APOD: Wolf-Rayet 124 (2023 Mar 18)

[bystander]

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[AVAO]

I wonder why the cloud looks so flat. Is it all in one plane which happens to be perpendicular to our line of sight?

In my opinion, it is virtually impossible for the nebula of WR 124 to be two dimensional. It has to be more or less spherical, or possibly two-lobed, in such a way that we are watching one of the lobes face on.

Ann

I think the shape is three dimensional in some way and looks different from each side.
My hypothesis is that this changes depending on the distribution of the surrounding smaller stars or stellar fragments
and for the following reason:

What I mean by this is that the molecular clouds visible in the IR around WR124 are NOT of its own, but are produced by the surrounding smaller stars or nuclei, due to the high radiation pressure of WR124 at its center. WR124 "triggers" only the developement. While this is somewhat contrary to what the current theory describes in detail, it is what I see when I zoom in on the details. I have previously advanced this thesis that the molecular shells of star formation are self-generated and not vice versa as in the classical star formation model. And I continue to stand by this thesis, even if Chris disagrees here, because I SEE that it must be different.




jac berne (flickr)

[Ann]

I wonder why the cloud looks so flat. Is it all in one plane which happens to be perpendicular to our line of sight?

In my opinion, it is virtually impossible for the nebula of WR 124 to be two dimensional. It has to be more or less spherical, or possibly two-lobed, in such a way that we are watching one of the lobes face on.

Ann

I think the shape is three dimensional in some way and looks different from each side.
My hypothesis is that this changes depending on the distribution of the surrounding smaller stars or stellar fragments
and for the following reason:

What I mean by this is that the molecular clouds visible in the IR around WR124 are NOT of its own, but are produced by the surrounding smaller stars or nuclei, due to the high radiation pressure of WR124 at its center. WR124 "triggers" only the developement. While this is somewhat contrary to what the current theory describes in detail, it is what I see when I zoom in on the details. I have previously advanced this thesis that the molecular shells of star formation are self-generated and not vice versa as in the classical star formation model. And I continue to stand by this thesis, even if Chris disagrees here, because I SEE that it must be different.




jac berne (flickr)

I think differently.

First of all, we see other Wolf-Rayet stars that are centrally placed inside a nebula. This in itself strongly suggests to me that the nebula is the star's own making.

Wolf-Rayet star WR 31a and surrounding nebula. Image credit: ESA/Hubble & NASA Acknowledgement: Judy Schmidt

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Nebula Thor's Helmet och WR star WR7. Credit:European Southern Observatory/B. Bailleul

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A fantastic Wolf-Rayet star is WR 140:

James Webb Space Telescope image of partial dust shells surrounding WR 140. Credit: JWST/MIRI/Judy Schmidt.

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Universe Today wrote:

These Bizarre Concentric Rings in Space are Real, Not an Optical Illusion. New Data from JWST Explains What’s Happening

(...) The answer, revealed today, is dust. A new paper published in Nature Astronomy explains how stellar winds in this odd binary system blasts dust into near-perfect concentric circles every time the two stars come close to each other in their eccentric orbits.

Click to play embedded YouTube video.

In this video, unless I'm very much mistaken, the larger star is a non-WR star, probably an O star, whereas the WR star is smaller (because it has already lost so much mass) and it blows a much stronger wind. Whenever the two stars come close, the extremely windy WR star blows gas off of the larger O star. Meanwhile, of course, the WR star keeps blowing off its own outer layers.

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

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AVAO, I think you have been fooled by the clumpy nature of the nebula surrounding Wolf-Rayet star WR 124. There are indeed bright-looking clumps in the nebula that seem to be connected to "cometary tails", as if these clumps were small stars losing gas because of the onslaught of furious ultraviolet light and fast stellar wind atoms and molecules. But these clumps are not stars, just denser knots of gas and dust. We see similar phenomena in planetary nebulas:

Bright clumps of gas an dust in the nebula surrounding star WR 124.

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Cometary knots of gas and dust in the Helix Nebula, which is a planetary nebula. Credits: NASA, NOAO, ESA, the Hubble Helix Nebula Team, M. Meixner (STScI), and T.A. Rector (NRAO).

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What we need to understand is that Wolf-Rayet are evolved stars that no longer support themselves by hydrogen fusion in their cores. Instead, there are layers of different fusion products surrounding their cores, and I think - think, mind you! - that different "fusion layers" turn off and on alternatively, which induces instability in the star and promotes mass loss.

Let's take a look at what I think is going to happen to our own Sun, after it has turned into a red giant and is going to cast off its outer layers:

Hydrogen shell and helium shell burning in an Asymtotic Giant Branch star of 1 solar mass. Source: https://cpics.homes/red-giant-carbon-fusion

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In case you're wondering, the Asymtotic Giant Branch will be our Sun's second and final rise to gianthood, after it has spent some time as a more modest red clump star, where it will be rather peacefully fusing helium to carbon and oxygen in its core (after it has used up all its core hydrogen and increased its core temperature enough to start core helium fusion in the first place).

But the Sun will run out of core helium, too, and then it will have a "dead" core of carbon and oxygen. Yes, "dead", because the Sun will never have a sufficiently hot core to begin fusing its core carbon and oxygen into heavier elements. Instead, the Sun will fuse helium in a shell around its core.

But wait, there is more. Not only will the Sun be fusing helium in a shell around its dead carbon/oxygen core, but it will also fuse hydrogen in a shell around its inner helium layer. The two actively fusing shells will affect each other in such a way that when one shell is in the process of fusing, the other shell will "turn off". The shells will turn on and off like a beating heart, except that this particular heartbeat will make the entire star pulsate. Eventually, the pulsations will grow so strong that the Sun is going to cast off its outer layers.

The way I understand it, something reasonably similar is going on with the Wolf-Rayet stars, except that their cores are very much hotter and can fuse much heavier elements than our Sun ever will.

We can still see the debris of the 1901 outburst of nova GK Persei. Credits: X-ray: NASA/CXC/RIKEN/D.Takei et al; Optical: NASA/STScI; Radio: NRAO/VLA

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White dwarf star GK Persei surrounded by the debris of its own outburst in 1901. The way I understand it, a companion star dumped matter onto white dwarf star GK Persei until GK Persei blew the accreted material off in a nova outburst.

A white dwarf is not a Wolf Rayet star, but I like the picture because it makes it so clear that stuff surrounding the central star has come from the central star itself.

Similarly, I'd say, Wolf Rayet stars keep blowing off their own outer layers, although through a different mechanism than the nova outbursts. And the WR stars do create short-lived nebulas around themselves, created from their own discarded atmospheres.

Ann