Starship Asterisk*

Arcs, Jets, and Shocks near NGC 1999

Explanation: This tantalizing array of nebulas and stars can be found about two degrees south of the famous star-forming Orion Nebula. The region abounds with energetic young stars producing jets and outflows that push through the surrounding material at speeds of hundreds of kilometers per second. The interaction creates luminous shock waves known as Herbig-Haro (HH) objects. For example, the graceful, flowing arc just right of center is cataloged as HH 222, also called the Waterfall Nebula. Seen below the Waterfall, HH 401 has a distinctive cone shape. The bright bluish nebula below and left of center is NGC 1999, a dusty cloud reflecting light from an embedded variable star. The entire cosmic vista spans over 30 light-years, near the edge of the Orion Molecular Cloud Complex some 1,500 light-years distant.

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Today's APOD is very colorful, which I like, of course. Mostly it demonstrates the chaos that follows multiple star formation in a very dusty region.





























Personally I'm really fascinated by NGC 1999, the blue reflection nebula that has a little black man poking his head out of it! Actually, of course, the "man" is a hole in the nebula. But the hole is intriguing in itself. How did it get there? Well, with so many jets in the area, I guess one of them hit a bulls eye in NGC 1999 and left the man-shaped black emptiness there! (I was about to write "the man-shaped black hole", but that wouldn't have been so good, would it?)

One thing that I really like about today's APOD is how it shows that NGC 1999 is surrounded by "extended red chaos" whose general outline makes it look like a rose. Suddenly the NGC 1999 region looks like another version of a "Rosette Nebula".

Ann

I understand most of the annotations for the 'rollover' part of the image, but cannot find what 'Re' means. As in: 'Re 24', 'Re 22', etc. I clicked through (most of) the links included in the description, but saw no references to what this could mean/stand for. Would someone point me in the right direction? [And thank you in advance!]

And this is one of the most vivid images APOD has used.

Indigo_Sunrise wrote: ↑Wed Mar 07, 2018 12:07 pm I understand most of the annotations for the 'rollover' part of the image, but cannot find what 'Re' means. As in: 'Re 24', 'Re 22', etc. I clicked through (most of) the links included in the description, but saw no references to what this could mean/stand for. Would someone point me in the right direction?

I'm thinking it might just mean "region"; an identified area of structure which isn't otherwise cataloged.

Emails indicate that the annotation was done by Sakib Rasool, who is now credited on the NASA APOD.
- RJN

Ann wrote: ↑Wed Mar 07, 2018 7:10 am ... Personally I'm really fascinated by NGC 1999, the blue reflection nebula that has a little black man poking his head out of it! Actually, of course, the "man" is a hole in the nebula. But the hole is intriguing in itself. How did it get there? Well, with so many jets in the area, I guess one of them hit a bulls eye in NGC 1999 and left the man-shaped black emptiness there! (I was about to write "the man-shaped black hole", but that wouldn't have been so good, would it?) ...
Ann

Ann, I too was quite intrigued by that hole in the reflection nebula. To me, it looks like the shape of a black chess pawn (tilted sideways). I think your conjecture of a jet must be correct (http://herschel.cf.ac.uk/results/ngc1999-hole-space agrees with you). That page also updates an earlier conjecture on the Hubble site at: http://hubblesite.org/image/952/news_release/2000-10 that had guessed the blackness was a Bok globule. But Herschel's data dispelled that idea, and it has since been decided that it really is a hole. (I'd love to see an image with sufficient resolution to see some far-away light coming through the hole.)

The Hubble link identified the star just to the left of the hole, that is producing the reflection nebula, as V380 Orionis. The Wikipedia article on it notes that this is actually at least 3 stars and a brown dwarf, and considers the hole to have been produced by this group:

One of the component stars of V380 Orionis appears to have launched a polar jet that helped to clear the keyhole-shaped hole in the surrounding nebula known as NGC 1999.
https://en.wikipedia.org/wiki/V380_Orionis

the original source for that conclusion being referenced there to: https://photojournal.jpl.nasa.gov/catalog/PIA13109.

I don't know how crazy the following idea is, but I could imagine that these stars made that hole, and have moved aside from it, or perhaps quieted down, and the hole is now beginning to fill back in, as the gas begins to expand back into the region. That's the best sense I can make of its very odd shape.

Thanks, Mark, that's really interesting!

Ann

MarkBour wrote: ↑Thu Mar 08, 2018 12:37 am
I don't know how crazy the following idea is, but I could imagine that these stars made that hole, and have moved aside from it, or perhaps quieted down, and the hole is now beginning to fill back in, as the gas begins to expand back into the region. That's the best sense I can make of its very odd shape.

The star or stars made a hole in the gas & dust.

I really doubt the dust would ever return ...
and figure it would take a really long time for the gas to fill in.

Chris Peterson wrote: ↑Wed Mar 07, 2018 2:48 pm

Indigo_Sunrise wrote: ↑Wed Mar 07, 2018 12:07 pm I understand most of the annotations for the 'rollover' part of the image, but cannot find what 'Re' means. As in: 'Re 24', 'Re 22', etc. I clicked through (most of) the links included in the description, but saw no references to what this could mean/stand for. Would someone point me in the right direction?

I'm thinking it might just mean "region"; an identified area of structure which isn't otherwise cataloged.

Actually, it's related to the fellow who did a survey of those type of objects, analogous to Arp objects.
In 1985 a Bo Reipurth published a survey.

Indigo_Sunrise wrote: ↑Wed Mar 07, 2018 12:07 pm I understand most of the annotations for the 'rollover' part of the image, but cannot find what 'Re' means. As in: 'Re 24', 'Re 22', etc. I clicked through (most of) the links included in the description, but saw no references to what this could mean/stand for. Would someone point me in the right direction? [And thank you in advance!]

And this is one of the most vivid images APOD has used.

Re is short for Reipurth, the surname of the professional astronomer Bo Reipurth who produced a catalogue of little nebulae associated with young stellar objects in various star forming regions all around the sky. The first part of ones found in southern dark clouds was published in 1981 while the majority are in the Orion region, which were published in 1985.

I agree with you, this is very colourful. The Ha exposures added to it really emphasise the various Herbig Haro objects. Most amateur images of reflection nebulae with HH objects are LRGB. For this one, the vivid colours show the importance of a really long exposure, which is pretty easy for an automated remote observatory located under dark skies.

Also for a widefield image taken from Chile by the Atacama Photographic Observatory, see here and here!

If anyone is in the mood for any scientific papers, check out the following:
The NGC1999 dark globule is not a globule
THE BRIGHTENING OF Re50N: ACCRETION EVENT OR DUST CLEARING?

Re 50 can be found somewhere in this image.

Thank you Chris Peterson, alter-ego and starsurfer, for your informative and very helpful replies.