APOD: NGC 2261: Hubble's Variable Nebula (2017 Nov 08)

APOD Robot · Post by **APOD Robot** » Wed Nov 08, 2017 5:06 am

NGC 2261: Hubble's Variable Nebula

Explanation: What causes Hubble's Variable Nebula to vary? The unusual nebula featured here changes its appearance noticeably in just a few weeks. Discovered over 200 years ago and subsequently cataloged as NGC 2661, the remarkable nebula is named for Edwin Hubble, who studied it early last century. Fitting, perhaps, the featured image was taken by another namesake of Hubble: the Space Telescope. Hubble's Variable Nebula is a reflection nebula made of gas and fine dust fanning out from the star R Monocerotis. The faint nebula is about one light-year across and lies about 2500 light-years away towards the constellation of the Unicorn (Monocerotis). The leading variability explanation for Hubble's Variable Nebula holds that dense knots of opaque dust pass close to R Mon and cast moving shadows onto the reflecting dust seen in the rest of the nebula.

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Boomer12k · Post by **Boomer12k** » Wed Nov 08, 2017 9:04 am

Amazing. Looks more like a "plume", than a shadow... but the jury is still out...hmmm... imagine giant Shadow Puppets...a shadow puppet show a light year across...

:---[===] *

BDanielMayfield · Post by **BDanielMayfield** » Wed Nov 08, 2017 1:03 pm

If a static image is worth a thousand words this must be worth a million:

APOD Robot wrote:Hubble's Variable Nebula

Looks like the shadow casting dust is possibly orbiting the star in a counter-clockwise direction.

Bruce

neufer · Post by **neufer** » Wed Nov 08, 2017 2:45 pm

Click to play embedded YouTube video.

BDanielMayfield wrote:
If a static image is worth a thousand words this must be worth a million:
APOD Robot wrote:Hubble's Variable Nebula
Looks like the shadow casting dust is possibly orbiting the star in a counter-clockwise direction.

geckzilla · Post by **geckzilla** » Wed Nov 08, 2017 3:47 pm

There's also this animation, which is a little smoother:
https://www.cloudynights.com/topic/5356 ... -24-weeks/

It does appear to be rotating counter-clockwise from our perspective, but given the pattern of the nebula, and light travel time, I find it hard to say for sure. Plus, it's hard to say what the orientation of the star is with respect to us.

Chris Peterson · Post by **Chris Peterson** » Wed Nov 08, 2017 4:04 pm

BDanielMayfield wrote:If a static image is worth a thousand words this must be worth a million:
APOD Robot wrote:Hubble's Variable Nebula
Looks like the shadow casting dust is possibly orbiting the star in a counter-clockwise direction.

Based on what frame of reference? (Taking top-up in the animation, I'd call that clockwise. There's also the conventional reference of north-up.)

Ann · Post by **Ann** » Wed Nov 08, 2017 4:06 pm

That's a great video, Geck, and that's a beautiful video, Art.

As for myself, when I read about a star, I always wonder what kind of a star it is. More specifically, how massive is it? Is it more massive than the Sun, about as massive as the Sun, or less massive?

According to Simbad Astronomical Database (and also according to the link provided by today's caption), R Mon is an Ae/Be star. That means that it is at least twice as massive as the Sun, and it could be several times as massive. In other words, it is (or it is going to be) a blue star.

So the faintly bluish color of the nebula could be for real.

http://adsabs.harvard.edu/abs/1997ApJ...489..210C wrote:

We have found that R Mon is a 0.69" binary star with a companion that dereddens onto the classical T Tauri locus. Based on the near-infrared photometry of this companion we believe it is a 1.5 M⊙, very young (<3 × 10⁵ yr) classical T Tauri star. The close presence of a young companion suggests that R Mon itself is a rare example of a very young isolated massive star.

Ann

Visual_Astronomer · Post by **Visual_Astronomer** » Wed Nov 08, 2017 5:45 pm

That's an amazingly detailed view. I have observed this nebula a couple of times, but I didn't realize the changes could occur in such a short span of time. It might be a worthy project to try to see the changes visually.

BDanielMayfield · Post by **BDanielMayfield** » Wed Nov 08, 2017 5:48 pm

Chris Peterson wrote:
BDanielMayfield wrote:If a static image is worth a thousand words this must be worth a million:
APOD Robot wrote:Hubble's Variable Nebula
Looks like the shadow casting dust is possibly orbiting the star in a counter-clockwise direction.
Based on what frame of reference? (Taking top-up in the animation, I'd call that clockwise. There's also the conventional reference of north-up.)

Yeah. And then there's a possible strobe effect where an actual rotation can appear to be reversed due to the cadence of the observations. Glad I wrote "possibly."

MarkBour · Post by **MarkBour** » Wed Nov 08, 2017 5:54 pm

I don't know if this has already been done, but one could check the hypothesis that this is opaque dust near the star casting shadows on the reflection nebula of reflecting gas further out ... if one can get high enough resolution, one should see the same shadows pass the star itself a little prior to them showing much larger on the surface of the nebula.* If one can get that data, it also should be able to be used to determine some distances.

* (I assume they can't resolve a shadow crossing the face of the star, but I'm guessing they could get the light profile showing dimming.)

It's interesting that the whole arrangement is acting like a nature-created magnifier for viewing the opaque gas cloud(s). Or, like a movie projector onto the reflection nebula acting as a screen.

BDanielMayfield suggested that the opaque dust might be in orbit around the star, rather than that it is just passing the star once. As Ann already pointed out, and the "R Mon" link in the APOD text mentions, R Mon is a binary with an accretion disk, so that is consistent with this statement. (In fact, they characterize the binary as "a very young active Herbig Ae/Be star".) If I'm reading it correctly, the link characterizes the larger star as being perhaps 10.4 M⊙. I wonder what tidal tug-of-war may possibly be actively creating the accretion disk and if this disk is the cloud that is casting the shadows.

Actually, although I like the "leading idea" just fine, and the following is only a flight of fancy, the whole region does look eerily like a smoldering ember, and the reflection nebula looks like the cloud of smoke rising from it. Why is the nebula laid out in a cone just to one side of this star?

Chris Peterson · Post by **Chris Peterson** » Wed Nov 08, 2017 6:26 pm

MarkBour wrote:I don't know if this has already been done, but one could check the hypothesis that this is opaque dust near the star casting shadows on the reflection nebula of reflecting gas further out ... if one can get high enough resolution, one should see the same shadows pass the star itself a little prior to them showing much larger on the surface of the nebula.* If one can get that data, it also should be able to be used to determine some distances.

* (I assume they can't resolve a shadow crossing the face of the star, but I'm guessing they could get the light profile showing dimming.)

It seems like the direction the shadows are being cast is different from the line between us and the star. The dust that casts the shadow may not lie between us and the star, and therefore we wouldn't see any correlated dimming.

neufer · Post by **neufer** » Wed Nov 08, 2017 6:57 pm

[img3=""Plato's Cave Allegory" by Markus Maurer"]https://upload.wikimedia.org/wikipedia/ ... e_Cave.png[/img3]

Chris Peterson wrote:
It seems like the direction the shadows are being cast is different from the line between us and the star. The dust that casts the shadow may not lie between us and the star, and therefore we wouldn't see any correlated dimming.

https://en.wikipedia.org/wiki/Allegory_of_the_Cave wrote:
<<Plato begins by having Socrates ask Glaucon to imagine a cave where people have been imprisoned from birth. Behind the prisoners is a fire, and between the fire and the prisoners is a raised walkway with a low wall, behind which people walk carrying objects or puppets "of men and other living things". The people walk behind the wall so their bodies do not cast shadows for the prisoners to see, but the objects they carry do. The prisoners are only able to see the shadows cast upon the cave wall in front of them. Socrates suggests that the shadows are reality for the prisoners because they have never seen anything else; they do not realize that what they see are shadows of objects in front of a fire, much less that these objects are inspired by real things outside the cave.>>

rj rl · Post by **rj rl** » Thu Nov 09, 2017 3:51 am

Chris Peterson wrote:
BDanielMayfield wrote:If a static image is worth a thousand words this must be worth a million:
APOD Robot wrote:Hubble's Variable Nebula
Looks like the shadow casting dust is possibly orbiting the star in a counter-clockwise direction.
Taking top-up in the animation, I'd call that clockwise. There's also the conventional reference of north-up.

could you explain? If it moves right to left at the top isn't it counterclockwise?

Chris Peterson · Post by **Chris Peterson** » Thu Nov 09, 2017 2:12 pm

rj rl wrote:
Chris Peterson wrote:
BDanielMayfield wrote:If a static image is worth a thousand words this must be worth a million:
Looks like the shadow casting dust is possibly orbiting the star in a counter-clockwise direction.
Taking top-up in the animation, I'd call that clockwise. There's also the conventional reference of north-up.
could you explain? If it moves right to left at the top isn't it counterclockwise?

Does that mean you are using the reference frame of the animated image? If so, what I'm seeing is a left-hand rule type of motion. I put my left hand in front of me, thumb up and finger curled, and the fingers are showing the direction of rotation, which in that reference would probably be called clockwise.

To be sure, I'm taking the nebula as being in front of the star. If it's behind the star, I'd look at the right-hand rule and counterclockwise motion.

neufer · Post by **neufer** » Thu Nov 09, 2017 2:30 pm

Chris Peterson wrote:
rj rl wrote:
Chris Peterson wrote:
Taking top-up in the animation, I'd call that clockwise.
could you explain? If it moves right to left at the top isn't it counterclockwise?
Does that mean you are using the reference frame of the animated image? If so, what I'm seeing is a left-hand rule type of motion. I put my left hand in front of me, thumb up and finger curled, and the fingers are showing the direction of rotation, which in that reference would probably be called clockwise. To be sure, I'm taking the nebula as being in front of the star. If it's behind the star, I'd look at the right-hand rule and counterclockwise motion.

neufer · Post by **neufer** » Thu Nov 09, 2017 5:34 pm

. http://asterisk.apod.com/viewtopic.php?f=31&t=37743

https://en.wikipedia.org/wiki/KIC_8462852 wrote:
<<KIC 8462852 (also Tabby's Star or Boyajian's Star) is an F-type main-sequence star located in the constellation Cygnus approximately 1,280 light-years from Earth. Unusual light fluctuations of the star, including up to a 22% dimming in brightness, were discovered by citizen scientists as part of the Planet Hunters project. The discovery was made from data collected by the Kepler space telescope, which observes changes in the brightness of distant stars to detect exoplanets.>>

Starship Asterisk*

APOD: NGC 2261: Hubble's Variable Nebula (2017 Nov 08)

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