Astronomers observing a distant planet-forming disk of dust and gas have found that it is much colder than expected. The findings, published in Astronomy & Astrophysics Letters, could have implications for how planetary systems form.
This research was carried out by an international team led by Stephane Guilloteau at the Laboratoire d'Astrophysique de Bordeaux, France. They studied the young star 2MASS J16281370-2431391, located 400 light-years from Earth, which is surrounded by a protoplanetary disk.
These disks are formed in the early stages of a planetary system; a similar disk of dust and gas gave rise to the planets, moons, and other bodies in our own Solar System. And with advances in telescopes, we are starting to get better and better at observing other disks in our galaxy.
This particular disk, nicknamed the “Flying Saucer” for its appearance, proved to be rather unusual. Most models predict that the temperature of dust grains in such disks should be between -258 and -253°C (absolute zero is -273.15°C). This disk, though, had grains at a much colder temperature of -266°C, at a distance about 15 billion kilometers (9 billion miles) from the star.
It might seem like a minor difference, but there are some intriguing implications. Namely, it means the dust grains may have different properties than those expected. For example, a colder temperature may mean the grains are larger, which suggests the disks could grow to huge masses, allowing for the formation of a range of planets at all distances from the stars – including giant planets in close orbits, something we have a lot of evidence for but no solid explanation for their formation.
“To work out the impact of this discovery on disk structure, we have to find what plausible dust properties can result in such low temperatures,” said study coauthor Emmanuel di Folco in a statement. “We have a few ideas – for example, the temperature may depend on grain size, with the bigger grains cooler than the smaller ones. But it is too early to be sure.”
These results were obtained by combining measurements from the Atacama Large Milimeter/submillimeter Array (ALMA) in Chile and the IRAM 30-meter telescope in Spain.