Starship Asterisk*

[img3="Quiet Corona and Upper Transition Region of the Sun - Credit: NASA/GSFC/SDO"]https://upload.wikimedia.org/wikipedia/ ... he_Sun.jpg[/img3][hr][/hr]

New work from a team of astronomers led by Carnegie’s Jennifer van Saders indicates that one recently developed method for determining a star’s age needs to be recalibrated for stars that are older than our Sun. This is due to new information about the way older stars spin, as spin rate is one of the few windows into stellar ages. Their findings, published in Nature, have implications for our own Solar System, as they indicate that our own Sun might be on the cusp of a transition in its magnetic field.

Just like planets, stars rotate around an axis. As stars age, this spin slows down due to the star’s magnetic field acting on its stellar wind, which is a flow of gas moving away from the star. The loss of mass, as the flowing gases get caught in the magnetic field and spin outward until they are ejected, affects the Sun’s angular momentum and causes the slowdown. In this way, the magnetic field acts like a brake.

About a decade ago, it was discovered that this phenomenon can be used to calculate the age of a Sun-like star if its rotation rate and mass are known. The process is called gyrochronology. However, in their new paper van Saders and her team demonstrate that stars don’t spin down exactly as expected when they get older. The correction affects the gyrochronological calculation for older stars. ...

• Nature (online 04 Jan 2016) DOI: 10.1038/nature16168