Free Astronomy Magazine January-February 2025

21 JANUARY-FEBRUARY 2025 ASTRO PUBLISHING like other circumstellar disks we’ve looked at,” said Andras Gáspár of the University of Arizona, a mem- ber of the research team. “The Vega disk is smooth, ridiculously smooth.” The big surprise to the research team is that there is no obvious ev- idence for one or more large plan- ets plowing through the face-on disk like snow tractors. “It’s making us rethink the range and variety among exoplanet systems,” said Kate Su of the University of Ari- zona, lead author of the paper pre- senting the Webb findings. Webb sees the infrared glow from a disk of particles the size of sand swirling around the sizzling blue-white star that is 40 times brighter than our Sun. Hubble captures an outer halo of this disk, with particles no bigger than the consistency of smoke that are reflecting starlight. The distribution of dust in the Vega debris disk is layered because the pressure of starlight pushes out the smaller grains faster than larger grains. “Different types of physics will locate different-sized parti- cles at different locations,” said Schuyler Wolff of the University of Arizona team, lead author of the paper presenting the Hubble find- ings. “The fact that we’re seeing dust particle sizes sorted out can help us understand the underlying dynamics in circumstellar disks.” The Vega disk does have a subtle gap, around 60 AU (astronomical units) from the star (twice the dis- tance of Neptune from the Sun), but otherwise is very smooth all the way in until it is lost in the glare of the star. This shows that there are no planets down at least to Nep- tune-mass circulating in large or- bits, as in our solar system, say the researchers. “We’re seeing in detail how much variety there is among circumstellar disks, and how that variety is tied into the underlying planetary sys- tems. We’re finding a lot out about the planetary systems – even when we can’t see what might be hidden planets,” added Su. “There’s still a lot of unknowns in the planet-for- mation process, and I think these new observations of Vega are going to help constrain models of planet formation.” Newly forming stars accrete mate- rial from a disk of dust and gas that is the flattened remnant of the cloud from which they are forming. In the mid-1990s Hubble found disks around many newly forming stars. The disks are likely sites of T he James Webb Space Telescope resolves the glow of warm dust in a disk halo, at 23 billion miles out. The outer disk (analogous to the solar system’s Kuiper Belt) extends from 7 billion miles to 15 billion miles. The inner disk extends from the inner edge of the outer disk down to close proximity to the star. There is a no- table dip in surface brightness of the inner disk from approximately 3.7 to 7.2 billion miles. The black spot at the center is due to lack of data from saturation. [NASA, ESA, CSA, STScI, S. Wolff (University of Arizona), K. Su (University of Arizona), A. Gáspár (University of Arizona)]