A mysterious binary star

Magnetic binary stars

An enormous magnetic binary star system has been discovered by Canadian PhD student, Matt Shultz of Queen’s University, Ontario.

The object is unusual because giant stars rarely have magnetic fields; and giant binary stars with magnetism are even less common, accounting for only about 2% of stars in the Milky Way. The discovery was made using the Canada-France-Hawaii Telescope on Mauna Kea, Hawaii.

The binary (a pair of stars orbiting around a common centre of mass) consists of two hot blue giants known as Epsilon Lupi, located roughly 500 light years away in the southern constellation of Lupus. Both stars are about seven to eight times the mass of the Sun and have a combined luminosity of around 6000 times that of the Sun. That’s bright! 

Astronomers have known for a while that Epsilon Lupi is a binary star system, but the magnetism is a surprise new discovery. The new research shows that the giant stars have opposite polarities – the north magnetic pole of one star points in the same direction as the south magnetic pole of the other. The stars are orbiting fairly close together, so this mysterious stellar pair might even share the same magnetic field.

Magnetic fields are common around cooler stars like our Sun, where the magnetism is generated by a dynamo driven by convection – or circulating heat currents – within the ‘convective zone’ of the star. But hot giant stars – like blue giants – have no convective zone, so where does their magnetism come from? There have been two suggested answers to this question: a magnetic field may be created when the stars formed; or dynamos could have been set up due to turbulent mixing of material when binaries collide. The second scenario is obviously not the case with Epsilon Lupi, as they have not yet collided.

Magnetism in this type of star is so unusual that astronomers still have a lot of work to do in understanding the mechanisms of these rare beasts. Epsilon Lupi might just be the star to give up its secrets and help solve this magnetic mystery.


© Melanie Davies 2015

 

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