APOD: A Beautiful Trifid (2021 Aug 12)

[APOD Robot]

A Beautiful Trifid

Explanation: The beautiful Trifid Nebula is a cosmic study in contrasts. Also known as M20, it lies about 5,000 light-years away toward the nebula rich constellation Sagittarius. A star forming region in the plane of our galaxy, the Trifid does illustrate three different types of astronomical nebulae; red emission nebulae dominated by light from hydrogen atoms, blue reflection nebulae produced by dust reflecting starlight, and dark nebulae where dense dust clouds appear in silhouette. But the red emission region roughly separated into three parts by obscuring dust lanes is what lends the Trifid its popular name. Pillars and jets sculpted by newborn stars, below and left of the emission nebula's center, appear in famous Hubble Space Telescope close-up images of the region. The Trifid Nebula is about 40 light-years across. Just too faint to be seen by the unaided eye, it almost covers the area of a full moon in planet Earth's sky.

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[Ann]

M20-SHO-crop-Rev-5-RGB-Ha-OIII-RiDK-700-19-July-2021-1024[1].jpg

The Trifid Nebula. Photo: Mike Selby.

Trifid nebula Mike Selby annotated.png

Trifid Nebula annotated.

What a beautiful APOD!

Here are a few annotations:

1) HD 164492, spectral class O7.5V, ionizing star of the Trifid Nebula. It is the brightest of a small grouping of stars, of which one is supposed to be an evolved supergiant star! Really...?

2) Dust pillar close to the small group of hot stars. Note that the dust pillar has a bright rim. It is directly illuminated by the stars.

3) Small jet protruding from a fat dust pillar. The jet has been emitted by a newborn star. Actually there are two jets!

4) HD 164514, an evolved supergiant star of spectral class A7Iab/b. Note the yellow color of this star, whose intrinsic color is probably as white as that of Summer Triangle star Altair. This star is the probable source of the blue reflection nebula surrounding the Trifid, and the star's own yellow color testifies to the fact that much of its blue light has been scattered by dust.

5) "Foreground dust" darkening and reddening the blue reflection nebula to a greenish gray color.

Cocoon Nebula Marcel Drechsler.png

Very deep view of the Cocoon Nebula. Photo: Marcel Drechsler.

The Trifid Nebula shows some similarities with the Cocoon Nebula. Many images show the Cocoon Nebula to be "all red", but many also show a faint outer blue rim around it. The very deep image of the Cocoon that I have posted here shows a very large blue reflection nebula surrounding the Cocoon. This reflection nebula is really there, but it is very faint.

My point is that the blue reflection nebula of the Trifid Nebula is not exclusively the product of the yellow-looking reddened A-type supergiant star immediately to the north of the Trifid. Instead, we should think of the small grouping of stars in the center of the Trifid as providing not only the ultraviolet light needed to ionize the red lobes of the Trifid, but also contributing significantly to the blue light surrounding this famous nebula.

Ann

[beryllium732]

Very interesting Ann!

Like the detailed explanations and markings! Much appreciated!

Does anyone know the origins of the Nebula? Is it neutral hydrogen floating freely that just started star production because of disturbance or was it created by a supernova remnant? What's the size of the nebulae? It must be very packed if it contains several thousands of protostars.

[Ann]

Very interesting Ann!

Like the detailed explanations and markings! Much appreciated!

Does anyone know the origins of the Nebula? Is it neutral hydrogen floating freely that just started star production because of disturbance or was it created by a supernova remnant? What's the size of the nebulae? It must be very packed if it contains several thousands of protostars.

The size of the nebula is about 40 light-years in diameter, as stated in the caption of the APOD.

But where does the nebula come from? It appears to be a part of a much larger nebular complex in Sagittarius, which also includes the Lagoon Nebula (M8) and NGC 6559.

The Trifid Nebula at top right, the Lagoon Nebula at center left and the NGC 6559 complex at top left. Photo: Christian vd Berge (DSLR Astrophotograhy).

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So in all probability there is (and there certainly has been in the past) a large reservoir of gas and dust in this part of the Milky Way, and the nebulas have condensed out of this gas.

But what makes nebulas form, generally speaking? My amateur understanding tells me that nebulas typically form in, or often at the tip of, long strings or lanes of dust:

Infrared image of the Cocoon Nebula by ESA's Herschel Telescope. The Cocoon nebula itself has been mapped as blue. Note the long stretch of dust that the Cocoon Nebula appears to be attacked to. The nebula seems to have formed at the tip of a long string of cosmic dust.

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A cosmic snake NASA JPL caltech.png

A cosmic serpent made of dust. The bright deep red object is a massive
star in the process of forming. Photo: NASA, JPL-Caltech/S. Carey

Stars are forming at the top of two pillars of gas and dust in teh Carina Nebula, emitting jets in the process. Photo: http://hubblesite.org/newscenter/archive/releases/2010/13/image/a/

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So what causes dust to form such long strings or lanes? Dunno... the rotation of the Milky Way itself? Magnetic forces?

Ann

Edit: Better correct myself before Chris corrects me. The long dusty strings or lanes are primarily made of gas, not dust. We just see the dust rather than the gas because the dust is opaque, whereas the gas is usually invisible and colorless, except when it's made to emit light (usually red) in emission nebulas. And stars form from gas, not from dust.

[NCTom]

Yep, thanks again, Ann. Most appreciative for all the extra information and supportive photos.

[Chris Peterson]

Edit: Better correct myself because Chris corrects me. The long dusty strings or lanes are primarily made of gas, not dust. We just see the dust rather than the gas because the dust is opaque, whereas the gas is usually invisible and colorless, except when it's made to emit light (usually red) in emission nebulas. And stars form from gas, not from dust.

I think these very dusty regions have something like 1-2% of their mass provided by dust. Of course, dust is much more massive than hydrogen, so that means even less if we consider the number of atoms. So yeah, mostly what we have here is hydrogen. What is interesting, though, is that big massive (mostly invisible) clouds of hydrogen have a hard time forming stars (although it obviously happened early in the Universe). Dust, even in these small concentrations, seems to be very important for catalyzing the process of star formation. People are working on understanding that process, but there are still a lot of questions.

[johnnydeep]

Ah, the unfortunately named Trifid nebula. It's name means "three lobes", which I supposed is all that could be discerned when it was discovered by Charles Messier in 1764, but there are clearly at least 4 well defined lobes visible in all modern pictures. Oh well, I still have a soft spot for it because of the movie "The Day Of The Triffids", even though this use of "triffid" has nothing to do with the nebula! See https://en.wikipedia.org/wiki/Triffid

[Fred the Cat]

Ah, the unfortunately named Trifid nebula. It's name means "three lobes", which I supposed is all that could be discerned when it was discovered by Charles Messier in 1764, but there are clearly at least 4 well defined lobes visible in all modern pictures. Oh well, I still have a soft spot for it because of the movie "The Day Of The Triffids", even though this use of "triffid" has nothing to do with the nebula! See https://en.wikipedia.org/wiki/Triffid

Agreed! SF about evolved plants should get more attention. Perhaps, “Four-Leafed Cleaver” – The day our luck ran out?

[johnnydeep]

Ah, the unfortunately named Trifid nebula. It's name means "three lobes", which I supposed is all that could be discerned when it was discovered by Charles Messier in 1764, but there are clearly at least 4 well defined lobes visible in all modern pictures. Oh well, I still have a soft spot for it because of the movie "The Day Of The Triffids", even though this use of "triffid" has nothing to do with the nebula! See https://en.wikipedia.org/wiki/Triffid

Agreed! SF about evolved plants should get more attention. Perhaps, “Four-Leafed Cleaver” – The day our luck ran out?

Good links. Of all those books, I think I've only read two: Dragon's Egg (on my own) and Rapaccini's Daughter (in high school). Dragon's Egg is probably my favorite "hard scifi" book of all time. I also liked the sequel Starquake though the novelty of the mind-blowing idea of life on (and eventually off!) a neutron star had somewhat worn off.

[orin stepanek]

.jpg

M20-SHO-crop-Rev-5-RGB-Ha-OIII-RiDK-700-19-July-2021-1024.jpg

like a beautiful Pansy!

[neufer]

Three flashing Geissler-style tubes arranged in a Y configuration

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<<The flux capacitor, which consists of a rectangular-shaped compartment with three flashing Geissler-style tubes arranged in a "Y" configuration, is described by Doc as "what makes time travel possible." The device is the core component of the time machine.

As the time machine nears 88 mph, light coming from the flux capacitor begins pulsing more rapidly until it becomes a steady stream. Doc originally conceived the idea for the flux capacitor on November 5, 1955, when he slipped on the edge of his toilet while hanging a clock in his bathroom and hit his head on the sink.

Although the films do not describe exactly how the flux capacitor works, Doc mentions at one point that the stainless steel body of the DeLorean has a direct and influential effect on the "flux dispersal", but he is interrupted before he can finish the explanation. The flux capacitor requires 1.21 gigawatts of electrical power to operate, which is roughly equivalent to the power produced by 15 typical commercial airplane jet engines.>>