APOD: The Light, the Dark, and the Dusty (2020 Mar 05)

[APOD Robot]

The Light, the Dark, and the Dusty

Explanation: This colorful skyscape spans about four full moons across nebula rich starfields along the plane of our Milky Way Galaxy in the royal northern constellation Cepheus. Near the edge of the region's massive molecular cloud some 2,400 light-years away, bright reddish emission region Sharpless (Sh) 155 is left of center, also known as the Cave Nebula. About 10 light-years across the cosmic cave's bright walls of gas are ionized by ultraviolet light from the hot young stars around it. Dusty blue reflection nebulae, like vdB 155 at lower right, and dense obscuring clouds of dust also abound on the interstellar canvas. Astronomical explorations have revealed other dramatic signs of star formation, including the bright red fleck of Herbig-Haro (HH) 168. Below center in the frame, the Herbig-Haro object emission is generated by energetic jets from a newborn star.

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[Mountainjim62]

Where did everybody go?

[Fred the Cat]

As our own world moves through the interstellar medium will it stir up some new information Detecting basic moleculess has helped but it seems a tenuous process.

[Ann]

I've been lazy. I should have said that this is a very fine picture of a very interesting nebula and a site of ongoing star formation.

The Cave Nebula. Photo and copyright: Casey Good.

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The Cave Nebula. Copyright: Steve Cannistra.

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While I really like today's APOD, I think Steve Cannistra's image provides some important information on which parts of the nebula are really bright and which are dark. As you can see, it is the rim of one of the dust pillars that is really bright, and this is where most of the action is taking place.

Sh2-155, the Cave Nebula. Image Credit & Copyright: Bill Snyder (Bill Snyder Photography).

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The central region of the Trifid Nebula (M20). Image: Subaru Telescope (NAOJ), Hubble Space Telescope, Martin Pugh; Processing: Robert Gendler.

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In the picture by Bill Snyder, you can clearly see a "pocket" or a "bright hole" near the top of the bright-rimmed dust pillar where new stars are forming.

The Cave Nebula reminds me a little of the Trifid Nebula. In the Trifid Nebula, the "pocket" where stars were forming has "burst open", revealing hot stars. And one wall of the dust feature is illuminated by the central star.

The Trifid Nebula is believed to be a very young nebula and site of massive star formation, about 300,000 years. The Cave Nebula, by contrast, is believed to be a site of star formation where new waves of star formation have been triggered by old ones.

It is tempting to think of the bright orange star as a once massive O-type star that has since turned into a red supergiant. Because the star is so centrally placed in the middle of the nebula, it is easy to think that the central cavity has been blown by the powerful stellar wind of a massive blue star which has since swollen into a red supergiant. But the orange star's parallax places it closer to us than the blue stars in the picture, and its proper motion is very different.

So it would seem that the orange star is a foreground object after all.

Ann