APOD: SH2-308: The Dolphin Head Nebula (2024 Jun 07)

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Expand view Topic review: APOD: SH2-308: The Dolphin Head Nebula (2024 Jun 07)

Re: APOD: SH2-308: The Dolphin Head Nebula (2024 Jun 07)

by Chris Peterson » Mon Jun 10, 2024 6:41 pm

VictorBorun wrote: Mon Jun 10, 2024 6:31 pm 2
Chris Peterson wrote: Mon Jun 10, 2024 4:07 pm
VictorBorun wrote: Mon Jun 10, 2024 3:57 pm

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
Image
A "cannonball pulsar" is a star (or stellar remnant) ejected from its original location. All we're seeing in this nebula is a shock front created by stellar winds... and I see no reason to assume it will be perfectly spherical, given that stars can and do throw off particles non-isometrically.

Also, what we're seeing here isn't material from the star, but surrounding material being ionized by particles from the star. So the shape of the nebula is determined in part by the density and density variations of the interstellar medium in that region.
Now I think you might imply something like this:
1) there used to be a triple stellar system, including an invisible red or brown or black dwarf
2) some time before the main star went Wolf-Rayet the dwarf was cannonballed out and a more massive companion was thrown into the main star;
3) then the cannonball dwarf created a track through the interstellar medium and the the main star went Wolf-Rayet;
4) then the Dolphin Head was created and in the place of the cannonball's track the shock wave met rarefied medium and formed the Nose
Seems like a stretch...

Re: APOD: SH2-308: The Dolphin Head Nebula (2024 Jun 07)

by VictorBorun » Mon Jun 10, 2024 6:31 pm

2
Chris Peterson wrote: Mon Jun 10, 2024 4:07 pm
VictorBorun wrote: Mon Jun 10, 2024 3:57 pm
Chris Peterson wrote: Mon Jun 10, 2024 1:08 pm

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
Image
A "cannonball pulsar" is a star (or stellar remnant) ejected from its original location. All we're seeing in this nebula is a shock front created by stellar winds... and I see no reason to assume it will be perfectly spherical, given that stars can and do throw off particles non-isometrically.

Also, what we're seeing here isn't material from the star, but surrounding material being ionized by particles from the star. So the shape of the nebula is determined in part by the density and density variations of the interstellar medium in that region.
Now I think you might imply something like this:
1) there used to be a triple stellar system, including an invisible red or brown or black dwarf
2) some time before the main star went Wolf-Rayet the dwarf was cannonballed out and a more massive companion was thrown into the main star;
3) then the cannonball dwarf created a track through the interstellar medium and the the main star went Wolf-Rayet;
4) then the Dolphin Head was created and in the place of the cannonball's track the shock wave met rarefied medium and formed the Nose

Re: APOD: SH2-308: The Dolphin Head Nebula (2024 Jun 07)

by Chris Peterson » Mon Jun 10, 2024 4:07 pm

VictorBorun wrote: Mon Jun 10, 2024 3:57 pm
Chris Peterson wrote: Mon Jun 10, 2024 1:08 pm
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
Image
A "cannonball pulsar" is a star (or stellar remnant) ejected from its original location. All we're seeing in this nebula is a shock front created by stellar winds... and I see no reason to assume it will be perfectly spherical, given that stars can and do throw off particles non-isometrically.

Also, what we're seeing here isn't material from the star, but surrounding material being ionized by particles from the star. So the shape of the nebula is determined in part by the density and density variations of the interstellar medium in that region.

Re: APOD: SH2-308: The Dolphin Head Nebula (2024 Jun 07)

by VictorBorun » Mon Jun 10, 2024 3:57 pm

Chris Peterson wrote: Mon Jun 10, 2024 1:08 pm
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
Image

Re: APOD: SH2-308: The Dolphin Head Nebula (2024 Jun 07)

by Chris Peterson » Mon Jun 10, 2024 1:08 pm

VictorBorun wrote: Mon Jun 10, 2024 7:13 am
Chris Peterson wrote: Sun Jun 09, 2024 2:03 pm
VictorBorun wrote: Sun Jun 09, 2024 1:51 pm

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?

Re: APOD: SH2-308: The Dolphin Head Nebula (2024 Jun 07)

by VictorBorun » Mon Jun 10, 2024 11:39 am

Ann wrote: Mon Jun 10, 2024 9:08 am
VictorBorun wrote: Mon Jun 10, 2024 7:13 am
Chris Peterson wrote: Sun Jun 09, 2024 2:03 pm
Not sure quite what structure you're referring to here.



Why would you expect one?
the bumpy surface covered by a pale smooth veil:
An anti-nose or a few ones are needed to conserve the total momentum without an invisible party

That kind of structure is not unique:


And jets can be asymmetrical. Just consider the jets of the giant black hole of M87:


Ann
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

Re: APOD: SH2-308: The Dolphin Head Nebula (2024 Jun 07)

by Ann » Mon Jun 10, 2024 9:08 am

VictorBorun wrote: Mon Jun 10, 2024 7:13 am
Chris Peterson wrote: Sun Jun 09, 2024 2:03 pm
VictorBorun wrote: Sun Jun 09, 2024 1:51 pm

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:
An anti-nose or a few ones are needed to conserve the total momentum without an invisible party

That kind of structure is not unique:


And jets can be asymmetrical. Just consider the jets of the giant black hole of M87:


Ann

Re: APOD: SH2-308: The Dolphin Head Nebula (2024 Jun 07)

by VictorBorun » Mon Jun 10, 2024 7:13 am

Chris Peterson wrote: Sun Jun 09, 2024 2:03 pm
VictorBorun wrote: Sun Jun 09, 2024 1:51 pm
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
SH2-308-The Dolphin Head Nebula (2024 Jun 07) -.jpg (22.15 KiB) Viewed 6635 times
An anti-nose or a few ones are needed to conserve the total momentum without an invisible party

Re: APOD: SH2-308: The Dolphin Head Nebula (2024 Jun 07)

by Ann » Sun Jun 09, 2024 5:19 pm

johnnydeep wrote: Sun Jun 09, 2024 5:02 pm
Ann wrote: Sat Jun 08, 2024 4:07 am
johnnydeep wrote: Fri Jun 07, 2024 9:03 pm

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

Re: APOD: SH2-308: The Dolphin Head Nebula (2024 Jun 07)

by johnnydeep » Sun Jun 09, 2024 5:02 pm

Ann wrote: Sat Jun 08, 2024 4:07 am
johnnydeep wrote: Fri Jun 07, 2024 9:03 pm
Ann wrote: Fri Jun 07, 2024 7:57 pm

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.

Re: APOD: SH2-308: The Dolphin Head Nebula (2024 Jun 07)

by Chris Peterson » Sun Jun 09, 2024 2:03 pm

VictorBorun wrote: Sun Jun 09, 2024 1:51 pm
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?

Re: APOD: SH2-308: The Dolphin Head Nebula (2024 Jun 07)

by VictorBorun » Sun Jun 09, 2024 1:51 pm

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

Re: APOD: SH2-308: The Dolphin Head Nebula (2024 Jun 07)

by Ann » Sat Jun 08, 2024 5:56 pm

prabhuastrophotography wrote: Sat Jun 08, 2024 2:23 pm
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

Re: APOD: SH2-308: The Dolphin Head Nebula (2024 Jun 07)

by prabhuastrophotography » Sat Jun 08, 2024 2:23 pm

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.

Re: APOD: SH2-308: The Dolphin Head Nebula (2024 Jun 07)

by Ann » Sat Jun 08, 2024 4:07 am

johnnydeep wrote: Fri Jun 07, 2024 9:03 pm
Ann wrote: Fri Jun 07, 2024 7:57 pm
johnnydeep wrote: Fri Jun 07, 2024 5:15 pm

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

Re: APOD: SH2-308: The Dolphin Head Nebula (2024 Jun 07)

by Chris Peterson » Sat Jun 08, 2024 3:00 am

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).

Re: APOD: SH2-308: The Dolphin Head Nebula (2024 Jun 07)

by Roy » 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.

Re: APOD: SH2-308: The Dolphin Head Nebula (2024 Jun 07)

by johnnydeep » Fri Jun 07, 2024 9:03 pm

Ann wrote: Fri Jun 07, 2024 7:57 pm
johnnydeep wrote: Fri Jun 07, 2024 5:15 pm
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!)

Re: APOD: SH2-308: The Dolphin Head Nebula (2024 Jun 07)

by Ann » Fri Jun 07, 2024 7:57 pm

johnnydeep wrote: Fri Jun 07, 2024 5:15 pm
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.

Ann

Re: APOD: SH2-308: The Dolphin Head Nebula (2024 Jun 07)

by Christian G. » Fri Jun 07, 2024 7:35 pm

johnnydeep wrote: Fri Jun 07, 2024 5:15 pm
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.

Re: APOD: SH2-308: The Dolphin Head Nebula (2024 Jun 07)

by Chris Peterson » Fri Jun 07, 2024 6:56 pm

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.)

Re: APOD: SH2-308: The Dolphin Head Nebula (2024 Jun 07)

by Ann » 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

Re: APOD: SH2-308: The Dolphin Head Nebula (2024 Jun 07)

by johnnydeep » Fri Jun 07, 2024 5:19 pm

Re: APOD: SH2-308: The Dolphin Head Nebula (2024 Jun 07)

by johnnydeep » Fri Jun 07, 2024 5:15 pm

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.

Re: APOD: SH2-308: The Dolphin Head Nebula (2024 Jun 07)

by Christian G. » 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!)

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