Brightest Summer Star is Magnetic

Written by The Night Sky Guy on June 24, 2009 – 11:38 am -

Astronomers today announced the first detection of a magnetic field on the star Vega, one of the brightest stars in the sky. Vega is a famous star among amateur and professional astronomers. Located at only 25 light years from Earth in the Lyra constellation, it is the fifth brightest star in the sky. It has been used as a reference star for brightness comparisons. Vega is twice as massive as the Sun and has only one tenth its age. Because it is both bright and nearby, Vega has been often studied but it is still revealing new aspects when it is observed with more powerful instruments. Vega rotates in less than a day, while the Sun’s rotation period is 27 days. The intense centrifugal force induced by this rapid rotation flattens its poles and generates temperature variations of more than 1000 degrees Celsius between the polar (warmer) and the equatorial regions of its surface. Vega is also surrounded by a disk of dust that suggests the presence of planets.

Find Vega near overhead summer night skies

Find Vega near overhead summer night skies

This time, astronomers analyzed the polarization of light emitted by Vega and detected a weak magnetic field at its surface. This is really not a big surprise because one knows that the charged particle motions inside stars can generate magnetic fields, and this is how solar and terrestrial magnetic fields are produced. However, for more massive stars than the Sun, such as Vega, theoretical models cannot predict the intensity and the structure of the magnetic field, so that astronomers had no clue to the strength of the signal they were looking for. After many unsuccessful attempts in past decades an observing campaign have made this first detection possible.

The strength of Vega magnetic field is about 50 micro-tesla, which is close to that of the mean field on Earth and on the Sun. This detection suggests that magnetic fields exist but have not been detected yet on many stars like Vega. Astronomers believe that this discovery will be a key step in understanding stellar magnetic fields and their influence on stellar evolution. As for Vega, it is now the prototype of a new class of magnetic stars and will definitely continue fascinating astronomers for years.

- Adapted from material from Astronomy &  Astrophysics journal press annoucment

 


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