Older dwarf stars have fewer flares and starspots

The triple star system nearest our sun – the Alpha Centauri system – contains a red dwarf star called Proxima. This cool red dwarf is the nearest star to the sun at a distance of 4.22 light years. Proxima Centauri is typical of the stars studied by Andrew West, who in 2006 found that stars closest to the plane of our Mllky Way galaxy tend to be more active, with more flares and starspots.

Red dwarfs are thought to be the most common stars in our Milky Way galaxy.

Red dwarfs are smaller, cooler, and fainter than our sun. Not one is visible to the unaided eye. Yet, of all the stars in our galaxy, 75% are thought to be red dwarfs.

Astronomer Andrew West at the University of California at Berkeley and his colleagues studied 2,601 red dwarf stars – a huge number – and discovered a striking correlation. They found that the closer a red dwarf is to the plane of our galaxy – that’s the flat part of the galaxy, containing most of its stars – the more likely that red dwarf is to have magnetic activity. That means flares, like those on our sun, and starspots which resemble sunspots.

Astronomers have long recognized that stars farther from the galactic plane tend to be older. So that’s more magnetic activity for younger red dwarfs near the plane of the galaxy. And it’s less magnetic activity – fewer flares and starspots – for older red dwarfs farther from the galactic plane. Like some people, it seems, these red dwarf stars become less active as they age.

Our thanks today to Research Corporation, a foundation for the advancement of science.

December 19, 2006

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