Astronomers see debris disk around young star Vega in unprecedented detail
Teams of astronomers used the combined power of NASA's Hubble and James Webb space telescopes to revisit the legendary Vega disk.
NASA, ESA, CSA, STScI, S. Wolff (University of Arizona), K. Su (University of Arizona), A. Gáspár (University of Arizona)
In the 1997 movie "Contact," adapted from Carl Sagan's 1985 novel, scientist Ellie Arroway, played by Jodi Foster, takes a space-alien-built wormhole ride to the star Vega. She emerges inside a snowstorm of debris encircling the star – but no obvious planets are visible.
According to a new paper by a team of astronomers at the University of Arizona, the filmmakers got it right. The team used NASA's Hubble Space Telescope and James Webb Space Telescope to get an unprecedented in-depth look at the nearly 100-billion-mile-diameter debris disk encircling Vega.
Located in the summer constellation Lyra, Vega is one of the brightest stars in the northern sky. Vega is legendary because it offered the first evidence for material orbiting a star – presumably the stuff for making planets – as potential abodes of life.
In 2005, NASA's infrared Spitzer Space Telescope mapped out a ring of dust around Vega. This was further confirmed by observations with other telescopes, but none of them could see much detail.
"Between the Hubble and Webb telescopes, you get this very clear view of Vega," said Andras Gáspár, associate research professor at the U of A Steward Observatory and a co-author of two papers to be published in The Astrophysical Journal. "It's a mysterious system because it's unlike other circumstellar disks we've looked at; the Vega disk is smooth – ridiculously smooth."
The big surprise to the research team is that there is no obvious evidence for one or more large planets plowing through the disk like snow tractors.
"It's making us rethink the range and variety among exoplanet systems," said Kate Su, a former research professor at Steward who is now at the Space Science Institute in Boulder, Colorado. Su led the paper presenting the findings from the James Webb Space Telescope.
The disk around Vega as seen by Hubble (left) and Webb (right). Hubble detects reflected light from dust the size of smoke particles largely in a halo on the periphery of the 100-billion-mile-wide disk. Webb 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.
NASA, ESA, CSA, STScI, S. Wolff (University of Arizona), K. Su (University of Arizona), A. Gáspár (University of Arizona)
Webb sees the infrared glow from a disk of sand-sized particles 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 particles at different locations," said Schuyler Wolff, an assistant research professor at Steward and 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."
"We're seeing in detail how much variety there is among circumstellar disks, and how that variety is tied into the underlying planetary systems," Su added. "We're finding a lot out about the planetary systems – even when we can't see what might be hidden planets. There's still a lot of unknowns in the planet formation process, and I think these new observations of Vega are going to help constrain models of planet formation."
Newly forming stars accrete material from a disk of dust and gas that is the flattened remnant of the cloud from which they form. In the mid-1990s, Hubble found disks around many newly forming stars. Fully matured stars like Vega have dusty disks enriched by ongoing "bumper car" collisions among orbiting asteroids and debris from evaporating comets. These are primordial bodies that can survive up to the present 450-million-year age of Vega. Dust in our solar system is also replenished by minor bodies ejecting dust at a rate of about 10 tons per second. This dust is shoved around by planets. This provides a strategy for detecting planets around other stars without seeing them directly – just by witnessing the effects they have on the dust.
"Vega continues to be unusual," Wolff said. "The architecture of the Vega system is markedly different from our own solar system, where giant planets like Jupiter and Saturn are keeping the dust from spreading the way it does with Vega."
"The Hubble and Webb observations together provide so much more detail that they are telling us something completely new about the Vega system that nobody knew before," said team member and Regents' Professor of Astronomy and Planetary Sciences George Rieke.
The James Webb Space Telescope is an international program led by NASA with the European Space Agency and Canadian Space Agency. The Hubble Space Telescope is a project of international cooperation between NASA and the European Space Agency.
