NASA's Hubble, Webb Probe Surprisingly Smooth Disk Around Vega

Hubble and Webb Observations of Vega Circumstellar Disk

Credits/Image: NASA, ESA, CSA, STScI, S. Wolff (University of Arizona), K. Su (University of Arizona), A. Gáspár (University of Arizona)

Vega Hubble Compass Image

Credits/Image: NASA, ESA, STScI, S. Wolff (University of Arizona)

Vega Webb Compass Image
Credits/Image: NASA, ESA, CSA, STScI, K. Su (University of Arizona), A. Gáspár (University of Arizona)

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In the 1997 movie "Contact," adapted from Carl Sagan's 1985 novel, the lead character scientist Ellie Arroway (played by actor 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.

It looks like the filmmakers got it right.

A team of astronomers at the University of Arizona, Tucson used NASA's Hubble and James Webb space telescopes for an unprecedented in-depth look at the nearly 100-billion-mile-diameter debris disk encircling 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 Gáspár of the University of Arizona, a member of the research team. "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 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 Arizona, lead author of the paper presenting 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 particles at different locations," said Schuyler Wolff of the University of Arizona team, 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 Vega disk does have a subtle gap, around 60 AU (astronomical units) from the star (twice the distance 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 Neptune-mass circulating in large orbits, as in our solar system, say the researchers.

Disk Diversity

Newly forming stars accrete material 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 planet formation, migration, and sometimes destruction. 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 (our Sun is approximately ten times older than Vega). Dust within our solar system (seen as the Zodiacal light) 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," said Wolff. "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."

For comparison, there is a nearby star, Fomalhaut, which is about the same distance, age and temperature as Vega. But Fomalhaut's circumstellar architecture is greatly different from Vega's. Fomalhaut has three nested debris belts.

Planets are suggested as shepherding bodies around Fomalhaut that gravitationally constrict the dust into rings, though no planets have been positively identified yet. "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?" said team member George Rieke of the University of Arizona, a member of the research team. "What's the difference? Did the circumstellar environment, or the star itself, create that difference? What's puzzling is that the same physics is at work in both," added Wolff.

First Clue to Possible Planetary Construction Yards

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. This was first hypothesized by Immanuel Kant in 1775. But it took over 200 years before the first observational evidence was collected in 1984. A puzzling excess of infrared light from warm dust was detected by NASA's IRAS (Infrared Astronomy Satellite). It was interpreted as a shell or disk of dust extending twice the orbital radius of Pluto from the star.

In 2005 NASA's infrared Spitzer Space Telescope mapped out a ring of dust around Vega . This was further confirmed by observations using submillimeter telescopes including Caltech's Submillimeter Observatory on Mauna Kea, Hawaii, and also the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile, and ESA's (European Space Agency's) Herschel Space Telescope, but none of these telescopes could see much detail. "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 Rieke.

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

The James Webb Space Telescope is the world's premier space science observatory. Webb is solving mysteries in our solar system, looking beyond to distant worlds around other stars, and probing the mysterious structures and origins of our universe and our place in it. Webb is an international program led by NASA with its partners, ESA (European Space Agency) and CSA (Canadian Space Agency).

The Hubble Space Telescope has been operating for over three decades and continues to make ground-breaking discoveries that shape our fundamental understanding of the universe. Hubble is a project of international cooperation between NASA and ESA (European Space Agency). NASA's Goddard Space Flight Center in Greenbelt, Maryland, manages the telescope and mission operations. Lockheed Martin Space, based in Denver, Colorado, also supports mission operations at Goddard. The Space Telescope Science Institute in Baltimore, Maryland, which is operated by the Association of Universities for Research in Astronomy, conducts Hubble science operations for NASA.

Source: HubbleSite/News

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About This Release

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Space Telescope Science Institute, Baltimore, Maryland

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Related Links and Documents

• Science Paper: The science paper by Schuyler Wolff et al. (on arXiv.org), PDF (3.38 MB)
• Science Paper: The science paper by Kate Su et al. (on arXiv.org), PDF (20.47 MB)
• NASA's Hubble Portal
• University of Arizona's Release

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A Giant, Sizzling Planet May be Orbiting the Star Vega

Artist's conception showing the scorching-hot planet KELT-9b orbiting its host star. A newly detected signal may indicate the presence of a similar planet orbiting the star Vega. The discovery of KELT-9b also included major contributions from CfA scientists. Credit: NASA/JPL-Caltech. High Resolution (jpg)-Low Resolution (jpg)

Cambridge, MA -Astronomers have discovered new hints of a giant, scorching-hot planet orbiting Vega, one of the brightest stars in the night sky.

The research, published this month in The Astronomical Journal, was led by Spencer Hurt, an astronomy undergraduate student at the University of Colorado Boulder. Hurt conducted the study during a 2019 summer research fellowship at the Center for Astrophysics | Harvard & Smithsonian, where he was mentored by astronomer Samuel Quinn.

The research focuses on an iconic and relatively young star, Vega, which is part of the constellation Lyra and has a mass twice that of our own sun. This celestial body sits just 25 light-years, or about 150 trillion miles, from Earth—pretty close, astronomically speaking.

Scientists can also see Vega with telescopes even when it’s light out, which makes it a prime candidate for research, says study co-author Quinn.

"It’s bright enough that you can observe it at twilight when other stars are getting washed out by sunlight," Quinn says.

Despite the star's fame, researchers have yet to find a single planet in orbit around Vega. That might be about to change: Drawing on a decade of observations from the ground, Hurt, Quinn and their colleagues unearthed a curious signal that could be the star's first-known world.

If the team's findings bear out, the alien planet would orbit so close to Vega that its years would last less than two-and-a-half Earth days. (Mercury, in contrast, takes 88 days to circle the sun). This candidate planet could also rank as the second hottest world known to science—with surface temperatures averaging a searing 5,390 degrees Fahrenheit.

Hurt says the group's research also helps to narrow down where other exotic worlds might be hiding in Vega's neighborhood.

"This is a massive system, much larger than our own solar system," Hurt says. "There could be other planets throughout that system. It's just a matter of whether we can detect them."

Youthful energy

Quinn would like to try. Scientists have discovered more than 4,000 exoplanets, or planets beyond Earth's solar system, to date. Few of those, however, circle stars that are as bright or as close to Earth as Vega. That means that, if there are planets around the star, scientists could get a really detailed look at them.

"It would be really exciting to find a planet around Vega because it offers possibilities for future characterization in ways that planets around fainter stars wouldn’t," Quinn says.

There's just one catch: Vega is what scientists call an A-type star, the name for objects that tend to be bigger, younger and much faster-spinning than our own sun. Vega, for example, rotates around its axis once every 16 hours—much faster than the sun with a rotational period that clocks in at 27 Earth days. Such a lightning-fast pace, Quinn says, can make it difficult for scientists to collect precise data on the star's motion and, by extension, any planets in orbit around it.

To take on that game of celestial hide-and-seek, he and colleagues pored through roughly 10 years of data on Vega collected by the Fred Lawrence Whipple Observatory in Arizona. In particular, the team was looking for a tell-tale signal of an alien planet—a slight jiggle in the star’s velocity.

"If you have a planet around a star, it tugs on the star, causing it to wobble back and forth," Quinn says.

Hot and puffy

The search may have paid off, Hurt says. The team discovered a signal that indicates that Vega might host what astronomers call a "hot Neptune" or maybe a "hot Jupiter."

"It would be at least the size of Neptune, potentially as big as Jupiter and would be closer to Vega than Mercury is to the sun," Hurt says.

That close to Vega, he adds, the candidate world might puff up like a balloon, and even iron would melt into gas in its atmosphere.

The researchers have a lot more work to do before they can definitively say that they’ve discovered this sizzling planet. Hurt noted that the easiest way to look for it might be to scan the stellar system directly to look for light emitted from the hot, bright planet.

For now, the student is excited to see his hard work reflected in the constellations: "Whenever I get to go outside and look at the night sky and see Vega, I say 'Hey, I know that star."

Other coauthors on the new study include David Latham, Gilbert Esquerdo, Michael Calkins, Perry Berlind, Christian Latham and George Zhou at the CfA; Andrew Vandeburg at the University of Wisconsin-Madison; and Ruth Angus at the American Museum of Natural History.

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