Monday, May 30, 2022

The Kapteyn Star, the closest halo star to the Solar System

The Kapteyn Star is only 12.8 light years away from Earth, making it the 24th closest star to the Sun, but its origin comes from far, far away. The star is in fact characterized by a very different dynamic than that of other stars in the vicinity of the Sun. Its orbit is in fact retrograde and moves in space at very high speed: think that only 10 thousand years ago the Kapteyn Star was 7 light years from Earth!

By reconstructing its evolutionary history starting from its motion in space and studying the abundance of elements in its atmosphere it was discovered that the Kapteyn Star most likely in the past belonged to the Omega Centauri globular cluster, What remains of a dwarf galaxy destroyed by the tidal forces of the Milky Way and now 16,000 light years from Earth.

You will probably now be curious to know how to observe this particular star so close to Earth with the naked eye. Unfortunately, despite its reduced distance, the Kapteyn Star has a magnitude of +10.9 and is therefore invisible to the naked eye. This is due to its physical properties: the star is in fact a red subdwarf with a surface temperature of only 3500 K, while its mass and diameter are less than 30% of solar ones. This implies a luminosity that is just 0.012 of the solar one, which makes the Kapteyn Star too weak to be seen by the naked eye from Earth.

Credit: Palomar Observatory,

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