APOD: M51: The Whirlpool Galaxy (2022 Sep 02)

[APOD Robot]

M51: The Whirlpool Galaxy

Explanation: Find the Big Dipper and follow the handle away from the dipper's bowl until you get to the last bright star. Then, just slide your telescope a little south and west and you'll come upon this stunning pair of interacting galaxies, the 51st entry in Charles Messier's famous catalog. Perhaps the original spiral nebula, the large galaxy with well defined spiral structure is also cataloged as NGC 5194. Its spiral arms and dust lanes clearly sweep in front of its companion galaxy (left), NGC 5195. The pair are about 31 million light-years distant and officially lie within the angular boundaries of the small constellation Canes Venatici. In direct telescopic views, M51 looks faint and fuzzy to the eye. But this remarkably deep image shows off details of the interacting galaxy's striking colors and galactic tidal debris. The image includes nearly 90 hours of narrowband data that also reveals a vast glowing cloud of reddish ionized hydrogen gas discovered in the M51 system.

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[VictorBorun]

I wonder if stellar arms are as chaotic as they seem.
There are foreground clouds at the left, can they eat into the visible picture of the M51 system?

[Ann]

Wow! I have never before seen that red "Barnad's Loop" of the M 51 system!

"Barnard's Loop" (faint red arc at left) of M51. Credit and copyright: Fabian Neyer.

It looks as if one of the tidal tails of satellite galaxy NGC 5195, as well as a gaseous outflow also seemingly from NGC 5195, have met a "wall of resistance" to its north. Yes, because north is at left in this APOD.

The tidal tail has been bent as it met the wall of resistance, and there really seems to be a diffuse beige-colored "wall" - the same color as the tidal tail of old stars from NGC 5195 - that forms a vertical structure in this APOD. And the gas that was pushed out of the central parts of NGC 5195 has been ionized so that it glows red in a galactic version of Barnard's Loop in Orion.

The real Barnard's Loop of Orion. Photo: Hewholooks at English Wikipedia.

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The Veil Nebula supernova remnant. Photo: Stub Mandrel.

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It seems certain, at least to me, that the red "arclet" of the M51 system (which is thousands of light-years long, of course) is a shock front of some sort.

The glowing Veil Nebula is a typical shock front. We know what kind of shock created the Veil Nebula, of course. It was a supernova explosion that flung several solar masses worth of stellar material slamming into the surrounding interstellar medium.

In the M51 system, millions of solar masses of stars and gas have been flung out of NGC 5195 because of its interaction with M51. And then these stars and this gas have slammed into a wall of resistance, likely a large gas cloud of some sort. The flung-out galactic gas and the shock front of the intergalactic gas it encountered have been ionized as one gaseous jet slammed into a more stationary body of gas like an out-of-control train. As for the stars in the stellar tidal tail, well, they just can't get past!

Ann

[orin stepanek]

Beautiful Whirlpool Galaxy! Sad that it is process of merger!
https://youtu.be/FiTmqrQ5bLU

[AVAO]

...It seems certain, at least to me, that the red "arclet" of the M51 system (which is thousands of light-years long, of course) is a shock front of some sort.

The glowing Veil Nebula is a typical shock front. We know what kind of shock created the Veil Nebula, of course. It was a supernova explosion that flung several solar masses worth of stellar material slamming into the surrounding interstellar matter.

In the M51 system, millions of solar masses of stars and gas have been flung out of NGC 5195 because of its interaction with M51. And then these stars and this gas have slammed into a wall of resistance, likely a large gas cloud of some sort. The flung-out galactic gas and the shock front of the intergalactic gas it encountered have been ionized as one gaseous jet slammed into a more stationary body of gas like an out-of-control train. As for the stars in the stellar tidal tail, well, they just can't get past!

Ann

What a great image, Fabian Neyer!

ThanX Ann

Is your theory based on specific sources?
...If I look at the region in radio wavelengths, I would rather suspect "dissipated" spiral arms. The comparison with Barnard's Loop makes sense, because it is also easily recognizable in radio ...

Jac


Original Radiowave Data (21cm): NRAO (National Radio Astronomy Observatory)

[Ann]

What a great image, Fabian Neyer!

ThanX Ann

Is your theory based on specific sources?
...If I look at the region in radio wavelengths, I would rather suspect "dissipated" spiral arms. The comparison with Barnard's Loop makes sense, because it is also easily recognizable in radio ...

Jac


Original Radiowave Data (21cm): NRAO (National Radio Astronomy Observatory)

No, sorry, my hypothesis is not based on any specific sources. I just describe what I see and try to think of other cosmic objects that look similar - galaxies, nebulas, clusters, jets etc - so that I have a basis for comparison.

I agree with you that the tidal tails of NGC 5195 do indeed look like "red and dead" spiral arms. I find it not at all unlikely that NGC 5195 may originally have been a spiral galaxy rather similar to NGC 4314.

NGC 4314, with a nuclear ring of star formation and 'red and dead' spiral arms. Credit: G. Fritz Benedict, Andrew Howell, Inger Jorgensen, David Chapell (University of Texas), Jeffery Kenney (Yale University), and Beverly J. Smith (CASA, University of Colorado), and NASA/ESA.

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As you can see, NGC 4314 is an "all red and dead" spiral galaxy, except for its nuclear ring of star formation. If NGC 5195 was originally anything like NGC 4314, that would explain its arm-like tidal tails of old stars, as well as its jet of gas from its center.

Thanks for the added info about the radio features of the M51 system!

Ann

[VictorBorun]

It looks as if one of the tidal tails of satellite galaxy NGC 5195, as well as a gaseous outflow also seemingly from NGC 5195, have met a "wall of resistance" to its north. Yes, because north is at left in this APOD.

I thought the stellar fraction of a disk galaxy has low viscosity; a disk or an arm hitting a denser media wall would get decomposed: the gas and the dust would stop while the stars (and rogue planets, and brown dwarfs) would move on

[Ann]

It looks as if one of the tidal tails of satellite galaxy NGC 5195, as well as a gaseous outflow also seemingly from NGC 5195, have met a "wall of resistance" to its north. Yes, because north is at left in this APOD.

I thought the stellar fraction of a disk galaxy has low viscosity; a disk or an arm hitting a denser media wall would get decomposed: the gas and the dust would stop while the stars (and rogue planets, and brown dwarfs) would move on

The math idiot (me) explains:

The stars were kicked out of their orbits around the center of NGC 5195 because they felt the gravitational force of the interaction between NGC 5195 and M51. No star was kicked out because a physical object actually hit it.

In the same way, the stars that were kicked out of their orbits around NGC 5195 and moved collectively as a long tidal tail felt the force of the wall of resistance when they approached it. They were deflected collectively because of this force.

But, hey! That is not correct! I must apologize to Einstein and take back what I said about "the force of gravity". There is no force of gravity, only curved spacetime.

Spacetime and matter. Illustration: Pk0001.

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The stars that moved around the center of NGC 5195 did so because of the way the mass of this galaxy caused spacetime to curve. As NGC 5195 started interacting with M51, the curvature of spacetime changed. This changed curvature caused stars in the outskirts of NGC 5195 to move, collectively, outward along the direction of the tangent.

As the stars approached whatever was producing the "wall of resistance", likely a gas cloud or even a clump of dark matter, the curvature of spacetime changed again, and the stars changed direction again.

Because, as astrophysicist John Wheeler put it:

Spacetime tells matter how to move.
Matter tells spacetime how to curve.

Ann

[VictorBorun]

I would rather suspect "dissipated" spiral arms.
Jac


Original Radiowave Data (21cm): NRAO (National Radio Astronomy Observatory)

Tried to find a better radio and found only a poorer one

[VictorBorun]

radio 21 cm over APOD

Click to view full size image 1 or image 2

Can't see if the red nebula on the right is a part of 21 cm radio fragmentary arm