North Star coming back to life
Monday, 21 Jul 2008 08:34
Artist's impression of Polaris and the constellations of the Big and Small Dippers
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The North star is puzzling scientists as it is coming back to life and they do not know why.
An international team of astronomers has observed that vibrations in the Pole star, which had been fading away to almost nothing over the last 100 years, have recovered and are now increasing.
Polaris is a 'Cepheid' variable star, getting brighter and fainter every four days.
"One hundred years ago Polaris varied by ten per cent, but over the last century the variations became smaller and smaller until ten years ago it only varied by two per cent," said Dr Alan Penny from the University of St Andrews.
"It was thought the structure of the star was changing to switch off the vibration. Yet the team has found that about ten years ago the vibrations started picking up and are now back up at the four per cent level."
The discovery was made using two small, relatively unknown telescopes in space and a telescope in Arizona.
The slow decline in variability was in itself unusual, as no other Cepheid is known to do this.
Astronomers thought that Polaris was ageing and its structure was changing so that it was no longer unstable.
Now Polaris has 'turned on' again this explanation seems unlikely and the researchers believe there may be a complex process in the outer layers of the star, with more than one mode of variability.
The finding was announced today at the "Cool Stars 15" conference at the University of St Andrews and will be published in the Astrophysical Journal.