Shrinking of the North Star

The North Star, or Polaris as astronomers calls it, has been guiding sailors and many others at night for centuries. Now astronomers found out that all is not well with its light cycles, it turns out that Polaris is losing mass equivalent to the earth each year. The idea was proposed by Hilding Neilson and his team at the University of Bonn. The researchers weighed Polaris which is a supergiant main star in the Polaris multiple star system by monitoring how its light cycles dims and brightens.

By detecting a star's light cycle one can know the mass of the star. How this works is like most supergiant stars like our sun is made up of gases in the layers around the core where fusion occurs. The gravitational force of the star pulls the outermost gas inward creating an opaque layer just below the surface. This surface acts like a pressure tank which hold light in. Once it reaches its limit it releases the light build up at once like a shaken bottle of coke. The light buildup will heat up the opaque layer expanding it and becomes transparent. After energy is disperse from the heated opaque layer it will be pulled down again the cycle continues.

The thing is that Polaris's light cycle hasn't remained constant. Observations made in 1844 reveal Polaris's pulse used to be 12 minutes slower than it is now, and 168 years of data suggest that Polaris's pulse regularly decreases by about 4.5 seconds each year. The best explanation from Neilson, is that Polaris is dispersing an earth's worth of mass into space every year, which would throw off the inner workings of the light cycle just enough to account for this big drop.

The good news is that Neilson says this mass loss is likely to be temporary in the star's life. The star isn't going to disappear anytime soon with this method of dispersing mass. Still this wont matter because Polaris isnt going to be our north star anymore. In another 1000 years Gamma Cephei will replace the alignment where Polaris is. So in the future we can still be certain that we can still navigate the sea by stars.


http://m.iopscience.iop.org/2041-8205/745/2/L32