Webb discovers dusty ‘cat’s tail’ in the Beta Pictoris system

Beta Pictoris, a young planetary system located just 63 light years away, continues to intrigue scientists even after decades of extensive study. It has the first dust disk observed around another star: a disk of debris produced by collisions between asteroids, comets and planetesimals.

Observations from NASA’s Hubble Space Telescope revealed a second debris disk in this system, tilted relative to the outer disk, which was seen first. Now, a team of astronomers using NASA’s James Webb Space Telescope to image the Beta Pictoris (Beta Pic) system has discovered a new, never-before-seen structure.

The team, led by Isabel Rebollido of the Center for Astrobiology in Spain, used Webb’s NIRCam (near infrared camera) and MIRI (mid infrared instrument) to study the composition of the primary and secondary debris disks previously detected by Beta Peak. The results exceeded their expectations, revealing a steeply inclined, cat’s tail-shaped dust branch extending from the southwest portion of the secondary debris disk.

“Beta Pictoris is the debris disk that has it all: it has a very bright and nearby star that we can study very well, as well as a complex circumstellar environment with a multi-component disk, exocomets and two imaged exoplanets” , Rebollido said. lead author of the study. “Although there had been previous observations from the ground in this wavelength range, they did not have the sensitivity and spatial resolution that we now have with Webb, so they did not detect this feature .”

The portrait of a star improved with Webb

Even with Webb or JWST, observing Beta Peak in the correct wavelength range (in this case, mid-infrared) was crucial to detecting the cat’s tail, as it only appeared in the MIRI data. Webb’s mid-infrared data also revealed temperature differences between Beta Pic’s two disks, likely due to compositional differences.

“We didn’t expect Webb to reveal that there are two different types of material around Beta Pic, but MIRI clearly showed us that the material in the secondary disk and the cat’s tail is hotter than that of the disk principal,” said Christopher Stark, coordinator of Beta Pic. -author of the study carried out at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “The dust that forms this disk and tail must be very dark, so we don’t see it easily in visible wavelengths, but in mid-infrared it glows.”

To explain the higher temperature, the team inferred that the dust could be a highly porous “organic refractory material”, similar to the material found on the surfaces of comets and asteroids in our solar system. For example, a preliminary analysis of material sampled from the asteroid Bennu by NASA’s OSIRIS-REx mission found it to be very dark and carbon-rich, much like what MIRI detected at Beta Pic.

The puzzling start of the tail warrants future research

However, a major question remains: what could explain the shape of the cat’s tail, a unique curved feature unlike what is seen in disks around other stars?

Rebollido and the team modeled various scenarios to try to imitate the cat’s tail and discover its origins. Although more research and testing is needed, the team presents a strong hypothesis that the cat’s tail is the result of a dust-producing event that occurred just a hundred years ago.

“Something happens, like a collision, and a lot of dust is produced,” said Marshall Perrin, a co-author of the study at the Space Telescope Science Institute in Baltimore, Maryland. “At first, the dust goes in the same orbital direction as its source, but then it also begins to spread out. The star’s light moves the smaller, fluffier dust particles away from the star more quickly, while the larger grains don’t move as much, creating a long tendril of dust.

“The cat’s tail is very unusual and reproducing the curvature with a dynamic model was difficult,” Stark explained. “Our model requires dust that can be expelled from the system extremely quickly, again suggesting that it is made of an organic refractory material.”

The team’s preferred model explains the acute angle of the tail relative to the disk as a simple optical illusion. Our perspective combined with the curved shape of the tail creates the observed angle of the tail, when in fact the arc of material only extends away from the disk at a five degree tilt. Taking into account the brightness of the tail, the team estimates that the amount of dust in the cat’s tail is equivalent to that of a large main-belt asteroid spread over 10 billion kilometers.

A recent dust-producing event within the Beta Pic debris disks could also explain a newly observed asymmetric extension of the tilted inner disk, as shown in MIRI data and visible only on the non-tail side. The recent production of collision dust could also explain a feature previously spotted by Atacama’s Large Millimeter/submillimeter Array in 2014: a cluster of carbon monoxide (CO) located near the cat’s tail. Given that the star’s radiation is expected to break down CO within about a hundred years, this still-present concentration of gas could be lingering evidence of the same event.

“Our research suggests that Beta Peak may be even more active and chaotic than we previously thought,” Stark said. “JWST continues to surprise us, even when observing the best-studied objects. We have a whole new window into these planetary systems.”

These results were presented at a press conference at the 243rd meeting of the American Astronomical Society in New Orleans, Louisiana.