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Scientists recently got a big surprise from NASA’s James Webb Space Telescope when they pointed to the observatory’s group of young stars called WL 20. The region has been studied by at least five telescopes since the 1970s, but it took Webb’s unprecedented resolution and special equipment to reveal what scientists long thought was one of the stars, WL 20S is actually a pair formed from 2 million to 4. million years ago.
The discovery was made using Webb’s Mid-Infrared Instrument (MIRI) and was presented June 12 at the 244th meeting of the American Astronomical Society. MIRI also found that the twins have corresponding jets of gas that flow into space from the north and south poles. “Our jaws dropped,” said astronomer Mary Barsony, lead author of a new paper describing the results. “After studying this source for decades, we thought we knew it pretty well. But without MIRI, we wouldn’t have known that these were two stars or that these rays exist. It’s really amazing. It’s like having brand new eyes.”
The team got another surprise when additional observations by the Atacama Large Millimeter/submillimeter Array (ALMA), an array of more than 60 radio antennas in Chile, showed that both stars are surrounded by discs of dust and gas. Based on the age of the stars, it is possible that planets can form in these disks. The combined results indicate that the binary stars are nearing the end of this early life, meaning that scientists have an opportunity to learn more about how stars transition from youth to adulthood.
“The power of these two telescopes together is truly incredible,” said Mike Ressler, MIRI project scientist at NASA’s Jet Propulsion Laboratory and co-author of the new study. “If we hadn’t seen that it was two stars, the ALMA results might have looked like a single disc with a hole in the middle. Instead, we have new information about two stars that are clearly at a critical stage in their lives, when the processes that shaped them are fading. “
Star jets
WL 20 is located in a much larger, well-studied star-forming region in the Milky Way galaxy called Rho Ophiuchi, a huge cloud of gas and dust about 400 light-years from Earth. In fact, WL 20 is hidden behind thick clouds of gas and dust that block most of the visible light (wavelengths that the human eye can see) from the stars there. Webb detects slightly longer wavelengths, called infrared, that can pass through these layers. MIRI detects the longest infrared wavelengths of Webb’s instruments, so it is well equipped to look at faint star-forming regions like WL 20.
Radio waves also often pass through dust, but they do not exhibit the same properties as infrared light. The disks of gas and dust surrounding WL 20S’s two stars emit light in the region astronomers call submillimeter; these discs also penetrate the surrounding gas clouds and have been detected by ALMA.
But scientists could have easily interpreted these observations as evidence of a single disk with a hole if MIRI hadn’t also detected two starbursts. Gas jets consist of ions or single atoms that have had some electrons removed and emit in the mid-infrared region, but not at submillimeter wavelengths. Only an infrared instrument with spatial and spectral resolution like MIRI would be able to see them.
ALMA can also observe clouds of remnant material forming around young stars. These clouds of gas and dust are composed of whole molecules, such as carbon monoxide, and emit light at these longer wavelengths. The absence of these clouds in the ALMA observations indicates that the stars have passed their initial stages of formation.
“It’s amazing that this region still has so much to teach us about the life cycle of stars,” Ressler said. “I’m curious to see what else Webb reveals.”
Photo: US NSF; NSF NRAO; ALMA; NASA/JPL-Caltech; B. Saxton
Bro: NASA