APOD: Bright Spiral Galaxy M81 (2014 Nov 19)

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APOD: Bright Spiral Galaxy M81 (2014 Nov 19)

Post by APOD Robot » Wed Nov 19, 2014 5:10 am

Image Bright Spiral Galaxy M81

Explanation: One of the brightest galaxies in planet Earth's sky is similar in size to our Milky Way Galaxy: big, beautiful M81. This grand spiral galaxy can be found toward the northern constellation of the Great Bear (Ursa Major). This superbly detailed view reveals M81's bright yellow nucleus, blue spiral arms, and sweeping cosmic dust lanes with a scale comparable to the Milky Way. Hinting at a disorderly past, a remarkable dust lane actually runs straight through the disk, to the left of the galactic center, contrary to M81's other prominent spiral features. The errant dust lane may be the lingering result of a close encounter between M81 and its smaller companion galaxy, M82. Scrutiny of variable stars in M81 has yielded one of the best determined distances for an external galaxy -- 11.8 million light-years.

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Re: APOD: Bright Spiral Galaxy M81 (2014 Nov 19)

Post by Ann » Wed Nov 19, 2014 5:15 am

This is a very beautiful picture of one of the most-photographed objects in the sky. I love the details and the vibrant RGB + Ha colors.

The caption says that the dust lane seen across the bulge of M81 is an innate part of M81. I thought it was believed to be a dusty streamer of cirrus in the Milky Way, seen across the face of M81.

I can see that the stellar spikes look quite different, and I wonder what starsurfer is going to say.

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Re: APOD: Bright Spiral Galaxy M81 (2014 Nov 19)

Post by Renato » Wed Nov 19, 2014 9:19 am

Are we looking at the Galaxy from the top or from the bottom? It is turning clockwise in any case.

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Re: APOD: Bright Spiral Galaxy M81 (2014 Nov 19)

Post by BDanielMayfield » Wed Nov 19, 2014 11:23 am

Ann wrote:I can see that the stellar spikes look quite different, and I wonder what starsurfer is going to say.

Ann
Well, I'll say that the differing numbers of spikes (the brightest have eight, then the less bright have four, but most stars have none) is a giveaway that this is an added effect. Personally, I feel that it detracts from an otherwise excellent image.

Bruce

Edit: Spike count correction.
Last edited by BDanielMayfield on Thu Nov 20, 2014 12:33 am, edited 1 time in total.
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Re: APOD: Bright Spiral Galaxy M81 (2014 Nov 19)

Post by geckzilla » Wed Nov 19, 2014 11:49 am

Unless he's using some data other than Subaru, HST, and Gendler's and hasn't told us, then yeah, those are all generated. He likes to do that. The mirroring of the image and the use of eight spikes do baffle me.
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Re: APOD: Bright Spiral Galaxy M81 (2014 Nov 19)

Post by Cousin Ricky » Wed Nov 19, 2014 12:40 pm

Renato wrote:Are we looking at the Galaxy from the top or from the bottom? It is turning clockwise in any case.
What do you mean by “top” or “bottom”?

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Re: APOD: Bright Spiral Galaxy M81 (2014 Nov 19)

Post by sunlight » Wed Nov 19, 2014 4:04 pm

Has any one ever wonder about this fellow having two nucleus??? If you look closely (or perhaps not so closely) one can see two bright nucleus: one stronger (at the right) than the other.

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Re: APOD: Bright Spiral Galaxy M81 (2014 Nov 19)

Post by Chris Peterson » Wed Nov 19, 2014 4:16 pm

sunlight wrote:Has any one ever wonder about this fellow having two nucleus??? If you look closely (or perhaps not so closely) one can see two bright nucleus: one stronger (at the right) than the other.
I think this is some sort of imaging artifact. M81 probably doesn't have a double nucleus. M31 is the only example I know of for a double nucleus spiral galaxy.

My guess would be dust lanes breaking up our view of the core.
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Re: APOD: Bright Spiral Galaxy M81 (2014 Nov 19)

Post by dsecrieru » Wed Nov 19, 2014 8:09 pm

Wasn't the vertical dust lane actually IFN (Integrated Flux Nebula) in our own galaxy, superimposed by chance over M81?

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Re: APOD: Bright Spiral Galaxy M81 (2014 Nov 19)

Post by Chris Peterson » Wed Nov 19, 2014 8:18 pm

dsecrieru wrote:Wasn't the vertical dust lane actually IFN (Integrated Flux Nebula) in our own galaxy, superimposed by chance over M81?
The IFN is extremely tenuous, only visible by reflected light in very deep images. It's nowhere near dense enough to significantly attenuate any bright objects behind it, including the core of M81.
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Re: APOD: Bright Spiral Galaxy M81 (2014 Nov 19)

Post by geckzilla » Wed Nov 19, 2014 8:32 pm

Chris Peterson wrote:
sunlight wrote:Has any one ever wonder about this fellow having two nucleus??? If you look closely (or perhaps not so closely) one can see two bright nucleus: one stronger (at the right) than the other.
I think this is some sort of imaging artifact. M81 probably doesn't have a double nucleus. M31 is the only example I know of for a double nucleus spiral galaxy.

My guess would be dust lanes breaking up our view of the core.
Here's a near-infrared picture of it from HST. It comes to a fine point and even saturates the sensor slightly. There are two slightly brighter lobes encircling the nucleus but definitely only one nucleus.
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Re: APOD: Bright Spiral Galaxy M81 (2014 Nov 19)

Post by stardog » Wed Nov 19, 2014 9:12 pm

From the view we have of M81, does it look to anyone else as if the upper right section is higher than the nucleus and is being swept up and away to the left?
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Re: APOD: Bright Spiral Galaxy M81 (2014 Nov 19)

Post by geckzilla » Wed Nov 19, 2014 9:24 pm

stardog wrote:From the view we have of M81, does it look to anyone else as if the upper right section is higher than the nucleus and is being swept up and away to the left?
Misalignment of two different data sets of the same section of the galaxy. Not real. (Assuming you are talking about the same thing I see. Maybe you mean something else.)

Edit: I think you are talking about something else. You mean it looks like the upper arm is inclined from the plane of the galaxy?
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Re: APOD: Bright Spiral Galaxy M81 (2014 Nov 19)

Post by Boomer12k » Wed Nov 19, 2014 11:52 pm

Awesome image....lots of star forming zones.

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Re: APOD: Bright Spiral Galaxy M81 (2014 Nov 19)

Post by Cousin Ricky » Thu Nov 20, 2014 9:34 am

stardog wrote:From the view we have of M81, does it look to anyone else as if the upper right section is higher than the nucleus and is being swept up and away to the left?
Given the absence of any real depth perception data in that regard, I'm going to assume that anything my brain computes is spurious.

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Re: APOD: Bright Spiral Galaxy M81 (2014 Nov 19)

Post by starsurfer » Thu Nov 20, 2014 12:29 pm

Ann wrote: I can see that the stellar spikes look quite different, and I wonder what starsurfer is going to say.
While the diffraction spikes are fake, what bothers me most about this image is that it is mirror reversed. However it is a fairly pleasant version of one of all time favourite spiral galaxies and I consider this slightly better than the official HST image.

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Re: APOD: Bright Spiral Galaxy M81 (2014 Nov 19)

Post by rcolombari » Thu Nov 20, 2014 10:13 pm

Hi,
yes, there are misalignments in some areas.
Unfortunately, at the time I did the assembling, I was not yet a Registar user so I assembled hundreds of sub-frames manually in PS (Subaru, HST and Gendler [RGB]) along 4/5 months.

For what concerns the spikes, Subaru stars were pretty compromised by blooming so, no choice, I had to mask them with fake ones.

Bests.

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Re: APOD: Bright Spiral Galaxy M81 (2014 Nov 19)

Post by BDanielMayfield » Thu Nov 20, 2014 11:48 pm

rcolombari wrote:For what concerns the spikes, Subaru stars were pretty compromised by blooming so, no choice, I had to mask them with fake ones.
Ah, so there can be good reasons for spiking up an astro-image. That's good to know. Thanks for your excellent work.

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Re: APOD: Bright Spiral Galaxy M81 (2014 Nov 19)

Post by geckzilla » Fri Nov 21, 2014 11:09 am

Chris Peterson wrote:M31 is the only example I know of for a double nucleus spiral galaxy.
Reading this I decided to be on the look out for more double nuclei in spirals. So far the only one is M83 but it's no secret. Maybe they aren't so rare but they may be so close together that it's difficult to find them? M83's was obscured by thick dust too.
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Re: APOD: Bright Spiral Galaxy M81 (2014 Nov 19)

Post by starsurfer » Fri Nov 21, 2014 2:58 pm

geckzilla wrote:
Chris Peterson wrote:M31 is the only example I know of for a double nucleus spiral galaxy.
Reading this I decided to be on the look out for more double nuclei in spirals. So far the only one is M83 but it's no secret. Maybe they aren't so rare but they may be so close together that it's difficult to find them? M83's was obscured by thick dust too.
Whatcha about M31?

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Re: APOD: Bright Spiral Galaxy M81 (2014 Nov 19)

Post by Chris Peterson » Fri Nov 21, 2014 3:18 pm

geckzilla wrote:
Chris Peterson wrote:M31 is the only example I know of for a double nucleus spiral galaxy.
Reading this I decided to be on the look out for more double nuclei in spirals. So far the only one is M83 but it's no secret. Maybe they aren't so rare but they may be so close together that it's difficult to find them? M83's was obscured by thick dust too.
AFAIK M31 is the only spiral galaxy known to have a double nucleus, and the only one where such a nucleus is visible in ordinary white light images. There is evidence that M83 has something odd going on around its central black hole that is creating a double nucleus, but that isn't certain, and is nowhere near as prominent as what we see in M31.

In part, it depends on what we mean by "double nucleus". At a fine enough scale, you could argue that every galaxy has multiple nucleuses.
Chris

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