JWST found rogue worlds that blur the line between stars and planets

Astronomers have found six new worlds that look like planets, but formed like stars. These so-called rogue worlds are between 5 and 15 times the mass of Jupiter, and one of them may even host the beginnings of a miniature solar system.

Ray Jayawardhana at Johns Hopkins University in Maryland and his colleagues found these strange worlds in the NGC 1333 star cluster using the James Webb Space Telescope. Despite being planet-sized, none of them orbits a star, indicating that they probably formed from the collapse of clouds of dust and gas, the same way that stars like our sun are born. Objects like these that form like stars but are not massive enough to sustain the nuclear fusion of hydrogen are called brown dwarfs or failed stars.

“In some ways, what’s most striking is what we didn’t find,” says Jayawardhana. “We didn’t find anything below 5 Jupiter masses, despite the fact that we had the sensitivity to do so.” That may indicate that brown dwarfs cannot form at smaller masses, meaning these are the very smallest objects that form like stars.

From their observations, the researchers determined that brown dwarfs make up about 10 per cent of the objects in NGC1333. That is far more than expected based on models of star formation, so there may be extra processes, such as turbulence, that drive the formation of these rogue worlds.

One of the brown dwarfs is particularly unusual – it has a ring of dust around it just like the one that formed the planets in our solar system. At about 5 Jupiter masses, it is the smallest world ever spotted with such a ring, and it may be the beginnings of a strange miniature planetary system around a failed star.

“From a miniature world around one these objects, you would see the [brown dwarf] glowing mainly in the infrared – it would be a very reddish glow – and over hundreds of millions of years it would be fading into obscurity,” says Jayawardhana. As the brown dwarf fades, any planets that may form around it will go into a deep freeze and the whole system will go dark, so these are not promising worlds to search for life.

Journal reference: The Astronomical Journal, in press