Skip to comments.Special star is a Rosetta Stone for understanding the sun's variability and climate effect
Posted on 01/09/2018 12:55:37 PM PST by Red Badger
A picture of dark sunspots and bright diffuse faculae (best seen around the edges). The study shows how the larger mix of heavy elements leave the spots unchanged, while increasing the contrast of the bright diffuse faculae. Credit: NASA/SDO
The spots on the surface on the sun come and go with an 11-year periodicity known as the solar cycle. The solar cycle is driven by the solar dynamo, which is an interplay between magnetic fields, convection and rotation. However, our understanding of the physics underlying the solar dynamo is far from complete. One example is the so-called Maunder Minimum, a period in the 17th century, where spots almost disappeared from the surface of the sun for a period of over 50 years.
Now, a large international team led by Christoffer Karoff from Aarhus University has found a star that can shed light on the physics underlying the solar dynamo. The star is located 120 light years away in the constellation of Cygnus, and on the surface, it looks just like the sun. It has the same mass, radius and agebut the chemical composition of the star is very different. It consists of around twice as many heavy elements as in the sun.
The team has succeeded in combining observations from the Kepler spacecraft with ground-based observations dating as far back as 1978, thereby reconstructing a 7.4-year cycle in this star. "The unique combination of a star almost identical to the sun, except for the chemical composition, with a cycle that has been observed from both the Kepler spacecraft and from ground makes this star a Rosetta Stone for the study of stellar dynamos," explains Karoff.
Heavy elements make the star more variable
By combining photometric, spectroscopic and asteroseismic data, the team collected the most detailed set of observations for a solar-like cycle in any star other than the sun. The observations revealed that the amplitude of the cycle seen in the star's magnetic field is more than twice as strong as what is seen on the sun, and the cycle is even stronger in visible light.
This allowed the team to conclude that more heavy elements make a stronger cycle. Based on models of the physics taking place in the deep interior and the atmosphere of the star, the team was also able to propose an explanation of the stronger cycle. Actually, they came up with a two-part explanation. First, the heavy elements make the star more opaque, which changes the energy transport deep inside the star from radiation to convection. This makes the dynamo stronger, affecting both the amplitude of the variability in the magnetic field and the rotation pattern near the surface. The latter effect was also measured. Second, the heavy elements affect the processes on the surface and in the atmosphere of the star. Specifically, the contrast between diffuse bright regions called faculae and the quiet solar background increases as the mix of heavy elements is increased. This makes the cyclic photometric variability of the star stronger.
Can help us understand how the sun affects our climate
The new study can help us understand how the irradiance of the sun has changed over time, which is likely to have an effect on our climate. In general special attention is paid to the Maunder Minimum, which coincided with a period of relatively cold climate, especially in Northern Europe. The new measurements offer an important constraint on the models trying to explain the weak activity and possible reduced brightness of the sun during the Maunder minimum.
Explore further: New clue to solving the mystery of the Sun's hot atmosphere
More information: Christoffer Karoff et al, The Influence of Metallicity on Stellar Differential Rotation and Magnetic Activity, The Astrophysical Journal (2018). DOI: 10.3847/1538-4357/aaa026
Journal reference: Astrophysical Journal
The Sun has absolutely no affect on the Earth's climate!
Did that fraud really say that?
To the best of my knowledge, current climate models treat the sun’s output as a constant. However the variation in the sun’s output is greater than any other source of energy on the planet.
Wait. If it has different composition from the Sun how can watching it predict the Sun’s behavior?
The Sun’s gonna do what it does and there is nothing we can do about it. Even if they could predict an ice age no one would do anything about it in govt anyhow until it is too late.
Not necessarily predict but understand the Sun’s behavior................
Our Sun is a variable star, with its output varying by 0.1% over an 11 year cycle...NASA says so...
Plug that into the eccentricity of the Earth’s orbit around the Sun, the obliquity and precession of the Earth’s axis, the reasons our climate varies are easy to understand...
Milankovitch Cycles here:
Human activity possibly plays some small role, but it’s like a gnat on an elephant’s ass...The Sun is the moving force for our climate...
Especially when you consider that pic at the top, the entire Earth is the size of one of the small specs.................
That is what is so scary about life on earth. Forget all the hype about climate change, asteroid impact, nukes, or, girl scout cookies.
We know so little about how stars actually work, we don’t know when the Sun will start acting up.
We GUESS that it won’t become an unstable red giant in the far future, but, do we KNOW that?
Look at stars like Delta Scorpius. https://en.wikipedia.org/wiki/Delta_Scorpii.
If there was any life on a planet around that star, it was fried very quickly.
It has a very similar composition to the sun, just with more 'trace' elements. This gives us some benchmarks with which to contrast their behavior. More trace elements yields a shorter sunspot cycle. Our sun has about 99.9% Hydrogen and Helium (3:1) and about .1% other stuff. That gives us a solar cycle of about 11 years. The other star has .2% other stuff. That gives it a cycle of about 7.4 years. There is probably a formula for the cycle time where the cycle time decays exponentially with the amount of trace elements present.
I suspect that the higher metallicity of that star may indicate that the star is significantly younger than the Sun. Either that or some nearby supernovae popped off before the star was formed, since the supernovae and late stage large stars are the source of most metals.
Note: In stellar chemistry, anything bigger than helium is a “metal”.
Yep. Our sun is only 4.5 billion years old, so there as been plenty of time for prior generations to have been born, lived, and died, and bigger stars burn faster to boot. How much 'metal' went into any given star should be highly variable. Back of the napkin calculations (based on the very thin data we have about the other star and our sun) suggest that a star like ours but with .3% trace elements would have a cycle of 5.3 years, .4% a cycle of 3.8 years, and so on. This might be the source of variability in Cepheids (a type of star that varies its output cyclically, with periods as short as a few days). They'd have to have trace elements on the order of .8%, and that's leaving out other factors like size and age, where they tend to differ substantially from our own sun. All speculative, however.
You are my sunshine, you are my sunshine.
Please don’t take my sunspots away!
Disclaimer: Opinions posted on Free Republic are those of the individual posters and do not necessarily represent the opinion of Free Republic or its management. All materials posted herein are protected by copyright law and the exemption for fair use of copyrighted works.