Astronomers from the University of Arizona, Tucson, have employed NASA's Hubble and James Webb space telescopes to conduct an unprecedented detailed examination of the nearly 100-billion-mile-diameter debris disk surrounding Vega. "Between the Hubble and Webb telescopes, you get this very clear view of Vega. It's a mysterious system because it's unlike other circumstellar disks we've looked at," said Andras Gaspar of the University of Arizona. "The Vega disk is smooth, ridiculously smooth."

The researchers were particularly surprised by the lack of evidence for any large planets disrupting the disk, similar to how snow tractors would plow through snow. "It's making us rethink the range and variety among exoplanet systems," commented Kate Su of the University of Arizona, lead author of the paper presenting the Webb findings.

Webb's observations detected an infrared glow from sand-sized particles swirling around Vega, which is 40 times more luminous than our Sun. In contrast, Hubble captured an outer halo of smaller particles, akin to smoke, reflecting the star's light.

The debris within the Vega disk shows distinct layering. The pressure of Vega's starlight pushes smaller grains outward faster than the larger ones. "Different types of physics will locate different-sized particles at different locations," explained Schuyler Wolff, lead author of the paper presenting the Hubble findings. "The fact that we're seeing dust particle sizes sorted out can help us understand the underlying dynamics in circumstellar disks."

The disk does show a subtle gap approximately 60 astronomical units (AU) from Vega, roughly twice the distance between Neptune and the Sun. Otherwise, the disk appears remarkably smooth, extending inwards until the star's glare obscures it. This suggests that no planets, at least down to Neptune's mass, are orbiting in large orbits within the disk, the researchers noted.

"We're seeing in detail how much variety there is among circumstellar disks, and how that variety is tied into the underlying planetary systems," added Su. "These new observations of Vega are going to help constrain models of planet formation."

Fully matured stars like Vega, which is 450 million years old, host dusty disks generated by collisions among orbiting asteroids and the remnants of evaporating comets. This disk diversity offers insight into planet formation and dynamics. "Vega continues to be unusual," Wolff said, noting that its architecture differs markedly from that of our solar system, where planets like Jupiter and Saturn help contain dust.

A nearby star, Fomalhaut, is similar to Vega in distance, age, and temperature, yet its circumstellar structure is dramatically different. Fomalhaut has three nested debris belts, possibly shepherded by unseen planets, although none have been definitively identified. "Given the physical similarity between the stars of Vega and Fomalhaut, why does Fomalhaut seem to have been able to form planets and Vega didn't?" questioned George Rieke of the University of Arizona. "What's the difference? Did the circumstellar environment, or the star itself, create that difference?" added Wolff.

Located in the constellation Lyra, Vega is among the brightest stars in the northern sky. It has long intrigued astronomers, with Immanuel Kant hypothesizing in 1775 about the material orbiting Vega potentially serving as the building blocks for planets. In 1984, NASA's IRAS (Infrared Astronomy Satellite) detected excess infrared light from warm dust around Vega, which was confirmed and mapped by subsequent observatories including NASA's Spitzer Space Telescope and the Atacama Large Millimeter/submillimeter Array (ALMA).

Two papers from the Arizona team will be published in The Astrophysical Journal.

The James Webb Space Telescope, led by NASA with ESA and CSA as partners, continues to explore mysteries across the universe, while Hubble, a collaborative project between NASA and ESA, has been instrumental in broadening our understanding for over three decades.

Related Links
Hubble Space Telescopes
Stellar Chemistry, The Universe And All Within It