Strange Star Observed With Sunspots at Its North and South Poles

May 6, 2016 | Joanne Kennell

On our star, the Sun, the sunspots are seen in a belt around the equator. Sunspots are cool areas caused by the strong magnetic fields where the flow of heat is slowed.
Photo credit: NASA

The location of the sunspots are completely different than those that form on our sun.

Stars, like the sun, are enormous balls of gas that release energy in the form of heat and light through an atomic process called nuclear fusion. Within the interior of the sun, charged particles swirl and spin, generating a magnetic field that can sometimes burst out onto the surface of the star — seen as sunspots.

Sunspots are “cool” areas caused by the magnetic field where the flow of heat is slowed, and on the sun, these sunspots are seen around the equator. However, astronomers have recently spotted a large, distant star where sunspots are located in a bizarre location — the poles.

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The massive star, named Zeta Andromeda, is about 16 times the size of the sun in diameter and located in the constellation Andromeda 180 light-years away. When a star is located too far away to be able to observe the details of its surface, astronomers often use the Doppler method to view sunspots. The process involves observing light wavelengths of a rotating star to construct a map of the surface temperature.

This method was considered the best way to observe the surface of distant stars, but now a new process allows researchers to get far more detail than they could previously with the use of even the largest telescopes. Astrophysicists from the Niels Bohr Institute gathered images from the CHARA Array, which consists of 6 telescopes, so they could observe visible and near-infrared light images simultaneously.

"With these new observations, we have many more details and extra high resolution. Our new measurements confirm that there are large sunspots at the poles" explained astrophysicist Heidi Korhonen, Dark Cosmology Centre at the Niels Bohr Institute at the University of Copenhagen, in a press release.

According to Korhonen, the sunspots do not appear at the north and south poles at the same time, and this asymmetry indicates that the star’s magnetic field is formed in a different way than the sun’s.

The location of the sunspots are so different from those on our sun because Zeta Andromeda is a different class of star entirely — it’s a binary star.

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In a binary star, two stars orbit one another, which causes the stars to rotate more quickly. Zeta, which is the larger of the two stars, rotates at 40 kilometers per second (25 miles per second), whereas the sun rotates at just 2 kilometers per second (1.2 miles per second).

Speed definitely plays a role.

"It is the rapid rotation that creates a different and very strong magnetic field. The strong magnetic field gives a more complicated dynamo effect that resembles what you see at the stage where a new star is being created. Here we are seeing the same effect in an old active star that is in its final stage," explained Korhonen.

On the sun, sunspots appear and disappear on a regular basis and their numbers increase periodically every 11 years. The magnetic field that creates the sunspots can also result in large, explosive discharges of plasma, known as solar storms, that can interact with Earth’s atmosphere.

If these solar winds are strong enough, they can disrupt satellites and the power grid, however, they can also result in a beautiful spectacle called the northern lights.

The results are published in the journal Nature.

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