Science

Le télescope spatial Webb découvre une étrange “empreinte digitale” cosmique

Loup Rayet 140 WR140

Les deux étoiles de Wolf-Rayet 140 produisent tous les huit ans des coquilles de poussière qui ressemblent à des anneaux, comme le montre cette image du télescope spatial James Webb de la NASA. Chaque anneau a été créé lorsque les étoiles se sont rapprochées et que leurs vents stellaires sont entrés en collision, comprimant le gaz et formant de la poussière. Crédit : NASA, ESA, CSA, STScI, JPL-Caltech

Une nouvelle image Webb montre au moins 17 anneaux de poussière créés par un type rare d’étoile et son compagnon enfermé dans une danse céleste.

Une vue cosmique remarquable est révélée dans une nouvelle image de Le télescope spatial James Webb de la NASA. Au moins 17 anneaux de poussière concentriques émanent mystérieusement d’une paire d’étoiles. Connu collectivement sous le nom de Wolf-Rayet 140, le duo est situé à un peu plus de 5 000 années-lumière de la Terre.

Les étoiles Wolf-Rayet (souvent abrégées en WR ou WR) sont des étoiles inhabituelles qui sont très massives (plus de 40 fois la masse de notre Soleil), extrêmement chaudes (de 20 000 K à environ 210 000 K) et exceptionnellement brillantes. Les étoiles Wolf-Rayet ont été découvertes en 1867 par CJ Wolf et G. Rayet. Ces étoiles éjectent continuellement leur atmosphère extérieure dans des coquilles de particules et de gaz en forme de bulles, créant un vent stellaire puissant. Environ 500 de ces étoiles ont été cataloguées à ce jour dans le[{” attribute=””>Milky Way.

Each ring was formed when the stellar winds (streams of gas they blow into space) from the two stars collided as they approached one another, compressing the gas and generating dust. About every eight years, the stars’ orbits bring them together; the dust loops mark the passage of time, much like the growth rings on a tree trunk.

“We’re looking at over a century of dust production from this system,” said Ryan Lau. “The image also illustrates just how sensitive this telescope is. Before, we were only able to see two dust rings, using ground-based telescopes. Now we see at least 17 of them.” Lau is an astronomer at NSF’s NOIRLab and lead author of a new study about the system, published on October 12 in the journal Nature Astronomy.

In addition to Webb’s overall sensitivity, its 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 wider than they appear in the image. Webb’s science instruments detect 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.

Les deux étoiles de Wolf-Rayet produisent 140 anneaux, ou coquilles, de poussière chaque fois que leurs orbites les rapprochent. Une visualisation de leurs orbites, montrée dans cette vidéo, aide à illustrer comment leur interaction produit le motif semblable à une empreinte digitale observé par[{” attribute=””>NASA’s Webb space telescope. Credit: NASA, ESA, CSA, STScI, NASA and ESA (European Space Agency). The Jet Propulsion Laboratory (JPL) in Southern California led the effort for NASA, and a multinational consortium of European astronomical institutes contributed for ESA.

A Wolf-Rayet star is an O-type star, born with at least 25 times more mass than our Sun, that is nearing the end of its life, when it will likely collapse and form a

Some other Wolf-Rayet systems form dust, but none is known to make rings like Wolf-Rayet 140 does. The unique ring pattern forms because the orbit of the Wolf-Rayet star in WR 140 is elongated, 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.

Comparing Sizes: The Sun and WR 140

This graphic shows the relative size of the Sun, upper left, compared to the two stars in the system known as Wolf-Rayet 140. The O-type star is roughly 30 times the mass of the Sun, while its companion is about 10 times the mass of the Sun.
Credit: NASA/JPL-Caltech

Lau and his co-authors think WR 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 smeared or dispersed. There are likely even more rings that have become so faint and dispersed, not even Webb can see them in the data.

Wolf-Rayet stars may seem exotic 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 dense enough for new stars to form. There is some evidence the Sun formed in such a scenario.

Using data from MIRI’s Medium Resolution Spectroscopy mode, the new study 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.

The catch is that while astronomers estimate that there should be at least a few thousand Wolf-Rayet stars in our galaxy, only about 600 have been found to date.

“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.”

More About the Mission

The world’s premier space science observatory. It will solve astronomical mysteries in our solar system, look beyond to distant planets orbiting other stars, and probe the enigmatic structures and origins of our universe. JWST is an international program led by NASA with its partners, ESA and CSA (Canadian Space Agency).

George Rieke with the University of Arizona is the MIRI U.S. science team lead. Gillian Wright with the UK Astronomy Technology Centre is the MIRI European principal investigator. Alistair Glasse with UK ATC is the MIRI instrument scientist, and Michael Ressler is the U.S. project scientist at JPL. Laszlo Tamas with UK ATC manages the European Consortium. The MIRI cryocooler development was led and managed by JPL, in collaboration with NASA’s Goddard Space Flight Center in Greenbelt, Maryland, and Northrop Grumman in Redondo Beach, California. Caltech manages JPL for NASA.

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