"What's happening in the universe?" Week 11
NASA's Webb Finds Signs of Possible Aurorae on Isolated Brown Dwarf
Astronomers using NASA’s James Webb Space Telescope have found a brown dwarf (an object more massive than Jupiter but smaller than a star) with infrared emission from methane, likely due to energy in its upper atmosphere. This is an unexpected discovery because the brown dwarf, W1935, is cold and lacks a host star; therefore, there is no obvious source for the upper atmosphere energy. The team speculates that the methane emission may be due to processes generating aurorae.
These findings are being presented at the 243rd meeting of the American Astronomical Society in New Orleans.
To help explain the mystery of the infrared emission from methane, the team turned to our solar system. Methane in emission is a common feature in gas giants like Jupiter and Saturn. The upper-atmosphere heating that powers this emission is linked to aurorae.
On Earth, aurorae are created when energetic particles blown into space from the Sun are captured by Earth’s magnetic field. They cascade down into our atmosphere along magnetic field lines near Earth’s poles, colliding with gas molecules and creating eerie, dancing curtains of light. Jupiter and Saturn have similar auroral processes that involve interacting with the solar wind, but they also get auroral contributions from nearby active moons like Io (for Jupiter) and Enceladus (for Saturn).
For isolated brown dwarfs like W1935, the absence of a stellar wind to contribute to the auroral process and explain the extra energy in the upper atmosphere required for the methane emission is a mystery. The team surmises that either unaccounted internal processes like the atmospheric phenomena of Jupiter and Saturn, or external interactions with either interstellar plasma or a nearby active moon may help account for the emission.
Hubble Finds Weird Home of Farthest Fast Radio Burst
Astronomers using NASA's Hubble Space Telescope have found a rare event in an oddball place.
It's called a fast radio burst (FRB), a fleeting blast of energy that can – for a few milliseconds – outshine an entire galaxy. Hundreds of FRBs have been detected over the past few years. They pop off all over the sky like camera flashes at a stadium event, but the sources behind these intense bursts of radiation remain uncertain.
This new FRB is particularly weird because it erupted halfway across the universe, making it the farthest and most powerful example detected to date.
And if that's not strange enough, it just got weirder based on the follow-up Hubble observations made after its discovery. The FRB flashed in what seems like an unlikely place: a collection of galaxies that existed when the universe was only 5 billion years old. The large majority of previous FRBs have been found in isolated galaxies.
FRB 20220610A was first detected on June 10, 2022, by the Australian Square Kilometer Array Pathfinder (ASKAP) radio telescope in Western Australia. The European Southern Observatory's Very Large Telescope in Chile confirmed that the FRB came from a distant place. The FRB was four times more energetic than closer FRBs.
"It required Hubble's keen sharpness and sensitivity to pinpoint exactly where the FRB came from," said lead author Alexa Gordon of Northwestern University in Evanston, Illinois. "Without Hubble's imaging, it would still remain a mystery as to whether this was originating from one monolithic galaxy or from some type of interacting system. It's these types of environments – these weird ones – that are driving us toward better understanding the mystery of FRBs."
Hubble's crisp images suggest this FRB originated in an environment where there may be as many as seven galaxies on a possible path to merging, which would also be very significant, researchers say.
"We are ultimately trying to answer the questions: What causes them? What are their progenitors and what are their origins? The Hubble observations provide a spectacular view of the surprising types of environments that give rise to these mysterious events," said co-investigator Wen-fai Fong, also of Northwestern University.
Though astronomers do not have a consensus on the possible mechanism behind this extraordinary phenomenon, it's generally thought that FRBs must involve some sort of compact object, like a black hole or neutron star. One extreme type of neutron star is called a magnetar – the most intensely magnetic type of neutron star in the universe. It has a magnetic field that is so strong that, if a magnetar were located halfway between Earth and the Moon, it would erase the magnetic strip on everyone's credit card in the world. Much worse yet, if an astronaut traveled within a few hundred miles of the magnetar, they would effectively be dissolved, because every atom in their body would be disrupted.
Possible mechanisms involve some kind of jarring starquake, or alternatively, an explosion caused when a magnetar's twisting magnetic field lines snap and reconnect. A similar phenomenon happens on the Sun, causing solar flares, but a magnetar's field is a trillion times stronger than the Sun's magnetosphere. The snapping would generate an FRB's flash, or might make a shock wave that incinerates surrounding dust and heats gas into a plasma.
NASA's Webb Discovers Dusty 'Cat's Tail' in Beta Pictoris System
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Beta Pictoris, a young planetary system located just 63 light-years away, continues to intrigue scientists even after decades of in-depth study. It possesses the first dust disk imaged 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, inclined with respect 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, previously unseen structure.
The team, led by Isabel Rebollido of the Astrobiology Center in Spain, used Webb’s NIRCam (Near-Infrared Camera) and MIRI (Mid-Infrared Instrument) to investigate the composition of Beta Pic’s previously detected main and secondary debris disks. The results exceeded their expectations, revealing a sharply inclined branch of dust, shaped like a cat’s tail, that extends from the southwest portion of the secondary debris disk.
“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 cirumstellar environment with a multi-component disk, exocomets, and two imaged exoplanets,” said Rebollido, lead author of the study. “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.”
A Star’s Portrait Improved with Webb
Even with Webb, or JWST, peering at Beta Pic in the right wavelength range — in this case, the mid-infrared — was crucial to detect the cat’s tail, as it only appeared in the MIRI data. Webb’s mid-infrared data also revealed differences in temperature between Beta Pic’s 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 Pic, but MIRI clearly showed us that the material of the secondary disk and cat’s tail is hotter than the main disk,” said Christopher Stark, a co-author of the study at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “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.”
To explain the hotter temperature, the team 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 Pic.
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