Almost a decade ago astronomers discovered a peculiar star system, BD +20 307, located 300 light-years from us. It has two stars about a billion years in age, and swirly, dusty debris all around it. What was peculiar about it was that the debris was warm, much warmer than it should have been. Astronomers realized that this was evidence of an impact collision between two exoplanets.
New observations, reported in The Astrophysical Journal, have shown that the infrared brightness is now more than 10 percent higher than it was nine years ago, a sign the system has gained even more warm dust over the last decade. These findings strengthen the view that a planetary collision was key to creating the unexpected warm dust.
“The warm dust around BD +20 307 gives us a glimpse into what catastrophic impacts between rocky exoplanets might be like,” said Maggie Thompson, a graduate student at the University of California, Santa Cruz, and lead author on the paper, in a statement. “We want to know how this system subsequently evolves after the extreme impact.”
Planets in star systems form from the dusty gas disks orbiting newborn stars. At first, these disks are warm, but as time goes on, they go from little pebbles slamming into each other to fully-formed planets. After a billion years, most of the dust not forming the planets should either have been pushed out of the system or pulled into the star, which is why the original detection was so striking. No one was expecting warm dust from a billion-year-old star.
The quick evolution of the system, observed by the Stratospheric Observatory for Infrared Astronomy, or SOFIA, is certainly intriguing and the team hopes to better understand how the BD +20 307 is evolving. This has implications for our own Solar System. The Moon is believed to have formed when a Mars-sized object impacted ancient Earth.
“This is a rare opportunity to study catastrophic collisions occurring late in a planetary system’s history,” said Dr Alycia Weinberger, from the Carnegie Institution for Science, and lead investigator on the project. “The SOFIA observations show changes in the dusty disk on a timescale of only a few years.”
The planetary collision hypothesis is not the only explanation for the data but it is the best explanation for the sudden increase in brightness witnessed over the last few years.