A remarkable young stellar system has been found that could upend our theories of how quickly planets form. By observing a disk of material around a star 325 light-years away, astronomers have seen a close-up view of a star still forming with at least one planet close by for the first time.
The research, by astronomers from the University of Leeds, was published today in the journal Monthly Notices of the Royal Astronomical Society.
The astronomers used the Very Large Telescope Interferometer (VLTI) in Chile to study this star, called HD 100546. They found that there is a large gap between the inner and outer disk of planet-forming material, providing evidence for a planet carving out its orbit, just like what is thought to have happened in our own Solar System. This star is about one thousand times younger than the Sun – around 5 million years old – so it provides a glimpse into the distant past.
“Nobody has ever been able to probe this close to a star that is still forming and which also has at least one planet so close in,” said lead author Dr. Ignacio Mendigutía, from the School of Physics and Astronomy at the university, in a statement. Systems like this, with a planet inside a gap in a proto-planetary disk – a disk of planet-forming dust and gas around a young star – are extremely rare; only one other has ever been found.
The planet orbits this star somewhere between 4 and 13 AU (astronomical units) – with 1 AU being the Earth-Sun distance. The inner disk extends up to 4 AU from the star, while the outer disk does not begin until beyond 10 AU – roughly the orbit of Saturn in our own Solar System – and extends out much further, possibly over 1,000 AU. It’s likely that other planets are in the system, or might be yet to form; one is thought to be around the 50 AU position.
The size of the gap suggests the inner planet is a gas giant larger than Jupiter. David Cabezas Jimeno (SEA).
The researchers were surprised to find that the inner planet had formed while the star itself was still in the process of formation. “We thought first that stars formed, then planets,” co-author Professor René Oudmaijer told IFLScience. “But apparently planets formed much quicker than we anticipated.” He noted that the timescales weren’t clear at the moment, but the study was pointing to more rapid planet formation.
This is interesting, as recent research has been trying to solve the mystery of how gas giant planets formed so quickly. If this latest observation is correct, it would suggest some planets can form even quicker than we thought.
Another surprising finding was that the inner planet around HD 100546 seems to be replenishing the disk of material closest to the star, while the star itself resembles others that are not thought to be in such a process of active planet formation. “It was a big surprise,” said Oudmaijer. “It means material must be channeled from the outer disk via the planet to the inner disk.”
The researchers now want to find out if what is happening in this system is typical of other solar systems, like our own. If so, we may need to revise our estimates for how quickly planets can form around stars.
