Star Duo Forms ‘Cosmic Fingerprint’ in Space

NASA’s James Webb Space Telescope has captured and revealed a remarkable cosmic sight at least 17 concentric dust rings emerging from a star duo. The star duo was located over 5,000 light-years from Earth and the duo is collectively known as Wolf-Rayet 140.

Credits: NASA, ESA, CSA, STScI, JPL-Caltech

The star duo in Wolf-Rayet 140 produces shells of dust every eight years that look like rings. Each ring was created when the stars came close together and their stellar winds collided, compressing the gas and forming dust. Each ring was created when the two stars came close together and the streams of gas they blow into space(stellar winds) met, compressing the gas and forming dust. The stars’ orbits bring them together about once every eight years. The dust loops mark the passage of time.

“We’re looking at over a century of dust production from this system,” said Ryan Lau, an astronomer at National Science Foundation’s NOIRLab and ascendancy author of a new study about the system, published today in the journal Nature Astronomy. “The image also illustrates just how sensitive this telescope is. Before, we could only see two dust rings, using ground-based telescopes. Now we see at least 17 of them.”

James Webb’s Mid-Infrared Instrument (MIRI) is uniquely qualified to study the dust rings or what Lau and his colleagues call shells because they are thicker and broader than they appear in the image. Webb’s science instruments can identify infrared light, a range of wavelengths invisible to the human eye. MIRI detects the longest infrared wavelengths, which means it can often see cooler objects including the dust rings than Webb’s other instruments can. MIRI’s spectrometer also revealed the composition of the dust, formed mostly from material ejected by a type of star known as a Wolf-Rayet star.

MIRI was developed through a 50-50 partnership between NASA and European Space Agency(ESA). The Jet Propulsion Laboratory in Southern California led the effort for NASA, and a multinational consortium of European astronomical institutes contributed to ESA.

A Wolf-Rayet star is an O-type star which is a hot, blue-white star of spectral type O. The star is born at least 49.725 x 1030 kilograms mass which is 25 times more mass than our Sun. When the Wolf-Rayet is nearing the end of its life when it will likely collapse and form a black hole. Burning hotter than in its youth, a Wolf-Rayet star generates powerful winds that push vast amounts of gas into space. The Wolf-Rayet star in this particular pair may have shed more than half its original mass via this process.

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Forming Dust in the Wind

Transforming gas into dust is like turning flour into bread: It requires specific conditions and ingredients. The most common element found in stars is hydrogen. It can’t form dust on its own. But because Wolf-Rayet stars shed so much mass (at least 49.725x1030 kilograms), they also emit more complex elements typically found deep in a star’s interior, including carbon. The heavy elements in the wind cool as they travel into space and are then compressed where the winds from both stars meet, like when two hands knead the dough.  

Some other Wolf-Rayet systems form dust, but none is known to make rings like Wolf-Rayet 140. The unique ring pattern forms because the orbit of the Wolf-Rayet star in WR 140 is elongated. It is not circular. Only when the stars come close together – about the same distance between Earth and the Sun and their winds collide is the gas under sufficient pressure to form dust. With circular orbits, Wolf-Rayet binaries can produce dust continuously.  

Size comparison of Sun, Wolf-Rayet Star, and O-typed star
Credits: NASA/JPL-Caltech

Lau and his co-authors think Wolf-Rayet 140’s winds also swept the surrounding area clear of residual material they might otherwise collide with, which may be why the rings remain so pristine rather than dispersed. There are likely even more rings that have become so faint and dispersed, not even James Webb can see them in the data.

Wolf-Rayet stars may seem alien compared to our Sun, but they may have played a role in star and planet formation. When a Wolf-Rayet star clears an area, the swept-up material can pile up at the outskirts and become heavy enough for new stars to form. 

The new study is done by using data from MIRI’s Medium Resolution Spectroscopy mode. It provides the best evidence yet that Wolf-Rayet stars produce carbon-rich dust molecules. What’s more, the preservation of the dust shells indicates that this dust can survive in the hostile environment between stars, going on to supply material for future stars and planets. 

Astronomers estimate that there should be at least a few thousand Wolf-Rayet stars in our galaxy, only about 600 have been found up to now.

“Even though Wolf-Rayet stars are rare in our galaxy because they are short-lived as far as stars go, it’s possible they’ve been producing lots of dust throughout the history of the galaxy before they explode and/or form black holes,” said Patrick Morris, an astrophysicist at Caltech in Pasadena, California, and a co-author of the new study. “I think with NASA’s new space telescope we’re going to learn a lot more about how these stars shape the material between stars and trigger new star formation in galaxies.”