APOD: The Elephant's Trunk in Cepheus (2024 Nov 21)

[APOD Robot]

The Elephant's Trunk in Cepheus

Explanation: Like an illustration in a galactic Just So Story, the Elephant's Trunk Nebula winds through the emission region and young star cluster complex IC 1396, in the high and far off constellation of Cepheus. Also known as vdB 142, this cosmic elephant's trunk is over 20 light-years long. The detailed telescopic view features the bright swept-back ridges and pockets of cool interstellar dust and gas that abound in the region. But the dark, tendril-shaped clouds contain the raw material for star formation and hide protostars within. Nearly 3,000 light-years distant, the relatively faint IC 1396 complex covers a large region on the sky, spanning over 5 degrees. This rendition spans a 1 degree wide field of view though, about the angular size of 2 full moons.

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[Ann]

Well, in the Just So story, the Baby Elephant got his trunk when the crocodile pulled on his nose, but the Elephant's Trunk Nebula got its trunk because the stellar wind and torrent of ultraviolet photons from a hot O-type binary star are bearing down on it!

On the Earth, winds are blowing 'sideways', but in nebulas, winds are bearing straight down on hapless 'trunks'! Credit: Azmeyart.

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Just so? Maybe not so. Credit: Rudyard Kipling.

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When everything else has been blown away by the terrifying power of the O-type star, the trunk - that is, the pillar - is the last man standing!

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It's hot in here! I'm the last man standing. Credit: Ray Majoran

Last man standing. Credit: Bernard Herrera.

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What makes the Elephant Trunk unusual compared with most other cosmic pillars is that we can clearly see that stars are being born inside the pillar's "head". They are born in there because the gas at the top of the Elephant's Trunk is being compressed by the stellar wind and ultraviolet light from the O-type star, and as gas gets denser, stars can be born from it.

Small stars are peeking out from inside the cavity in the Elephant's Trunk Nebula at upper left. Credit: KPNO/NOIRLab/NSF/AURA/Jeff Hapeman/Adam Block

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Let's admire Alan Dyer's portrait of IC 1396, where the Elephant's Trunk Nebula is located:

IC-1396-Mu-Cephei-92mm-5DII[1].jpg

IC 1396, with giant and very cool red giant Mu Cephei at upper left.
Where is the Elephant's Trunk Nebula? Oh, it's immediately to the right
of hot central O-type star HD 206267! Credit: Alan Dyer.

So where in the sky is the Elephant's Trunk Nebula located? After all, it's good to know your neighbors!

It's good to know your neighbors!

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IC 1396, home of the Elephant's Trunk Nebula in Cepheus, is located north of the North America Nebula in Cygnus. Credit: Pere Sanz.

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Ann

[Ann]

I've got to say something more about Mu Cephei, the red supergiant star seemingly located on the northeastern rim of IC 1396, but probably located much farther away.

IC-1396-Mu-Cephei-92mm-5DII[1].jpg

Reddish-pink emission nebula IC 1396 with bloated red supergiant Mu Cephei
seemingly located at the northeastern (upper left) rim of it. Credit: Alan Dyer.

I'm usually not very interested in red supergiant stars. But Mu Cephei is something else.

The Gaia parallax of Mu Cephei is almost impossibly tiny, 0.1190 milliarcseconds, which corresponds to a distance of some 27,000 light-years!! Coupled with its apparent V luminosity of 4.08, making it a fourth magnitude star, a distance of 27,000 light-years would correspond to an absolute V luminosity of some 1,300,000 solar luminosities!!! That's crazy!

And that's not all. The infrared, I, magnitude of Mu Cephei is 0.22. Coupled with a distance of 27,000 light-years, that makes for an infrared luminosity of some 45 million solar luminosities!!! Is that even possible?

(And the far infrared (K) luminosity of Mu Cephei is -1.72, which at a distance of 27,000 light-years would make it emit some 270 million times the far infrared luminosity of the Sun!!!)

Admittedly, the uncertainty of the Gaia parallax is larger than the parallax itself. If we make the parallax as large as the Gaia uncertainty will allow us, at 0.3827 milliarcseconds, then the distance to Mu Cephei is "only" some 8,500 light-years. That's still very far away, and very much farther away than almost any other fourth magnitude star in the sky. And even at a distance of "only" 8,500 light-years, the absolute I magnitude of Mu Cephei is still more than four million times that of the Sun.

Amazing!

Ann

[Christian G.]

I'm usually not very interested in red supergiant stars.

Mu_Cephei_%22The_Garnet_Star%22_2023_(Ha_and_OIII).png

[Ann]

I'm usually not very interested in red supergiant stars.

Click to view full size image

Ha ha, Christian, that's so funny!

Ann