APOD: Messier 101 (2021 Nov 27)

[APOD Robot]

Messier 101

Explanation: Big, beautiful spiral galaxy M101 is one of the last entries in Charles Messier's famous catalog, but definitely not one of the least. About 170,000 light-years across, this galaxy is enormous, almost twice the size of our own Milky Way. M101 was also one of the original spiral nebulae observed by Lord Rosse's large 19th century telescope, the Leviathan of Parsontown. Assembled from 51 exposures recorded by the Hubble Space Telescope in the 20th and 21st centuries, with additional data from ground based telescopes, this mosaic spans about 40,000 light-years across the central region of M101 in one of the highest definition spiral galaxy portraits ever released from Hubble. The sharp image shows stunning features of the galaxy's face-on disk of stars and dust along with background galaxies, some visible right through M101 itself. Also known as the Pinwheel Galaxy, M101 lies within the boundaries of the northern constellation Ursa Major, about 25 million light-years away.

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[VictorBorun]

to my eye it looks like the dusty arms are less round than the stellar arms and cross then at angle about 10°

[Ann]

M101. Credit: Credit: Hubble Legacy Archive, ESA, NASA; Processing and additional imaging - Robert Gendler

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M101. Image Credit: NASA, ESA, CFHT, NOAO; Acknowledgement - K.Kuntz (GSFC), F.Bresolin (U.Hawaii), J.Trauger (JPL), J.Mould (NOAO), Y.-H.Chu (U. Illinois)

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Well, there is nothing for it: Today's APOD doesn't speak strongly to me, because of the "flat" colors. I so much prefer the overall color profile of Robert Gendler's image.

Yes, but... When you look at a larger version of today's APOD and start getting into details...!!!

Have you ever seen such a lovely 3-armed background galaxy?

Some notable objects in the upper right part of the APOD.

Let's look at the annotations of the picture at right:

L = Low surface brightness galaxy

1A = Lenticular (barred) galaxy with a large yellow halo
2A = Elliptical galaxy with a large yellow halo
3A = Barred red-and-dead galaxy with a yellow tidal tail

4A = Edge-on spiral galaxy with a yellow bulge and a (rather extensive) blue disk
5A = Starforming disk galaxy, probably interacting with galaxy 4A.

Do 4A and 5A belong to the same group of galaxies as 1A, 2A and 3A (which certainly belong together themselves)? They might, but I doubt it.

6 = Clump of stars belonging to M101. Note the presence of both blue and red stars here.

7 = Very bright red supergiant star in M101 or very redshifted background galaxy? I guess it is a galaxy.

8 = A rather small region of intense star formation in M101. The turquoise color probably means we are looking at a nebula (or nebulas). The arc-shaped formation is either an arc-shaped nebula (as in the California nebula) or an arc of stars arching over a dense core of stars.

9 = A group of very faint, differently colored (including very red) background galaxies. There appears to be at least one red M101 star here too.

10 = Two red background galaxies.

11 = A globular cluster? If so, it must be very compact.

NGC 6946. Image credit: ESA/Hubble & NASA, A. Leroy, K.S. Long

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Galaxy NGC 6946 by Hubble. Note the small bright white clump of stars surrounded by a "cloud" or an halo of stars at upper right. I think that #8 in my annotated image might possibly be a young version of this.

Ann

[orin stepanek]

Yep; not a comet! Beautiful galaxy; and all spirals are!

[NCTom]

Is it part of the process of combining the multiple images that causes the long, narrow blurred streaks from 9 to 6 in the enlargement? And a big thanks to Ann for the added annotation (AGAIN!) It made that part of the galaxy come alive.

[VictorBorun]

4A = Edge-on spiral galaxy with a yellow bulge and a (rather extensive) blue disk
5A = Starforming disk galaxy, probably interacting with galaxy 4A.
Ann

I wonder how this scale and all the galaxies compare to what can be seen from M101 of the Milky Way, Magellanic Clouds, Andromeda, Triangulum, the Council of Giants?

[Ann]

4A = Edge-on spiral galaxy with a yellow bulge and a (rather extensive) blue disk
5A = Starforming disk galaxy, probably interacting with galaxy 4A.
Ann

I wonder how this scale and all the galaxies compare to what can be seen from M101 of the Milky Way, Magellanic Clouds, Andromeda, Triangulum, the Council of Giants?

Are you asking how big M101 appears to be in the Earth's sky?

This APOD from January 23, 2016 gives you a good idea:

Big Dipper, Deep Sky. Image Credit & Copyright: Lorand Fenyes

M101 looks very small in our skies, as you can see. Then again, the Big Dipper is, yes, big.

Ann

[Chris Peterson]

4A = Edge-on spiral galaxy with a yellow bulge and a (rather extensive) blue disk
5A = Starforming disk galaxy, probably interacting with galaxy 4A.
Ann

I wonder how this scale and all the galaxies compare to what can be seen from M101 of the Milky Way, Magellanic Clouds, Andromeda, Triangulum, the Council of Giants?

Are you asking how big M101 appears to be in the Earth's sky?

This APOD from January 23, 2016 gives you a good idea:

lf_dipper_subt[1].jpg

Big Dipper, Deep Sky. Image Credit & Copyright: Lorand Fenyes

M101 looks very small in our skies, as you can see. Then again, the Big Dipper is, yes, big.

Ann

M101 is the same apparent size as the full Moon. Whether we call that big or small is a matter of opinion. (I'd say that it's pretty small, but that we tend to think the Moon is much larger than it actually is.) And, of course, there's the fact that the Moon has a hard, well defined edge, while galaxies do not.

[Fred the Cat]

Unraveling the history of stars born in the Milky Way is like looking for individual strings in a ball of yarn.

[johnnydeep]

The text says this APOD spans about 40000 ly, and that the full galaxy's size is 170000 ly, or over four times the width and height of this image? That is, the full extent would fill this black space if imaged in its entirety?

The full extent of M101?

Seems hard to believe, unless those arms get really diffuse really far away. But perhaps this is just another case of "trying to pin down a galaxy's size is a fools errand"

[johnnydeep]

Here's a more compact version of Ann's handy annotations:

Area near M101 with Ann's Annotations

[Fred the Cat]

The text says this APOD spans about 40000 ly, and that the full galaxy's size is 170000 ly, or over four times the width and height of this image? That is, the full extent would fill this black space if imaged in its entirety?

M101 full extent.JPG

Seems hard to believe, unless those arms get really diffuse really far away. But perhaps this is just another case of "trying to pin down a galaxy's size is a fools errand"

There are ways.

[VictorBorun]

4A = Edge-on spiral galaxy with a yellow bulge and a (rather extensive) blue disk
5A = Starforming disk galaxy, probably interacting with galaxy 4A.
Ann

I wonder how this scale and all the galaxies compare to what can be seen from M101 of the Milky Way, Magellanic Clouds, Andromeda, Triangulum, the Council of Giants?

Are you asking how big M101 appears to be in the Earth's sky?

This APOD from January 23, 2016 gives you a good idea:

lf_dipper_subt[1].jpg

Big Dipper, Deep Sky. Image Credit & Copyright: Lorand Fenyes

M101 looks very small in our skies, as you can see. Then again, the Big Dipper is, yes, big.

Ann

yes, and more. That Clutch of Constables — I mean of stellar clusters, galaxies and interacting galaxies, how does it compare with our backyard?

I take it the Council of Giants is a flat disk of large galaxies containing a diameter-opposite pair of elliptic giants with some companions and our Local Cluster (Milky Way+Andromeda) somewhere inside that diameter; this Local Sheet is a mini-brane formed not by a gravitational collapse of a clump but rather by inflation of two neighboring voids.

Will our Local Sheet look similar to 4A+5A as them to us? Or much denser, or much thinner?

[danielismeh]

Amazing!

[Ann]

Here's a more compact version of Ann's handy annotations:

Click to view full size image

Thanks a billion, Johnny!

Ann

[alter-ego]

The text says this APOD spans about 40000 ly, and that the full galaxy's size is 170000 ly, or over four times the width and height of this image? That is, the full extent would fill this black space if imaged in its entirety?


M101 full extent.JPG


Seems hard to believe, unless those arms get really diffuse really far away. But perhaps this is just another case of "trying to pin down a galaxy's size is a fools errand"

The carefully measured field of view of this image is close to 13.2' x 10.3'. At 25 Mly distance, the composite image then corresponds to a size of
96000 ly x 74000 ly. I'm not sure where the 40000-ly came from unless the reference to the "central region" does not map directly to the APOD. Maybe the "central region" corresponds to roughly half the size (1/4 the area) of the APOD).
M101 is seen below within a field of view = M101's apparent size as listed in Wiki (28.8' x 26.9'). The yellow box identifies the APOD image FoV. The ratio of the two areas more correctly ≈ 5.7 instead of ~12 as your earlier full-extent graphic comparison indicates.
 

[johnnydeep]

The text says this APOD spans about 40000 ly, and that the full galaxy's size is 170000 ly, or over four times the width and height of this image? That is, the full extent would fill this black space if imaged in its entirety?


M101 full extent.JPG


Seems hard to believe, unless those arms get really diffuse really far away. But perhaps this is just another case of "trying to pin down a galaxy's size is a fools errand"

There are ways.

True, but IMO, down the "halo" path leads to some pretty meaningless galaxy sizes. Plus I wonder if these halos are more or less dense than the typical interstellar medium between the actual stars in the galaxy (though I do realize that likely varies quite a lot). Is the halo's constituent matter even gravitationally bound to the rest of the galaxy? And for a related thought: should an individual star's size include its corona, or the full extent of its stellar wind?

[johnnydeep]

The text says this APOD spans about 40000 ly, and that the full galaxy's size is 170000 ly, or over four times the width and height of this image? That is, the full extent would fill this black space if imaged in its entirety?


M101 full extent.JPG


Seems hard to believe, unless those arms get really diffuse really far away. But perhaps this is just another case of "trying to pin down a galaxy's size is a fools errand"

The carefully measured field of view of this image is close to 13.2' x 10.3'. At 25 Mly distance, the composite image then corresponds to a size of
96000 ly x 74000 ly. I'm not sure where the 40000-ly came from unless the reference to the "central region" does not map directly to the APOD. Maybe the "central region" corresponds to roughly half the size (1/4 the area) of the APOD).
M101 is seen below within a field of view = M101's apparent size as listed in Wiki (28.8' x 26.9'). The yellow box identifies the APOD image FoV. The ratio of the two areas more correctly ≈ 5.7 instead of ~12 as your earlier full-extent graphic comparison indicates.
 
M101 - APOD FoV Comparison.jpg

Thanks - that makes more sense. But even in that smaller - though still quite large! - full extent image, although I can pretty clearly see wispy extended arm tendrils in the upper part of the image, I don't see anything in the lower part. Perhaps some image processing tricks will reveal something...

[alter-ego]

The text says this APOD spans about 40000 ly, and that the full galaxy's size is 170000 ly, or over four times the width and height of this image? That is, the full extent would fill this black space if imaged in its entirety?


M101 full extent.JPG


Seems hard to believe, unless those arms get really diffuse really far away. But perhaps this is just another case of "trying to pin down a galaxy's size is a fools errand"

The carefully measured field of view of this image is close to 13.2' x 10.3'. At 25 Mly distance, the composite image then corresponds to a size of
96000 ly x 74000 ly. I'm not sure where the 40000-ly came from unless the reference to the "central region" does not map directly to the APOD. Maybe the "central region" corresponds to roughly half the size (1/4 the area) of the APOD).
M101 is seen below within a field of view = M101's apparent size as listed in Wiki (28.8' x 26.9'). The yellow box identifies the APOD image FoV. The ratio of the two areas more correctly ≈ 5.7 instead of ~12 as your earlier full-extent graphic comparison indicates.
 
M101 - APOD FoV Comparison.jpg

Thanks - that makes more sense. But even in that smaller - though still quite large! - full extent image, although I can pretty clearly see wispy extended arm tendrils in the upper part of the image, I don't see anything in the lower part. Perhaps some image processing tricks will reveal something...

I cropped an amateur image (below) to the same Wiki FoV. I believe it reveals faint structures that touch all 4 edges, at least close enough to reasonably accept M101's visible size is the published 170,000 ly.
Note: Wiki lists M101's distance = 21 Mly, and the apparent-size FoV is then 164,000 ly x 176,000 ly.
 

I'm sure there's more to see with imaging/processing techniques to reveal even fainter structures, but aren't required here to be consistent with the published size.

[johnnydeep]

The carefully measured field of view of this image is close to 13.2' x 10.3'. At 25 Mly distance, the composite image then corresponds to a size of
96000 ly x 74000 ly. I'm not sure where the 40000-ly came from unless the reference to the "central region" does not map directly to the APOD. Maybe the "central region" corresponds to roughly half the size (1/4 the area) of the APOD).
M101 is seen below within a field of view = M101's apparent size as listed in Wiki (28.8' x 26.9'). The yellow box identifies the APOD image FoV. The ratio of the two areas more correctly ≈ 5.7 instead of ~12 as your earlier full-extent graphic comparison indicates.
 
M101 - APOD FoV Comparison.jpg

Thanks - that makes more sense. But even in that smaller - though still quite large! - full extent image, although I can pretty clearly see wispy extended arm tendrils in the upper part of the image, I don't see anything in the lower part. Perhaps some image processing tricks will reveal something...

I cropped an amateur image (below) to the same Wiki FoV. I believe it reveals faint structures that touch all 4 edges, at least close enough to reasonably accept M101's visible size is the published 170,000 ly.
Note: Wiki lists M101's distance = 21 Mly, and the apparent-size FoV is then 164,000 ly x 176,000 ly.
 
M101_Wiki Apparent Size_Same FoV.jpg

I'm sure there's more to see with imaging/processing techniques to reveal even fainter structures, but aren't required here to be consistent with the published size.

Thanks! I can see the wispy arms a little better in this color-inverted version of that pic:

M101 Color Inverted Showing Wispy Arms

m101 inverted showing wispy arms.png (232.84 KiB) Viewed 5720 times