APOD: Ou4: The Giant Squid Nebula (2022 Oct 12)

[APOD Robot]

Ou4: The Giant Squid Nebula

Explanation: A mysterious squid-like cosmic cloud, this nebula is very faint, but also very large in planet Earth's sky. In the image, composed with 30 hours of narrowband image data, it spans nearly three full moons toward the royal constellation Cepheus. Discovered in 2011 by French astro-imager Nicolas Outters, the Squid Nebula's bipolar shape is distinguished here by the telltale blue-green emission from doubly ionized oxygen atoms. Though apparently surrounded by the reddish hydrogen emission region Sh2-129, the true distance and nature of the Squid Nebula have been difficult to determine. Still, a more recent investigation suggests Ou4 really does lie within Sh2-129 some 2,300 light-years away. Consistent with that scenario, the cosmic squid would represent a spectacular outflow of material driven by a triple system of hot, massive stars, cataloged as HR8119, seen near the center of the nebula. If so, this truly giant squid nebula would physically be over 50 light-years across.

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[Ann]

Ou4: The Giant Squid Nebula
Image Credit & Copyright: Tommy Lease

That's a fine image! And the phenomenon itself, with this kind of giant bipolar outflow from a triplet of hot stars that are apparently all still fusing hydrogen in their cores, although the most massive one seems to be running out, is indeed remarkable. No other system with an outflow even remotely similar to this one has been identified, to my knowledge.

APOD Robot wrote:

...the true distance and nature of the Squid Nebula have been difficult to determine.

And there appears to be no Gaia parallax for this triple star, either. That's really a pity. Because if it turned out that HD 202214 is much closer than we think it is, then we might have to think of it as the central star of a planetary nebula.

I don't think that Ou4 is a planetary nebula. But I would like to know!

Ann

[orin stepanek]

Unusal looking Nebula; but still!>cool!
Wouldn't it be weird for planets in a multiple star system?

[johnnydeep]

SquidFinal3smaller1024[1].jpg

Ou4: The Giant Squid Nebula
Image Credit & Copyright: Tommy Lease

That's a fine image! And the phenomenon itself, with this kind of giant bipolar outflow from a triplet of hot stars that are apparently all still fusing hydrogen in their cores, although the most massive one seems to be running out, is indeed remarkable. No other system with an outflow even remotely similar to this one has been identified, to my knowledge.

APOD Robot wrote:

...the true distance and nature of the Squid Nebula have been difficult to determine.

And there appears to be no Gaia parallax for this triple star, either. That's really a pity. Because if it turned out that HD 202214 is much closer than we think it is, then we might have to think of it as the central star of a planetary nebula.

I don't think that Ou4 is a planetary nebula. But I would like to know!

Ann

Wait, the "recent investigation" link says:

Conclusions: The apparent position of Ou4 and the properties studied in this work are consistent with the hypothesis that Ou4 is located inside the Sh 2-129 H ii region, suggesting that it was launched some 90 000 yr ago by HR 8119 [aka HD 202214]. The outflow total kinetic energy is estimated to be ≈4 × 1047 ergs. However, we cannot rule out the alternative possibility that Ou4 is a bipolar planetary nebula or the result of an eruptive event on a massive AGB or post-AGB star not yet identified.

Are you suggesting something different could be going on? Or maybe I'm not appreciating that the bipolar "squid" shape (Ou4) could be anything BUT be caused by the clearly central HR 8119. Or maybe the exact definition of a PN is not clear to me.

[Ann]

SquidFinal3smaller1024[1].jpg

Ou4: The Giant Squid Nebula
Image Credit & Copyright: Tommy Lease

That's a fine image! And the phenomenon itself, with this kind of giant bipolar outflow from a triplet of hot stars that are apparently all still fusing hydrogen in their cores, although the most massive one seems to be running out, is indeed remarkable. No other system with an outflow even remotely similar to this one has been identified, to my knowledge.

APOD Robot wrote:

...the true distance and nature of the Squid Nebula have been difficult to determine.

And there appears to be no Gaia parallax for this triple star, either. That's really a pity. Because if it turned out that HD 202214 is much closer than we think it is, then we might have to think of it as the central star of a planetary nebula.

I don't think that Ou4 is a planetary nebula. But I would like to know!

Ann

Wait, the "recent investigation" link says:

Conclusions: The apparent position of Ou4 and the properties studied in this work are consistent with the hypothesis that Ou4 is located inside the Sh 2-129 H ii region, suggesting that it was launched some 90 000 yr ago by HR 8119 [aka HD 202214]. The outflow total kinetic energy is estimated to be ≈4 × 1047 ergs. However, we cannot rule out the alternative possibility that Ou4 is a bipolar planetary nebula or the result of an eruptive event on a massive AGB or post-AGB star not yet identified.

Are you suggesting something different could be going on? Or maybe I'm not appreciating that the bipolar "squid" shape (Ou4) could be anything BUT be caused by the clearly central HR 8119. Or maybe the exact definition of a PN is not clear to me.

The reason why I was asking is that I remember that the nature of Ou4 was discussed when it was first discovered, and at least some people thought that it was probably some sort of a planetary nebula. Some planetary nebulas do share the extreme bipolar nature of Ou4:

Ou4: The Giant Squid Nebula.
Image Credit & Copyright: Tommy Lease

Bipolar planetary nebula M2-9. Image: Bruce Balick (University of Washington), Vincent Icke (Leiden University, The Netherlands), Garrelt Mellema (Stockholm University), and NASA/ESA

---

Many planetary nebulas are dominated by OIII emission, and Ou4 is "all OIII". So Ou4 could have been a planetary nebula.

My objection to the idea that Ou4 would be a planetary nebula is that it is (or appears to be) located inside a fairly normal-looking hydrogen alpha emission nebula, and we don't expect planetary nebulas to be located inside emission nebulas. The central stars of planetary nebulas used to spend millions of years being cool red giants, which are incapable of ionizing an Hα nebula (or any sort of emission nebula).

Ou4 inside red emission nebula Sh2-129. Image: Maurizio Cabibbo

---

But my main objection is that the central star of Ou4 is wrong for a central star of a planetary nebula. The star, HD 202214, very much appears to be a hot massive star of spectral class B0 or O9. Such a has has a mass of, probably, at least 15 solar masses. But the central star of a planetary nebula has a mass of around 1 solar mass, and never more than 1.4 solar masses. HD 202214 is also too cool, probably at some 30,000 K, for a central star of a planetary nebula. Their temperaturers are typically at least 50,000 K, and often more.

Therefore, if Gaia could prove that HD 202214 is so far away that it has to be a massive still hydrogen-fusing star, and not so nearby that it might be a light-weight burnt-out stellar cinder, we would know that Ou4 is not a planetary nebula.

Ann

[johnnydeep]

SquidFinal3smaller1024[1].jpg

Ou4: The Giant Squid Nebula
Image Credit & Copyright: Tommy Lease

That's a fine image! And the phenomenon itself, with this kind of giant bipolar outflow from a triplet of hot stars that are apparently all still fusing hydrogen in their cores, although the most massive one seems to be running out, is indeed remarkable. No other system with an outflow even remotely similar to this one has been identified, to my knowledge.



And there appears to be no Gaia parallax for this triple star, either. That's really a pity. Because if it turned out that HD 202214 is much closer than we think it is, then we might have to think of it as the central star of a planetary nebula.

I don't think that Ou4 is a planetary nebula. But I would like to know!

Ann

Wait, the "recent investigation" link says:

Conclusions: The apparent position of Ou4 and the properties studied in this work are consistent with the hypothesis that Ou4 is located inside the Sh 2-129 H ii region, suggesting that it was launched some 90 000 yr ago by HR 8119 [aka HD 202214]. The outflow total kinetic energy is estimated to be ≈4 × 1047 ergs. However, we cannot rule out the alternative possibility that Ou4 is a bipolar planetary nebula or the result of an eruptive event on a massive AGB or post-AGB star not yet identified.

Are you suggesting something different could be going on? Or maybe I'm not appreciating that the bipolar "squid" shape (Ou4) could be anything BUT be caused by the clearly central HR 8119. Or maybe the exact definition of a PN is not clear to me.

The reason why I was asking is that I remember that the nature of Ou4 was discussed when it was first discovered, and at least some people thought that it was probably some sort of a planetary nebula. Some planetary nebulas do share the extreme bipolar nature of Ou4:

SquidFinal3smaller1024[1].jpg

Ou4: The Giant Squid Nebula.
Image Credit & Copyright: Tommy Lease

Bipolar planetary nebula M2-9. Image: Bruce Balick (University of Washington), Vincent Icke (Leiden University, The Netherlands), Garrelt Mellema (Stockholm University), and NASA/ESA

---

Many planetary nebulas are dominated by OIII emission, and Ou4 is "all OIII". So Ou4 could have been a planetary nebula.

My objection to the idea that Ou4 would be a planetary nebula is that it is (or appears to be) located inside a fairly normal-looking hydrogen alpha emission nebula, and we don't expect planetary nebulas to be located inside emission nebulas. The central stars of planetary nebulas used to spend millions of years being cool red giants, which are incapable of ionizing an Hα nebula (or any sort of emission nebula).

Ou4 inside red emission nebula Sh2-129. Image: Maurizio Cabibbo

---

But my main objection is that the central star of Ou4 is wrong for a central star of a planetary nebula. The star, HD 202214, very much appears to be a hot massive star of spectral class B0 or O9. Such a has has a mass of, probably, at least 15 solar masses. But the central star of a planetary nebula has a mass of around 1 solar mass, and never more than 1.4 solar masses. HD 202214 is also too cool, probably at some 30,000 K, for a central star of a planetary nebula. Their temperaturers are typically at least 50,000 K, and often more.

Therefore, if Gaia could prove that HD 202214 is so far away that it has to be a massive still hydrogen-fusing star, and not so nearby that it might be a light-weight burnt-out stellar cinder, we would know that Ou4 is not a planetary nebula.

Ann

Thanks, Ann. Turns out you and geckzilla (and a bunch of others) had a learned rip-roaring discussion about Ou4 back in 2014 - viewtopic.php?t=33663, and I admit to not understanding all the nuances, particularly the impact the fact that the central star system of Ou4 is a binary and maybe even a trinary, has.

[abhagwat]

I was watching BBC Earth on wierd things in nature......and they were showing a squid egg blob in an ocean......much similar to the APOD squid nebula! Have look. https://www.nationalgeographic.com/adve ... ls-science

[Ann]

Wait, the "recent investigation" link says:



Are you suggesting something different could be going on? Or maybe I'm not appreciating that the bipolar "squid" shape (Ou4) could be anything BUT be caused by the clearly central HR 8119. Or maybe the exact definition of a PN is not clear to me.

The reason why I was asking is that I remember that the nature of Ou4 was discussed when it was first discovered, and at least some people thought that it was probably some sort of a planetary nebula. Some planetary nebulas do share the extreme bipolar nature of Ou4:

Click to view full size image

Ou4: The Giant Squid Nebula.
Image Credit & Copyright: Tommy Lease

Bipolar planetary nebula M2-9. Image: Bruce Balick (University of Washington), Vincent Icke (Leiden University, The Netherlands), Garrelt Mellema (Stockholm University), and NASA/ESA

---

Many planetary nebulas are dominated by OIII emission, and Ou4 is "all OIII". So Ou4 could have been a planetary nebula.

My objection to the idea that Ou4 would be a planetary nebula is that it is (or appears to be) located inside a fairly normal-looking hydrogen alpha emission nebula, and we don't expect planetary nebulas to be located inside emission nebulas. The central stars of planetary nebulas used to spend millions of years being cool red giants, which are incapable of ionizing an Hα nebula (or any sort of emission nebula).

Ou4 inside red emission nebula Sh2-129. Image: Maurizio Cabibbo

---

But my main objection is that the central star of Ou4 is wrong for a central star of a planetary nebula. The star, HD 202214, very much appears to be a hot massive star of spectral class B0 or O9. Such a has has a mass of, probably, at least 15 solar masses. But the central star of a planetary nebula has a mass of around 1 solar mass, and never more than 1.4 solar masses. HD 202214 is also too cool, probably at some 30,000 K, for a central star of a planetary nebula. Their temperaturers are typically at least 50,000 K, and often more.

Therefore, if Gaia could prove that HD 202214 is so far away that it has to be a massive still hydrogen-fusing star, and not so nearby that it might be a light-weight burnt-out stellar cinder, we would know that Ou4 is not a planetary nebula.

Ann

Thanks, Ann. Turns out you and geckzilla (and a bunch of others) had a learned rip-roaring discussion about Ou4 back in 2014 - viewtopic.php?t=33663, and I admit to not understanding all the nuances, particularly the impact the fact that the central star system of Ou4 is a binary and maybe even a trinary, has.

Thanks, Johnny. Yeah, I remember, that was a fun discussion. What Geck meant in that thread is that an exceedingly faint foreground or background white dwarf might be hidden in the glare of HD 202214, the hot triple star that is ionizing the red emission nebula, Sh2-129. (Unless she meant that HD 202214 was the white dwarf, but from my amateur standpoint I'll rule that out. If a white dwarf is there, it has to be another star than HD 202214, but it has to be very close to this bright star.

Seeing a puny white dwarf next to a brilliant O-type subgiant might be like trying to see a foreground or a background candle while staring at brilliant flashlight. If such a faint white dwarf is hidden in the glare of HD 202214, then it might indeed be ionizing a planetary nebula, and then Ou4 might only be a foreground or a background object in front or behind emission nebula Sh2-129.

I find such a scenario very unlikely, but admittedly not impossible. It's a shame that we have so few ultraviolet-sensitive telescopes these days, and Hubble itself is probably the best of them, but I would really like Hubble to search for a possible ultraviolet-bright white dwarf very close to HD 202214 that could be ionizing Ou4. And if no such white dwarf is found, then I would really like Gaia to measure the parallax of HD 202214 to absolutely rule out the ever-so-slim possibility that this apparent subgiant is in fact a white dwarf in disguise.

You may be right that the binary or even "trinary" nature of HD 202214 might make it difficult for Gaia to measure the parallax of this stellar system.

Ann

[johnnydeep]

...
Thanks, Johnny. Yeah, I remember, that was a fun discussion. What Geck meant in that thread is that an exceedingly faint foreground or background white dwarf might be hidden in the glare of HD 202214, the hot triple star that is ionizing the red emission nebula, Sh2-129. (Unless she meant that HD 202214 was the white dwarf, but from my amateur standpoint I'll rule that out. If a white dwarf is there, it has to be another star than HD 202214, but it has to be very close to this bright star.

Seeing a puny white dwarf next to a brilliant O-type subgiant might be like trying to see a foreground or a background candle while staring at brilliant flashlight. If such a faint white dwarf is hidden in the glare of HD 202214, then it might indeed be ionizing a planetary nebula, and then Ou4 might only be a foreground or a background object in front or behind emission nebula Sh2-129.

I find such a scenario very unlikely, but admittedly not impossible. It's a shame that we have so few ultraviolet-sensitive telescopes these days, and Hubble itself is probably the best of them, but I would really like Hubble to search for a possible ultraviolet-bright white dwarf very close to HD 202214 that could be ionizing Ou4. And if no such white dwarf is found, then I would really like Gaia to measure the parallax of HD 202214 to absolutely rule out the ever-so-slim possibility that this apparent subgiant is in fact a white dwarf in disguise.

You may be right that the binary or even "trinary" nature of HD 202214 might make it difficult for Gaia to measure the parallax of this stellar system.

Ann

Why is that? Parallax is measured by the shift against background stars, and all 2 (or 3) stars in the HD 202214 system would participate in the shifting essentially equally, would they not?

[Ann]

...
Thanks, Johnny. Yeah, I remember, that was a fun discussion. What Geck meant in that thread is that an exceedingly faint foreground or background white dwarf might be hidden in the glare of HD 202214, the hot triple star that is ionizing the red emission nebula, Sh2-129. (Unless she meant that HD 202214 was the white dwarf, but from my amateur standpoint I'll rule that out. If a white dwarf is there, it has to be another star than HD 202214, but it has to be very close to this bright star.

Seeing a puny white dwarf next to a brilliant O-type subgiant might be like trying to see a foreground or a background candle while staring at brilliant flashlight. If such a faint white dwarf is hidden in the glare of HD 202214, then it might indeed be ionizing a planetary nebula, and then Ou4 might only be a foreground or a background object in front or behind emission nebula Sh2-129.

I find such a scenario very unlikely, but admittedly not impossible. It's a shame that we have so few ultraviolet-sensitive telescopes these days, and Hubble itself is probably the best of them, but I would really like Hubble to search for a possible ultraviolet-bright white dwarf very close to HD 202214 that could be ionizing Ou4. And if no such white dwarf is found, then I would really like Gaia to measure the parallax of HD 202214 to absolutely rule out the ever-so-slim possibility that this apparent subgiant is in fact a white dwarf in disguise.

You may be right that the binary or even "trinary" nature of HD 202214 might make it difficult for Gaia to measure the parallax of this stellar system.

Ann

Why is that? Parallax is measured by the shift against background stars, and all 2 (or 3) stars in the HD 202214 system would participate in the shifting essentially equally, would they not?

It is just my impression that there might be something about these binary or trinary stars that might make it hard for Gaia to measure their parallaxes. But it might also be that nebulosity close to a star makes measurements of parallaxes difficult.

Consider Eta Carinae, possibly the brightest star in the Milky Way. (Or not, oh well... the Pistol star and others, oh well...)

However, it would certainly be interesting to know the parallax of Eat Carinae and thus the distance to this star, wouldn't it? Well, Gaia hasn't measured it. See the Simbad entry for this star.

Eta Carinae. Photo: Jon Morse (University of Colorado) & NASA/Hubble Space Telescope

---

Eta Carinae is immersed inside a nebula. It is also a binary star, where the components are in eccentric orbits around the center of gravity of the system. Maybe that makes it hard to measure the parallax of this iconic star.

Why else would Gaia not measure it?

Ann

[johnnydeep]

...
Thanks, Johnny. Yeah, I remember, that was a fun discussion. What Geck meant in that thread is that an exceedingly faint foreground or background white dwarf might be hidden in the glare of HD 202214, the hot triple star that is ionizing the red emission nebula, Sh2-129. (Unless she meant that HD 202214 was the white dwarf, but from my amateur standpoint I'll rule that out. If a white dwarf is there, it has to be another star than HD 202214, but it has to be very close to this bright star.

Seeing a puny white dwarf next to a brilliant O-type subgiant might be like trying to see a foreground or a background candle while staring at brilliant flashlight. If such a faint white dwarf is hidden in the glare of HD 202214, then it might indeed be ionizing a planetary nebula, and then Ou4 might only be a foreground or a background object in front or behind emission nebula Sh2-129.

I find such a scenario very unlikely, but admittedly not impossible. It's a shame that we have so few ultraviolet-sensitive telescopes these days, and Hubble itself is probably the best of them, but I would really like Hubble to search for a possible ultraviolet-bright white dwarf very close to HD 202214 that could be ionizing Ou4. And if no such white dwarf is found, then I would really like Gaia to measure the parallax of HD 202214 to absolutely rule out the ever-so-slim possibility that this apparent subgiant is in fact a white dwarf in disguise.

You may be right that the binary or even "trinary" nature of HD 202214 might make it difficult for Gaia to measure the parallax of this stellar system.

Ann

Why is that? Parallax is measured by the shift against background stars, and all 2 (or 3) stars in the HD 202214 system would participate in the shifting essentially equally, would they not?

It is just my impression that there might be something about these binary or trinary stars that might make it hard for Gaia to measure their parallaxes. But it might also be that nebulosity close to a star makes measurements of parallaxes difficult.

Consider Eta Carinae, possibly the brightest star in the Milky Way. (Or not, oh well... the Pistol star and others, oh well...)

However, it would certainly be interesting to know the parallax of Eat Carinae and thus the distance to this star, wouldn't it? Well, Gaia hasn't measured it. See the Simbad entry for this star.

Eta Carinae. Photo: Jon Morse (University of Colorado) & NASA/Hubble Space Telescope

---

Eta Carinae is immersed inside a nebula. It is also a binary star, where the components are in eccentric orbits around the center of gravity of the system. Maybe that makes it hard to measure the parallax of this iconic star.

Why else would Gaia not measure it?

Ann

Yeah, I suppose a sufficiently diffuse object could be difficult to pinpoint accurately enough for a meaningful parallax measurement. I figured that since stars are essentially point sources that it wouldn't be a problem. But if a binary or trinary system is resolvable into separate stars maybe that could mess up the parallax measurement. ...Although, in that case, each star in the system could theoretically be measured for parallax separately.