Extraordinarily smooth rings of dust surround the star Vega in this infrared view taken by the James Webb Space Telescope. The outer dust ring is analogous to the solar system’s Kuiper belt and extends from 7 billion miles (11 billion km) away from Vega to 15 billion miles (24 billion km) away; beyond it, a warm halo of dust extends 23 billion miles (37 billion km). Credits: NASA, ESA, CSA, STScI, S. Wolff (University of Arizona), K. Su (University of Arizona), A. Gáspár (University of Arizona)
Vega, located in the constellation Lyra, is the fifth brightest star in the night sky. It is known to be surrounded by a disk of particle debris that is nearly 100 billion miles (160 billion kilometers) in diameter. The star and its orbiting disk have been photographed countless times by various observatories and satellites, although only recently was Vega’s disk captured with unprecedented clarity thanks to both the James Webb Space Telescope (JWST) and the Hubble Space Telescope .
“Between the Hubble and Webb telescopes you get a very clear view of Vega. It is a mysterious system because it is different from other circumstellar disks we have observed,” JWST study member Andras Gáspár of the University of Arizona said in a press release.
Data from JWST and Hubble allowed astronomers to observe an extraordinarily smooth disk with no clear signs of planet formation, leaving scientists perplexed as to how this could happen.
Smooth sailing
When stars are in the early stages of formation, they accumulate surrounding nebulosity and create a protoplanetary disk. As the disk forms, planets can begin to form as particles collide with each other. The clumps gradually get larger until they become planetesimals (large, but not quite planets yet) and act like snowplows that clear their paths.
Well, that’s normal behavior, but Vega seems to be the exception. “Vega’s record is smooth, ridiculously smooth,” Gáspár said. And the JWST data study says it is also “remarkably symmetrical and… accurately centered on the star.”
The very high resolution image shows a faint gap within the disk, estimated to be about 60 astronomical units (AU; 1 AU is the average Earth-Sun distance of 93 million miles [150 million km]) from the star. But astronomers expected to see more.
Another star, called Fomalhaut, is located about 25 light-years away in the constellation Piscis Austrinus. The star is almost identical to Vega – in distance, temperature and age – but the dust disks around them couldn’t be more different. The Fomalhaut disk contains three belts that extend up to 23 billion kilometers from its center, suggesting they were created by unseen planets.
“Given the physical similarity between the stars of Vega and Fomalhaut, why does Fomalhaut appear to have been able to form planets and Vega not?” said team member George Rieke of the University of Arizona. Schuyler Wolff, the lead author of the Hubble data study, added: “What’s the difference? Was it the circumstellar environment, or the star itself, that created this difference? What is disconcerting is that the same physics is at work in both.”
The reason behind such huge differences in the behavior of the circumstellar disk between two similar stars remains a mystery for now. But team members from both studies are determined to continue investigating and benefit from the combined JWST and Hubble data.
