by Ann » Thu Oct 13, 2022 6:12 am
It is obvious that WR 140 is not just any old Wolf-Rayet star, if we compare it with WR 124. Of course, it must be said that the two images are not comparable, because the one of WR 140 was taken by JWST's mid-infrared instrument MIRI, whereas the portrait of WR 124 was taken by Hubble in visible light.
Nevertheless, it is obvious that something remarkable is going on with WR 140.
Wikipedia wrote about WR 140:
It is now regarded as the prototype colliding-wind binary.
Shortly after periastron passage [closest passage] every eight years, the infrared brightness increases dramatically and then slowly drops again over a period of months. Here stellar winds collide with the dust formation created by the Wolf-Rayet star, causing the unusual bulges and angles in the concentric shells of dust. The dust typically emitted by Wolf-Rayet systems is not so coherent or concentric as those of WR 140. The dust lanes around Wolf-Rayets are most commonly observed as some variety of spiral. This is thought to be the result of the dueling solar winds in binary systems, which compress clouds of dust into distinct shock fronts. The concentric nature of WR 140's dust shells is not well understood, although it may be related to nuclear processes in the Wolf-Rayet star's core.
So nobody quite knows what is going on with WR 140, although the shells clearly form as a consequence of the two components of the binary star passing close to one another. Their strong winds affect the dust that is produced by WR 140.
The enormous dust production of WR stars happens because the star keeps switching on and switching off helium fusion in a thin shell around its (inert) core:
As the Wolf-Rayet star in WR 140 neared the end of its short life its core ran out of hydrogen to fuse into helium.
The core then began to collapse, but:
This collapse eventually began to slow as it grew more intense and heated the star's interior. Along the edge of the core a thin shell experienced temperatures and pressures sufficient to begin helium fusion.
...
The star began to inflate...
The thin shell of helium fusion eventually caused enough expansion to moderate, or even extinguish its own reaction. The star once again began to collapse.
However, at the surface this loss of internal radiation pressure had the effect of blowing the outermost layers of the star's photosphere into space.
Once more the star began to fuse helium at a greater rate and temporarily regained its former radiation pressure. This helium fusion once again stalled, and the subsequent gravitational collapse dislodged another layer of photosphere into space.
These pulses will continue as long as this cycle of intermittent helium fusion can repeat itself.
WR 140 is not the only WR star to produce concentric shells (or, more likely, a spiral of dust) around itself. WR 112 does so too:
Click to play embedded YouTube video.
WR 112 has been photographed by the Keck Telescope, not by JWST's MIRI. Yeah, there is a difference. Anyway, check out the video. It is interesting.
The astronomer in the video talks about face-on and edge-on WR stars. WR 104 is a face-on one.
Wikipedia wrote:
The WR star is surrounded by a distinctive spiral Wolf–Rayet nebula, often referred to as a pinwheel nebula.
The rotational axis of the binary system, and likely of the two closest stars, is directed approximately towards Earth. Within the next few hundred thousand years, the Wolf–Rayet star is predicted to probably become a core-collapse-supernova with
a small chance of producing a long duration gamma-ray burst.
And
if WR 104 is to produce a gamma ray burst,
it has a small chance of hitting us!! 
Yikes!!!
It is a good thing that space is big, so that any narrow gamma ray jet has a good chance of missing us!
Ann
[float=left][img3="Dust Shells around WR 140 from Webb. Image Credit: NASA, ESA, CSA, JWST, MIRI, ERS Program 1349; Processing: Judy Schmidt"]https://apod.nasa.gov/apod/image/2209/WR140_WebbSchmidt_960.jpg[/img3][/float][float=right][img3="Nebula M1-67 around Wolf-Rayet star WR 124. Image: NASA/ESA."]https://upload.wikimedia.org/wikipedia/commons/thumb/7/7f/A_cosmic_couple.jpg/1024px-A_cosmic_couple.jpg[/img3][/float]
[clear][/clear]
It is obvious that WR 140 is not just any old Wolf-Rayet star, if we compare it with WR 124. Of course, it must be said that the two images are not comparable, because the one of WR 140 was taken by JWST's mid-infrared instrument MIRI, whereas the portrait of WR 124 was taken by Hubble in visible light.
Nevertheless, it is obvious that something remarkable is going on with WR 140.
[quote][url=https://en.wikipedia.org/wiki/WR_140]Wikipedia[/url] wrote about WR 140:
It is now regarded as the prototype colliding-wind binary.
Shortly after periastron passage [closest passage] every eight years, the infrared brightness increases dramatically and then slowly drops again over a period of months. Here stellar winds collide with the dust formation created by the Wolf-Rayet star, causing the unusual bulges and angles in the concentric shells of dust. The dust typically emitted by Wolf-Rayet systems is not so coherent or concentric as those of WR 140. The dust lanes around Wolf-Rayets are most commonly observed as some variety of spiral. This is thought to be the result of the dueling solar winds in binary systems, which compress clouds of dust into distinct shock fronts. The concentric nature of WR 140's dust shells is not well understood, although it may be related to nuclear processes in the Wolf-Rayet star's core.[/quote]
So nobody quite knows what is going on with WR 140, although the shells clearly form as a consequence of the two components of the binary star passing close to one another. Their strong winds affect the dust that is produced by WR 140.
[float=right][img3="Switching on and switching off helium fusion."]https://www.computerhope.com/jargon/o/on-off.jpg[/img3][/float][b][color=#FF0000]The enormous dust production of WR stars happens because the star keeps switching on and switching off helium fusion in a thin shell around its (inert) core[/color][/b]:
[quote]As the Wolf-Rayet star in WR 140 neared the end of its short life its core ran out of hydrogen to fuse into helium.[/quote]
The core then began to collapse, but:
[quote]This collapse eventually began to slow as it grew more intense and heated the star's interior. Along the edge of the core a thin shell experienced temperatures and pressures sufficient to begin helium fusion.
...
The star began to inflate...
The thin shell of helium fusion eventually caused enough expansion to moderate, or even extinguish its own reaction. The star once again began to collapse.
[b][color=#FF0000]However, at the surface this loss of internal radiation pressure had the effect of blowing the outermost layers of the star's photosphere into space.[/color][/b]
Once more the star began to fuse helium at a greater rate and temporarily regained its former radiation pressure. This helium fusion once again stalled, and the subsequent gravitational collapse dislodged another layer of photosphere into space.
[b][color=#FF0000]These pulses will continue as long as this cycle of intermittent helium fusion can repeat itself.[/color][/b][/quote]
WR 140 is not the only WR star to produce concentric shells (or, more likely, a spiral of dust) around itself. WR 112 does so too:
[youtube]https://www.youtube.com/watch?v=6ql2e5J2DZA[/youtube]
WR 112 has been photographed by the Keck Telescope, not by JWST's MIRI. Yeah, there is a difference. Anyway, check out the video. It is interesting.
The astronomer in the video talks about face-on and edge-on WR stars. WR 104 is a face-on one.
[float=right][img3="Face-on WR star WR 104. Image: Keck Telescope."]https://upload.wikimedia.org/wikipedia/commons/9/92/Wr104_sslkeck_big.jpg[/img3][/float][quote][url=https://en.wikipedia.org/wiki/WR_104]Wikipedia[/url] wrote:
The WR star is surrounded by a distinctive spiral Wolf–Rayet nebula, often referred to as a pinwheel nebula. [b][color=#0040FF]The rotational axis of the binary system, and likely of the two closest stars, is directed approximately towards Earth.[/color][/b] Within the next few hundred thousand years, the Wolf–Rayet star is predicted to probably become a core-collapse-supernova with [b][color=#FF0000]a small chance of producing a long duration gamma-ray burst.[/color][/b][/quote]
And [b][i]if[/i][/b] WR 104 is to produce a gamma ray burst, [b][i][color=#FF0000]it has a small chance of hitting us!![/color][/i][/b] 🌠 Yikes!!! :shock:
It is a good thing that space is big, so that any narrow gamma ray jet has a good chance of missing us!
Ann