Editor’s Note: This post highlights data from Webb science in progress, which has not yet been through the peer-review process.
NASA’s James Webb Space Telescope obtained images of
the Ring Nebula, one of the best-known examples of a planetary nebula. Much like the Southern Ring Nebula, one of Webb’s first images, the Ring Nebula displays intricate
structures of the final stages of a dying star. Roger Wesson from Cardiff
University tells us more about this phase of a Sun-like star’s stellar
lifecycle and how Webb observations have given him and his colleagues valuable
insights into the formation and evolution of these objects, hinting at a key
role for binary companions.
NASA’s James Webb Space Telescope has observed the well-known Ring Nebula
in unprecedented detail. Formed by a star throwing off its outer layers as it
runs out of fuel, the Ring Nebula is an archetypal planetary nebula. This new image from Webb’s NIRCam
(Near-Infrared Camera) shows intricate details of the filament structure of the
inner ring. There are some 20,000 dense globules in the nebula, which are rich
in molecular hydrogen. In contrast, the inner region shows very hot gas. The
main shell contains a thin ring of enhanced emission from carbon-based
molecules known as polycyclic aromatic hydrocarbons (PAHs). Download the
full-resolution version from the Space Telescope Science Institute. Credit: ESA/Webb, NASA, CSA, M. Barlow
(University College London), N. Cox (ACRI-ST), R. Wesson (Cardiff University)
“Planetary nebulae were once thought to be simple, round objects with a
single dying star at the center. They were named for their fuzzy, planet-like
appearance through small telescopes. Only a few thousand years ago, that star
was still a red giant that was shedding most of its mass. As a last farewell,
the hot core now ionizes, or heats up,
this expelled gas, and the nebula responds with colorful emission of light.
Modern observations, though, show that most planetary nebulae display
breathtaking complexity. It begs the question: how does a spherical star create
such intricate and delicate non-spherical structures?
“The Ring Nebula is an ideal target to unravel some of the mysteries of
planetary nebulae. It is nearby, approximately 2,200 light-years away, and
bright – visible with binoculars on a clear summer evening from the northern
hemisphere and much of the southern. Our team, named the ESSENcE (Evolved StarS
and their Nebulae in the JWST Era) team, is an international group of experts
on planetary nebulae and related objects. We realized that Webb observations
would provide us with invaluable insights, since the Ring Nebula fits nicely in
the field of view of Webb’s NIRCam (Near-Infrared Camera) and MIRI
(Mid-Infrared Instrument) instruments, allowing us to study it in unprecedented
spatial detail. Our proposal to observe it was accepted (General
Observers program 1558), and Webb
captured images of the Ring Nebula just a few weeks after science operations
started on July 12, 2022.
“When we first saw the images, we were stunned by the amount of detail in
them. The bright ring that gives the nebula its name is composed of about
20,000 individual clumps of dense molecular hydrogen gas, each of them about as
massive as the Earth. Within the ring, there is a narrow band of emission from
polycyclic aromatic hydrocarbons, or PAHs – complex carbon-bearing molecules
that we would not expect to form in the Ring Nebula. Outside the bright ring,
we see curious “spikes” pointing directly away from the central star, which are
prominent in the infrared but were only very faintly visible in Hubble Space
Telescope images. We think these could be due to molecules that can form in the
shadows of the densest parts of the ring, where they are shielded from the
direct, intense radiation from the hot central star.
“Our MIRI images provided us with the sharpest and clearest view yet of the faint molecular halo outside the bright ring. A surprising revelation was the presence of up to ten regularly-spaced, concentric features within this faint halo. These arcs must have formed about every 280 years as the central star was shedding its outer layers. When a single star evolves into a planetary nebula, there is no process that we know of that has that kind of time period. Instead, these rings suggest that there must be a companion star in the system, orbiting about as far away from the central star as Pluto does from our Sun. As the dying star was throwing off its atmosphere, the companion star shaped the outflow and sculpted it. No previous telescope had the sensitivity and the spatial resolution to uncover this subtle effect.
“So how did a spherical star form such a structured and complicated nebulae as the Ring Nebula? A little help from a binary companion may well be part of the answer.”
Related Links:
Authors:
- Roger Wesson is a research associate in the School of Physics and
Astronomy at Cardiff University, UK and a co-investigator on the ESSENcE
program.
- Mikako Matsuura is a reader (equivalent to associate professor) in the
School of Physics and Astronomy at Cardiff University, UK and a
co-investigator on the ESSENcE program.
- Albert A. Zijlstra is a professor of astrophysics at the University of
Manchester, UK and a co-investigator on the ESSENcE program.
Posted on 3James Webb Space Telescope
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