The first images of a nebula from the James Webb Space Telescope gave astronomers remarkable insights into the death of the star that created these beautiful haloes of gas and dust. Among the first five image sets from the James Webb Space Telescope (JWST) released in July were a set of remarkably detailed photographs of the Southern Ring Nebula, a stunning nebula about 2,500 light years away.
The source of this expanding cloud of gas, whose inner diameter is nearly 400 times the size of our solar system, is a dying star releasing gas and dust over tens of thousands of years — which may be affected by up to three nearby companion stars. The star was 530 million years old as it died, a fraction of our own Sun’s current age of five billion years. Astronomy professor Orsola De Marco, from Macquarie University’s Research Centre for Astronomy, Astrophysics, and Astrophotonics, said:
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“This was a star that lived fast and died young, compared to our five-billion-year-old Sun that is unlikely to eject its own planetary nebula for another five billion years.”
De Marco is the lead author of a research paper published in Nature. She co-authored the paper with more than 60 other astronomers from 21 countries, which suggests fascinating theories and models to explain puzzling patterns and complex structures the new images reveal within the gas cloud, she said:
“To reconstruct the death of the star that spawned this cloud, the planetary nebula itself can be viewed like a murder scene.”
Planetary nebulae have nothing to do with planets, she adds, and are typically a giant cloud of gas surrounding one or more stars. She added:
“Nebulae were nicknamed ‘planetary nebulae’ by the astronomer William Herschel in the 1780s because their rounded shapes reminded him of how planets looked through a telescope.”
Spiral tracks reveal a multi-star system
The dying star in the middle of the Southern Ring nebula (whose formal and far less-imaginative astronomical name is NGC3132) is today a white dwarf, but in its youth, it had 2.9 times the mass of our Sun. De Marco says the infrared light from the hot star illuminated a dusty disk and spiral tracks, providing strong clues about the stars that make up this nebula — and the role they may have played in the central star’s death, adding:
“The images show spiral tracks that look like broken arches in the nebula’s halo — which tells us that there’s a companion star orbiting nearby, at 40 to 60 times the Sun-Earth distance. One or even two companion stars closer still are likely responsible for the formation of a dusty disk that was first detected by JWST, as well as for numerous protuberances we can see in the walls of the ionized nebular cavity.”
The gravitational forces of two or three companion stars in this close system likely hastened the demise of the now-dying white dwarf — which in turn may have cannibalized one or two of its companion stars. The dying star at the nebula’s source sits obviously next to a bright star which is also an associated companion — but De Marco calls this highly obvious star an innocent bystander, too far from the crime scene to have taken part in the central star’s demise.
Bright bystander helps track a star’s decay
The bright “innocent bystander” star did serve one useful purpose, though: it played a key role in helping astronomers calculate the changing mass of the white dwarf over its lifetime, De Marco said:
“The single biggest problem we have in galactic astronomy is working out the distance to astronomical objects, so when we see a star with a certain apparent brightness, we ask – is it dim and close? Or is it bright and far away? This bright, bystander star in the nebula had its distance accurately measured by the Gaia space observatory, and since we know it resides inside the nebula, we now know the distance to the nebula itself and its originating star.”
With the distance known, the JWST images allowed astronomers to calculate the most precise value we’ve ever had for the original mass of a star that makes a planetary nebula. In this case, the source star was originally 2.9 times the size of our own Sun; additional modeling tells us the mass of the star as it is today: 0.6 times the mass of our Sun.
As President of the International Astronomical Union Commission focusing on Planetary Nebulae, De Marco is one of the world’s leading authorities on these nebulae.
Nebulae are the spectacular clouds of cosmic gas and dust that form as dying stars that were originally up to 10 times the mass of our Sun, shed their outer layers, become white dwarf stars, and then ebb away. As these gas clouds drift into interstellar space, they carry away new elements created within the star, like carbon and nitrogen, that ultimately form new stars and planets. De Marco said:
“Studying planetary nebulae helps us understand the cosmic recycling of chemical elements that result in galactic evolution.”
On July 12, NASA released images of the Southern Ring nebula from both the near-infrared and the mid-infrared James Webb Space Telescope cameras, each collecting different light wavelengths that can see much fainter and with far better resolution than other space telescopes.
How astronomers from over 20 countries decoded the JWST images
Phones, emails, and astronomy message boards ran hot as nebulae specialists worldwide conferred with each other over what could be causing various patterns such as spirals and bumps appearing in and near the ionized cavity around the dying star. De Marco said:
“The mid-infrared picture showed the dying star — which is really hot, at 130,000 Kelvin — shining as bright as its companion, but that made no sense because the mid-infrared wavelength shows cool objects. Then we thought, perhaps that’s because the hot dying star is shrouded in the dust — something is known to happen occasionally when the hot star has a dusty disk.”
Astronomers gathered online, theories and models were developed, and De Marco co-ordinated the resulting paper published in Nature Astronomy, “The messy death of a multiple star system and the resulting planetary nebula as observed by JWST.”
Astronomers in the final paper came from Australia, Belgium, Brazil, Canada, France, Germany, Greece, Hong Kong, Hungary, Ireland, Israel, Italy, Japan, Mexico, South Africa, Spain, Sweden, Taiwan, The Netherlands, the UK, and the U.S. The group agrees that the dying star was “at least a stellar quartet” and has developed a model showing how it could have created the dusty disk and the spiral tracks observed in the halo of the nebula.
The images have also helped astronomers gain insights into astrophysical processes, including colliding winds and binary star interactions, says De Marco, adding:
“Our own Sun’s death in around five billion years could also spawn a planetary nebula, but since the Sun is likely a single star, that nebula won’t be nearly as spectacular as the Southern Ring nebula.”
Provided by Macquarie University [Note: Materials may be edited for content and length.]