A giant exoplanet discovered around the most massive stars hosting known planets
Planet b Centauri b shouldn’t even exist – but the image above is confirmation that it does exist.
The image, taken by the Very Large Telescope of the European Southern Observatory in Chile, shows the binary star system b Centauri on the left, its two stars not quite resolved. At magnitude 4, b Centauri, located some 325 light years away, is visible to the naked eye, but it should not be confused with Beta (β) Centauri, which is one of the brightest stars in the sky. .
The arrow in the image above points to the planet. By convention, the first planet discovered in a system is given the suffix “b”, resulting in the unusual name: b Centauri b. It is a gas giant orbiting its host stars at a distance of approximately 560 times that of the Earth from the Sun. This makes it one of the most distant exoplanet orbits to date. (The apparent rings around the star and the planet are image artifacts, and the object in the top right is an unrelated background star.)
The mass of the planet is about 11 times that of Jupiter, which puts it at the top of objects that can still be called planets. Objects with masses of 13 or more Jupiters are classified as brown dwarfs or failed stars.
But it’s the two host stars that make this system truly different from any other astronomer so far: the stars have a combined mass estimated to be six to 10 times that of the Sun. It may not seem like much, but it is at least double the mass of any other known star (or stars) confirmed to host a planet. The largest star in the system is spectral type B, the second hottest category. And the problem with planets forming around such hot stars is that they emit a lot of powerful ultraviolet and x-ray radiation, which should disrupt the process of planetary formation.
“Finding a planet around b Centauri was very exciting because it completely changes the image of massive stars as hosts on the planet,” said Markus Janson, astronomer at Stockholm University in Sweden, in a report. Janson is the first author of the new study, published on December 8 in Nature.
The finding raises the possibility that b Centauri b formed by a different process than predicted by conventional theory. This theory is a bottom-up pattern called nucleus accretion, in which dust grains from the protoplanetary disk – which surrounds the nascent star – begin to stick together. Eventually, these snowballed dust grains develop to form concentrated planetary cores that begin to capture more rocky debris. If they are massive enough, they can start collecting gas to form an atmosphere.