APOD: Approaching the Bubble Nebula (2017 May 31)

Comments and questions about the APOD on the main view screen.
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APOD: Approaching the Bubble Nebula (2017 May 31)

Post by APOD Robot » Wed May 31, 2017 4:10 am

Image Approaching the Bubble Nebula

Explanation: What would it look like to approach the Bubble Nebula? Blown by the wind and radiation from a massive star, this bubble now spans seven light-years in diameter. The hot star inside is thousands of times more luminous than our Sun, and is now offset from the nebula's center. The visualization starts with a direct approach toward the Bubble Nebula (NGC 7635) and then moves around the nebula while continuing the approach. The featured time-lapse visualization is extrapolated from images with the orbiting Hubble Space Telescope and the WIYN telescope on Kitt Peak in Arizona, USA. The 3D-computer model on which this visualization is based includes artistic interpretations, and distances are significantly compressed.

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Re: APOD: Approaching the Bubble Nebula (2017 May 31)

Post by john luke packard » Wed May 31, 2017 4:35 am

Just don't enter the nebula, the communications will fail, the warp core will freeze and the aliens will eat you alive. :lol2:

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Re: APOD: Approaching the Bubble Nebula (2017 May 31)

Post by BDanielMayfield » Wed May 31, 2017 9:02 am

Interesting simulation and explanation. One thing about the simulation is a bit strange and unrealistic though is the lack of stars around the Bubble itself. The sim has us flying through an apparent wall of stars into an apparent stellar void. The density of stars is much more likely to be fairly uniform throughout the entire area.

I look forward keenly to what Ann has to say about the progenitor star, a 44 solar massed O6.5 blue giant, or is it on the main sequence still? I also look forward to discussion about the large offset of this star from the Bubble's center.

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Re: APOD: Approaching the Bubble Nebula (2017 May 31)

Post by Nitpicker » Wed May 31, 2017 9:56 am

I wonder if it would be more, or less realistic to simply zoom in on a 2-D image?

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Re: APOD: Approaching the Bubble Nebula (2017 May 31)

Post by BDanielMayfield » Wed May 31, 2017 10:56 am

Nitpicker wrote:I wonder if it would be more, or less realistic to simply zoom in on a 2-D image?
It would be more realistic, but it would just look like peering deeper into space instead of looking like we were going there, which is cool. Personally, I would not have compressed the star distances. I get that they wanted to focus attention on the Bubble Nebula without stars cluttering up the view, but it sacrificed realism to do so in this way.
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Re: APOD: Approaching the Bubble Nebula (2017 May 31)

Post by Nitpicker » Wed May 31, 2017 11:01 am

I suspect the distance to each star is not so well known. Many would be closer to and some would be further from us, than the bubble. And we probably can't tell the difference.

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Re: APOD: Approaching the Bubble Nebula (2017 May 31)

Post by BDanielMayfield » Wed May 31, 2017 11:21 am

Nitpicker wrote:I suspect the distance to each star is not so well known. Many would be closer to and some would be further from us, than the bubble. And we probably can't tell the difference.
Stellar distances are approximated, but known within error ranges. The more distant stars show more dust extinction in their spectra and are reddened.
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Re: APOD: Approaching the Bubble Nebula (2017 May 31)

Post by neufer » Wed May 31, 2017 12:39 pm

Click to play embedded YouTube video.
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Re: APOD: Approaching the Bubble Nebula (2017 May 31)

Post by Chris Peterson » Wed May 31, 2017 1:28 pm

Nitpicker wrote:I suspect the distance to each star is not so well known. Many would be closer to and some would be further from us, than the bubble. And we probably can't tell the difference.
At this distance, Gaia is capable of providing decent accuracy (but at this point in the mission, may not have done so yet). The larger uncertainty is in the distance to the nebula itself, so we might have a reasonable ability to model the starfield in 3D but not know where to place the nebula in it.
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Re: APOD: Approaching the Bubble Nebula (2017 May 31)

Post by Ann » Wed May 31, 2017 2:16 pm

BDanielMayfield wrote: I look forward keenly to what Ann has to say about the progenitor star, a 44 solar massed O6.5 blue giant, or is it on the main sequence still? I also look forward to discussion about the large offset of this star from the Bubble's center.

Bruce
Thanks for your coincidence in me, Bruce!

Unfortunately I can't say a lot more than what Wikipedia has to offer about this star:
Wikipedia wrote:
BD+60°2522 is a bright O-class star that has produced the Bubble Nebula (NGC 7635) with its stellar wind. The exact classification of the star is uncertain, with a number of spectral peculiarities and inconsistencies between the appearance of the star itself and the effects on the nearby nebulosity, but it is undoubtedly a highly luminous hot massive star.[6] Direct spectroscopy yields a spectral class of O6.5 and an effective temperature around 37,500K. It is a member of the Cassiopeia OB2 stellar association in the Perseus Arm[8] of the galaxy at about 8,500 light years distance.[9]

Although BD+60°2522 is around two million years old, the surrounding nebula is apparently only about 40,000 years old. The bubble is expected to be formed as a shock front where the stellar wind meets interstellar material at supersonic speeds. The wind from BD+60°2522 is travelling outwards at 1,800 - 2,500 km/s, causing the star to lose over a millionth of the mass of the sun every year.
I would guess that the star is somewhat evolved, but not highly evolved. The surrounding nebula, 40,000 years old, clearly shows that the star had an outburst 40,000 years ago.
The Squid Nebula (Ou4), centered on young triple star HR 8119.
Source: https://www.cloudynights.com/topic/5088 ... 16-newton/
The mysterious OIII-rich Squid Nebula in Cepheus appears to be centered on what appears to be an unevolved, main sequence B0V star. However, not everyone agrees that HR 8119 is unevolved.
Bright Star catalog wrote about HR 8119:
Also classified O9 and B0II. Spectrophotometric classification by Chalonge, B0II. Most observers give B0V, perhaps O9V or B0IV.
So most astronomers who have taken an interest in HR 8119 seem to think that it is an unevolved B0-type star, and it appears to have had an outburst. Note that the Squid Nebula appears to be very large, 50 light-years across, in which case BD+60°2522 must have had its outburst more than 50,000 years ago (since the nebula wouldn't move outward at the speed of light). So the Squid Nebula appears to be older than the Bubble Nebula, but HR 8119 is a "lesser star" than BD+60°2522.
The Trapezium (center) of the Orion Nebula,
with Theta-1 C Orionis at bottom center of the small lozenge shape.






Let's return to BD+60°2522. According to Wikipedia, the spectral type of this star is O6.5(f)(n)p, its mass is around 44 M, and its temperature is 37,500 K. These figures make for an interesting comparison with Theta-1 C Orionis, the brightest star of the Trapezium in Orion and the star providing most of the ionization of the Orion Nebula.
Jim Kaler wrote about Theta-1 C Orionis:
By far the leader of the pack is Theta-1 C, a great 40-solar-mass star with a temperature of 40,000 Kelvin (making it the hottest "naked eye" star, though the 4 are inseparable without optical aid), a huge luminosity 210,000 times that of the Sun (85 percent of the Trapezium's total), and a 1000 kilometer/second wind with 100,000 times the flow rate of the solar wind.
Jim Kaler also said that the spectral class of Theta-1 C Orionis is O6. To me it seems obvious that Theta-1 C Orionis must be an unevolved main sequence star, because it is so young. It is only too obvious that the Orion Nebula is young, and the main ionizing source of it must be young, too. Fascinatingly, Wikipedia on Theta-1 C Orionis says that Theta-1 C Orionis is 2.5 ± 0.5 Myr years old or some 2.5 million years old, but Wikipedia on the Trapezium says that the Trapezium (of which Theta-1 C Orionis is a part) is only 3 × 105 years, that is, only 300,000 years old!

If you ask me, Theta-1 C Orionis is not 2.5 million years old. It might be 300,000 years old, or it might perhaps be half a million years old, but not a lot more. This means that Theta-1 C Orionis is younger than BD+60°2522 (some half a million years, versus 2 million years). Theta-1 C Orionis belongs to a slightly earlier (and hotter) spectral class than BD+60°2522, O6 versus O6.5(f)(n)p. But BD+60°2522 appears to be a little hotter than Theta-1 C Orionis, 44,000 K versus 40,000 K. But there are several possible explanations for this small temperature difference, such as the direction from which we see these two stars (a more pole-on position will make the star appear hotter) and the possibility that the moderately recent outburst of BD+60°2522 might mean that enough of its outermost layers have been blown off that we can see deeper into the hot interior of this star.

To summarize, BD+60°2522 and Theta-1 C Orionis appear to be quite similar, but Theta-1 C Orionis is definitely younger and undoubtedly quite unevolved. The evolutionary status of BD+60°2522 is more uncertain.

However, Wikipedia on Theta-1 C Orionis says that the luminosity of Theta-1 C Orionis is 204,000 L, versus 398,000 L for BD+60°2522. If true, that would mean that BD+60°2522 is almost twice as bright as Theta-1 C Orionis, and in my opinion, that means that BD+60°2522 must be a larger star. This, too, might have to do with age: medium-mass and high-mass stars slowly grow larger even during their main sequence life time. But mass will also play a part, if BD+60°2522 is a main sequence star and even slightly more massive than Theta-1 C Orionis.

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Re: APOD: Approaching the Bubble Nebula (2017 May 31)

Post by BDanielMayfield » Wed May 31, 2017 3:12 pm

Ann wrote:Thanks for your coincidence in me, Bruce!
My confidence in your ability to come up with a fascinating story about a blue star is hardly coincidental. :)

Since BD+60°2522 is still a main sequence star it should be stable then, should it not? What could explain the apparent outburst?

Perhaps it collided with something 40,000 years ago. Or, perhaps this isn't really the sign of an unusual outburst at all. Could the bubble just be caused from its massive stellar winds interacting with a dusty interstellar medium?

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Re: APOD: Approaching the Bubble Nebula (2017 May 31)

Post by neufer » Wed May 31, 2017 3:19 pm

BDanielMayfield wrote:
Since BD+60°2522 is still a main sequence star it should be stable then, should it not? What could explain the apparent outburst?

Perhaps it collided with something 40,000 years ago. Or, perhaps this isn't really the sign of an unusual outburst at all.
Could the bubble just be caused from its massive stellar winds interacting with a dusty interstellar medium?
The bubble could just be caused from its massive stellar winds interacting with a dusty interstellar medium.
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    BD+60°2522 burn, and Hubble bubble.
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Re: APOD: Approaching the Bubble Nebula (2017 May 31)

Post by Chris Peterson » Wed May 31, 2017 3:29 pm

BDanielMayfield wrote:Since BD+60°2522 is still a main sequence star it should be stable then, should it not? What could explain the apparent outburst?
It is far from certain that BD+60°2522 is a main sequence star. Quite a few papers place it off the main sequence evolving towards a Wolf-Rayet star.
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Re: APOD: Approaching the Bubble Nebula (2017 May 31)

Post by Ann » Wed May 31, 2017 3:40 pm

BDanielMayfield wrote:
Ann wrote:Thanks for your coincidence in me, Bruce!
My confidence in your ability to come up with a fascinating story about a blue star is hardly coincidental. :)

Since BD+60°2522 is still a main sequence star it should be stable then, should it not? What could explain the apparent outburst?

Perhaps it collided with something 40,000 years ago. Or, perhaps this isn't really the sign of an unusual outburst at all. Could the bubble just be caused from its massive stellar winds interacting with a dusty interstellar medium?

Bruce
I'm not sure that very massive stars are so very stable. Not always.
Wikipedia wrote about O-type stars:
Stars of this type are particularly rare; only 0.00003% of the main sequence are O-type stars.
And because O-type stars are so rare it is hard to know what their "normal" behavior is. Of course, the more massive they are, the more unstable they are likely to be. BD+60°2522, while very massive, is very far from being any sort of record breaker. Check out this list to get some perspective on what kind of beast BD+60°2522 is.

I don't think we can trust all 40+ solar mass main sequence O-type stars not to have outbursts on occasion.

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Re: APOD: Approaching the Bubble Nebula (2017 May 31)

Post by BDanielMayfield » Wed May 31, 2017 4:39 pm

Chris Peterson wrote:
BDanielMayfield wrote:Since BD+60°2522 is still a main sequence star it should be stable then, should it not? What could explain the apparent outburst?
It is far from certain that BD+60°2522 is a main sequence star. Quite a few papers place it off the main sequence evolving towards a Wolf-Rayet star.
Ann wrote:I'm not sure that very massive stars are so very stable. Not always.
Wikipedia wrote about O-type stars:
Stars of this type are particularly rare; only 0.00003% of the main sequence are O-type stars.
And because O-type stars are so rare it is hard to know what their "normal" behavior is. Of course, the more massive they are, the more unstable they are likely to be. BD+60°2522, while very massive, is very far from being any sort of record breaker. Check out this list to get some perspective on what kind of beast BD+60°2522 is.

I don't think we can trust all 40+ solar mass main sequence O-type stars not to have outbursts on occasion.

Ann
Thanks Chris and Ann. So instabilities in stars this massive are to be expected, regardless of age. No great stretch then to believe that it was a transient outburst that blew the bubble, so to speak.

What about the off-center position of this star inside the "Bubble"? If it is 7 ly across then it looks like the star has moved about 2 lys in 40,000 years. Is this reasonable? The brighter parts of the Nebula look like a bow shock in the direction of the star's motion, so my guess is that it is (reasonable).

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Re: APOD: Approaching the Bubble Nebula (2017 May 31)

Post by BDanielMayfield » Wed May 31, 2017 4:51 pm

neufer wrote:
BDanielMayfield wrote:
Since BD+60°2522 is still a main sequence star it should be stable then, should it not? What could explain the apparent outburst?

Perhaps it collided with something 40,000 years ago. Or, perhaps this isn't really the sign of an unusual outburst at all.
Could the bubble just be caused from its massive stellar winds interacting with a dusty interstellar medium?
The bubble could just be caused from its massive stellar winds interacting with a dusty interstellar medium.
I still think this idea of just massive stellar winds causing the Bubble is very much in play.
It would be the simplest solution, would it not?
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Re: APOD: Approaching the Bubble Nebula (2017 May 31)

Post by MarkBour » Wed May 31, 2017 5:41 pm

neufer wrote:(Art Linkletter parody video)
Where did you find that? A funny parody. Made funnier since I did not realize it was a parody at first.
------------------------------------
I love the image of BD+60°2522 in the linked Wikipedia article. At its higher resolution it is both beautiful and full of interesting features. In it, one can see what appear to be smaller bubbles within the larger bubble.

When it is said that the bubble is estimated at 40,000 years of age (and not worrying about light travel time to us), the interpretation I make of that claim is that it is supposed a major outburst sent a large pulse of ejecta from the star 40,000 years ago and that this outburst material has been expanding ever since. Without any particular outburst, would not constant and steady stellar winds be capable of forming the bubble just as well? The particles would travel at relatively high speed unimpeded through the region that has already been cleared out, then continually catch up to and slow down and build up at the visible front, forming the surface of the bubble. (I see this was asked and answered already by BDanielMayfield and neufer.) But I wonder what the 40,000 year estimate is about. Perhaps just an extrapolation from the current speed of the expansion of the bubble surface.

The bubble appears elongated to the right (mostly "southwest", given the directions marked on the image). The star may be moving from the initial center, or perhaps also contributing -- there may have been more material on the left side to stop the progress than there is on the right, so the bubble has expanded more on the right. But since it is so nearly spherical in its entire left half, it does seem likely that the star has moved (northward). If there are any sufficiently close stars to rival BD+60°2522, then perhaps over time we would see their winds deforming the bubble. In the image, there are a couple of stars that look nearby and similar to me, though they may not be. I wonder about the possibility that the nebula is already the work of more than one star.

I'd like to check back on this shape in another 50,000 years or so.
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Re: APOD: Approaching the Bubble Nebula (2017 May 31)

Post by BDanielMayfield » Wed May 31, 2017 6:55 pm

MarkBour wrote:I love the image of BD+60°2522 in the linked Wikipedia article. At its higher resolution it is both beautiful and full of interesting features. In it, one can see what appear to be smaller bubbles within the larger bubble.
Yes, there are smaller "bubbles" near the star, and they are asymmetric. These areas close to the star wouldn't be involved with the interstellar medium because earlier winds and/or eruptions would have already swept this region clear. This lends weight to the stellar instability side of the question. (Darn it, my argument has been blown away.)
When it is said that the bubble is estimated at 40,000 years of age (and not worrying about light travel time to us), the interpretation I make of that claim is that it is supposed a major outburst sent a large pulse of ejecta from the star 40,000 years ago and that this outburst material has been expanding ever since. Without any particular outburst, would not constant and steady stellar winds be capable of forming the bubble just as well? The particles would travel at relatively high speed unimpeded through the region that has already been cleared out, then continually catch up to and slow down and build up at the visible front, forming the surface of the bubble. (I see this was asked and answered already by BDanielMayfield and neufer.)
We didn't answer conclusively, but were merely noting what seemed like a reasonable possibility. A better look inside makes me reconsider. How about you neufer?

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Re: APOD: Approaching the Bubble Nebula (2017 May 31)

Post by neufer » Wed May 31, 2017 7:44 pm


BDanielMayfield wrote:
We didn't answer conclusively, but were merely noting what seemed like a reasonable possibility. A better look inside makes me reconsider. How about you neufer?

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Re: APOD: Approaching the Bubble Nebula (2017 May 31)

Post by Ann » Wed May 31, 2017 11:05 pm

MarkBour wrote:
When it is said that the bubble is estimated at 40,000 years of age (and not worrying about light travel time to us), the interpretation I make of that claim is that it is supposed a major outburst sent a large pulse of ejecta from the star 40,000 years ago and that this outburst material has been expanding ever since. Without any particular outburst, would not constant and steady stellar winds be capable of forming the bubble just as well? The particles would travel at relatively high speed unimpeded through the region that has already been cleared out, then continually catch up to and slow down and build up at the visible front, forming the surface of the bubble. (I see this was asked and answered already by BDanielMayfield and neufer.) But I wonder what the 40,000 year estimate is about. Perhaps just an extrapolation from the current speed of the expansion of the bubble surface.

The bubble appears elongated to the right (mostly "southwest", given the directions marked on the image). The star may be moving from the initial center, or perhaps also contributing -- there may have been more material on the left side to stop the progress than there is on the right, so the bubble has expanded more on the right. But since it is so nearly spherical in its entire left half, it does seem likely that the star has moved (northward). If there are any sufficiently close stars to rival BD+60°2522, then perhaps over time we would see their winds deforming the bubble. In the image, there are a couple of stars that look nearby and similar to me, though they may not be. I wonder about the possibility that the nebula is already the work of more than one star.
HD 148937 with nebula NGC 6164-6165, a rare O-type star in Norma.
Source: http://www.foldtime.com/astronomy/nebul ... 0Norma.htm
The Soap Bubble Nebula, a planetary nebula in Cygnus.
T. Rector (U. Alaska Anchorage), H. Schweiker (WIYN), NOAO, AURA, NSF



















Looking for counterparts to BD+60°2522, I settled on HD 148937 in Norma. This star is surrounded by a bipolar or "figure 8" nebula. There have been several opinions on this star among astronomers, such as the now rejected idea that HD 148937 is the central star of a planetary nebula, or that it is an evolved star of the Wolf Rayet type, or that it is a particularly young massive star.
L. Mahy, D. Hutsemékers, Y. Nazé, P. Royer, V. Lebouteiller and C. Waelkens wrote:
The magnetic star HD 148937 is the only Galactic Of?p star surrounded by a nebula.
...
The Hα image displays a bipolar or “8”-shaped ionized nebula, whilst the infrared images show dust to be more concentrated around the central object.
...
Evolutionary tracks suggest that these ejecta have occured ~1.2–1.3 and ~0.6 Myr ago, respectively.
...
The combined analyses of the known kinematics and of the new abundances of the nebula suggest either a helical morphology for the nebula, possibly linked to the magnetic geometry, or the occurrence of a binary merger.
So HD 148937 is the only star of its kind in the Milky Way known to astronomers. It is hard to know what to make of such a star. The paper, whose abstract I partly quoted, seems to think that the two nebulas surrounding this star are the results of outbursts that happened ~1.2–1.3 and ~0.6 Myr ago. They don't seem to say that the nebulas are the result of a steady stellar wind. They do consider a merger as the cause of (at least one?) of the nebulas.

While HD 148937 and its surrounding nebulas are not considered a planetary nebula, the Soap Bubble Nebula certainly is. I don't know if the Soap Bubble nebula is exactly unique, because there are certainly other highly symmetrical planetary nebulas in existence. But it seems clear to me that symmetrical and bipolar nebulas must form in different ways. Stellar winds are undoubtedly involved, but I think that these shells are the results of individual outbursts rather than steady winds.

If HD 148937 is unique in the Milky Way, I believe that BD+60°2522 is very unusual, too. And its spherical nebula, surrounding a massive star, is probably even rarer. I don't know of any other such spherical nebula surrounding a massive star. But from what I think I know about stellar behavior, I find it more likely that the nebular shell of BD+60°2522 is the result of a discrete outburst rather than of a steady stellar wind.

The structures inside the nebula might mean that there has been more than one outburst, although that doesn't seem very likely to me. Alternatively, there might have been one major outburst followed by a much weaker but quite steady stellar wind.

Also the asymmetrical shape of the nebula is almost certainly the result of differences in the interstellar medium on different sides of the nebula. On one side, the expanding nebula appears to have run into an interstellar molecular cloud, which has compressed that side of the nebula. On the other side, the nebula is expanding much more freely into much emptier space.

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Re: APOD: Approaching the Bubble Nebula (2017 May 31)

Post by Ann » Wed May 31, 2017 11:47 pm

The merger hypothesis of HD 148937 is interesting, because we know that most massive stars are members of binary or multiple systems. This made me think of V838 Monocerotis.
Wikipedia wrote:
V838 Monocerotis (V838 Mon) is a red variable star in the constellation Monoceros about 20,000 light years (6 kpc) from the Sun.[5] The previously unknown star was observed in early 2002 experiencing a major outburst, and was possibly one of the largest known stars for a short period following the outburst.
...
Click to play embedded YouTube video.
The reason for the outburst is still uncertain, but several conjectures have been put forward, including an eruption related to stellar death processes and a merger of a binary star or planets.
...
The star brightened to about a million times solar luminosity[7] and absolute magnitude of −9.8,[3] ensuring that at the time of maximum V838 Monocerotis was one of the most luminous stars in the Milky Way galaxy. The brightening was caused by a rapid expansion of the outer layers of the star.
...
Some details are emerging on the nature of the star that experienced the outburst.
...
It appears that the star is considerably more massive and luminous than the Sun. The star probably has a mass of from 5 to 10 times solar,[13] and a luminosity of from 550 to 5,000 times solar. The star may have originally had a radius roughly 5 times solar and temperature of 4,700–30,000 K.[5] Munari et al. (2005) suggest that the progenitor star is in fact a very massive supergiant with a mass of about 65 times solar. They also conclude that the system may be only about 4 million years old.[14]
...
The outburst may have been the result of a so-called mergeburst, the merger of two main sequence stars (or an 8 M☉ main sequence star and a 0.3 M☉ pre-main sequence star). This model is strengthened by the apparent youth of the system and the fact that multiple stellar systems may be unstable. The less massive component may have been in a very eccentric orbit or deflected towards the massive one. Computer simulations have shown the merger model to be plausible. The simulations also show that the inflated envelope would have come almost entirely from the smaller component. In addition, the merger model explains the multiple peaks in the light curve observed during the outburst.
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Re: APOD: Approaching the Bubble Nebula (2017 May 31)

Post by Nitpicker » Wed May 31, 2017 11:57 pm

Chris Peterson wrote:
Nitpicker wrote:I suspect the distance to each star is not so well known. Many would be closer to and some would be further from us, than the bubble. And we probably can't tell the difference.
At this distance, Gaia is capable of providing decent accuracy (but at this point in the mission, may not have done so yet). The larger uncertainty is in the distance to the nebula itself, so we might have a reasonable ability to model the starfield in 3D but not know where to place the nebula in it.
Assuming the bubble nebula is about 10,000 ly from Earth and even assuming the 3-D star field model (including the star creating the bubble) has been derived from Gaia data, the distances from Earth, to the stars that are close (in 3-D) to the bubble would still only be known to the nearest couple of hundred light years. Yet the bubble has a diameter of perhaps no more than 10 light years. I am still uncertain as to whether all the stars are indeed foreground stars, with no background stars, but I can certainly see the necessity to compress the distance range of the stars, if we are to accept the artistic impression that we are approaching the bubble to a distance of less than (I guess) 1,000 ly, from an initial distance of no more than 4,000 ly (based on the amount the bubble size increases in the video). Of course, we could be starting from Earth, with the camera zooming out as it speeds through space, much faster than light. Either way, I suppose that makes it a reverse time-lapse, as we arrive before we leave.

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Ann
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Re: APOD: Approaching the Bubble Nebula (2017 May 31)

Post by Ann » Thu Jun 01, 2017 12:48 am

Good thing Nitpicker interrupted me, or I would have made my third post in a row.
Orion with the Lambda Orionis Nebula at top.
Photo: Stanislav Volskiy.
The Bubble Nebula.
Photo: Yves Van den Broek




















When I was thinking of other spherical nebulas surrounding massive stars, I remembered the Lambda Orionis Nebula. But although there are signs that the Lambda Orionis Nebula had a quite sudden beginning, it lacks a sharp edge. Therefore, the Bubble Nebula and the Lambda Orionis Nebula look quite different to me.

I don't think that the Lambda Orionis Nebula is the product of a sudden eruption. More likely, the spherical shape of it is the result of the magnificent ionizing power of Lambda Orionis, Meissa, a great evolved O8-type star. The nebula is simply a measure of the reach of the ultraviolet photons emitted by Meissa. The rather blurry edge of the nebula is the result of the stellar wind hitting a denser environment.

The sharp edge of the Bubble Nebula speaks of another kind of origin.

Ann
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Re: APOD: Approaching the Bubble Nebula (2017 May 31)

Post by Nitpicker » Thu Jun 01, 2017 12:57 am

Ann wrote:Good thing Nitpicker interrupted me, or I would have made my third post in a row.
Nothing wrong with a hat trick. I've had several. It is easy to do from a time-zone far from the USA. (One also needs an over-developed urge to post, I suppose.)

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Re: APOD: Approaching the Bubble Nebula (2017 May 31)

Post by MarkBour » Fri Jun 02, 2017 5:48 pm

BDanielMayfield wrote:We didn't answer conclusively, but were merely noting what seemed like a reasonable possibility. A better look inside makes me reconsider. How about you neufer?

Bruce
Right. And that is all I was saying -- not very clearly -- that you both has indicated it was a reasonable possibility.

Ann, thanks for the other examples to consider. I appreciate your scholarly approach. And your take on it appears to be that these stars are prone to tantrums, so that becomes the more likely explanation.

The way it has been described to me, most stars will create some sort of a bubble in their natal cocoon, but I gather that this APOD is not a typical star at all. And I just now figured out that the Bubble Nebula is not the same as the Soap Bubble Nebula.
Mark Goldfain