APOD: CG4: The Globule and the Galaxy (2023 Jan 04)

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APOD: CG4: The Globule and the Galaxy (2023 Jan 04)

Post by APOD Robot » Wed Jan 04, 2023 5:06 am

Image CG4: The Globule and the Galaxy

Explanation: Can a gas cloud eat a galaxy? It's not even close. The "claw" of this odd looking "creature" in the featured photo is a gas cloud known as a cometary globule. This globule, however, has ruptured. Cometary globules are typically characterized by dusty heads and elongated tails. These features cause cometary globules to have visual similarities to comets, but in reality they are very much different. Globules are frequently the birthplaces of stars, and many show very young stars in their heads. The reason for the rupture in the head of this object is not yet known. The galaxy to the left of the globule is huge, very far in the distance, and only placed near CG4 by chance superposition.

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Re: APOD: CG4: The Globule and the Galaxy (2023 Jan 04)

Post by JoeinCT » Wed Jan 04, 2023 6:39 am

I was amazed at how much the globule looks like a sandworm from Frank Herbert's DUNE about to eat a spice harvester.

Joe

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Re: APOD: CG4: The Globule and the Galaxy (2023 Jan 04)

Post by jagganath69 » Wed Jan 04, 2023 7:34 am

I'm curious: what's the galaxy's designation ?

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Re: APOD: CG4: The Globule and the Galaxy (2023 Jan 04)

Post by daddyo » Wed Jan 04, 2023 8:09 am

JoeinCT wrote: Wed Jan 04, 2023 6:39 am I was amazed at how much the globule looks like a sandworm from Frank Herbert's DUNE about to eat a spice harvester.

Joe
Or perhaps there are a few more planet killers out there (galaxy even) https://memory-alpha.fandom.com/wiki/Planet_killer

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Re: APOD: CG4: The Globule and the Galaxy (2023 Jan 04)

Post by Ann » Wed Jan 04, 2023 8:22 am

Please! The link, the featured photo, took us to a Facebook page, and since I don't have Facebook, I was unable to find any information at all about the image. Surely the links to information about the APOD in question should go to pages that are open to all?

So all I can do is compare the APOD with an image where I do have technical information:


Let's start with Terry Robison's image, for which I have exposure details:

Red 28 X 600 seconds

Green 27 X 600 seconds

Blue 32 X 600 seconds

Lum 66 X 900 seconds

Total Exposure: 31.0 hours

So Terry Robison took 28 exposures, each one lasting 600 seconds, through a red filter. He took four more exposures, 32, through a blue filter, and one less, 27, through a green filter. See a larger version of Robison's image here.

One thing that is immediately obvious about Terry Robison's image is that the cometary globule does not look red at all. This tells us two things. The red light in the globule is all ionized hydrogen, Hα, and when you don't use an Hα filter, which Robison didn't, the Hα is so faint that it barely shows up at all.

But the Hα is real all right, just faint. Note that the red light in the APOD is strongest in the "maw" of the globule, as if the ionized light mostly comes from inside. But there are no obvious signs of any star formation in CG4. The red light must originate from hydrogen in the globule being ionized by ultraviolet light entirely from the outside.

Where is the ionizing ultraviolet light coming from? I was unable to find an image showing you both the source of ionization and the (more or less) exact position of the globule, but the image below will give you an idea:

Vela supernova remnant annotated Robert Gendler Roberto Colombari.png
Vela supernova remnant and bright star Gamma Velorum.
Image: Robert Gendler & Roberto Colombari.

In the image, I have marked both the position of the Vela supernova remnant and bright star Gamma Velorum, which is in fact an extremely hot and harshly ultraviolet star. I have also marked, near the right edge of the image, a group of four stars. The brightest of these is itself a hot ultraviolet star.

If you were to move off the right edge frame of the picture, for a distance slightly less than the distance between Gamma Velorum and the group of four stars, you would come to the position of cometary globule CG4.

In other words, this globule is probably affected by ultraviolet light from the Vela supernova remnant as well as from Gamma Velorum.

Ann
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Re: APOD: CG4: The Globule and the Galaxy (2023 Jan 04)

Post by De58te » Wed Jan 04, 2023 9:44 am

jagganath69 wrote: Wed Jan 04, 2023 7:34 am I'm curious: what's the galaxy's designation ?
According to the Wikipedia page for CG 4, the spiral galaxy to be 'devoured' is designated, ESO 257-19.

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Re: APOD: CG4: The Globule and the Galaxy (2023 Jan 04)

Post by johnnydeep » Wed Jan 04, 2023 2:39 pm

daddyo wrote: Wed Jan 04, 2023 8:09 am
JoeinCT wrote: Wed Jan 04, 2023 6:39 am I was amazed at how much the globule looks like a sandworm from Frank Herbert's DUNE about to eat a spice harvester.

Joe
Or perhaps there are a few more planet killers out there (galaxy even) https://memory-alpha.fandom.com/wiki/Planet_killer
You beat me to that comparison. I like this disturbingly look-alike image in particular:

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"To B̬̻̋̚o̞̮̚̚l̘̲̀᷾d̫͓᷅ͩḷ̯᷁ͮȳ͙᷊͠ Go......Beyond The F͇̤i̙̖e̤̟l̡͓d͈̹s̙͚ We Know."{ʲₒʰₙNYᵈₑᵉₚ}

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Re: APOD: CG4: The Globule and the Galaxy (2023 Jan 04)

Post by Chris Peterson » Wed Jan 04, 2023 2:44 pm

Ann wrote: Wed Jan 04, 2023 8:22 am Please! The link, the featured photo, took us to a Facebook page, and since I don't have Facebook, I was unable to find any information at all about the image. Surely the links to information about the APOD in question should go to pages that are open to all?
I second that. No links for APODs to social media sites. The original content should be well described and posted somewhere accessible to everyone. Or not accepted.
Chris

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Re: APOD: CG4: The Globule and the Galaxy (2023 Jan 04)

Post by orin stepanek » Wed Jan 04, 2023 3:58 pm

cg4_selby_960.jpg
saw this before; looks like a threatening monster! :mrgreen:
imagem_ht_07-04-23.jpg
imagem_ht_07-04-23.jpg (10.26 KiB) Viewed 5984 times
Silly kitties! :lol2:
Orin

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Re: APOD: CG4: The Globule and the Galaxy (2023 Jan 04)

Post by starsurfer » Wed Jan 04, 2023 11:04 pm

I'm reminded of the scene from Empire Strikes Back where the asteroid monster tries to eat the Millenium Falcon.

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Re: APOD: CG4: The Globule and the Galaxy (2023 Jan 04)

Post by sc02492 » Wed Jan 04, 2023 11:15 pm

Chris Peterson wrote: Wed Jan 04, 2023 2:44 pm
Ann wrote: Wed Jan 04, 2023 8:22 am Please! The link, the featured photo, took us to a Facebook page, and since I don't have Facebook, I was unable to find any information at all about the image. Surely the links to information about the APOD in question should go to pages that are open to all?
I second that. No links for APODs to social media sites. The original content should be well described and posted somewhere accessible to everyone. Or not accepted.
Agreed. Furthermore, I would require that details be provided in a separate link regarding how the images were actually acquired. Exposure duration, filters, optics, processing techniques, etc.. The kind of information that most of us involved in astrophotography would consider standard.

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Re: APOD: CG4: The Globule and the Galaxy (2023 Jan 04)

Post by orin stepanek » Thu Jan 05, 2023 1:22 am

hmmm!
th-171175593.jpg
Kirk always wins! :wink:
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Re: APOD: CG4: The Globule and the Galaxy (2023 Jan 04)

Post by jagganath69 » Thu Jan 05, 2023 9:19 am

De58te wrote: Wed Jan 04, 2023 9:44 am
jagganath69 wrote: Wed Jan 04, 2023 7:34 am I'm curious: what's the galaxy's designation ?
According to the Wikipedia page for CG 4, the spiral galaxy to be 'devoured' is designated, ESO 257-19.
THANK YOU!

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