APOD: M51: The Whirlpool Galaxy from Hubble (2022 Jun 13)

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APOD: M51: The Whirlpool Galaxy from Hubble (2022 Jun 13)

Post by APOD Robot » Mon Jun 13, 2022 4:05 am

Image M51: The Whirlpool Galaxy from Hubble

Explanation: The Whirlpool Galaxy is a classic spiral galaxy. At only 30 million light years distant and fully 60 thousand light years across, M51, also known as NGC 5194, is one of the brightest and most picturesque galaxies on the sky. The featured image is a digital combination of images taken in different colors by the Earth-orbiting Hubble Space Telescope, highlighting many sharp features. Anyone with a good pair of binoculars, however, can see this Whirlpool toward the constellation of the Hunting Dogs (Canes Venatici). M51 is a spiral galaxy of type Sc and is the dominant member of a whole group of galaxies. Astronomers speculate that M51's spiral structure is primarily due to its gravitational interaction with the smaller galaxy on the image left.

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Re: APOD: M51: The Whirlpool Galaxy from Hubble (2022 Jun 13)

Post by rj rl » Mon Jun 13, 2022 8:03 am

What would point to the spiral structure being due to the interactions with the companion? As opposed to it being spiral galaxy for usual reasons, whatever they might be

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Re: APOD: M51: The Whirlpool Galaxy from Hubble (2022 Jun 13)

Post by heehaw » Mon Jun 13, 2022 8:51 am

Hey! How come it's suddenly on its side?

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Re: APOD: M51: The Whirlpool Galaxy from Hubble (2022 Jun 13)

Post by AVAO » Mon Jun 13, 2022 10:36 am

APOD Robot wrote: Mon Jun 13, 2022 4:05 am ...At only 30 million light years distant and fully 60 thousand light years across, ....
Let's look to the facts:
Whirlpool Galaxy (NGC 5194): Distance: 31 Mly [https://www.nasa.gov/feature/goddard/20 ... ool-galaxy]
Dwarf Galaxy NGC 5195 is interacting with the Whirlpool Galaxy: Distance 25 ± 3 Mly (7.7 ± 1.0 Mpc)[https://arxiv.org/abs/astro-ph/0011223]

This means NGC 5195 is AHEAD of the Whirlpool Galaxy.
The two galaxies should therefore be at least 3 Mly apart.
This gives a fairly long intergalactic bridge.

Can this be right?
Last edited by AVAO on Mon Jun 13, 2022 10:42 am, edited 1 time in total.

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Re: APOD: M51: The Whirlpool Galaxy from Hubble (2022 Jun 13)

Post by Ann » Mon Jun 13, 2022 10:40 am

AVAO wrote: Mon Jun 13, 2022 10:36 am
APOD Robot wrote: Mon Jun 13, 2022 4:05 am ...At only 30 million light years distant and fully 60 thousand light years across, ....
Let's look to the facts:
Whirlpool Galaxy (NGC 5194): Distance: 31 Mly [https://www.nasa.gov/feature/goddard/20 ... ool-galaxy]
Dwarf Galaxy NGC 5195 is interacting with the Whirlpool Galaxy: Distance 25 ± 3 Mly (7.7 ± 1.0 Mpc)[https://arxiv.org/abs/astro-ph/0011223]

This means NGC 5195 is AHEAD of the Whirlpool Galaxy.
Can this be right?
There is no way that M51 and NGC 5195 are separated by at least 3 and possibly up to 9 light-years. These two galaxies are close together, certainly closer than Andromeda and the Milky Way, which are separated by some 2.5 light-years. And M31 and the Milky Way aren't even obviously interacting yet.

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Re: APOD: M51: The Whirlpool Galaxy from Hubble (2022 Jun 13)

Post by AVAO » Mon Jun 13, 2022 10:45 am

Ann wrote: Mon Jun 13, 2022 10:40 am
AVAO wrote: Mon Jun 13, 2022 10:36 am
APOD Robot wrote: Mon Jun 13, 2022 4:05 am ...At only 30 million light years distant and fully 60 thousand light years across, ....
Let's look to the facts:
Whirlpool Galaxy (NGC 5194): Distance: 31 Mly [https://www.nasa.gov/feature/goddard/20 ... ool-galaxy]
Dwarf Galaxy NGC 5195 is interacting with the Whirlpool Galaxy: Distance 25 ± 3 Mly (7.7 ± 1.0 Mpc)[https://arxiv.org/abs/astro-ph/0011223]

This means NGC 5195 is AHEAD of the Whirlpool Galaxy.
Can this be right?
There is no way that M51 and NGC 5195 are separated by at least 3 and possibly up to 9 light-years. These two galaxies are close together, certainly closer than Andromeda and the Milky Way, which are separated by some 2.5 light-years. And M31 and the Milky Way aren't even obviously interacting yet.

Ann
ThanX Ann
I have the same opinion on that.
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Re: APOD: M51: The Whirlpool Galaxy from Hubble (2022 Jun 13)

Post by De58te » Mon Jun 13, 2022 11:29 am

Your link doesn't actually give the distance of NGC 5195.

According to the European Space Agency webpage, https://sci.esa.int/web/hubble/-/37004- ... y-ngc-5195 it says that the Whirlpool is 31 million light years away, and that NGC 5195 is passing BEHIND the Whirlpool. Not in front.

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Re: APOD: M51: The Whirlpool Galaxy from Hubble (2022 Jun 13)

Post by Ann » Mon Jun 13, 2022 11:51 am

rj rl wrote: Mon Jun 13, 2022 8:03 am What would point to the spiral structure being due to the interactions with the companion? As opposed to it being spiral galaxy for usual reasons, whatever they might be
Interacting with a companion can indeed enhance the spiral structure of a galaxy.

Let's look at a few examples:


M81 is a grand design (=two-armed) spiral galaxy just like M51. Its arms are nowhere near as long or bright as the arms of M51. But in my opinion, interactions with M82 and NGC 3077 contributes to M81's grand design spiral shape.

Interacting with a small companion can both enhance and mess up a galaxy's spiral shape:


NGC 1097 and NGC 1512 are both interacting with a small companion, which has strongly influenced their shapes.


Not all interactions take place between very unequal partners:


Apparently similarly-massive spiral galaxies NGC 5426 and NGC 5427 are interacting in a way that has most probably enhanced the spiral shape of both of them. The arms of NGC 5427 are so bright and well defined that they are almost comparable with the arms of M51.

Sometimes the interaction between a large galaxy and a small companion can lead to dramatic results:


NGC 6872 has been called the largest spiral galaxy in the nearby universe, due to its enormously "out-stretched" arms.

But not all spiral galaxies interact with a companion:

NGC 2857 and friends Photonen Fangen.png
NGC 2857 and friends. Image: Photonen Fangen.

Exquisitely elegant spiral galaxy NGC 2857 has no companion... Or wait, did I speak too soon? Several galaxies can be seen in the field of NGC 2857. To the upper left (north east) of it is galaxy PGC 26694. Perhaps that is a small companion?

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Re: APOD: M51: The Whirlpool Galaxy from Hubble (2022 Jun 13)

Post by rj rl » Mon Jun 13, 2022 12:03 pm

Thanks for detailed explanation, Ann! I thought galaxies are well capable of producing grand design spirals on their own, perhaps I was mistaken.

NCTom

Re: APOD: M51: The Whirlpool Galaxy from Hubble (2022 Jun 13)

Post by NCTom » Mon Jun 13, 2022 12:26 pm

The central nucleus (yellow) seems particularly small for this size galaxy. Is this a result of the photo processing?

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Re: APOD: M51: The Whirlpool Galaxy from Hubble (2022 Jun 13)

Post by orin stepanek » Mon Jun 13, 2022 2:01 pm

M51_HubbleMiller_1080.jpg
Beautiful; just beautiful!
M51-SL14-RGB-196-Final-cC_1024.png
I like this view too! 8-) :D
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Re: APOD: M51: The Whirlpool Galaxy from Hubble (2022 Jun 13)

Post by Ann » Mon Jun 13, 2022 2:28 pm

rj rl wrote: Mon Jun 13, 2022 12:03 pm Thanks for detailed explanation, Ann! I thought galaxies are well capable of producing grand design spirals on their own, perhaps I was mistaken.
They probably are, but I think interactions help!

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Re: APOD: M51: The Whirlpool Galaxy from Hubble (2022 Jun 13)

Post by Chris Peterson » Mon Jun 13, 2022 3:24 pm

rj rl wrote: Mon Jun 13, 2022 12:03 pm Thanks for detailed explanation, Ann! I thought galaxies are well capable of producing grand design spirals on their own, perhaps I was mistaken.
I don't think there is any widely accepted theory of galaxy arm formation that depends upon interactions between galaxies. Spiral arms form from a combination of factors that all are part of single galaxies.

Interactions between galaxies typically prevent spirals from forming, or destroy existing ones. Examples where interactions enhance existing spirals are the exception, not the rule.
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Re: APOD: M51: The Whirlpool Galaxy from Hubble (2022 Jun 13)

Post by Ann » Mon Jun 13, 2022 5:27 pm

Chris Peterson wrote: Mon Jun 13, 2022 3:24 pm
rj rl wrote: Mon Jun 13, 2022 12:03 pm Thanks for detailed explanation, Ann! I thought galaxies are well capable of producing grand design spirals on their own, perhaps I was mistaken.
I don't think there is any widely accepted theory of galaxy arm formation that depends upon interactions between galaxies. Spiral arms form from a combination of factors that all are part of single galaxies.

Interactions between galaxies typically prevent spirals from forming, or destroy existing ones. Examples where interactions enhance existing spirals are the exception, not the rule.
I agree, Chris. Our best theory of the nature of spiral arms is the density wave theory, which says, basically, that because stars move on elliptical (more or less elongated) paths instead of in perfect circles, their large-scale collective movements in galactic disks will create spiral patterns. See the video below for a better explanation.

Click to play embedded YouTube video.

That said, I have certainly come across the hypothesis that the arms of M51 got longer because of the galaxy's interaction with NGC 5194. This si what the arms would have looked like if they had not been elongated through its interaction with the smaller elliptical:

M51 ESA annotated original arms.png

Can I guarantee that the arms of M51 would have ended where I say they would have ended in the annotated picture of M51, if it hadn't been for M51's interaction with NGC 5194? Of course not. I have just read that the interaction made the arms longer, and I thought it was fascinating.

I certainly agree that the merger of two spiral galaxies normally results in an elliptical galaxy. After all, there must be a reason why we see so many yellow elliptical galaxies in dense galaxy groups, where mergers must be common.

Dry merger IC 1181 IC 1178 Detlef Hartmann.png
A "dry" merger between IC 1179 and IC 1181 in the Hercules Cluster of galaxies.

But mergers can indeed "enhance" spiral galaxies instead of destroying them, even if it happens very rarely. Some years ago, astronomers found a few rare beasts called super spiral galaxies. They are humongous spirals, much too big to have formed by any other mechanisms than mergers:

NASA wrote:

A strange new kind of galactic beast has been spotted in the cosmic wilderness. Dubbed "super spirals," these unprecedented galaxies dwarf our own spiral galaxy, the Milky Way, and compete in size and brightness with the largest galaxies in the universe...

Super spirals can shine with anywhere from eight to 14 times the brightness of the Milky Way. They possess as much as 10 times our galaxy's mass. Their gleaming, starry disks stretch from twice to even four times the width of the Milky Way galaxy's approximately 100,000 light-year-wide disk, with the largest super spiral spanning a whopping 440,000 light-years. Super spirals also give off copious ultraviolet and mid-infrared light, signifying a breakneck pace of churning out new stars. Their star formation rate is as high as 30 times that of our own run-of-the-mill galaxy.

According to established astrophysical theory, spiral galaxies should not be able to attain any of these feats because their size and star-making potential are limited. As spiral galaxies grow by gravitationally attracting fresh, cool gas from intergalactic space, their masses reach a tipping point in which any newly captured gas rushes in too rapidly. This headlong gas heats up and prevents subsequent star formation in a process known as "quenching." Bucking this conventional wisdom, though, super spirals remain unquenched.

A vital hint about the potential origin of super spirals is that four out of the 53 seen by Ogle and colleagues clearly contain two galactic nuclei, instead of just one as usual. Double nuclei, which look like two egg yolks frying in a pan, are a telltale sign of two galaxies having just merged together. Conventionally, mergers of spiral galaxies are destined to become bloated, elliptical galaxies. Yet Ogle and colleagues speculate that a special merger involving two, gas-rich spiral galaxies could see their pooled gases settle down into a new, larger stellar disk -- presto, a super spiral.

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Re: APOD: M51: The Whirlpool Galaxy from Hubble (2022 Jun 13)

Post by beryllium732 » Mon Jun 13, 2022 11:24 pm

A beautiful image!

I have two questions. How come there's a lot of star forming regions of blue o-type stars and dust so near the black hole? Why doesn't it have the typical yellow bulge like many other galaxies have like our own or Andromedas? Does the galaxy really consist of so many blue star regions or is just a different colour made by Hubble?

The string of blue stars on the left side of the image is because it's been dragged by the gravitational force by the smaller galaxy consisting of a lot of yellow older stars?

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Re: APOD: M51: The Whirlpool Galaxy from Hubble (2022 Jun 13)

Post by AVAO » Tue Jun 14, 2022 3:24 am

De58te wrote: Mon Jun 13, 2022 11:29 am Your link doesn't actually give the distance of NGC 5195.

According to the European Space Agency webpage, https://sci.esa.int/web/hubble/-/37004- ... y-ngc-5195 it says that the Whirlpool is 31 million light years away, and that NGC 5195 is passing BEHIND the Whirlpool. Not in front.

"Some astronomers believe that the Whirlpool's arms are so prominent because of the effects of a close encounter with NGC 5195, the small, yellowish galaxy at the outermost tip of one of the Whirlpool's arms. At first glance, the compact galaxy appears to be tugging on the arm. Hubble's clear view, however, shows that NGC 5195 is passing behind the Whirlpool. The small galaxy has been gliding past the Whirlpool for hundreds of millions of years."

I'm not sure if this statement from the ESA website is really correct.

The Hubble closeup looks like this:

Image
https://live.staticflickr.com/65535/521 ... 6bc3_h.jpg Jac Berne (flickr)

If we then superimpose this with the infrared from Spitzer, we can see that the bright filament arm induced by NGC 5195 clearly correlates with the somewhat less recognizable dust arm in the Hubble image. For me this shows clearly that the two galaxies are in direct interaction

AVAO


Image
https://live.staticflickr.com/65535/521 ... 4639_h.jpg Jac Berne (flickr)

For comparison you can see here the somewhat larger situation in IR wavelengths:

Image
Jac Berne (flickr)

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Re: APOD: M51: The Whirlpool Galaxy from Hubble (2022 Jun 13)

Post by Ann » Tue Jun 14, 2022 5:26 am

beryllium732 wrote: Mon Jun 13, 2022 11:24 pm A beautiful image!

I have two questions. How come there's a lot of star forming regions of blue o-type stars and dust so near the black hole? Why doesn't it have the typical yellow bulge like many other galaxies have like our own or Andromedas? Does the galaxy really consist of so many blue star regions or is just a different colour made by Hubble?

The string of blue stars on the left side of the image is because it's been dragged by the gravitational force by the smaller galaxy consisting of a lot of yellow older stars?
We know that massive blue stars can form very near massive black holes. There are O-type stars quite close to the supermassive black hole of the Milky Way, Sgr A*, too.

Annotated image of the center of the Milky Way NASA ESA Spitzer Q D Wang.png
Center of the Milky Way. Sgr A* is the supermassive black hole.
The Arches Cluster and the Quintuplet Cluster contain O-type stars.
Image: NASA, ESA and Q.D. Wang

In the Milky Way, the massive Arches Cluster and Quintuplet Cluster are located some 100 light-years from our galaxy's supermassive black hole, Sgr A*. But there are massive stars even closer to Sgr A*:

Click to play embedded YouTube video.

A star called S2 has been found orbiting the black hole of the Milky Way at a distance that brings it, at closest approach, some four times the distance between the Sun and Neptune. S2 is a hot star, not an O-type star but the next best thing, a star of spectral class B0-B3. Read about S2 here.


In a way you are asking why M51 is so blue, when many or most other galaxies - like, say, Andromeda - seem to be so yellow. The short answer is that M51 is small galaxy that hasn't undergone a lot of star formation in the past, and therefore it doesn't have a huge underlying population of long-lived faint red and yellow stars. It also hadn't used up much of its available gas before it encountered NGC 5194, the yellow elliptical galaxy that it is interacting with. The interaction "stirred" the gas of M51 and made it form a lot of bright blue stars, which has given the entire galaxy a bluish appearance.

I really want to bring home the fact that M51 is a smallish galaxy:
Wikipedia wrote:

The Whirlpool Galaxy lies 28 million light-years from Earth and has an estimated diameter of 76,000 light-years. Overall the galaxy is about 43% the size of the Milky Way. Its mass is estimated to be 160 billion solar masses, or around 10.3% of the mass of Milky Way Galaxy.
Some 10% of the mass of the Milky Way is not that much.

Let's compare M51 with Andromeda:


Compare the huge bright yellowish bulge of Andromeda with the small (or non-existent?) bulge of M51.

According to Wikipedia, astronomers still argue about whether or not Andromeda is more massive than the Milky Way. But the way I understand it, Andromeda really is believed to contain more stars in its disk than the Milky Way does, and our own galaxy may or may not contain more dark matter than Andromeda.

So Andromeda is a large bright massive star-rich galaxy whose stars are predominantly old and red or yellow:
Wikipedia wrote:

Compared to the Milky Way, the Andromeda Galaxy appears to have predominantly older stars with ages >7×109 years. The estimated luminosity of the Andromeda Galaxy, ~2.6×1010 L, is about 25% higher than that of our own galaxy...

The rate of star formation in the Milky Way is much higher, with the Andromeda Galaxy producing only about one solar mass per year compared to 3–5 solar masses for the Milky Way...

This suggests that the latter once experienced a great star formation phase, but is now in a relative state of quiescence, whereas the Milky Way is experiencing more active star formation...

According to recent studies, the Andromeda Galaxy lies in what in the Galaxy color–magnitude diagram is known as the "green valley"...

In simulated galaxies with similar properties to the Andromeda Galaxy, star formation is expected to extinguish within about five billion years, even accounting for the expected, short-term increase in the rate of star formation due to the collision between the Andromeda Galaxy and the Milky Way.
So Andromeda has experienced great star formation in the past, which left behind myriads of small long-lived red and yellow stars. But now its rate of star formation has run down, and it is expected to stop forming stars almost completely in 5 billion years' time.

Andromeda shines brightly in yellow because of its tremendous numbers of old red and yellow stars, whereas smallish M51 has not had much star formation in the past and therefore only has a small underlying old yellow population. Now M51 is bluish because of its present high rate of star formation.

Finally, you asked about a string of blue stars on the left side of the image. I think you mean this:

APOD 13 June 2022 slightly annotated.png

The part that I marked in blue (at lower left) is simply the arm of M51 that has been stretched due to tidal forces of the encounter with NGC 5194. The blue stars belong to M51. As you said, the blue stars have been dragged there by the gravitational forces of NGC 5194.

Ann
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Re: APOD: M51: The Whirlpool Galaxy from Hubble (2022 Jun 13)

Post by beryllium732 » Tue Jun 14, 2022 8:28 am

Ann wrote: Tue Jun 14, 2022 5:26 am
beryllium732 wrote: Mon Jun 13, 2022 11:24 pm A beautiful image!

I have two questions. How come there's a lot of star forming regions of blue o-type stars and dust so near the black hole? Why doesn't it have the typical yellow bulge like many other galaxies have like our own or Andromedas? Does the galaxy really consist of so many blue star regions or is just a different colour made by Hubble?

The string of blue stars on the left side of the image is because it's been dragged by the gravitational force by the smaller galaxy consisting of a lot of yellow older stars?
We know that massive blue stars can form very near massive black holes. There are O-type stars quite close to the supermassive black hole of the Milky Way, Sgr A*, too.

Annotated image of the center of the Milky Way NASA ESA Spitzer Q D Wang.png
Center of the Milky Way. Sgr A* is the supermassive black hole.
The Arches Cluster and the Quintuplet Cluster contain O-type stars.
Image: NASA, ESA and Q.D. Wang

In the Milky Way, the massive Arches Cluster and Quintuplet Cluster are located some 100 light-years from our galaxy's supermassive black hole, Sgr A*. But there are massive stars even closer to Sgr A*:

Click to play embedded YouTube video.

A star called S2 has been found orbiting the black hole of the Milky Way at a distance that brings it, at closest approach, some four times the distance between the Sun and Neptune. S2 is a hot star, not an O-type star but the next best thing, a star of spectral class B0-B3. Read about S2 here.


In a way you are asking why M51 is so blue, when many or most other galaxies - like, say, Andromeda - seem to be so yellow. The short answer is that M51 is small galaxy that hasn't undergone a lot of star formation in the past, and therefore it doesn't have a huge underlying population of long-lived faint red and yellow stars. It also hadn't used up much of its available gas before it encountered NGC 5194, the yellow elliptical galaxy that it is interacting with. The interaction "stirred" the gas of M51 and made it form a lot of bright blue stars, which has given the entire galaxy a bluish appearance.

I really want to bring home the fact that M51 is a smallish galaxy:
Wikipedia wrote:

The Whirlpool Galaxy lies 28 million light-years from Earth and has an estimated diameter of 76,000 light-years. Overall the galaxy is about 43% the size of the Milky Way. Its mass is estimated to be 160 billion solar masses, or around 10.3% of the mass of Milky Way Galaxy.
Some 10% of the mass of the Milky Way is not that much.

Let's compare M51 with Andromeda:


Compare the huge bright yellowish bulge of Andromeda with the small (or non-existent?) bulge of M51.

According to Wikipedia, astronomers still argue about whether or not Andromeda is more massive than the Milky Way. But the way I understand it, Andromeda really is believed to contain more stars in its disk than the Milky Way does, and our own galaxy may or may not contain more dark matter than Andromeda.

So Andromeda is a large bright massive star-rich galaxy whose stars are predominantly old and red or yellow:
Wikipedia wrote:

Compared to the Milky Way, the Andromeda Galaxy appears to have predominantly older stars with ages >7×109 years. The estimated luminosity of the Andromeda Galaxy, ~2.6×1010 L, is about 25% higher than that of our own galaxy...

The rate of star formation in the Milky Way is much higher, with the Andromeda Galaxy producing only about one solar mass per year compared to 3–5 solar masses for the Milky Way...

This suggests that the latter once experienced a great star formation phase, but is now in a relative state of quiescence, whereas the Milky Way is experiencing more active star formation...

According to recent studies, the Andromeda Galaxy lies in what in the Galaxy color–magnitude diagram is known as the "green valley"...

In simulated galaxies with similar properties to the Andromeda Galaxy, star formation is expected to extinguish within about five billion years, even accounting for the expected, short-term increase in the rate of star formation due to the collision between the Andromeda Galaxy and the Milky Way.
So Andromeda has experienced great star formation in the past, which left behind myriads of small long-lived red and yellow stars. But now its rate of star formation has run down, and it is expected to stop forming stars almost completely in 5 billion years' time.

Andromeda shines brightly in yellow because of its tremendous numbers of old red and yellow stars, whereas smallish M51 has not had much star formation in the past and therefore only has a small underlying old yellow population. Now M51 is bluish because of its present high rate of star formation.

Finally, you asked about a string of blue stars on the left side of the image. I think you mean this:


APOD 13 June 2022 slightly annotated.png

The part that I marked in blue (at lower left) is simply the arm of M51 that has been stretched due to tidal forces of the encounter with NGC 5194. The blue stars belong to M51. As you said, the blue stars have been dragged there by the gravitational forces of NGC 5194.

Ann
Thank you again Ann! I always love your well written and easy to understand your writeups. I feel sad that Andromeda or the Milky Way will almost stop their star production in about five billion years.