each forming a star.

4)A proto-star with a disk is formed, disk breaks up and forms another star.

Number three is considered the most feasible, but there is new research coming out all the time that tries to support any one of the four ideas.
====================================================
"There are more things in heaven and earth, Horatio,
Than are dreamt of in your philosophy."
Hamlet
Act I, scene 5

*

Offline RD

  • Neilep Level Member
  • ******
  • 8185
    • View Profile
How do binary star systems form?
« Reply #2 on: 18/09/2008 19:29:36 »
Some galaxies form bars.
If an accretion disc could do the same, (on a smaller scale), the concentration of matter in the bar could form two satellite stars.
These satellites could eventually coalesce, as they have similar orbits, producing a binary system.

[Isn't this a question about symmetry breaking ?]

*

Offline LeeE

  • Neilep Level Member
  • ******
  • 3382
    • View Profile
    • Spatial
How do binary star systems form?
« Reply #3 on: 19/09/2008 17:18:25 »
AFAIK, multiple star systems are not limited to binaries and can have three, four or more stars in a single system.  A lot will depend upon the distances between the individual stars though - close binaries may well have formed by capture but distantly separated multiple star systems are more likely to have formed from individual gas clouds that were already gravitationally bound.
...And its claws are as big as cups, and for some reason it's got a tremendous fear of stamps! And Mrs Doyle was telling me it's got magnets on its tail, so if you're made out of metal it can attach itself to you! And instead of a mouth it's got four arses!

*

Offline Evie

  • Sr. Member
  • ****
  • 200
  • "Back off man...I'm a Scientist."
    • View Profile
    • My Website
How do binary star systems form?
« Reply #4 on: 19/09/2008 19:34:11 »
I found an article that expains the above four theories quite well: http://www.astrophysicsspectator.com/topics/stars/BinaryStarBirth.html

The article, along with others that I have read, states that capture is probably the most unlikely scenario. Most capture models require a third star as well, not just two, that intercept. Recent studies suggest that there are either two different ways that binary systems form (one for short-period systems, one for long-period), or that the collapse of the molecular cloud can account for all binary systems.
====================================================
"There are more things in heaven and earth, Horatio,
Than are dreamt of in your philosophy."
Hamlet
Act I, scene 5

*

Offline Soul Surfer

  • Neilep Level Member
  • ******
  • 3345
  • keep banging the rocks together
    • View Profile
    • ian kimber's web workspace
How do binary star systems form?
« Reply #5 on: 26/09/2008 23:51:47 »
There are very many binary and multiple stars far to many to be caused by capture processes.  The formation of multiple stars is basically required for stability because of the requirement to conserve angular momentum as the clouds contract.  If a cloud contains too much angular momentum to form a single body the clouds are forced to split up so that multiple bodies form in orbit around each other.  most single stars will have planitary systems to get rid of a slight excess angular momentum too.  there is more angular momenum in the planets than in the sun rotaing.  If all tis angular momentum were piled into the sun it would be rotating so fast that it would be unstable.
Learn, create, test and tell
evolution rules in all things
God says so!

*

lyner

  • Guest
How do binary star systems form?
« Reply #6 on: 27/09/2008 00:36:54 »
The angular momentum idea gets my vote. If the original cloud has a lot of angular momentum then a single star couldn't form (it would have to be spinning too fast) and it would also require a vast number of planets to share the angular momentum. It is quite reasonable to expect two stars would result from the resolution of the situation.

I guess binary systems would tend not to have planets as they would be soon ejected or collide / be captured by one of the pair. Anyone know about this?