<p>The magnetic braking in contact binary stars AFAIK is assumed to be similar to the magnetic braking mechanism that spins down the rotation of single stars.</p>

<p>A stellar wind couples to the large scale magnetic field and maintains this coupling out to the Alfven radius (where the thermal pressure and magnetic pressure are roughly equal). At this point the wind decouples, stops co-rotating with the star and hence removes a certain amount of specific angular momentum.</p>

<p>The situation will be more complicated in a binary system (entangled, asymmetric fields etc.) but the basic principle will be the same. Many contact binaries have fast rotation and strong, dynamo-generated magnetic fields.</p>

CC BY-SA 4.0
2018-11-03T20:12:03.733Z
@Muze see https://astronomy.stackexchange.com/help/serial-voting-reversed
ProfRob
CC BY-SA 4.0
2018-11-03T20:34:24.933Z
@RobJeffries https://astronomy.meta.stackexchange.com/questions/455/at-what-point-does-up-voting-become-serial
Muze
CC BY-SA 4.0
2018-10-30T18:10:52.430Z
2018-10-30T18:10:52.430Z
ProfRob
<p>What is the reason of Magnetic Braking in contact binary stars?<br>
Just dark spots?<br>
I mean hot spots can have this effect on binaries.</p>

CC BY-SA 4.0
2018-10-30T08:32:21.857Z
have you done any prior research?
James K
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2018-10-30T09:36:00.747Z
yes I can just find the dark spot explanation.
sara
CC BY-SA 4.0
2018-10-30T10:10:50.503Z
Magnetic braking causes a system to lose angular momentum in many rotating objects including, e.g., a magnetar and a binary. The angular momentum loss then is transformed into other energy such as radiation.
Kornpob Bhirombhakdi
CC BY-SA 4.0
2018-11-03T17:42:37.100Z
Welcome new user!  That's a fascinating question.
Fattie
<astrophysics><binary-star><magnetic-field>
What is the reason for magnetic braking?
sara
# What is the reason for magnetic braking?

(Asked by: username_0 on 2018-10-30)

What is the reason of Magnetic Braking in contact binary stars?  
Just dark spots?  
I mean hot spots can have this effect on binaries.

**Tags:** astrophysics, binary-star, magnetic-field

> **Comments:**
> **username_1**: have you done any prior research?  
> **username_0**: yes I can just find the dark spot explanation.  
> **username_2**: Magnetic braking causes a system to lose angular momentum in many rotating objects including, e.g., a magnetar and a binary. The angular momentum loss then is transformed into other energy such as radiation.  
> **username_3**: Welcome new user!  That's a fascinating question.  

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## 1 answers

### Answer by username_4 on 2018-10-30. Score: 4

The magnetic braking in contact binary stars AFAIK is assumed to be similar to the magnetic braking mechanism that spins down the rotation of single stars.

A stellar wind couples to the large scale magnetic field and maintains this coupling out to the Alfven radius (where the thermal pressure and magnetic pressure are roughly equal). At this point the wind decouples, stops co-rotating with the star and hence removes a certain amount of specific angular momentum.

The situation will be more complicated in a binary system (entangled, asymmetric fields etc.) but the basic principle will be the same. Many contact binaries have fast rotation and strong, dynamo-generated magnetic fields.

> **Comments:**
> **username_4**: @username_5 see https://astronomy.stackexchange.com/help/serial-voting-reversed  
> **username_5**: @RobJeffries https://astronomy.meta.stackexchange.com/questions/455/at-what-point-does-up-voting-become-serial  

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