Astronomers have had a big surprise with the discovery that a star known as WL 20S, which has been studied extensively since the 1970s, is actually not one but a pair of stars.
The discovery of the surprising twin was made with the James Webb Space Telescope during a survey of a group of young stars called WL 20.
In addition, observations with the Atacama Large Millimeter/submillimeter Array (ALMA) show disks of dust and gas around both stars. Since the stars are relatively young with an age of 2 to 4 million years, it is possible that planets can form within these disks.
The discovery that WL 20S is a pair of stars was made using the Webb Telescope’s Mid-Infrared Instrument (MIRI) and presented at the 244th meeting of the American Astronomical Society on June 12, 2024.
MIRI data also shows that the twin stars have matching jets of gas spewing into space from their north and south poles.
“Our jaws dropped,” says astronomer Mary Barsony, lead author of a paper describing the results.
“After decades of studying this source, we thought we knew it pretty well. But without MIRI, we wouldn’t have known these were two stars or that these jets existed. That’s really amazing. It’s like we have brand new eyes. “
Discovering the twins and jets
WL 20 is located in a star-forming region of our Milky Way known as Rho Ophiuchi, just 400 light-years from Earth.
Like a typical star-forming region, it is a huge cloud of gas and dust, and therefore difficult to examine internally in visible light.
Because the James Webb Space Telescope observes in infrared, it can look through the dust and see what lurks in star-forming regions like WL 20.
The same goes for ALMA, which observes at a wavelength called ‘submillimeter’ and can also penetrate the gas clouds of a star-forming region.
ALMA was able to observe the two disks of gas and dust surrounding the WL 20S stars, but according to the astronomers behind the study, this could have been interpreted as a single disk with a hole in it.
It is the discovery of the two stellar jets by MIRI that shows that WL 20S is a pair of twin stars.
The gas jets are composed of ions, or individual atoms with some electrons stripped away, and they glow in the mid-infrared, but not to a submillimeter, meaning Webb’s MIRI could see them, but ALMA could not.
However, ALMA can observe the leftover materials surrounding very young stars after their formation.
The absence of such clouds in ALMA observations shows that the stars have already passed their initial formation phase.
All this means that the twin stars are transitioning from youth to adulthood, giving astronomers the opportunity to observe this key period in a star’s life cycle.
“The power of these two telescopes together is truly incredible,” said Mike Ressler, project scientist for MIRI at NASA’s Jet Propulsion Laboratory and co-author of the new study.
‘If we hadn’t seen that these were two stars, the ALMA results might have looked like a single disk with a hole in the center. Instead, we have new data about two stars who are clearly at a pivotal point in their lives. , when the processes that created them are disappearing.
“It’s amazing that this region still has so much to teach us about the life cycle of stars. I’m excited to see what else Webb will reveal.”