The James Webb Space Telescope (JWST) has seen Beta Pictoris like never before, capturing a previously unseen structure that is giving the young planetary system a dusty cat’s tail.
Located 63 light-years away from us, Beta Pictoris is a star about twice the size of the Sun and eight times as bright, surrounded by a disk of gas and dust in which there are indications that planets have formed.
Beta Pictoris was the first planetary system around which astronomers discovered a dusty disk of material composed of debris caused by the collision of asteroids and planetesimals during the system’s violent early years. After this, astronomers using the Hubble Space Telescope discovered a second disk containing debris and material in the Beta Pictoris system.
Using JWST instruments – the Near-Infrared Camera (NIRCam) and Mid-Infrared Instrument (MIRI) – a team of astronomers has discovered a new layer of structure in the system, in the form of a sharply inclined dust branch extending from the southwest extends portion of the secondary debris disk.
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“Beta Pictoris is the debris disk that has it all: it has a very bright, nearby star that we can study very well,” study team leader Isabel Rebollido, a scientist at the Astrobiology Center in Spain, said in a statement.
“Although there have been previous ground-based observations in this wavelength range, they did not have the sensitivity and spatial resolution that we have now with the JWST, so they did not detect this feature,” Rebollido added.
The Beta Pictoris loosestrife only appeared for the MIRI instrument because it shines brightest in mid-infrared light, which may also explain why it was previously missed.
Rebollido and her team also noticed another characteristic of Beta Pictoris. They saw a temperature difference between the two disks of the planetary system, indicating that they may have different compositions.
“We didn’t expect the JWST to reveal that there are two different types of material around Beta Pictoris, but MIRI clearly showed us that the material from the secondary disk and cat’s tail is hotter than the main disk,” says co-author Christopher. Stark, of NASA Goddard Space Flight Center in Maryland, said in the same statement. “The dust that forms that disk and tail must be very dark, so we can’t easily see it at visible or near-infrared wavelengths — but in the mid-infrared it glows.”
The team theorizes that the higher-temperature disk is made up of dark, highly porous material similar to that seen on the surfaces of comets and asteroids in our solar system, known as “organic refractory.”
What caused the kink in the cosmic cat’s tail?
While animal behaviorists think cats put a curve in their vertically extended tails as a greeting or to indicate friendliness or playfulness, Rebollido and colleagues aren’t sure what gives this cosmic cat’s tail its shape. This curved feature is not something seen in the material disks in other planet birth systems.
To unravel this cat’s cradle, the team modeled several scenarios to try to recreate the cat’s tail structure and thus explain its origins.
“The cat’s tail feature is highly unusual, and reproducing the curvature with a dynamic model was difficult,” Stark explains. “Our model requires dust that can be pushed out of the system extremely quickly, which again suggests that it is made of organic refractory material.”
This research led the team to determine that the cat’s tail was likely caused by a dust-producing event that, from our perspective here on Earth, occurred only about 100 years ago.
“Something happens – like a collision – and a lot of dust is produced,” co-author Marshall Perrin of the Space Telescope Science Institute in Baltimore said in the statement. “At first the dust goes in the same path direction as the source, but then it also starts to spread.”
Perrin added that the star’s light pushes the smallest, fluffiest dust grains away from the star more quickly, while the larger grains are harder to shift and so don’t move as much, creating a long dust tendril.
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As for the sharp angle at which the dust tail protrudes from the debris disk, Rebollido and colleagues think this is just an optical illusion caused by the angle at which JWST observed Beta Pictoris. The actual angle at which the dust trail extends from the debris disk is only 5 degrees.
Taking into account the brightness of this newly discovered feature, the astronomers were also able to determine that the dust in the tail is equal to the mass of an average asteroid in the main belt between Jupiter and Mars, spread out over a length of about 9.9 billion. miles (16 billion kilometers).
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The dust development that gave Beta Pictoris its feline character may also be responsible for another curious feature of the system. The researchers believe that the same collision could be the cause of an asymmetry in Beta Pictoris that was previously observed in 2014 by the Atacama Large Millimeter/submillimeter Array (ALMA).
This asymmetry takes the form of a clump of carbon monoxide located near the cat’s tail. Since radiation from the central star should not take more than a century to break down this carbon monoxide clump, the fact that the gas concentration is still present could be evidence of the same event.
“Our research suggests that Beta Pic may be even more active and chaotic than we previously thought,” concluded Stark. “The JWST continues to surprise us even when we look at the best-studied objects. We have a completely new window on these planetary systems.”
The team’s research was presented this week at the 243rd meeting of the American Astronomical Society in New Orleans.