In this new #JWST NIRCam image of the supernova remnant Cassiopeia A (Cas A), we see the remains of a star that first imploded and then exploded about 340 years ago (from our point of view), leaving behind a tangle of gas, dust, and magnetic fields.
A #thread with some details of what we are seeing in the image.
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Read more: https://webbtelescope.org/contents/news-releases/2023/news-2023-149
Here is a video that walks through some of the important features of the JWST NIRCam view of the Cassiopeia A supernova remnant, from the tiny knots of gas leftover from the star’s explosion to the light echoes scattered across the field of view.
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https://webbtelescope.org/contents/media/videos/2023/149/01HH3QHZ4F3JXEGDXWS2SS2MVR
Earlier this year, we saw another view of Cas A with JWST, a mid-inferred view of the supernova remnant from MIRI.
Comparing the images, we see the red and orange colored gas in the outer part of the main shell in the MIRI image appears wispy white in the NIRCam image. This is where the shock from the supernova explosion is hitting the surrounding gas.
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In mid-infrared light, we see glowing dust, heated by the shock.
The dust is too cool to emit much near-infrared light. But, we see light emitted by charged particles, like electrons, spiraling around magnetic fields at nearly the speed of light. This is known as synchrotron radiation.
The light is emitted almost equally at all infrared wavelengths, so it appears white. We see synchrotron light in Cas A across the EM spectrum from radio to X-rays.
📷: A. Wilhelm
https://publishup.uni-potsdam.de/frontdoor/index/index/docId/51291
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Supernova remnants (SNRs) are discussed as the most promising sources of galactic cosmic rays (CR). The diffusive shock acceleration (DSA) theory predicts particle spectra in a rough agreement with observations. Upon closer inspection, however, the photon spectra of observed SNRs indicate that the particle spectra produced at SNRs shocks deviate from the standard expectation. This work suggests a viable explanation for a softening of the particle spectra in SNRs. The basic idea is the re-acceleration of particles in the turbulent region immediately downstream of the shock. This thesis shows that at the re-acceleration of particles by the fast-mode waves in the downstream region can be efficient enough to impact particle spectra over several decades in energy. To demonstrate this, a generic SNR model is presented, where the evolution of particles is described by the reduced transport equation for CR. It is shown that the resulting particle and the corresponding synchrotron spectra are significantly softer compared to the standard case. Next, this work outlines RATPaC, a code developed to model particle acceleration and corresponding photon emissions in SNRs. RATPaC solves the particle transport equation in test-particle mode using hydrodynamic simulations of the SNR plasma flow. The background magnetic field can be either computed from the induction equation or follows analytic profiles. This work presents an extended version of RATPaC that accounts for stochastic re-acceleration by fast-mode waves that provide diffusion of particles in momentum space. This version is then applied to model the young historical SNR Tycho. According to radio observations, Tycho’s SNR features the radio spectral index of approximately −0.65. In previous modeling approaches, this fact has been attributed to the strongly distinctive Alfvénic drift, which is assumed to operate in the shock vicinity. In this work, the problems and inconsistencies of this scenario are discussed. Instead, stochastic re-acceleration of electrons in the immediate downstream region of Tycho’s SNR is suggested as a cause for the soft radio spectrum. Furthermore, this work investigates two different scenarios for magnetic-field distributions inside Tycho’s SNR. It is concluded that magnetic-field damping is needed to account for the observed filaments in the radio range. Two models are presented for Tycho’s SNR, both of them feature strong hadronic contribution. Thus, a purely leptonic model is considered as very unlikely. Additionally, to the detailed modeling of Tycho’s SNR, this dissertation presents a relatively simple one-zone model for the young SNR Cassiopeia A and an interpretation for the recently analyzed VERITAS and Fermi-LAT data. It shows that the γ-ray emission of Cassiopeia A cannot be explained without a hadronic contribution and that the remnant accelerates protons up to TeV energies. Thus, Cassiopeia A is found to be unlikely a PeVatron.
The NIRCam view gives us some clues about the nature of the bubble-like structures in the MIRI view's “green monster.” The structures seen in the loop of gas, seen in green on the right side of the MIRI image, were initially difficult to explain.
However, since they show up in the NIRCam image, faintly outlined in white and purple emission, researchers believe that they are holes left behind when ejecta from the supernova explosion shot through the gas like bullets.
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Looking closely at the NIRCam image, we see orange- and pink-colored filaments. These are knots of gas ejected from the star itself. Some of them are tiny — less than 100 times the distance between the Sun and the Earth. This suggests the star shattered like glass when it exploded.
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https://webbtelescope.org/contents/media/images/2023/149/01HGGZDJX7RZR07HWZ6YEQ74CR
In the lower left, we see yellowish, striated structures. These are clumps of gas behind the supernova remnant that were hit by a flash of ultraviolet light from the original explosion, heated up, and then emitted a flash of infrared light back toward us on a delay. This is known as a light echo.
The largest clump in the lower right (box 4) is nicknamed "Baby Cas A." It's located about 170 light-years behind the supernova remnant.
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🎞️ https://www.spitzer.caltech.edu/video/ssc2008-09v2-dissecting-a-light-echo
Cas A's light echo was first discovered in infrared light by the Spitzer Space Telescope in 2005. Later observations by Spitzer show the flash moving through the filamentary gas and dust in the area around the supernova remnant (the remnant is the small circular feature in the center).
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Follow-up observations looked at the visible light echo from light reflecting off of the dust. The light traveled to these distant dust clouds and was reflected back, creating a ~340-year delay. This allowed researchers to recover a spectrum of the original explosion, letting us know that Cas A was a Type IIb supernova — a massive star that lost most of its outer layers before exploding.
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https://ui.adsabs.harvard.edu/abs/2008Sci...320.1195K/abstract
Cassiopeia A is the youngest supernova remnant known in the Milky Way and a unique laboratory for supernova physics. We present an optical spectrum of the Cassiopeia A supernova near maximum brightness, obtained from observations of a scattered light echo more than three centuries after the direct light of the explosion swept past Earth. The spectrum shows that Cassiopeia A was a type IIb supernova and originated from the collapse of the helium core of a red supergiant that had lost most of its hydrogen envelope before exploding. Our finding concludes a long-standing debate on the Cassiopeia A progenitor and provides new insight into supernova physics by linking the properties of the explosion to the wealth of knowledge about its remnant.
@barrygoldman1 We will get more details in the AAS meeting in January, but for now, all I have is the quote from the PI in the press release:
“With NIRCam’s resolution, we can now see how the dying star absolutely shattered when it exploded, leaving filaments akin to tiny shards of glass behind. It’s really unbelievable after all these years studying Cas A to now resolve those details, which are providing us with transformational insight into how this star exploded.”
https://webbtelescope.org/contents/news-releases/2023/news-2023-149
@kellylepo no, but it was surprising. back in my college days in the dorm with hard walls i got frustrated one day heaved a raw potato at the wall hoping it would make satisfying SPLAT but no, it shatterd, 100s of tiny shards we were finding all over the place for weeks.
did not expect that behavior.
a gallon plastic container filled with frozen water ALSO doesn't shatter, it BOUNCES like crazy! ah... youth...
I think there is some poetic license being used here. The image is being used as a metaphor for a Christmas tree ornament 🎄. Hence, words like round, shatter, shards, glass, green monster, etc. We can be sure that the paper will use different words 😉
Also, there is a good bit of fluffy words in that statement by the PI, which is standard fare these days 😜
There’s a superficial resemblance in parts of the structure we see here to the large scale filaments of the universe. Am I imagining a connection?
@f800gecko Like jets, filaments and voids are structures that show up on all scales in astronomy.
The physics here is similar-ish to what is seen in the large-scale structure universe. Denser things tend to clump via gravity, and smaller features are being blown up by expansion.
But, some of the features in Cas A come from the details of the explosion and the structure surrounding the gas, which doesn't happen with the Universe.
@barrygoldman1 Part of why supernovas are valuable for cosmology is because they are so bright. Light echos are much fainter than the original explosion.
But, they are useful for finding what type of supernova caused nearby supernova remnants: https://en.wikipedia.org/wiki/Light_echo#Supernovae
Kelly Lepo
Air_Cooled_Nut
Barry Goldman
AkaSci 🛰️
Kyle Memoir 🍉🐧
