APOD: NGC 7635: The Bubble Nebula (2016 Apr 22)

[APOD Robot]

NGC 7635: The Bubble Nebula

Explanation: Blown by the wind from a massive star, this interstellar apparition has a surprisingly familiar shape. Cataloged as NGC 7635, it is also known simply as The Bubble Nebula. Although it looks delicate, the 7 light-year diameter bubble offers evidence of violent processes at work. Above and left of the Bubble's center is a hot, O-type star, several hundred thousand times more luminous and around 45 times more massive than the Sun. A fierce stellar wind and intense radiation from that star has blasted out the structure of glowing gas against denser material in a surrounding molecular cloud. The intriguing Bubble Nebula and associated cloud complex lie a mere 7,100 light-years away toward the boastful constellation Cassiopeia. This sharp, tantalizing view of the cosmic bubble is a composite of Hubble Space Telescope image data from 2016, released to celebrate the 26th anniversary of Hubble's launch.

<< Previous APOD

This Day in APOD

Next APOD >>

[/b]

[bystander]

http://asterisk.apod.com/viewtopic.php?p=256689#p256689

[Ann]

The Bubble Nebula is a fascinating structure, and the link posted by bystander leads to some hugely interesting information about this iconic wind-blown sphere.

For example, let's compare the Bubble Nebula with the well-known Trifid Nebula. The Trifid Nebula is larger - according to wikipedia, a star forming part of the Trifid Nebula is located about 8 light-years from the ionizing central star, while the entire diameter of the Bubble Nebula is about 7 light-years. But the central star of the Bubble Nebula is about 45 times more massive than the Sun, whereas the central star of the Trifid Nebula is "only" a bit more than 20 times the mass of the Sun.

We may also compare the Bubble Nebula with the inner part of the Rosette Nebula. In today's APOD, we can clearly see some blue fluff to the lower right of the central star. There is a lot of similar(?) blue fluff in the Rosette Nebula.

One fascinating detail in today's APOD is that we may be seeing one of those famous "fingers" of dust carved out by massive stars from a face on, or fingerprint on, perspective. Seemingly inside the Bubble Nebula (but more likely behind it) is a yellow structure, seen at about 12 o'clock. There is a perfect yellow ring in that structure, which reminds me of a volcanic caldera. It's like looking down into the smoking opening of a mountain of gas and dust.

This is a fine APOD, very close up and personal!

Ann

[Boomer12k]

Stupendous... Hubble never ceases to amaze me...

:---[===] *

[wjohnson]

Clicking on the Cassiopeia link, I'm glad to see there are at least some folks in Hawaii that are interested in astronomy!

[heehaw]

Um. Above and to the left...O-type star. Um. Do I take it that the two obvious stars (with the diffraction patterns) are foreground objects? Is the O star at the bottom tip of the orange nebulosity? If so, why is the bubble not centered on that star? Uneven interstellar resistance as it expanded? If so, why so beautifully circular?

[Gus]

Given a diameter of seven lys, are there any other stars located inside the Bubble Nebula? If so how would the "intense radiation" from that O-type star affect them?

[BobStein-VisiBone]

...why is the bubble not centered on that star? Uneven interstellar resistance as it expanded? If so, why so beautifully circular?

I wondered the same thing, heehaw. Thanks for noticing the real origin of the bubble is the whiter star, not the pink ones.

I think maybe it's not so beautifully circular. See that bulge on the right? Centered on the real "star" of this show, the bubble from the 3 o'clock position to 6 o'clock is roughly equidistant from the star, i.e. circular. But the rest of the bubble is smooshed in to varying degrees.

Perhaps here is where the bubble would be if it weren't retarded by cold gasses.

[Ann]

...why is the bubble not centered on that star? Uneven interstellar resistance as it expanded? If so, why so beautifully circular?

I wondered the same thing, heehaw. Thanks for noticing the real origin of the bubble is the whiter star, not the pink ones.

I think maybe it's not so beautifully circular. See that bulge on the right? Centered on the real "star" of this show, the bubble from the 3 o'clock position to 6 o'clock is roughly equidistant from the star, i.e. circular. But the rest of the bubble is smooshed in to varying degrees.

Perhaps here is where the bubble would be if it weren't retarded by cold gasses.

I like your illustration, BobStein-Visibone. You are quite right that the bubble is "smooshed in" to varying degrees, depending on how much gas and dust was in the way when the bubble wanted to expand.

However, the ionizing star of the bubble is indeed the pink star at 10 o'clock inside the bubble. There is no white-looking star in today's APOD. Guess what I dislike most about typical mapped color astrophotograpy? It is that it makes blue stars look pink.

That pink star, SAO 20575, is indeed a blisteringly hot O-type star. It is intrinsically blue, although reddened by dust. But in spite of the reddening, there is no way it would look pink to our eyes. No way.

Are the other stars that seem to be inside the bubble foreground stars, or are they related to SAO 20575 and located at more or less the same distance? Unfortunately I can't say, because my software tells me almost nothing about those other stars - certainly not how far away they are! But if they are actually inside the bubble and not too far way from the mighty O-star, will they be damaged by it?

I'd say no. Stars are typically born in clusters, and there is always at least one star in there that is hotter and more "evil" than the others. But as far as I know, the other stars in the cluster typically survive just fine. On the other hand, I think it is indeed possible that the terrible wind of a massive O-star can destroy the protoplanetary disks of other stars in its vicinity, thus (perhaps) making those stars barren, with no planets.

Ann

[BobStein-VisiBone]

Thanks for the correction, Ann! So our protagonist is the pinkly-rendered star with diffraction lines just to the left of my crosshairs? How sure are you this is the source of the stellar winds that blew this bubble?

There is some bright whitish (rendered) source of light at the tip of the yellowish goop. Or is that just reflection from the star?

You said before "we can see clearly some blue fluff to the lower left of the central star." That makes sense if the whitish thing is the star, but not the pinkish thing. If it was the pinkish star I'd say there's blue fluff below and right. And if that's the case then we see lots of little new evidence of stellar wind sculpturing.

[neufer]

[b][color=#0000FF]NGC 7635 Parallel 3D by JP Metsavainio[/color][/b]

---

[b][color=#0000FF]NGC 7635 Cross Vision 3D by JP Metsavainio[/color][/b]

---

<<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. Direct spectroscopy yields a spectral class of O6.5 and an effective temperature around 37,500K.>>

Apparent magnitude (V) 8.67
Absolute magnitude (MV) -5.5
Distance 2,400 pc
Mass 44 M☉
Radius 15 R☉
Luminosity 398,000 L☉

[Ann]

Thanks for the correction, Ann! So our protagonist is the pinkly-rendered star with diffraction lines just to the left of my crosshairs? How sure are you this is the source of the stellar winds that blew this bubble?

There is some bright whitish (rendered) source of light at the tip of the yellowish goop. Or is that just reflection from the star?

You said before "we can see clearly some blue fluff to the lower left of the central star." That makes sense if the whitish thing is the star, but not the pinkish thing. If it was the pinkish star I'd say there's blue fluff below and right. And if that's the case then we see lots of little new evidence of stellar wind sculpturing.

You're right! My bad!

The whitish stuff is gas evaporating off a dusty pillar due to the harsh radiation from a hot star.

There might well be a star forming at the tip of that pillar, but it is certainly not an O-type star. To the very best of my knowledge, truly massive stars are not born inside evaporating pillars of dust, at least not when the pillars can be thought of as the tattered remnants of a once-fertile site of star formation.

Ann