Could stars become planets

Massive and low-mass planets can arise in the same way

Charleston (USA) / Heidelberg - For several years, astronomers have been discussing the probability that massive stars also have massive planets. Because with stars with a particularly large mass, the prerequisites for the formation of planets, as we know them from our solar system, are possibly worse, since the stars emit enormous amounts of high-energy radiation. This radiation could decompose and disperse parts of a protoplanetary disk before planets form from them. A group of researchers has now come across a star with two and a half times the mass of the Sun, around which a gas planet orbits. This has 13 times the mass of Jupiter and was actually created from a protoplanetary disk, the scientists report in the "Astrophysical Journal Letters" magazine.

Kappa Andromedae and companion

The "Superjupiter" was found at the star Kappa Andromedae in the constellation Andromeda, about 170 light years from Earth. Joseph Carson from the College of Charleston in the USA and the Max Planck Institute for Astronomy and his team observed him with the Subaru telescope, an 8-meter reflector telescope on the summit of Mauna Kea in Hawaii. The newly discovered companion - Kappa Andromedae b - orbits its central star at a distance that is almost twice the distance between the sun and Neptune, the outermost planet of the solar system. Carson and his colleagues were able to directly image Kappa Andromedae b by combining temporal sequences of individual images and thus filtering out a large part of the starlight that normally outshines the planet. They took advantage of the fact that the orientation of the telescope changes relative to the observed section of sky over longer periods of observation. In this way, scattered light and planetary light could be separated.

What is particularly interesting about the discovery is that the object moves around a young, massive star. Because at 30 million years, Kappa Andromedae is significantly younger than, for example, our sun, which is five billion years old. In addition, the distance between planet and star is comparatively small, it corresponds to twice the orbit radius of Neptune, the outermost planet in our solar system. Most of the objects of this type recorded so far have significantly larger orbits. Both the age of the star and the distance indicate that the planet formed like planets of lower mass: in a protoplanetary disk of gas and dust that surrounded the young star during its earliest stages of development. The researchers conclude that at least stars with few solar masses can produce large planets in protoplanetary disks. Their knowledge could influence models of planet formation.

With the direct detection, the exoplanet can be observed immediately. Investigations of the emitted light should now provide data on the chemical composition of the gas giant's atmosphere and help to determine its orbit data more precisely. In addition, the astronomers want to search for other planets.