Starship Asterisk*

M27: Not a Comet

Explanation: While hunting for comets in the skies above 18th century France, astronomer Charles Messier diligently kept a list of the things he encountered that were definitely not comets. This is number 27 on his now famous not-a-comet list. In fact, 21st century astronomers would identify it as a planetary nebula, but it's not a planet either, even though it may appear round and planet-like in a small telescope. Messier 27 (M27) is an excellent example of a gaseous emission nebula created as a sun-like star runs out of nuclear fuel in its core. The nebula forms as the star's outer layers are expelled into space, with a visible glow generated by atoms excited by the dying star's intense but invisible ultraviolet light. Known by the popular name of the Dumbbell Nebula, the beautifully symmetric interstellar gas cloud is over 2.5 light-years across and about 1,200 light-years away in the constellation Vulpecula. This spectacular color image incorporates broad and narrowband observations recorded by the 8.2 meter Subaru telescope.

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This is awesome... and the "ancient man" face... inside just to right of center... a "monster" lurks out of the left side, his arm reaching towards the "old man"...
Broad and Narrow Bands, eh... a great combo here. The different layers and outer "aura" in red is just so cool.
A "cosmic egg" in space... maybe to seed gas and elements for another star some day...

Even with my cheap DSI camera you can see some "puffs" and other features...

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That's really good, Boomer!!!

APOD Robot wrote:
Messier 27 (M27) is an excellent example of a gaseous emission nebula created as a sun-like star runs out of nuclear fuel in its core.

I very much doubt that the progenitor of the Dumbbell Nebula was any less massive than Sirius, and it may well have been as massive as Regulus. Surely these stars are not sun-like? Check out Sirius and Vega in this fascinating although unfortunately Russian-language youtube video, which does have English subtitles.
Anyway, today's APOD is for starsurfer!

Ann

Sun-like in the sense that they eventually form PNs, perhaps? That is, they have a mass range between 0.8 and 8 solar masses (according to Wikipedia).

Are we able to subscribe to an e-mail list, so that we get this in our inbox each morning?

Ann wrote:That's really good, Boomer!!!

APOD Robot wrote:
Messier 27 (M27) is an excellent example of a gaseous emission nebula created as a sun-like star runs out of nuclear fuel in its core.

I very much doubt that the progenitor of the Dumbbell Nebula was any less massive than Sirius, and it may well have been as massive as Regulus. Surely these stars are not sun-like? Check out Sirius and Vega in this fascinating although unfortunately Russian-language youtube video, which does have English subtitles.

Click to play embedded YouTube video.

Click to view full size image

Source: https://www.surfertoday.com/surfing/123 ... wars-world

Anyway, today's APOD is for starsurfer!

Ann

Thanks for the nice and amusing picture Ann!
I would say today's APOD is for the whole world but I do have a fondness for haloes around planetary nebulae (particularly unphotographed ones)!
I think I first saw the halo around M27 about 10 years ago maybe in an image by Tony Hallas. I wonder if M27 has cometary knots?

Maybe my imagination but there seems to be a bit more prominent line of gas going from lower left to upper right through the middle of the nebula. Can we tell if this is equatorial for the star remnant, polar, or neither?

Nitpicker wrote:Sun-like in the sense that they eventually form PNs, perhaps? That is, they have a mass range between 0.8 and 8 solar masses (according to Wikipedia).

That is how I read "sun-like" in this context too.

Planetary Nebulae wrote:When a star like our Sun comes to age, having longly burned away all the hydrogen to helium in its core in its main sequence phase, and in a later evolutionary state following the red giant stadium (the "Horizontal Branch" state, for their places in the Color-Magnitude Diagram (CMD) or Hertzsprung-Russell Diagram (HRD)), also the helium to carbon and oxygen, its nuclear reactions come to an end in its core, while helium burning goes on in a shell. This process makes the star expanding, and causes its outer layers to pulsate as a long-periodic Mira-type variable, also called AGB star (for "Asymptotic Giant Branch" star, also for their places in the CMD or HRD), which becomes more and more unstable, and loses mass in strong stellar winds. The instability finally causes the ejection of a significant part of the star's mass in an expanding shell. The stellar core remains as an extremely hot, small central star, which emits high energetic radiation. At this stage, the central stars of planetary nebulae (CSPN), or Planetary Nebulae Nuclei (PNN), are among the hottest stars observed in the universe. Observation shows that most of the central stars are within a narrow mass range of 0.5 to 0.7 solar masses.

I wonder how efficient these Sun-like stars are in returning left over gas (H & He) and metals (all other elements) back to space. Stars on the low 0.8 initial mass end haven't had nearly enough time to form PNs yet. The more massive a star is, the shorter its main sequence lifetime, but also the rarer the star is. And, since the PN phase is so fleeting, I wonder what can be inferred about the initial masses of the PN stars in that "narrow mass range of 0.5 to 0.7 solar masses." This suggests that normal stars are very efficient at returning all their unused gas back to space. They also must send a lot of C, N and O back to space too.

Bruce

Edited to strike out false statement. I was thinking 0.08, not 0.8 solar masses.

There appear to be polar jets from the 2 and 8 o'clock positions. My imagination?

BDanielMayfield wrote:

Nitpicker wrote:Sun-like in the sense that they eventually form PNs, perhaps? That is, they have a mass range between 0.8 and 8 solar masses (according to Wikipedia).

That is how I read "sun-like" in this context too.

Planetary Nebulae wrote: Observation shows that most of the central stars are within a narrow mass range of 0.5 to 0.7 solar masses.

That's really interesting, and it does suggest that Stein 2051 B is in fact a somewhat massive white dwarf.

I wonder how efficient these Sun-like stars are in returning left over gas (H & He) and metals (all other elements) back to space. Stars on the low 0.8 initial mass end haven't had nearly enough time to form PNs yet. The more massive a star is, the shorter its main sequence lifetime, but also the rarer the star is. And, since the PN phase is so fleeting, I wonder what can be inferred about the initial masses of the PN stars in that "narrow mass range of 0.5 to 0.7 solar masses." This suggests that normal stars are very efficient at returning all their unused gas back to space. They also must send a lot of C, N and O back to space too.

Bruce

Edited to strike out false statement. I was thinking 0.08, not 0.8 solar masses.

I don't think you should have struck that out. First of all, I think that the consensus among astronomers is that stars of only 0.08 solar masses will either never turn into planetary nebulas, or, alternatively, no one has the faintest idea what these tiny little critters will do when they are ready to hang up their sun hats some trillions or quadrillions years from now.

Second, as for stars of an initial mass of 0.8 solar masses, I believe that extremely few of them have had time to turn into white dwarfs surrounded by planetary nebulas.

I found an admittedly terribly old paper by Baum, W. A., Hiltner, W. A., Johnson, H. L., & Sandage, A. R, published in Astrophysical Journal, vol. 130, p.749.The paper is from 1959. Yes, I know. But here's part of what they wrote in their abstract:

Baum, W. A., Hiltner, W. A., Johnson, H. L., & Sandage, A. R, wrote:

Comparison of the resulting color-magnitude diagram of M13 with the main sequence of the Hyades gives a distance modulus to M13 of m - M = 14.3 ± 0.3. The corresponding absolute magnitude of the RR Lyrae stars in M13 is M_v = +0.3 ± 0.3. The turnoff point of the main sequence occurs at M_bol = +4.1 ± 0.3, which corresponds to an age of about 10¹⁰ years, according to the models of Hazelgrove and Hoyle.

Yes, I know - this paper is just too old to be taken all that seriously. Let's look at what it said, nevertheless. The authors said that M13 is 10¹⁰ years, which would be the same as 10 billion years. Not too shabby. However,Wikipedia says that the average luminosity of RR Lyrae stars is about +0.75, or about 40 to 50 times brighter than the Sun. That's a lot fainter than the 1959 estimate of an absolute magnitude for the M13 RR Lyrae stars of +0.3. (I must protest against Wikipedia, though: Vega, the well-known first-magnitude A0-type main sequence star, has an absolute visual magnitude of 0.6036 ± 0.0060, which corresponds to 47.71 ± 0.26 solar luminosities. So the average luminosity of RR Lyrae stars, if they are as bright as Vega, should be +0.6, not +0.75.)
Well, if that 1959 paper overestimated the brightness of the M13 RR Lyrae stars, it would also have overestimated the brightness of the M13 stars at the turning point of the main sequence. Baum, Sandage et.al. estimated that the absolute magnitude of the M13 stars at the turning point of the main sequence was +4.1 ± 0.3.

Okay, but guess what the absolute magnitude of the Sun is? It is 4.83, a lot fainter than the M13 stars that are just about to leave the main sequence! And if we say that the paper overestimated the RR Lyrae stars by 0.45 magnitudes and overestimated the main sequence stars by the same amount, then the absolute magnitude of the stars about to leave the main sequence in M13 is about 4.55 ± 0.3, still at least as bright as the Sun and probably brighter!

And according to Wikipedia, the RR Lyrae stars themselves are evolved stars that started out as main sequence stars of 0.8 solar masses. So the 0.8 solar mass stars in M13, which is 11.65 billion years old, have not yet turned into white dwarfs with planetary nebulas. The 0.8 solar mass stars may not be Methuselahs, but I believe most of them are still going pretty strong!

Ann

Bob King has a recent, related article at Sky & Telescope online, "Nights of the Living Dead — What Stars Leave Behind."

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