APOD: M27: Not a Comet (2011 Sep 01)

[APOD Robot]

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 impressive color composite highlights details within the well-studied central region and fainter, seldom imaged features in the nebula's outer halo. It incorporates broad and narrowband images recorded using filters sensitive to emission from sulfur, hydrogen and oxygen atoms.

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[cketter]

Although the false color images are stunning, why do they never seem to have a color key? Which color represents sulfur? Which one oxygen? etc.

[Ann]

Less than an hour ago I posted a comment on this particular image elsewhere here at Starship Asterisk*. I'm going to paste that comment here:

Martin Pugh's portrait of M27 is the most beautiful one I've seen of this particular planetary. I really like the "dynamic details" of the nebula, too. A "bar" or "jet" which looks bright "inside" the main oval nebula becomes extremely dark outside. Suddenly the dark "jets" seem to hit something and break sharply. Two bluish curved "trails" are, well, "trailing" behind, as if the entire nebula was rotating clockwise. Really fascinating and beautiful!

I love the colors of this image. Please note the incredibly blue central star. If you follow one of the links of today's APOD, you can see that the estimated tempereature of central star of M28 is 85,000 Kelvin. Without a shred of a doubt, that temperature makes the central star of M27 by far the hottest star in this image.

Well done, Martin, and congratulations!

Ann

[Ann]

Although the false color images are stunning, why do they never seem to have a color key? Which color represents sulfur? Which one oxygen? etc.

Normally sulphur is shown as red, hydrogen as green and oxygen as blue in narrowband imaging of planetary nebulae. Judging from the appearance of today's APOD, I'd say that that is almost certainly how sulphur, hydrogen and oxygen have been mapped in today's APOD.

However, the narrowband imaging has been combined with ordinary RGB photography. The star colors are perfect, which they wouldn't have been in a purely narrowband image.

So to summarize, narrowband imaging has been used to bring out details of the nebula, and RGB photography has been used to give the background stellar field realistic colors.

Ann

[islader2]

IMHO, planetary nebulae were identified and named such before the 21st century, Robot. Thanx.

[orin stepanek]

Center star looks green! Or maybe it's my perception!

Click to view full size image

[owlice]

Orin, it looks green to me, too. It looks blue-green in the larger image, but still quite green.

[dlm378@charter.net]

What is the blue circle at nearly the perfect center of the picture?

[Ann]

Center star looks green! Or maybe it's my perception!

Click to view full size image

It's about as blue as this color. That's blue for my money!

Ann

[JohnD]

It's 1200 light years across, and glowing in the Uv from the central star remmnant.
Contrast with Monocerotis V838, whose 'light echoes' were seen by Hubble to illuminate a surrounding shell of debris (?)
These varied over months, while M27 has gone on shining steadily for more that 1200 years, as shown by the way its nebula, that wide, is evenly illuminated.
http://hubblesite.org/newscenter/archiv ... 0/image/b/
I know, the two stars are very different, one is very big and unstable , the other tiny and past its firework stage.
But I think it's an interesting contrast.

John

[Ann]

What is the blue circle at nearly the perfect center of the picture?

Perhaps you mean the central star that is illuminating the nebula?

Ann

[orin stepanek]

It's about as blue as this color. That's blue for my money!

Ann

That's right! Ann loves Blue That's OK Ann; toward the green side for me.

[Beyond]

When i first saw the star in the middle, i thought - Ann's gonna love this picture with the big blue star in the middle. Then i start reading the posts and got to orin's stating it was green. So i went back and looked again and Lo and Behold, it did look kinda greenish. So i clicked on it to bring up the bigger picture, and it looked blue, but with a hint of greenish to it. Hmm... It looks like orin has a good 'power of suggestion'.

edit: Now i find that owlice sees green also. Gee - thanks you two Now i see it between Ann's blue and orin's green.

[astrolabe]

Hello All,

When I saw this image my first thought was whether or not the spectral association of the elements of a main subject also affected the appearance of stars (and Galaxies?) within the surrounding field. I thought that it must be so and was then verified here. Thanks.