Explanation: Blown by fast winds from a hot, massive star, this cosmic bubble is huge. Cataloged as Sharpless 2-308 it lies some 5,000 light-years away toward the well-trained constellation Canis Major and covers slightly more of the sky than a Full Moon. That corresponds to a diameter of 60 light-years at its estimated distance. The massive star that created the bubble, a Wolf-Rayet star, is the bright one near the center of the nebula. Wolf-Rayet stars have over 20 times the mass of the Sun and are thought to be in a brief, pre-supernova phase of massive star evolution. Fast winds from this Wolf-Rayet star create the bubble-shaped nebula as they sweep up slower moving material from an earlier phase of evolution. The windblown nebula has an age of about 70,000 years. Relatively faint emission captured by narrowband filters in the deep image is dominated by the glow of ionized oxygen atoms mapped to a blue hue. Presenting a mostly harmless outline, SH2-308 is also known as The Dolphin-head Nebula.
I was following link for "Wolf-Rayet stars" and wondered -
1) Where do "Sharpless 2-308" and "R136a1" fit into largest known stars (e.g. compared to Antares to VY Canis Majoris range) ?
and
2) I came across this paragraph -
"Consequently, R136a1, and stars like it, are a mystery to astronomers. They defy what we think we know about how stars form. One hypothesis is that R136a1 did not form directly from the collapse of a molecular hydrogen cloud, but rather is the result of two massive stars colliding. A very close pair of stars could eventually merge to form a stellar behemoth."
I had no idea 2 stars could collide and could combine into 1 giant (Like 2 black holes combining into one). I always thought one star will eat the other (we see the "artist's visualization") but is that called a "merger" ?
shaileshs wrote: ↑Fri Jun 07, 2024 5:27 am
I was following link for "Wolf-Rayet stars" and wondered -
1) Where do "Sharpless 2-308" and "R136a1" fit into largest known stars (e.g. compared to Antares to VY Canis Majoris range) ?
and
2) I came across this paragraph -
"Consequently, R136a1, and stars like it, are a mystery to astronomers. They defy what we think we know about how stars form. One hypothesis is that R136a1 did not form directly from the collapse of a molecular hydrogen cloud, but rather is the result of two massive stars colliding. A very close pair of stars could eventually merge to form a stellar behemoth."
I had no idea 2 stars could collide and could combine into 1 giant (Like 2 black holes combining into one). I always thought one star will eat the other (we see the "artist's visualization") but is that called a "merger" ?
The nebula surrounding the Wolf-Rayet star is not part of the star itself, any more than planetary nebulas are part of the central white dwarf illuminating the nebulas.
When it comes to the sizes of stars, the largest stars are the red supergiants and hypergiants. I asked Google what star is the largest known one in the local universe (because we can't really know about stars much farther away), and I was told that the record holder is UY Scuti. According to BBC Science Focus, the radius of this star is 1.2 billion km (738 million miles). I asked Google how much that is in light-years, and was told that it is 0.000126842809 light-years. Yes, that's the radius, not the diameter, but as you can see, it is plainly impossible for a star to have either a diameter or a radius of 60 light-years.
As for stellar mergers, astronomers are convinced that they happen. It has been theorized that a star with a mass of more than 100 solar masses can't form by itself in the local universe (it may have been possible during the Cosmic Dawn), so if we find stars that carry a much greater mass than 100 solar masses, we should assume that they have formed through the merger of at least two stars.
The reason why astronomers believe that stars can't form with a mass of much more than 100 solar masses is that stars that massive have to "run their fusion engines" at such absolutely terrific speeds that the stars therefore also blow a terrific wind. This wind will blow away any molecular clouds in the vicinity of the star and prevent any more gas from clouds from reaching the star.
But a merger is another matter. The stellar wind will not blow away another star that, for some reason, approaches the other star, or starts orbiting it in an unstable orbit, until a merger occurs.
V838 Monocerotis was a fairly ordinary blue star until it underwent a probable merger. For a brief period, it was one of the most luminous stars in the galaxy.
The Dolphin Head nebula looks so much like a dolphin head that there really is no need to overdo the colour to make it look still more like a dolphin head! Which often astrographers tend to do I find, in blue-greens, but not in this case, it's just the right amount in my view!
A fascinating aspect when seeing this object even with modest equipment is that you can observe two extreme stars in the same field of view: the Wolf-Rayet of course which is the dolphin's "eye", and its "blowhole" is a red supergiant.
Which leads me to questions I always have about the evolution of massive stars: If you have two equally massive main sequence O stars, both say 30 solar masses, both as hot and luminous, what makes one evolve to be a red supergiant and the other a Wolf-Rayet instead? Or a blue supergiant for that matter?
In the same vein, say you have two red supergiants, again of the same mass, and eventually one swings far left of the HR diagram and turns into a Wolf-Rayet while the other remains a red supergiant - why? If mass alone is not the factor, what is?
(I just love these extreme stars!)
Christian G. wrote: ↑Fri Jun 07, 2024 1:28 pm
The Dolphin Head nebula looks so much like a dolphin head that there really is no need to overdo the colour to make it look still more like a dolphin head! Which often astrographers tend to do I find, in blue-greens, but not in this case, it's just the right amount in my view!
A fascinating aspect when seeing this object even with modest equipment is that you can observe two extreme stars in the same field of view: the Wolf-Rayet of course which is the dolphin's "eye", and its "blowhole" is a red supergiant.
Which leads me to questions I always have about the evolution of massive stars: If you have two equally massive main sequence O stars, both say 30 solar masses, both as hot and luminous, what makes one evolve to be a red supergiant and the other a Wolf-Rayet instead? Or a blue supergiant for that matter?
In the same vein, say you have two red supergiants, again of the same mass, and eventually one swings far left of the HR diagram and turns into a Wolf-Rayet while the other remains a red supergiant - why? If mass alone is not the factor, what is?
(I just love these extreme stars!)
Don't know, but two characteristics of W-R stars are a fast rotation rate and a high metallicity (proportion of elements heavier than hydrogen and helium). Perhaps those properties have something to do with it.
Last edited by johnnydeep on Fri Jun 07, 2024 5:19 pm, edited 1 time in total.
-- "To B̬̻̋̚o̞̮̚̚l̘̲̀᷾d̫͓᷅ͩḷ̯᷁ͮȳ͙᷊͠ Go......Beyond The F͇̤i̙̖e̤̟l̡͓d͈̹s̙͚ We Know."{ʲₒʰₙNYᵈₑᵉₚ}
I am acutely aware that 9,999 people out of 10,000 will stare in amazement at today's picture of the Dolphin Nebula and not give a hoot about the appearance of the ionizing star. Or maybe we are talking about 99,999,999 out of 100,000,000 people. Just one of all these people will be unhappy.
Well, I am the one dissenting voice. To me it is incredibly important that EZ Canis Majoris, the Wolf Rayet star ionizing the Dolphin Nebula, is not only intrinsically blue (like all WR stars), but that the light that reaches us from this star, after traversing 5,000 light-years and encountering innumerable dust particles, is still blue, or at least bluish, or at least bluer than the light from Vega that has come to us from 25 light-years.
Blue Vega over Milky Way. EZ CMa is bluer. Credit: Marcin Rosadziński
So I tried to find another picture that did justice to the colors of the two important stars in and near the Dolphin Ndebula, and I really recommend this one by David Viaene:
True-color EZ CMa and true-color omi1 CMa and the Dolphin Nebula
by David Viaene.
So, yeah. I want blue EZ CMa and yellow omicron 1 CMa of the Dolphin Nebula to look like they do in David Viaene's image.
But take heart, Prabhu Kutti! Remember all the people applauding your image of this most remarkable dolphin in the sky.
Ann wrote: ↑Fri Jun 07, 2024 6:33 pm
I am acutely aware that 9,999 people out of 10,000 will stare in amazement at today's picture of the Dolphin Nebula and not give a hoot about the appearance of the ionizing star. Or maybe we are talking about 99,999,999 out of 100,000,000 people. Just one of all these people will be unhappy.
So, yeah. I want blue EZ CMa and yellow omicron 1 CMa of the Dolphin Nebula to look like they do in David Viaene's image.
But take heart, Prabhu Kutti! Remember all the people applauding your image of this most remarkable dolphin in the sky.
Well, that's a challenge with an image made through just a pair of narrowband filters. It's impossible to get accurate star colors with that setup. There are tricks that can be done by removing all the stars, processing them separately, and adding them back in. Or by taking another image at the same coordinates with RGB filters and then using that for the stars. But in the end, this image isn't about the stars, but about the emission nebula (which, of course, isn't "true" color, either.)
Chris
*****************************************
Chris L Peterson
Cloudbait Observatory https://www.cloudbait.com
Christian G. wrote: ↑Fri Jun 07, 2024 1:28 pm
The Dolphin Head nebula looks so much like a dolphin head that there really is no need to overdo the colour to make it look still more like a dolphin head! Which often astrographers tend to do I find, in blue-greens, but not in this case, it's just the right amount in my view!
A fascinating aspect when seeing this object even with modest equipment is that you can observe two extreme stars in the same field of view: the Wolf-Rayet of course which is the dolphin's "eye", and its "blowhole" is a red supergiant.
Which leads me to questions I always have about the evolution of massive stars: If you have two equally massive main sequence O stars, both say 30 solar masses, both as hot and luminous, what makes one evolve to be a red supergiant and the other a Wolf-Rayet instead? Or a blue supergiant for that matter?
In the same vein, say you have two red supergiants, again of the same mass, and eventually one swings far left of the HR diagram and turns into a Wolf-Rayet while the other remains a red supergiant - why? If mass alone is not the factor, what is?
(I just love these extreme stars!)
Don't know, but two characteristics of W-R stars are a fast rotation rate and a high metallicity (proportion of elements heavier than hydrogen and helium). Perhaps those properties have something to do with it.
Thanks. So Wolf-Rayets rotate fast on top of everything else, insane stars! And all on the verge of going supernova. When EZ CMa does, it will be a magnificent sight, the Dolphin Head will have a super bright shining eye! Before its head goes.
Christian G. wrote: ↑Fri Jun 07, 2024 1:28 pm
The Dolphin Head nebula looks so much like a dolphin head that there really is no need to overdo the colour to make it look still more like a dolphin head! Which often astrographers tend to do I find, in blue-greens, but not in this case, it's just the right amount in my view!
A fascinating aspect when seeing this object even with modest equipment is that you can observe two extreme stars in the same field of view: the Wolf-Rayet of course which is the dolphin's "eye", and its "blowhole" is a red supergiant.
Which leads me to questions I always have about the evolution of massive stars: If you have two equally massive main sequence O stars, both say 30 solar masses, both as hot and luminous, what makes one evolve to be a red supergiant and the other a Wolf-Rayet instead? Or a blue supergiant for that matter?
In the same vein, say you have two red supergiants, again of the same mass, and eventually one swings far left of the HR diagram and turns into a Wolf-Rayet while the other remains a red supergiant - why? If mass alone is not the factor, what is?
(I just love these extreme stars!)
Don't know, but two characteristics of W-R stars are a fast rotation rate and a high metallicity (proportion of elements heavier than hydrogen and helium). Perhaps those properties have something to do with it.
I'm on very shaky ground here, but I think Johnny is right. I think rotation may indeed have something to do with how fast a star exhausts in core hydrogen and turns into a red giant. I think that a sufficiently fast rotation may mix the interior gases of a hot star in such a way that more hydrogen is fed into the core, which should lead to a prolonged main sequence lifetime.
As for why some massive stars "turn blue" before going supernova, all I can say that very metal-poor low- and medium-mass stars "turn blue" after they have been red giants, and then they turn red again, and then they shed their outer atmospheres and become white dwarfs.
Will very metal-poor massive stars behave in the same way? I really don't know, but we may note that the progenitor of the closest unobscured supernova in many centuries, SN 1987A, was a blue supergiant. It was also located in the Large Magellanic Cloud, which means that it was probably a lot more metal-poor than almost any massive star in the Milky Way. Astronomers believe that this star was first a red supergiant, and then it turned into a blue supergiant before it exploded.
Stars that belong to the same cluster could well have different rotation rates, but I find it unlikely that such stars (that were born from the same gas cloud) will have very different metallicities.
Christian G. wrote: ↑Fri Jun 07, 2024 1:28 pm
The Dolphin Head nebula looks so much like a dolphin head that there really is no need to overdo the colour to make it look still more like a dolphin head! Which often astrographers tend to do I find, in blue-greens, but not in this case, it's just the right amount in my view!
A fascinating aspect when seeing this object even with modest equipment is that you can observe two extreme stars in the same field of view: the Wolf-Rayet of course which is the dolphin's "eye", and its "blowhole" is a red supergiant.
Which leads me to questions I always have about the evolution of massive stars: If you have two equally massive main sequence O stars, both say 30 solar masses, both as hot and luminous, what makes one evolve to be a red supergiant and the other a Wolf-Rayet instead? Or a blue supergiant for that matter?
In the same vein, say you have two red supergiants, again of the same mass, and eventually one swings far left of the HR diagram and turns into a Wolf-Rayet while the other remains a red supergiant - why? If mass alone is not the factor, what is?
(I just love these extreme stars!)
Don't know, but two characteristics of W-R stars are a fast rotation rate and a high metallicity (proportion of elements heavier than hydrogen and helium). Perhaps those properties have something to do with it.
I'm on very shaky ground here, but I think Johnny is right. I think rotation may indeed have something to do with how fast a star exhausts in core hydrogen and turns into a red giant. I think that a sufficiently fast rotation may mix the interior gases of a hot star in such a way that more hydrogen is fed into the core, which should lead to a prolonged main sequence lifetime.
...
Ann
Wait - did you mean a shortened main sequence lifetime? Aren't W-R stars on the shortened path? I (CAVEAT: truthfully, I've never fully understood what the ubiquitously useful Hertzsprung-Russell diagrams are really all about!)
-- "To B̬̻̋̚o̞̮̚̚l̘̲̀᷾d̫͓᷅ͩḷ̯᷁ͮȳ͙᷊͠ Go......Beyond The F͇̤i̙̖e̤̟l̡͓d͈̹s̙͚ We Know."{ʲₒʰₙNYᵈₑᵉₚ}
So, a roughly spherical bubble 60 ly in diameter, 70,000 years old = the wave front is expanding at an average vvelocity of about 140 kilometers per second. The bubble mut contain everal thousand star systems. I keep wondering what that wave front would do to a middling G-class system like ours, near (10 ly) or far (39 ly), sweeping through.
Roy wrote: ↑Sat Jun 08, 2024 2:19 am
So, a roughly spherical bubble 60 ly in diameter, 70,000 years old = the wave front is expanding at an average vvelocity of about 140 kilometers per second. The bubble mut contain everal thousand star systems. I keep wondering what that wave front would do to a middling G-class system like ours, near (10 ly) or far (39 ly), sweeping through.
Absolutely nothing. If you were on a planet in that region, you wouldn't even be aware of the shock front unless you had high tech instrumentation. What we're seeing here is optically dim, invisible to human eyes. That light is produced by extremely hot and extremely rarified plasma (in the lab it would be called a hard vacuum).
Chris
*****************************************
Chris L Peterson
Cloudbait Observatory https://www.cloudbait.com
Don't know, but two characteristics of W-R stars are a fast rotation rate and a high metallicity (proportion of elements heavier than hydrogen and helium). Perhaps those properties have something to do with it.
I'm on very shaky ground here, but I think Johnny is right. I think rotation may indeed have something to do with how fast a star exhausts in core hydrogen and turns into a red giant. I think that a sufficiently fast rotation may mix the interior gases of a hot star in such a way that more hydrogen is fed into the core, which should lead to a prolonged main sequence lifetime.
...
Ann
Wait - did you mean a shortened main sequence lifetime? Aren't W-R stars on the shortened path? I (CAVEAT: truthfully, I've never fully understood what the ubiquitously useful Hertzsprung-Russell diagrams are really all about!)
Yes, more massive stars have shorter lifetimes. The more massive a star is, the faster it uses up its fuel, because its "fusion engine" has to run at a furious rate to counteract the star's own gravity that otherwise threatens to overwhelm it. (And that's a real threat: Astronomers have recently found some evidence that massive stars can indeed just collapse into a black hole without going supernova first.)
What stars need in order to be more long-lived is fresh hydrogen delivered to their cores.
The most lightweight stars, the red dwarfs, are "fully convective" inside, which is to say that their insides are "boiling", and the boiling process continually brings fresh hydrogen into their cores so that their core hydrogen fusion engines (which run very slowly) can keep running for trillions of years.
More massive stars are "radiative" in or near their cores. (Don't ask me to explain the possible difference.) The Sun, which is considerably more massive than a red dwarf, is "radiative" near its core and "convective" ("boiling") further out:
Very massive stars are fully radiative and lack a convective zone. I'm not sure that rotation can really bring any more hydrogen into the core of a really massive star, because the "outward push" of the energy generated in their cores is so strong. I will say, however, that if a massive star receives a helping of fresh hydrogen into its core by whatever mechanism, it will most likely stay on the main sequence longer, and turn into a red giant later, than a star of equal mass that has not received an extra helping of hydrogen into its core.
Ann
Last edited by Ann on Sat Jun 08, 2024 5:40 pm, edited 1 time in total.
Ann wrote: ↑Fri Jun 07, 2024 6:33 pm
I am acutely aware that 9,999 people out of 10,000 will stare in amazement at today's picture of the Dolphin Nebula and not give a hoot about the appearance of the ionizing star. Or maybe we are talking about 99,999,999 out of 100,000,000 people. Just one of all these people will be unhappy.
Well, I am the one dissenting voice. To me it is incredibly important that EZ Canis Majoris, the Wolf Rayet star ionizing the Dolphin Nebula, is not only intrinsically blue (like all WR stars), but that the light that reaches us from this star, after traversing 5,000 light-years and encountering innumerable dust particles, is still blue, or at least bluish, or at least bluer than the light from Vega that has come to us from 25 light-years.
Vega over Milky Way Marcin Rosadziński.png
Blue Vega over Milky Way. EZ CMa is bluer. Credit: Marcin Rosadziński
So I tried to find another picture that did justice to the colors of the two important stars in and near the Dolphin Ndebula, and I really recommend this one by David Viaene:
EZ Canis Majoris and Sharpless 308 Davy Viaene.png
True-color EZ CMa and true-color omi1 CMa and the Dolphin Nebula
by David Viaene.
So, yeah. I want blue EZ CMa and yellow omicron 1 CMa of the Dolphin Nebula to look like they do in David Viaene's image.
But take heart, Prabhu Kutti! Remember all the people applauding your image of this most remarkable dolphin in the sky.
Ann
I usually take RGB stars separately and replace the narrowband stars which are mostly red/magenta, but for this I did not capture RGB stars, this image is a combination of only two narrowband emission, Ha and Oiii because of this the colors are not accurate.
Ann wrote: ↑Fri Jun 07, 2024 6:33 pm
I am acutely aware that 9,999 people out of 10,000 will stare in amazement at today's picture of the Dolphin Nebula and not give a hoot about the appearance of the ionizing star. Or maybe we are talking about 99,999,999 out of 100,000,000 people. Just one of all these people will be unhappy.
Well, I am the one dissenting voice. To me it is incredibly important that EZ Canis Majoris, the Wolf Rayet star ionizing the Dolphin Nebula, is not only intrinsically blue (like all WR stars), but that the light that reaches us from this star, after traversing 5,000 light-years and encountering innumerable dust particles, is still blue, or at least bluish, or at least bluer than the light from Vega that has come to us from 25 light-years.
Vega over Milky Way Marcin Rosadziński.png
Blue Vega over Milky Way. EZ CMa is bluer. Credit: Marcin Rosadziński
So I tried to find another picture that did justice to the colors of the two important stars in and near the Dolphin Ndebula, and I really recommend this one by David Viaene:
EZ Canis Majoris and Sharpless 308 Davy Viaene.png
True-color EZ CMa and true-color omi1 CMa and the Dolphin Nebula
by David Viaene.
So, yeah. I want blue EZ CMa and yellow omicron 1 CMa of the Dolphin Nebula to look like they do in David Viaene's image.
But take heart, Prabhu Kutti! Remember all the people applauding your image of this most remarkable dolphin in the sky.
Ann
I usually take RGB stars separately and replace the narrowband stars which are mostly red/magenta, but for this I did not capture RGB stars, this image is a combination of only two narrowband emission, Ha and Oiii because of this the colors are not accurate.
I take it you are the photographer behind the Dolphin Head Nebula APOD? Thank you so much for weighing in here.
When it comes to my criticism of your picture, I said that 99,999 people out of 100,000 will like it. I mean it. I have never met anyone who cares about color the way I do, so I am, frankly, not representative of the people who will look at your image.
Your image isn't about color, but about structure. I do understand that, so I should have kept my mouth shut. The thing is that color is so incredibly important to me that I can't stop talking about it, and in particular, I can't stop talking about the color blue.
So let me say to you now that your picture brings out the structure of the Dolphin Head Nebula beautifully well, and clearly better than the photographer whose image I praised (and still love) because of his accurate star colors.
Thank you for your contribution to the Astronomy Picture of the Day site, and good luck in the future!
Ann wrote: ↑Sat Jun 08, 2024 5:56 pm
Your image isn't about color, but about structure.
Ann
talking about the structure, I wonder why there seems to be a smooth pale cover about 1 ly above bumpy and solid surface (though it's hard vacuum for a laboratory)?
And why the Nose has no anti-nose feature at 4 or 5 o'clock
Ann wrote: ↑Sat Jun 08, 2024 5:56 pm
Your image isn't about color, but about structure.
Ann
talking about the structure, I wonder why there seems to be a smooth pale cover about 1 ly above bumpy and solid surface (though it's hard vacuum for a laboratory)?
Not sure quite what structure you're referring to here.
And why the Nose has no anti-nose feature at 4 or 5 o'clock
Why would you expect one?
Chris
*****************************************
Chris L Peterson
Cloudbait Observatory https://www.cloudbait.com
I'm on very shaky ground here, but I think Johnny is right. I think rotation may indeed have something to do with how fast a star exhausts in core hydrogen and turns into a red giant. I think that a sufficiently fast rotation may mix the interior gases of a hot star in such a way that more hydrogen is fed into the core, which should lead to a prolonged main sequence lifetime.
...
Ann
Wait - did you mean a shortened main sequence lifetime? Aren't W-R stars on the shortened path? I (CAVEAT: truthfully, I've never fully understood what the ubiquitously useful Hertzsprung-Russell diagrams are really all about!)
Yes, more massive stars have shorter lifetimes. The more massive a star is, the faster it uses up its fuel, because its "fusion engine" has to run at a furious rate to counteract the star's own gravity that otherwise threatens to overwhelm it. (And that's a real threat: Astronomers have recently found some evidence that massive stars can indeed just collapse into a black hole without going supernova first.)
What stars need in order to be more long-lived is fresh hydrogen delivered to their cores.
The most lightweight stars, the red dwarfs, are "fully convective" inside, which is to say that their insides are "boiling", and the boiling process continually brings fresh hydrogen into their cores so that their core hydrogen fusion engines (which run very slowly) can keep running for trillions of years.
More massive stars are "radiative" in or near their cores. (Don't ask me to explain the possible difference.) The Sun, which is considerably more massive than a red dwarf, is "radiative" near its core and "convective" ("boiling") further out:
Very massive stars are fully radiative and lack a convective zone. I'm not sure that rotation can really bring any more hydrogen into the core of a really massive star, because the "outward push" of the energy generated in their cores is so strong. I will say, however, that if a massive star receives a helping of fresh hydrogen into its core by whatever mechanism, it will most likely stay on the main sequence longer, and turn into a red giant later, than a star of equal mass that has not received an extra helping of hydrogen into its core.
Ann
Ok, then I am no closer to seeing why W-R stars differ from other very large non W-R stars. Or maybe I'm just not understanding you.
-- "To B̬̻̋̚o̞̮̚̚l̘̲̀᷾d̫͓᷅ͩḷ̯᷁ͮȳ͙᷊͠ Go......Beyond The F͇̤i̙̖e̤̟l̡͓d͈̹s̙͚ We Know."{ʲₒʰₙNYᵈₑᵉₚ}
Wait - did you mean a shortened main sequence lifetime? Aren't W-R stars on the shortened path? I (CAVEAT: truthfully, I've never fully understood what the ubiquitously useful Hertzsprung-Russell diagrams are really all about!)
Yes, more massive stars have shorter lifetimes. The more massive a star is, the faster it uses up its fuel, because its "fusion engine" has to run at a furious rate to counteract the star's own gravity that otherwise threatens to overwhelm it. (And that's a real threat: Astronomers have recently found some evidence that massive stars can indeed just collapse into a black hole without going supernova first.)
What stars need in order to be more long-lived is fresh hydrogen delivered to their cores.
The most lightweight stars, the red dwarfs, are "fully convective" inside, which is to say that their insides are "boiling", and the boiling process continually brings fresh hydrogen into their cores so that their core hydrogen fusion engines (which run very slowly) can keep running for trillions of years.
More massive stars are "radiative" in or near their cores. (Don't ask me to explain the possible difference.) The Sun, which is considerably more massive than a red dwarf, is "radiative" near its core and "convective" ("boiling") further out:
Very massive stars are fully radiative and lack a convective zone. I'm not sure that rotation can really bring any more hydrogen into the core of a really massive star, because the "outward push" of the energy generated in their cores is so strong. I will say, however, that if a massive star receives a helping of fresh hydrogen into its core by whatever mechanism, it will most likely stay on the main sequence longer, and turn into a red giant later, than a star of equal mass that has not received an extra helping of hydrogen into its core.
Ann
Ok, then I am no closer to seeing why W-R stars differ from other very large non W-R stars. Or maybe I'm just not understanding you.
WR stars are not very large, because they are shedding a huge amount of their mass at a pretty furious rate. They used to be normal-sized O-type stars (which are big, but not humongous), but then they evolved into WR stars. No, I can't explain how that happened, but I do believe that it only happens to very massive stars indeed.
This is a poor analogy, but take a look at this video anyway. A sheep was lost in the woods and grew a truly tremendous coat of wool. The wool was removed and the sheep got, I guess you have say, much smaller.
Click to play embedded YouTube video.
WR stars are like that sheep in that they have shed enormous amounts of their mass. In the process, and unlike the sheep, they have revealed hotter and hotter layers of their interiors, so they are extremely hot. They are often surrounded by a nebula of their own making (the nebula is their own cast-off outer layers).
Ann wrote: ↑Sat Jun 08, 2024 5:56 pm
Your image isn't about color, but about structure.
Ann
talking about the structure, I wonder why there seems to be a smooth pale cover about 1 ly above bumpy and solid surface (though it's hard vacuum for a laboratory)?
Not sure quite what structure you're referring to here.
And why the Nose has no anti-nose feature at 4 or 5 o'clock
Why would you expect one?
the bumpy surface covered by a pale smooth veil:
SH2-308-The Dolphin Head Nebula (2024 Jun 07) -.jpg (22.15 KiB) Viewed 6614 times
An anti-nose or a few ones are needed to conserve the total momentum without an invisible party
talking about the structure, I wonder why there seems to be a smooth pale cover about 1 ly above bumpy and solid surface (though it's hard vacuum for a laboratory)?
Not sure quite what structure you're referring to here.
And why the Nose has no anti-nose feature at 4 or 5 o'clock
why a pair of jets in M87 should differ is clear: near the central black hole they are relativistically fast and thus only the forward one is bright for an observer in this galaxy, and far out the track is a dissipating cloud which depends upon interstellar gas in the outskirts of M87.
How can The Dolphin Head be one-nosed, I still don't get
The vail around Tycho supernova remnant in X-rays is great. And mysterious
talking about the structure, I wonder why there seems to be a smooth pale cover about 1 ly above bumpy and solid surface (though it's hard vacuum for a laboratory)?
Not sure quite what structure you're referring to here.
And why the Nose has no anti-nose feature at 4 or 5 o'clock
Why would you expect one?
the bumpy surface covered by a pale smooth veil:SH2-308-The Dolphin Head Nebula (2024 Jun 07) -.jpg
How can you tell that a bumpy surface underlies a smooth shell? Why not a smooth surface with a lacy structure? That is going to look "lumpy" when viewed through it and smooth when viewed edge on.
An anti-nose or a few ones are needed to conserve the total momentum without an invisible party
What momentum is not being conserved? This isn't a planetary nebula, it is a shock front created by winds coming off a star. Does a CME from the Sun require a matching one from the opposite hemisphere to conserve any momentum?
Chris
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Chris L Peterson
Cloudbait Observatory https://www.cloudbait.com
VictorBorun wrote: ↑Mon Jun 10, 2024 7:13 am
An anti-nose or a few ones are needed to conserve the total momentum without an invisible party
What momentum is not being conserved? This isn't a planetary nebula, it is a shock front created by winds coming off a star. Does a CME from the Sun require a matching one from the opposite hemisphere to conserve any momentum?
my guess was that the nose is a dissipating track of massive fast-moving body, something like “Cannonball Pulsar” only of smaller mass and greater size
SH2-308: The Dolphin Head Nebula
