A curious object has been spotted by astronomers looking for the youngest planets in the universe.
PTFO8-8695 b is believed to be a hot Jupiter, a gas giant planet orbiting its host star incredibly closely. But this potential planet is not like any other. Its outer layers are being slowly eaten by its host star, a very young star 1,100 light-years from Earth. The team believes the planet is in a slow death spiral towards the star.
“A handful of known planets are in similarly small orbits, but because this star is only 2 million years old this is one of the most extreme examples,” said Rice University astronomer Christopher Johns-Krull, lead author of the study, in a statement.
The presence of a planet so close to such a young star raises many questions on how this planet formed. The researchers' study has been accepted for publication in The Astrophysical Journal, with the pre-print paper available to read online.
“We don't know the ultimate fate of this planet. It likely formed farther away from the star and has migrated into a point where it's being destroyed,” explained Johns-Krull.
“We know there are close-orbiting planets around middle-aged stars that are presumably in stable orbits. What we don't know is how quickly this young planet is going to lose its mass and whether it will lose too much to survive."
Planets are not observed directly; they are found by looking at features in the light of the stars. Young stars are very active, which can make it very difficult to confirm if a planet is there or not. One such feature, however, is called H-Alpha, and it’s the light emitted by an excited hydrogen atom.
"We saw one component of the hydrogen emission start on one side of the star's emission and then move over to the other side," said Lisa Prato, an astronomer at Lowell Observatory and co-leader of the team with Johns-Krull.
"When a planet transits a star, you can determine the orbital period of the planet and how fast it is moving toward you or away from you as it orbits. So, we said, 'If the planet is real, what is the velocity of the planet relative to the star?' And it turned out that the velocity of the planet was exactly where this extra bit of H-alpha emission was moving back and forth."
If the emission is a planet, it is only between 3 and 4 percent of the size of its star (at most, twice the mass of Jupiter) but the H-alpha emission is quite large and almost as bright as the star. A planet whose hydrogen is being slowly sucked away would fit the observations very well.
Main image credit: A. Passwaters/Rice University/Skyhawk92