APOD: A View Toward M101 (2017 May 20)

[APOD Robot]

A View Toward M101

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 galaxy. M101 was also one of the original spiral nebulae observed by Lord Rosse's large 19th century telescope, the Leviathan of Parsontown. M101 shares this modern telescopic field of view with spiky foreground stars within the Milky Way, and more distant background galaxies. The colors of the Milky Way stars can also be found in the starlight from the large island universe. Its core is dominated by light from cool yellowish stars. Along its grand spiral arms are the blue colors of hotter, young stars mixed with obscuring dust lanes and pinkish star forming regions. 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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[JohnNoe]

Bad link to Leviathan (telescope) in latest APOD.

[Boomer12k]

Such a nice picture! Very expansive, with a wide view of the outer arm areas. Is there something close by disrupting it, or was it a merger... it looks like merger to me as the bottom looks like a swirl from a small galaxy. MBG... my best guess...

Here is my image from my Meade 10" LX200 GPS. Not as bright and clear, not as expensive a camera, not as long an exposure...but you can see the same yellowish center, and blu-ish arms...I think is about 30-45 sec. exposure. DSI 2 Color camera.
I now have filters, and might try them out.

WE have finally hit Summer conditions, getting hot in the next couple days. Hopefully VERY clear, will take Meade 8" LS scope to nearby field and get some pix. Might post some in the Cafe...

Clear Skies, all...
:---[===] *

[Ann]

Well done Boomer!

And it's a very fine APOD. I'll probably come back to comment more on it later.

Ann

[heehaw]

I like this psychologically, in that the picture is not centered on the galaxy!

[rstevenson]

Bad link to Leviathan (telescope) in latest APOD.

Yes. Here's a better one...
Leviathan of Parsonstown

Rob

[sillyworm]

Nice capture Boomer! Is that light hazy bluish area SW of the Galaxy PART of one of the arms?

[Ann]

Click to view full size image

M101 and interacting dwarf galaxy NGC 5474.
Photo: Kfir Simon.

In my opinion, M101 doesn't look like it has undergone any recent mergers. Actual mergers mess up galaxies terrifically and destroy the spiral structure of spiral galaxies, but the inner spiral structure of M101 looks too well-preserved to have undergone such a catastrophe.

Clearly, though, M101 is in the throes of tidal forces stretching and tearing at its long spiral arms. My belief is that the main culprit of stirring up the seas through which M101 is sailing is its satellite galaxy NGC 5474. As you can see in the picture at left, NGC 5474 has been caught in the storm itself, and it has come close to having its entire bulge torn loose from its starforming disk. A very fine 565,25 KB picture of NGC 5474 is here.

As you can see in Kfir Simon's image, the tidal forces created by the interaction between M101 and NGC 5474 have made the disk of NGC 5474 become displaced "to the right", and the spiral arms of M101 become displaced "to the left". (The small satellite galaxy visible in today's APOD at 6 o'clock is NGC 5477, and it can be seen at 7 o'clock in Kfir Simon's picture. But NGC 5477 is probably too puny to have affected the shape of M101 very much.)

An interesting aspect of the interaction between M101 and NGC 5474 is that the arms of M101 appears to have become longer because of it, while arms of NGC 5474 seems to have mostly merged with the galaxy's disk. Nevertheless, some faint outer arm features of NGC 5474 can be seen in Kfir Sion's image.

It should be pointed out that M101 has many other satellite galaxies as well, and one or several of the other satellites may have contributed to giving M101 its long spiral arms and its asymmetrical spiral pattern.

Click to view full size image

M81. Photo: NASA, ESA and the Hubble Heritage Team (STScI/AURA).

M101 can be said to be all bluster and little substance! No, that is a terrible exaggeration, but it is true that M101 must be quite lightweight for its humongous size. That is because the yellow population of M101 is quite small, and old yellow stars are quite massive in relation to how little light they produce. Therefore, if a galaxy produces a lot of yellow light, that is a dead giveaway that the galaxy is quite massive for its size. Look at the huge yellow bulge of galaxy M81, and compare that bulge with the neat little bulge of M101!

Wikipedia wrote about M101:
M101 is a large galaxy comparable in size to the Milky Way. With a diameter of 170,000 light-years it is roughly equal the size of the Milky Way. It has a disk mass on the order of 100 billion solar masses, along with a small central bulge of about 3 billion solar masses.

Well, I thought the diameter of the Milky Way was considered to be "only" about 100,000 light-years. On the other hand, the Milky Way may well be more massive than the Pinwheel galaxy.

Wikipedia wrote about the Milky Way:
The Milky Way is the second-largest galaxy in the Local Group, with its stellar disk approximately 100,000 ly (30 kpc) in diameter, and, on average, approximately 1,000 ly (0.3 kpc) thick.
...
Estimates of the mass of the Milky Way vary, depending upon the method and data used. At the low end of the estimate range, the mass of the Milky Way is 5.8×10¹¹ solar masses (M_☉), somewhat less than that of the Andromeda Galaxy.

I think 5.8×10¹¹ is equal to 580 billion solar masses, which suggests that the Milky Way is 5.8 times more massive than M101.

So M101 is popping fireworks like crazy, but there may not be all that much substance behind its sound and fury!

Ann

[neufer]

Wikipedia wrote about M101:
M101 is a large galaxy comparable in size to the Milky Way. With a diameter of 170,000 light-years it is roughly equal the size of the Milky Way. It has a disk mass on the order of 100 billion solar masses, along with a small central bulge of about 3 billion solar masses.

Well, I thought the diameter of the Milky Way was considered to be "only" about 100,000 light-years. On the other hand, the Milky Way may well be more massive than the Pinwheel galaxy.

<<The Milky Way is the second-largest galaxy in the Local Group, with its stellar disk approximately 100,000 ly in diameter, and, on average, approximately 1,000 ly thick. A ring-like filament of stars wrapping around the Milky Way may belong to the Milky Way itself, rippling above and below the relatively flat galactic plane. If so, that would mean a diameter of 150,000–180,000 light-years.

Estimates of the mass of the Milky Way vary, depending upon the method and data used. At the low end of the estimate range, the mass of the Milky Way is 5.8×10¹¹ solar masses (M_☉), somewhat less than that of the Andromeda Galaxy.>>

I think 5.8×10¹¹ is equal to 560 [sic] billion solar masses, which suggests that the Milky Way is 5.6 times more massive than M101.

• M101 has a disk mass on the order of 100 billion solar mass.
  
  That clearly excludes dark matter mass and other components.
  
  (M101 also has over twice the number of stars as the Milky Way.)

[Ann]

(M101 also has over twice the number of stars as the Milky Way.)

Not that I necessarily doubt you on this, but I haven't been able to confirm your claim as I searched the net. Could you please post a link?

EDIT: I take it back! It is in the Wikipedia article!

Okay. I'll still say that if many of the stars in M101 are young, then the claim that M101 has a trillion stars seems uncertain to me. Remember that most stars are reddish, small and faint. Are we sure that M101 has had time to create so many small red stars, considering its incredibly blue colors? M101 has a B-V index of 0.450, which is indeed pretty incredible for a galaxy of such a size.

Ann

[Ann]

Deborah Byrd of Earthsky wrote:
Astronomers have peered into eight relatively nearby elliptical galaxies and made a discovery suggesting that small, dim red dwarf stars in these sorts of galaxies might be 20 times more plentiful than in our spiral-shaped Milky Way galaxy.
...
Until now, astronomers hadn’t been able to detect them in galaxies other than our own Milky Way and its nearest neighbors. Astronomers have used powerful instruments on the Keck Observatory in Hawaii to detect the faint signature of red dwarfs in eight massive, relatively nearby galaxies called elliptical galaxies, which are located between about 50 million and 300 million light-years away. They discovered that the red dwarfs, which are only between 10 and 20 percent as massive as the sun, were much more bountiful than expected.
...
The team discovered that there are about 20 times more red dwarfs in elliptical galaxies than in the Milky Way, said Charlie Conroy of the Harvard-Smithsonian Center for Astrophysics, who was also involved in the research.

Click to view full size image

Massive elliptical galaxy M87.
Photo: David Malin.

I don't know if the claim that small red dwarfs are so plentiful in massive elliptical galaxies has been confirmed, but the suggestion makes sense to me. Large elliptical galaxies, which are usually found in dense galactic clusters, must have merged with many other galaxies to grow as massive as they are. They have stopped forming stars long ago, but small red stars are almost immortal, and the massive elliptical galaxies must have grown huge numbers of red dwarfs by themselves, as well as incorporated more and more and more of these little red critters from other galaxies over time.

And these big elliptical galaxies have red colors, too. Really. The B-V of M87 is 0.960, and the U-B of the same galaxy is a whopping and extremely red 0.740. I can believe that M87 contains tremendous numbers of (small red) stars, but I'm far more doubtful when it comes to M101.

Ann

[Snowwie]

A View Toward M101
About 170,000 light-years across, this galaxy is enormous, almost twice the size of our own Milky Way galaxy.

Wasn't it recently made clear that the Milky Way was far more bigger than previous thought?

Not only because it appeared to rotate faster than previous thought but also....
that because it was corrugated its size could be well up to 150,000 to 180,000 light years, making it on par with the size of M101.

Even Wikipedia confirms this:
https://en.wikipedia.org/wiki/Pinwheel_Galaxy

Oh never mind I asked, It has been asked in the topic itself.

[danhammang]

Beautiful shot. Thanks for sharing.

[Ann]

• M101 has a disk mass on the order of 100 billion solar mass.
  
  That clearly excludes dark matter mass and other components.
  
  (M101 also has over twice the number of stars as the Milky Way.)

I've tried and tried to confirm your claim that M101 has over twice the number of stars as the Milky Way. The claim that M101 has a trillion stars, 10¹² comes from Wikipedia. But Wikipedia itself doesn't provide a link to its claim.

But I decided to try to find out how many stars there are in Malin 1, a tremendously huge low-mass surface brightness galaxy. That, too, provided extremely frustrating. Nevertheless, I did find this:

Click to view full size image

Malin 1. Galaz et al., 2016/NASA/JPL-Caltech

Ken Croswell wrote:

Discovered in 1986, Malin 1 is the largest spiral galaxy known. Its spiral disk is 650,000 light-years across--several times bigger than the Milky Way's--but the stars are so spread out from one another that the disk looks extremely diffuse, having what astronomers call a low surface brightness.
...
Despite its diffuse light, Malin 1 emits eight times more light than the entire Milky Way, which is itself a giant galaxy. Furthermore, Malin 1 abounds with gas, containing 50 billion solar masses of atomic hydrogen gas--more than ten times the amount in the Milky Way.
...
Within 30,000 light-years of Malin 1's center lies a normal barred spiral galaxy having a Hubble type of SB0 or SBa. The galaxy's central bulge is 10,000 light-years across, and its bar is 30,000 light-years long. The disk is smooth with no signs of dust lanes or star-forming regions.
...
(Aaron) Barth calculates that 80 percent of Malin 1's light comes from that extended disk, not from the normal disk he has discovered.

According to Wikipedia, which links to Barth, Aaron J. (March 2007). "A Normal Stellar Disk in the Galaxy Malin 1". The Astronomical Journal. 133 (3): 1085–1091. arXiv:astro-ph/0701018], Malin 1 has a mass of about 10¹² solar masses. That would be about ten times more than the disk mass of M101, according to https://en.wikipedia.org/wiki/Pinwheel_ ... 01_mass-11] and Comte, G.; Monnet, G. & Rosado, M. (1979). "An optical study of the galaxy M 101 - Derivation of a mass model from the kinematic of the gas". Astronomy and Astrophysics. 72: 73–81.

Okay, let's see now. Malin 1 emits eight times more light than the Milky Way - doesn't that mean that it must contain many more stars than Milky Way? Alternatively, it might mean that the individual stars of Malin 1 are, on average, brighter than the stars of the Milky Way. Okay, that's possible:

S. Boissier et al. wrote:
Based on our model, the extreme disk of Malin 1 is found to have a long history of relatively low star formation (about 2 M_⊙ yr−1).

The star formation rate of the Milky Way is believed to be about 1 M_⊙ yr−1, so Malin 1 would convert twice as much gas into stars as the Milky Way during a given year. This higher rate of star formation in Malin 1 would also produce a larger number of high-mass and therefore more luminous stars. As for M101, it has definitely produced a terrific number of high-mass stars!

Let's assume that the number of stars of Malin 1 is either somewhat similar to the number of stars in the Milky Way, or somewhat higher, perhaps double that of the Milky Way. But Malin 1 has ten times more gas than the Milky Way. Of course, Malin 1 is definitely more massive than the Milky Way, too, perhaps twice as massive. To me, it's hard to believe that Malin 1 doesn't contain a lot of dark matter, too. Or perhaps it doesn't? Could it be that Malin 1 has formed out of a huge blob of gas that has somehow "come loose" from its dark matter moorings. So perhaps the Milky Way contains more dark matter than Malin 1 - and perhaps more dark matter than M101, too?

Questions, questions. I will stop discussing the mass and the number of stars of M101, Malin 1 and the Milky Way now!

Ann

[starsurfer]

• M101 has a disk mass on the order of 100 billion solar mass.
  
  That clearly excludes dark matter mass and other components.
  
  (M101 also has over twice the number of stars as the Milky Way.)

I've tried and tried to confirm your claim that M101 has over twice the number of stars as the Milky Way. The claim that M101 has a trillion stars, 10¹² comes from Wikipedia. But Wikipedia itself doesn't provide a link to its claim.

But I decided to try to find out how many stars there are in Malin 1, a tremendously huge low-mass surface brightness galaxy. That, too, provided extremely frustrating. Nevertheless, I did find this:

Click to view full size image

Malin 1. Galaz et al., 2016/NASA/JPL-Caltech

Ken Croswell wrote:

Discovered in 1986, Malin 1 is the largest spiral galaxy known. Its spiral disk is 650,000 light-years across--several times bigger than the Milky Way's--but the stars are so spread out from one another that the disk looks extremely diffuse, having what astronomers call a low surface brightness.
...
Despite its diffuse light, Malin 1 emits eight times more light than the entire Milky Way, which is itself a giant galaxy. Furthermore, Malin 1 abounds with gas, containing 50 billion solar masses of atomic hydrogen gas--more than ten times the amount in the Milky Way.
...
Within 30,000 light-years of Malin 1's center lies a normal barred spiral galaxy having a Hubble type of SB0 or SBa. The galaxy's central bulge is 10,000 light-years across, and its bar is 30,000 light-years long. The disk is smooth with no signs of dust lanes or star-forming regions.
...
(Aaron) Barth calculates that 80 percent of Malin 1's light comes from that extended disk, not from the normal disk he has discovered.

According to Wikipedia, which links to Barth, Aaron J. (March 2007). "A Normal Stellar Disk in the Galaxy Malin 1". The Astronomical Journal. 133 (3): 1085–1091. arXiv:astro-ph/0701018], Malin 1 has a mass of about 10¹² solar masses. That would be about ten times more than the disk mass of M101, according to https://en.wikipedia.org/wiki/Pinwheel_ ... 01_mass-11] and Comte, G.; Monnet, G. & Rosado, M. (1979). "An optical study of the galaxy M 101 - Derivation of a mass model from the kinematic of the gas". Astronomy and Astrophysics. 72: 73–81.

Okay, let's see now. Malin 1 emits eight times more light than the Milky Way - doesn't that mean that it must contain many more stars than Milky Way? Alternatively, it might mean that the individual stars of Malin 1 are, on average, brighter than the stars of the Milky Way. Okay, that's possible:

S. Boissier et al. wrote:
Based on our model, the extreme disk of Malin 1 is found to have a long history of relatively low star formation (about 2 M_⊙ yr−1).

The star formation rate of the Milky Way is believed to be about 1 M_⊙ yr−1, so Malin 1 would convert twice as much gas into stars as the Milky Way during a given year. This higher rate of star formation in Malin 1 would also produce a larger number of high-mass and therefore more luminous stars. As for M101, it has definitely produced a terrific number of high-mass stars!

Let's assume that the number of stars of Malin 1 is either somewhat similar to the number of stars in the Milky Way, or somewhat higher, perhaps double that of the Milky Way. But Malin 1 has ten times more gas than the Milky Way. Of course, Malin 1 is definitely more massive than the Milky Way, too, perhaps twice as massive. To me, it's hard to believe that Malin 1 doesn't contain a lot of dark matter, too. Or perhaps it doesn't? Could it be that Malin 1 has formed out of a huge blob of gas that has somehow "come loose" from its dark matter moorings. So perhaps the Milky Way contains more dark matter than Malin 1 - and perhaps more dark matter than M101, too?

Questions, questions. I will stop discussing the mass and the number of stars of M101, Malin 1 and the Milky Way now!

Ann

Your post reminds me of the galaxy UGC 1382. Did you know there is a Malin 2?

[Ann]

Your post reminds me of the galaxy UGC 1382. Did you know there is a Malin 2?

I believe I've heard of Malin 2, but I don't think it was as remarkable as Malin 1, so I haven't googled it.

But thanks for reminding me of UGC 1832!

Click to view full size image

UGC 1832, the "Frankenstein" galaxy.
At left, in optical light, UGC 1382 appears to be a simple elliptical galaxy.
But spiral arms emerged when astronomers incorporated ultraviolet
and deep optical data (middle). Combining that with a view of low-density
hydrogen gas (shown in green at right), scientists discovered that UGC 1382 is gigantic.
Credits: NASA/JPL/Caltech/SDSS/NRAO/L. Hagen and M. Seibert

NASA wrote:

A new study to be published in the Astrophysical Journal reveals the secret of UGC 1382, a galaxy that had originally been thought to be old, small and typical. Instead, scientists using data from NASA telescopes and other observatories have discovered that the galaxy is 10 times bigger than previously thought and, unlike most galaxies, its insides are younger than its outsides, almost as if it had been built using spare parts.

"This rare, 'Frankenstein' galaxy formed and is able to survive because it lies in a quiet little suburban neighborhood of the universe, where none of the hubbub of the more crowded parts can bother it," said study co-author Mark Seibert of the Observatories of the Carnegie Institution for Science, Pasadena, California. "It is so delicate that a slight nudge from a neighbor would cause it to disintegrate."

Indeed, there are clear similarities between Malin 1 and UGC 1832. Both have normal-sized to small bright yellow centers and huge, faint, blue arms. UGC 1832 sits in an enormous reservoir of gas, too. Importantly, both galaxies live in "quiet neighborhoods", where they are safe from interactions with "neighboring bullies".

Click to view full size image

M101 and NGC 5474. Photo: Kfir Simon.

I've been thinking some more about the number of stars in M101. Wikipedia says that this galaxy contains a trillion stars, but does not provide a link to its claim.

Yes, but now take a look at Kfir Simon's picture of M101 and NGC 5474, which I showed in a previous post, too. Look at the huge faint outer arms of M101 which are revealed in Kfir Simon's image. These faint outer arms appear to consist of a mostly old, non-blue population. Since old non-blue stars are faint, the vast outer arms must contain huge numbers of stars. So maybe M101 does contain a trillion stars after all.

Adam Block's image of M101 also gives the appearance of a truly vast galaxy, but Kfir Simon's picture makes the outer arms look more non-blue and therefore more rich in small stars.

Well, interesting! M101 does show some similarities to a low surface brightness galaxy with enormous arms.

Ann