Dr. Christopher Stark from NASA’s Goddard Space Flight Center and his colleagues present new coronagraphic images from the NIRCam (Near-Infrared Camera) and MIRI (Mid-Infrared Instrument) instruments onboard the NASA/ESA/CSA James Webb Space Telescope that reveal previously unseen structures in the debris disk around the young star Beta Pictoris.
Beta Pictoris is a young planetary system located approximately 63 light-years away from Earth.
It is estimated to be only 20 million years old and is known to host a gas giant, Beta Pictoris b.
In a new study, Dr. Stark and co-authors used Webb’s NIRCam and MIRI instruments to investigate the composition of Beta Pictoris’ main and secondary debris disks.
“Beta Pictoris is the debris disk that has it all: It has a really bright, close star that we can study very well, and a complex circumstellar environment with a multi-component disk, exocomets, and two imaged exoplanets,” said Astrobiology Center astronomer Isabel Rebollido.
“While there have been previous observations from the ground in this wavelength range, they did not have the sensitivity and the spatial resolution that we now have with Webb, so they didn’t detect this feature.”
Even with Webb, peering at Beta Pictoris in the right wavelength range was crucial to detect a never-before-seen dust trail resembling a cat’s tail, as it only appeared in the MIRI data.
Webb’s mid-infrared data also revealed differences in temperature between Beta Pictoris’ two disks, which likely is due to differences in composition.
“We didn’t expect Webb to reveal that there are two different types of material around Beta Pictoris, but MIRI clearly showed us that the material of the secondary disk and cat’s tail is hotter than the main disk,” Dr. Stark said.
“The dust that forms that disk and tail must be very dark, so we don’t easily see it at visible wavelengths — but in the mid-infrared, it’s glowing.”
This artist’s impression shows exocomets orbiting beta Pictoris. Image credit: L. Calçada / ESO.
To explain the hotter temperature, the astronomers deduced that the dust may be highly porous ‘organic refractory material,’ similar to the matter found on the surfaces of comets and asteroids in our Solar System.
For example, a preliminary analysis of material sampled from asteroid Bennu by NASA’s OSIRIS-REx mission found it to be very dark and carbon-rich, much like what MIRI detected at Beta Pictoris.
However, a major lingering question remains: what could explain the shape of the cat’s tail, a uniquely curved feature unlike what is seen in disks around other stars?
The researchers modeled various scenarios in an attempt to emulate the cat’s tail and unravel its origins.
Though further research and testing is required, the team presents a strong hypothesis that the cat’s tail is the result of a dust production event that occurred a mere one hundred years ago.
“Something happens — like a collision — and a lot of dust is produced,” said Dr. Marshall Perrin, an astronomer at the Space Telescope Science Institute.
“At first, the dust goes in the same orbital direction as its source, but then it also starts to spread out.”
“The light from the star pushes the smallest, fluffiest dust particles away from the star faster, while the bigger grains do not move as much, creating a long tendril of dust.”
“The cat’s tail feature is highly unusual, and reproducing the curvature with a dynamical model was difficult,” Dr. Stark said.
“Our model requires dust that can be pushed out of the system extremely rapidly, which again suggests it’s made of organic refractory material.”
“We preferred model explains the sharp angle of the tail away from the disk as a simple optical illusion.”
“Our perspective combined with the curved shape of the tail creates the observed angle of the tail, while in fact, the arc of material is only departing from the disk at a five-degree incline.”
“Taking into consideration the tail’s brightness, we estimate the amount of dust within the cat’s tail to be equivalent to a large main belt asteroid spread out across 10 billion miles.”
A recent dust production event within Beta Pictoris’ debris disks could also explain a newly-seen asymmetric extension of the inclined inner disk, as shown in the MIRI data and seen only on the side opposite of the tail.
“Our research suggests that Beta Pictoris may be even more active and chaotic than we had previously thought,” Dr. Stark said.
“Webb continues to surprise us, even when looking at the most well-studied objects. We have a completely new window into these planetary systems.”
The results were presented this week at AAS243, the 243rd meeting of the American Astronomical Society in New Orleans, the United States.
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Christopher Stark et al. 2024. JWST’s New View of Beta Pictoris Suggests Recent Episodic Dust Production From an Eccentric, Inclined Secondary Debris Disk. AAS243, abstract # 4036
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