<p>Magnetic activity depends on rotation due to the dynamo mechanism. Younger stars in general rotate faster. They (stars like the sun) spin down because their ionised winds interact with their magnetic fields and gradually remove angular momentum. A star like the Sun at 100 million years old may have had a rotation period of 0.5-5 days - much faster than the present-day Sun.</p>

<p>Roughly speaking, magnetic activity scales with the square of angular velocity, so young stars can be orders of magnitude more active than the Sun, manifested as much stronger coronal X-ray emission, flares and much greater coverage of starspots and strong magnetic fields.</p>

<p>Conversely, stars older than the Sun should be a bit less active, although the rate of spindown slows with rotation rate and so the changes beyond a few billion years are not so great and not so well calibrated.</p>

<p>A useful review article would be Ribas et al. (2005)</p>

<p><a href="http://adsabs.harvard.edu/abs/2005ApJ...622..680R" rel="nofollow">http://adsabs.harvard.edu/abs/2005ApJ...622..680R</a></p>

CC BY-SA 3.0
2014-06-20T23:20:10.133Z
2014-06-20T23:20:10.133Z
user1907
<p>As in the Earth and more than in the the giant gaseous planets the Sun's magnetic field is generated like in a dynamo. A few facts about it:</p>

<ul>
<li>The rotating plasma inside the Sun acts like a dynamo creating it's
magnetic field.</li>
<li>The plasma is ionized so all interact with the magnetic field and
vice-versa.</li>
<li>The sun as a fluid body also has <strong>Differential rotation</strong>, that
means the equatorial part of it rotates faster than the poles. This provokes what is known as the <strong>Solar cycle</strong> every 11 years.</li>
</ul>

<p>At the begining of the <strong>Solar cycle</strong> the Sun's magnetic field is pointed North-South as in the Earth. During the cycle the differential rotation makes the plasma interact with the magnetic field causing it to be displaced. This makes the first the <strong>Sun's spots</strong> appear near the poles. As the cycle advances the magnetic field get more and more scrambled, it's orientation changes to west-east and the spots appear closet to the equator. Finally the magnetic field can't hold the "pressure" and "breaks" like a rubber band creating the biggest spots and flares. The magnetic field stabilizes again but with a south-north polarity and the cycles begins again.</p>

<p>Take a look at this <a href="http://ircamera.as.arizona.edu/NatSci102/NatSci102/movies/solarcycle.gif" rel="nofollow noreferrer" title="Solar Cycle">gif image</a> that shows how the cycle go.</p>

<p>And in this image you can see what is know as the butterfly diagram that shows how the Sun's spots are located closer to the equator as the cycle advances. And it lasts 11 years.
<img src="https://i.sstatic.net/WjzxJ.gif" alt="enter image description here"></p>

CC BY-SA 4.0
2023-02-10T01:06:13.447Z
Just read these papers

The world's largest turbulence simulation unmasks the flow of energy in astrophysical plasmas 


https://www.pppl.gov/news/2022/worlds-largest-turbulence-simulation-unmasks-flow-energy-astrophysical-plasmas


Reconnection-driven energy cascade in magnetohydrodynamic turbulence

https://www.science.org/doi/10.1126/sciadv.abn7627
darius
CC BY-SA 3.0
2014-05-23T13:19:16.657Z
I was looking for an answer over the lifetime of the Sun (billions of years).
ehsteve
CC BY-SA 3.0
2014-05-23T06:39:13.050Z
2014-05-23T06:39:13.050Z
Joan.bdm
<p>As a Sun-like star is born from a collapsed nebula and generates energy by nuclear fusion some of that energy is converted to magnetic fields which fuel solar activity. How does that activity evolve as the star itself evolves?</p>

CC BY-SA 3.0
2014-05-23T09:19:16.160Z
To add to Joan's answer, it is one of the active research problems in Stellar Physics. We have no satisfactory explanation as to why should the diagram repeat itself after 11 years. What's so special about that number?
Cheeku
<the-sun><solar-flare>
How does solar activity (e.g. flares, coronal mass ejections) change over the life cycle of a Sun-like star?
ehsteve
# How does solar activity (e.g. flares, coronal mass ejections) change over the life cycle of a Sun-like star?

(Asked by: username_0 on 2014-05-23)

As a Sun-like star is born from a collapsed nebula and generates energy by nuclear fusion some of that energy is converted to magnetic fields which fuel solar activity. How does that activity evolve as the star itself evolves?

**Tags:** the-sun, solar-flare

> **Comments:**
> **username_1**: To add to Joan's answer, it is one of the active research problems in Stellar Physics. We have no satisfactory explanation as to why should the diagram repeat itself after 11 years. What's so special about that number?  

---

## 2 answers

### Answer by username_2 on 2014-06-20. Score: 2 | Accepted answer

Magnetic activity depends on rotation due to the dynamo mechanism. Younger stars in general rotate faster. They (stars like the sun) spin down because their ionised winds interact with their magnetic fields and gradually remove angular momentum. A star like the Sun at 100 million years old may have had a rotation period of 0.5-5 days - much faster than the present-day Sun.

Roughly speaking, magnetic activity scales with the square of angular velocity, so young stars can be orders of magnitude more active than the Sun, manifested as much stronger coronal X-ray emission, flares and much greater coverage of starspots and strong magnetic fields.

Conversely, stars older than the Sun should be a bit less active, although the rate of spindown slows with rotation rate and so the changes beyond a few billion years are not so great and not so well calibrated.

A useful review article would be Ribas et al. (2005)

<http://adsabs.harvard.edu/abs/2005ApJ...622..680R>


---

### Answer by username_3 on 2014-05-23. Score: 2

As in the Earth and more than in the the giant gaseous planets the Sun's magnetic field is generated like in a dynamo. A few facts about it:

* The rotating plasma inside the Sun acts like a dynamo creating it's
  magnetic field.
* The plasma is ionized so all interact with the magnetic field and
  vice-versa.
* The sun as a fluid body also has **Differential rotation**, that
  means the equatorial part of it rotates faster than the poles. This provokes what is known as the **Solar cycle** every 11 years.

At the begining of the **Solar cycle** the Sun's magnetic field is pointed North-South as in the Earth. During the cycle the differential rotation makes the plasma interact with the magnetic field causing it to be displaced. This makes the first the **Sun's spots** appear near the poles. As the cycle advances the magnetic field get more and more scrambled, it's orientation changes to west-east and the spots appear closet to the equator. Finally the magnetic field can't hold the "pressure" and "breaks" like a rubber band creating the biggest spots and flares. The magnetic field stabilizes again but with a south-north polarity and the cycles begins again.

Take a look at this [gif image](http://ircamera.as.arizona.edu/NatSci102/NatSci102/movies/solarcycle.gif "Solar Cycle") that shows how the cycle go.

And in this image you can see what is know as the butterfly diagram that shows how the Sun's spots are located closer to the equator as the cycle advances. And it lasts 11 years.
![enter image description here](https://i.sstatic.net/WjzxJ.gif)

> **Comments:**
> **username_0**: I was looking for an answer over the lifetime of the Sun (billions of years).  
> **username_4**: Just read these papers  The world's largest turbulence simulation unmasks the flow of energy in astrophysical plasmas    https://www.pppl.gov/news/2022/worlds-largest-turbulence-simulation-unmasks-flow-energy-astrophysical-plasmas   Reconnection-driven energy cascade in magnetohydrodynamic turbulence  https://www.science.org/doi/10.1126/sciadv.abn7627  

---

