Extraordinary pair: Star discovered that was once traveling in another star
Theoretically, a star can travel within another star without the two merging. Now an example may have been discovered for the first time.
Artistic representation of a young neutron star
(Image: ESO/L.Calçada.)
A research team from China has apparently discovered for the first time a binary star system that was formed by a process in which one of the two was traveling inside the other. The research group has now made this public in the scientific journal Science and explained that the two objects are an enormously fast rotating pulsar and a so-called helium star. How such a system can form is “not fully understood”, but the theories include a so-called common envelope (CE) phase, in which one-star travels in the atmosphere of the other and tears away its envelope.
Rare, but not unique
As research leader Jin Lin Han from the Chinese Academy of Sciences explained to the US magazine Gizmodo, he and his team found the signals from the neutron star five years ago. A few months later, they were able to confirm that it is a pulsar, but that it has a companion that it orbits once every 3.6 hours. For a sixth of this time, however, it is obscured by this invisible companion, which is “strange” because it would have to be larger for this. Normally, pulsars are accompanied by white dwarf stars, the compact remnant of a dead star. In this case, however, it is probably the core of a star that has been deprived of all its hydrogen.
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The group used simulations to determine the probable history of the star system's formation. According to this, the neutron star moved closer and closer to its companion until it finally penetrated its outer shell. There it literally sucked out the material, increasing its rotational speed further and further. After just about 1000 Earth years, no shell remained, and since then, only the helium core of the second star has remained. The pulsar itself now rotates around its axis once every 10.55 milliseconds. The research team believes that there are probably between 16 and 84 such systems in the Milky Way.
(mho)
