APOD: M104: The Sombrero Galaxy (2021 May 14)

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APOD: M104: The Sombrero Galaxy (2021 May 14)

Post by APOD Robot » Fri May 14, 2021 4:11 am

Image M104: The Sombrero Galaxy

Explanation: A gorgeous spiral galaxy, M104 is famous for its nearly edge-on profile featuring a broad ring of obscuring dust lanes. Seen in silhouette against an extensive central bulge of stars, the swath of cosmic dust lends a broad brimmed hat-like appearance to the galaxy suggesting a more popular moniker, the Sombrero Galaxy. This sharp optical view of the well-known galaxy made from ground-based image data was processed to preserve details often lost in overwhelming glare of M104's bright central bulge. Also known as NGC 4594, the Sombrero galaxy can be seen across the spectrum, and is host to a central supermassive black hole. About 50,000 light-years across and 28 million light-years away, M104 is one of the largest galaxies at the southern edge of the Virgo Galaxy Cluster. Still the colorful spiky foreground stars in this field of view lie well within our own Milky Way galaxy.

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Re: APOD: M104: The Sombrero Galaxy (2021 May 14)

Post by Ann » Fri May 14, 2021 6:00 am

Since I am the self-appointed Galaxy Woman of Starship Asterisk* (not that Geck wouldn't run me over like a steamroller if she made comments here more often), I should say something about M104, the Sombrero Galaxy!

M104 GALEX.png

And let me start by saying that this galaxy is not one of my favorites. Why? You guessed it - it is totally non-blue! GALEX, the now-defunct space telescope that photographed galaxies at ultraviolet wavelengths, took this small blurry picture of M104. As you can see in the picture above, the image looks all yellow, which means that there are no concentrations of hot blue stars anywhere in this galaxy. Oh no, say I!


But there are more interesting things to say about M104. Did you know that the Sombrero is a Kinder Surprise Chocolate Egg of a galaxy, which is to say that it is two galaxies in one?


Jason Major of Universetoday.com wrote:

The Sombrero galaxy has a split personalty, according to recent observations by NASA’s Spitzer Space Telescope. Infrared imaging has revealed a hazy elliptical halo of stars enveloping a dual-structured inner disk; before this, the Sombrero galaxy was thought to be only disk-shaped...

Spitzer discerned that the flat disk within the galaxy is made up of two sections — an inner disk composed almost entirely of stars with no dust, and an outer ring containing both dust and stars.
In the Spitzer image, red means dust and blue means stars. It is easy to spot the red dust ring. But can you see the dark blue "gap" inside the ring, which means that there are relatively few stars there, and further in, a more light-colored and more star-rich disk?
Jason Major wrote:

“The Sombrero is more complex than previously thought,” said Dimitri Gadotti of the European Southern Observatory in Chile and lead author of the report. “The only way to understand all we know about this galaxy is to think of it as two galaxies, one inside the other.”

Although it might seem that the Sombrero is the result of a collision between two separate galaxies, that’s actually not thought to be the case. Such an event would have destroyed the disk structure that’s seen today; instead, it’s thought that the Sombrero accumulated a lot of extra gas billions of years ago when the Universe was populated with large clouds of gas and dust. The extra gas fell into orbit around the galaxy, eventually spinning into a flattened disk and forming new stars.

So not only is M104 a galactic Kinder Chocolate Egg Surprise, but it is also the planet Saturn of galaxies! Its disk - at least its outer disk - has fallen into orbit around the galaxy's elliptical center (with its central supermassive 1 billion solar masses black hole) in the same way that the rings of Saturn have fallen into orbit around the Solar System's large sixth planet!

Fancy that! 🪐

Ann
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Re: APOD: M104: The Sombrero Galaxy (2021 May 14)

Post by XgeoX » Fri May 14, 2021 9:58 am

What an absolute gem of a galaxy and what a great view we have of it. It’s one that will get people interested in astronomy!

By the way... do not adjust your tv set!

Image

Look familiar? 🙂

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Re: APOD: M104: The Sombrero Galaxy (2021 May 14)

Post by orin stepanek » Fri May 14, 2021 11:48 am

m104apodsub800c.jpg
If we were approaching M104; would it appear like this;

Or,


m104.jpg
like this!


I mean, why does the halo look so much fuller on the one than the other? Today's APOD, the Sombrero looks completely flat; on the other, not so! :?
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Re: APOD: M104: The Sombrero Galaxy (2021 May 14)

Post by NCTom » Fri May 14, 2021 2:17 pm

Similar to Orin's question, just how large is the central bulge of this galaxy and is it common for a galaxy to have a star halo around it seemingly twice its diameter?

Also, there is a blue something at the bottom of the photo just right of center, especially clear on the enlargement. Why so blue?

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Re: APOD: M104: The Sombrero Galaxy (2021 May 14)

Post by neufer » Fri May 14, 2021 3:03 pm

orin stepanek wrote:
Fri May 14, 2021 11:48 am

If we were approaching M104; would it appear like this;

Or, like this!

I mean, why does the halo look so much fuller on the one than the other? Today's APOD, the Sombrero looks completely flat; on the other, not so! :?
As Ann points out, the flat Sombrero is an IR view that zeros in on the flat dusty disk.

If we were approaching M104; would it appear blue shifted so we would observe the flat IR dusty disk.
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Re: APOD: M104: The Sombrero Galaxy (2021 May 14)

Post by Ann » Fri May 14, 2021 3:15 pm

NCTom wrote:
Fri May 14, 2021 2:17 pm
Similar to Orin's question, just how large is the central bulge of this galaxy and is it common for a galaxy to have a star halo around it seemingly twice its diameter?

Also, there is a blue something at the bottom of the photo just right of center, especially clear on the enlargement. Why so blue?
As to why M104 looks the way it does, check out my first post here. To summarize, M104 is "two galaxies in one", an elliptical galaxy with an accreted ring of stars and dust orbiting around it, not entirely unlike the rings of Saturn.

"The blue something" at bottom right in the APOD looks like just another star, except that it's very blue.

There are a couple of things it could be. It could be a white dwarf, and it could also possibly be a quasar, maybe even a blazar, which is an active galaxy where we look straight into the maw of the jet rushing our way from the supermassive black hole. We should bear in mind that white dwarfs and quasars are likely to be very faint, the white dwarfs because they are intrinsically faint, and the quasars because they are terribly distant. In theory, the blue starlike thing could also be a singularly bright and blue supernova in our own galaxy, but you can bet your boots we would have heard about it if there had been a new supernova in the Milky Way. And we are extremely unlikely to see a supernova in another galaxy in a picture like this, because it would have to be exceedingly faint - bear in mind that we don't even see a host galaxy! Maybe the mystery object could even be a small bright unusually blue planetary nebula.

The most likely object, in my opinion, is a distant unreddened O-type (or even an early B-type) star, particularly one that we see rotating pole on, so that it would it look especially blue from our perspective. If so, it would be a "normal but rare" object in the Milky Way.

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Re: APOD: M104: The Sombrero Galaxy (2021 May 14)

Post by johnnydeep » Fri May 14, 2021 9:00 pm

It may not be one of Ann's favorite galaxies, but it sure is in my top 10, even more so after the interesting stuff Ann posted about it! I like the famous Hubble photo the best, as I feel it shows it's true majesty most convincingly. That is, the one shown here - https://svs.gsfc.nasa.gov/30855


Oh to be living in a nearby dwarf companion galaxy! (Are there any I wonder?)

EDIT: it appears there might be? From https://www.messier-objects.com/messier ... ero-galaxy
An ultracompact dwarf galaxy (UCD), a very compact galaxy with a high stellar population, was discovered in the vicinity of M104 in 2009. The companion galaxy has a half-light radius of only 47.9 light years and an absolute magnitude of -12.3. Ultracompact dwarfs are suspected to be cores of dwarf elliptical galaxies that have lost their outlying stars and gas as a result of tidal interactions.
Though perhaps this UCD is only "in the vicinity of M104" visually and not absolutely.

EDIT 2: But I suppose living in one of those 2000 globular clusters - preferably one at about 45 degrees off the plane of the main disk - would suffice quite nicely!
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Re: APOD: M104: The Sombrero Galaxy (2021 May 14)

Post by orin stepanek » Fri May 14, 2021 9:29 pm

neufer wrote:
Fri May 14, 2021 3:03 pm
orin stepanek wrote:
Fri May 14, 2021 11:48 am

If we were approaching M104; would it appear like this;

Or, like this!

I mean, why does the halo look so much fuller on the one than the other? Today's APOD, the Sombrero looks completely flat; on the other, not so! :?
As Ann points out, the flat Sombrero is an IR view that zeros in on the flat dusty disk.

If we were approaching M104; would it appear blue shifted so we would observe the flat IR dusty disk.

Thanks Art!
Orin

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Re: APOD: M104: The Sombrero Galaxy (2021 May 14)

Post by orin stepanek » Fri May 14, 2021 9:31 pm

johnnydeep wrote:
Fri May 14, 2021 9:00 pm
It may not be one of Ann's favorite galaxies, but it sure is in my top 10, even more so after the interesting stuff Ann posted about it! I like the famous Hubble photo the best, as I feel it shows it's true majesty most convincingly. That is, the one shown here - https://svs.gsfc.nasa.gov/30855


Oh to be living in a nearby dwarf companion galaxy! (Are there any I wonder?)

EDIT: it appears there might be? From https://www.messier-objects.com/messier ... ero-galaxy
An ultracompact dwarf galaxy (UCD), a very compact galaxy with a high stellar population, was discovered in the vicinity of M104 in 2009. The companion galaxy has a half-light radius of only 47.9 light years and an absolute magnitude of -12.3. Ultracompact dwarfs are suspected to be cores of dwarf elliptical galaxies that have lost their outlying stars and gas as a result of tidal interactions.
Though perhaps this UCD is only "in the vicinity of M104" visually and not absolutely.

EDIT 2: But I suppose living in one of those 2000 globular clusters - preferably one at about 45 degrees off the plane of the main disk - would suffice quite nicely!

Mine also! :thumb_up:
Orin

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Re: APOD: M104: The Sombrero Galaxy (2021 May 14)

Post by heehaw » Fri May 14, 2021 10:59 pm

Oh I don't want to become a bore on this subject, but of course we love pictures of galaxies because we can, well, SEE them. But we know that what we CANNOT see (dark matter) is most of what is actually there. I don't fault us: think how boring APOD would be if nothing but blank pictures each and every day! Yes, even with little whirls of optical light within most, if not all. There is a huge future (I hope) for low-surface-brightness astronomy: some visible matter marking dark matter locations. It is fun that we have the utterly mysterious dark matter right in our noses and yet invisible. It need not be more particles (though I personally think it is); it could be exotic curvature and lots of other things. Whee! Hope we sort it out before I, er, expire.

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Re: APOD: M104: The Sombrero Galaxy (2021 May 14)

Post by johnnydeep » Fri May 14, 2021 11:29 pm

heehaw wrote:
Fri May 14, 2021 10:59 pm
Oh I don't want to become a bore on this subject, but of course we love pictures of galaxies because we can, well, SEE them. But we know that what we CANNOT see (dark matter) is most of what is actually there. I don't fault us: think how boring APOD would be if nothing but blank pictures each and every day! Yes, even with little whirls of optical light within most, if not all. There is a huge future (I hope) for low-surface-brightness astronomy: some visible matter marking dark matter locations. It is fun that we have the utterly mysterious dark matter right in our noses and yet invisible. It need not be more particles (though I personally think it is); it could be exotic curvature and lots of other things. Whee! Hope we sort it out before I, er, expire.
Yes, dark matter is fascinating. Even before we know anything about it! I suppose it could even consist of a whole family of different particles, much like normal matter consists of the particles and forces of the Standard Model.

But is it really a given that dark matter is right here in our earthly environment, and that we are indeed “swimming” in it, yet totally unawares?
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Re: APOD: M104: The Sombrero Galaxy (2021 May 14)

Post by Chris Peterson » Fri May 14, 2021 11:42 pm

johnnydeep wrote:
Fri May 14, 2021 11:29 pm
heehaw wrote:
Fri May 14, 2021 10:59 pm
Oh I don't want to become a bore on this subject, but of course we love pictures of galaxies because we can, well, SEE them. But we know that what we CANNOT see (dark matter) is most of what is actually there. I don't fault us: think how boring APOD would be if nothing but blank pictures each and every day! Yes, even with little whirls of optical light within most, if not all. There is a huge future (I hope) for low-surface-brightness astronomy: some visible matter marking dark matter locations. It is fun that we have the utterly mysterious dark matter right in our noses and yet invisible. It need not be more particles (though I personally think it is); it could be exotic curvature and lots of other things. Whee! Hope we sort it out before I, er, expire.
Yes, dark matter is fascinating. Even before we know anything about it! I suppose it could even consist of a whole family of different particles, much like normal matter consists of the particles and forces of the Standard Model.

But is it really a given that dark matter is right here in our earthly environment, and that we are indeed “swimming” in it, yet totally unawares?
A given? No. Highly likely? Yes.
Chris

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Re: APOD: M104: The Sombrero Galaxy (2021 May 14)

Post by johnnydeep » Sat May 15, 2021 12:15 am

Chris Peterson wrote:
Fri May 14, 2021 11:42 pm
johnnydeep wrote:
Fri May 14, 2021 11:29 pm
heehaw wrote:
Fri May 14, 2021 10:59 pm
Oh I don't want to become a bore on this subject, but of course we love pictures of galaxies because we can, well, SEE them. But we know that what we CANNOT see (dark matter) is most of what is actually there. I don't fault us: think how boring APOD would be if nothing but blank pictures each and every day! Yes, even with little whirls of optical light within most, if not all. There is a huge future (I hope) for low-surface-brightness astronomy: some visible matter marking dark matter locations. It is fun that we have the utterly mysterious dark matter right in our noses and yet invisible. It need not be more particles (though I personally think it is); it could be exotic curvature and lots of other things. Whee! Hope we sort it out before I, er, expire.
Yes, dark matter is fascinating. Even before we know anything about it! I suppose it could even consist of a whole family of different particles, much like normal matter consists of the particles and forces of the Standard Model.

But is it really a given that dark matter is right here in our earthly environment, and that we are indeed “swimming” in it, yet totally unawares?
A given? No. Highly likely? Yes.
And from what I’ve read, I guess we at least know that dark matter seems to be “attracted” to normal matter since galaxies appear to be embedded in large clumps of it, and that there is less of it between galaxies. That is, it is not uniformly distributed throughout space. But there could be - or maybe it’s likely as you said - that there are small clouds of dark matter surrounding each and every atom in interstellar and intergalactic space, and by extension, around every particle here on earth.
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Re: APOD: M104: The Sombrero Galaxy (2021 May 14)

Post by Chris Peterson » Sat May 15, 2021 12:54 am

johnnydeep wrote:
Sat May 15, 2021 12:15 am
Chris Peterson wrote:
Fri May 14, 2021 11:42 pm
johnnydeep wrote:
Fri May 14, 2021 11:29 pm


Yes, dark matter is fascinating. Even before we know anything about it! I suppose it could even consist of a whole family of different particles, much like normal matter consists of the particles and forces of the Standard Model.

But is it really a given that dark matter is right here in our earthly environment, and that we are indeed “swimming” in it, yet totally unawares?
A given? No. Highly likely? Yes.
And from what I’ve read, I guess we at least know that dark matter seems to be “attracted” to normal matter since galaxies appear to be embedded in large clumps of it, and that there is less of it between galaxies. That is, it is not uniformly distributed throughout space. But there could be - or maybe it’s likely as you said - that there are small clouds of dark matter surrounding each and every atom in interstellar and intergalactic space, and by extension, around every particle here on earth.
It is not uniformly distributed in intergalactic space. But the halos around galaxies extend all the way to the center. So we're swimming in the middle of the dark matter cloud that is part of the Milky Way.
Chris

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Re: APOD: M104: The Sombrero Galaxy (2021 May 14)

Post by Ann » Sat May 15, 2021 3:31 am

johnnydeep wrote:
Fri May 14, 2021 9:00 pm
It may not be one of Ann's favorite galaxies, but it sure is in my top 10, even more so after the interesting stuff Ann posted about it! I like the famous Hubble photo the best, as I feel it shows it's true majesty most convincingly. That is, the one shown here - https://svs.gsfc.nasa.gov/30855


Oh to be living in a nearby dwarf companion galaxy! (Are there any I wonder?)

EDIT: it appears there might be? From https://www.messier-objects.com/messier ... ero-galaxy
An ultracompact dwarf galaxy (UCD), a very compact galaxy with a high stellar population, was discovered in the vicinity of M104 in 2009. The companion galaxy has a half-light radius of only 47.9 light years and an absolute magnitude of -12.3. Ultracompact dwarfs are suspected to be cores of dwarf elliptical galaxies that have lost their outlying stars and gas as a result of tidal interactions.
Though perhaps this UCD is only "in the vicinity of M104" visually and not absolutely.

EDIT 2: But I suppose living in one of those 2000 globular clusters - preferably one at about 45 degrees off the plane of the main disk - would suffice quite nicely!
Click to play embedded YouTube video.

You wouldn't want to live inside a globular cluster. The tidal forces might easily kick you star around, mess up the orbits of the planets, and possibly kick your planet out of its solar system altogether! :cry:

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Re: APOD: M104: The Sombrero Galaxy (2021 May 14)

Post by johnnydeep » Sat May 15, 2021 3:06 pm

Ann wrote:
Sat May 15, 2021 3:31 am
johnnydeep wrote:
Fri May 14, 2021 9:00 pm
It may not be one of Ann's favorite galaxies, but it sure is in my top 10, even more so after the interesting stuff Ann posted about it! I like the famous Hubble photo the best, as I feel it shows it's true majesty most convincingly. That is, the one shown here - https://svs.gsfc.nasa.gov/30855


Oh to be living in a nearby dwarf companion galaxy! (Are there any I wonder?)

EDIT: it appears there might be? From https://www.messier-objects.com/messier ... ero-galaxy
An ultracompact dwarf galaxy (UCD), a very compact galaxy with a high stellar population, was discovered in the vicinity of M104 in 2009. The companion galaxy has a half-light radius of only 47.9 light years and an absolute magnitude of -12.3. Ultracompact dwarfs are suspected to be cores of dwarf elliptical galaxies that have lost their outlying stars and gas as a result of tidal interactions.
Though perhaps this UCD is only "in the vicinity of M104" visually and not absolutely.

EDIT 2: But I suppose living in one of those 2000 globular clusters - preferably one at about 45 degrees off the plane of the main disk - would suffice quite nicely!
Click to play embedded YouTube video.

You wouldn't want to live inside a globular cluster. The tidal forces might easily kick you star around, mess up the orbits of the planets, and possibly kick your planet out of its solar system altogether! :cry:

Ann
I would have thought that since globular clusters are so long lived (often greater than 10 billion years) that they would be stable places to live, but apparently not, due to the closely packed stars. From https://en.wikipedia.org/wiki/Globular_ ... omposition
Globular clusters can contain a high density of stars; on average about 0.4 stars per cubic parsec, increasing to 100 or 1000 stars per cubic parsec in the core of the cluster.[45] The typical distance between stars in a globular cluster is about 1 light year,[46] but at its core the separation between stars averages about a third of a light year, 13 times closer than Proxima Centauri.[47]

Globular clusters are not thought to be favorable locations for the survival of planetary systems. Planetary orbits are dynamically unstable within the cores of dense clusters because of the perturbations of passing stars. A planet orbiting at 1 astronomical unit around a star that is within the core of a dense cluster such as 47 Tucanae would only survive on the order of 108 years.[48] There is a planetary system orbiting a pulsar (PSR B1620−26) that belongs to the globular cluster M4, but these planets likely formed after the event that created the pulsar.[49]
But perhaps a star in the outskirts of a globular cluster where the average distance between stars is >4 ly would be ok. In any event, I think I could still live happily ever after in a globular cluster for the rest of my hopefully 100 year life!
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Re: APOD: M104: The Sombrero Galaxy (2021 May 14)

Post by johnnydeep » Sat May 15, 2021 3:10 pm

Chris Peterson wrote:
Sat May 15, 2021 12:54 am
johnnydeep wrote:
Sat May 15, 2021 12:15 am
Chris Peterson wrote:
Fri May 14, 2021 11:42 pm


A given? No. Highly likely? Yes.
And from what I’ve read, I guess we at least know that dark matter seems to be “attracted” to normal matter since galaxies appear to be embedded in large clumps of it, and that there is less of it between galaxies. That is, it is not uniformly distributed throughout space. But there could be - or maybe it’s likely as you said - that there are small clouds of dark matter surrounding each and every atom in interstellar and intergalactic space, and by extension, around every particle here on earth.
It is not uniformly distributed in intergalactic space. But the halos around galaxies extend all the way to the center. So we're swimming in the middle of the dark matter cloud that is part of the Milky Way.
Ok. I just hope I live long enough to learn what dark matter really is!
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Re: APOD: M104: The Sombrero Galaxy (2021 May 14)

Post by VictorBorun » Sun May 16, 2021 5:34 pm

Chris Peterson wrote:
Sat May 15, 2021 12:54 am
we're swimming in the middle of the dark matter cloud that is part of the Milky Way.
I think the main speculation is that dark matter particles interact only via gravitation.
The relic photons got less energetic since Big Bang ~a^4, and so the normal particles emitting photons were able to get less energetic somewhat between ~a^3 and ~a^4.
But the dark particles' cooling lagged behind ~a^3.
The dark particles in the Milky Way must orbit at 200 km/s in odd planes and directions, so we not as much drift in the dark matter flow as ram against fierce but powerless dark winds.
If one day we learn to resonance with dark particles we might be able to make ourselves sort of dark sails to navigate across the Milky Way.

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Re: APOD: M104: The Sombrero Galaxy (2021 May 14)

Post by johnnydeep » Sun May 16, 2021 7:02 pm

VictorBorun wrote:
Sun May 16, 2021 5:34 pm
Chris Peterson wrote:
Sat May 15, 2021 12:54 am
we're swimming in the middle of the dark matter cloud that is part of the Milky Way.
I think the main speculation is that dark matter particles interact only via gravitation.
The relic photons got less energetic since Big Bang ~a^4, and so the normal particles emitting photons were able to get less energetic somewhat between ~a^3 and ~a^4.
But the dark particles' cooling lagged behind ~a^3.
The dark particles in the Milky Way must orbit at 200 km/s in odd planes and directions, so we not as much drift in the dark matter flow as ram against fierce but powerless dark winds.
If one day we learn to resonance with dark particles we might be able to make ourselves sort of dark sails to navigate across the Milky Way.
If dark matter interacts only - or even primarily - via gravity, why wouldn't it be orbiting with the rest of the non-dark matter in the milky way?

Related question: do we know if the dark matter cloud that the milky way is embedded in is uniformly distributed in a spherical shape, or is it more concentrated where the non-dark matter is concentrated? I would highly suspect the latter.
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Re: APOD: M104: The Sombrero Galaxy (2021 May 14)

Post by Chris Peterson » Sun May 16, 2021 7:48 pm

VictorBorun wrote:
Sun May 16, 2021 5:34 pm
Chris Peterson wrote:
Sat May 15, 2021 12:54 am
we're swimming in the middle of the dark matter cloud that is part of the Milky Way.
I think the main speculation is that dark matter particles interact only via gravitation.
And possibly the weak nuclear force, as well. The main feature is lack of interaction with the electromagnetic force.
Chris

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Re: APOD: M104: The Sombrero Galaxy (2021 May 14)

Post by Chris Peterson » Sun May 16, 2021 7:54 pm

johnnydeep wrote:
Sun May 16, 2021 7:02 pm
VictorBorun wrote:
Sun May 16, 2021 5:34 pm
Chris Peterson wrote:
Sat May 15, 2021 12:54 am
we're swimming in the middle of the dark matter cloud that is part of the Milky Way.
I think the main speculation is that dark matter particles interact only via gravitation.
The relic photons got less energetic since Big Bang ~a^4, and so the normal particles emitting photons were able to get less energetic somewhat between ~a^3 and ~a^4.
But the dark particles' cooling lagged behind ~a^3.
The dark particles in the Milky Way must orbit at 200 km/s in odd planes and directions, so we not as much drift in the dark matter flow as ram against fierce but powerless dark winds.
If one day we learn to resonance with dark particles we might be able to make ourselves sort of dark sails to navigate across the Milky Way.
If dark matter interacts only - or even primarily - via gravity, why wouldn't it be orbiting with the rest of the non-dark matter in the milky way?

Related question: do we know if the dark matter cloud that the milky way is embedded in is uniformly distributed in a spherical shape, or is it more concentrated where the non-dark matter is concentrated? I would highly suspect the latter.
It is orbiting with the rest of the non-dark matter in the Milky Way.

Models most consistent with observation suggest that dark matter halos are ellipsoidal (although they can be spherical... a special case) and have a density profile described by a power law, with the highest density in the center (which in the case of galactic halos would lie close to the ordinary matter center of the galaxy).
Chris

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johnnydeep
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Re: APOD: M104: The Sombrero Galaxy (2021 May 14)

Post by johnnydeep » Sun May 16, 2021 8:20 pm

Chris Peterson wrote:
Sun May 16, 2021 7:54 pm
johnnydeep wrote:
Sun May 16, 2021 7:02 pm
VictorBorun wrote:
Sun May 16, 2021 5:34 pm


I think the main speculation is that dark matter particles interact only via gravitation.
The relic photons got less energetic since Big Bang ~a^4, and so the normal particles emitting photons were able to get less energetic somewhat between ~a^3 and ~a^4.
But the dark particles' cooling lagged behind ~a^3.
The dark particles in the Milky Way must orbit at 200 km/s in odd planes and directions, so we not as much drift in the dark matter flow as ram against fierce but powerless dark winds.
If one day we learn to resonance with dark particles we might be able to make ourselves sort of dark sails to navigate across the Milky Way.
If dark matter interacts only - or even primarily - via gravity, why wouldn't it be orbiting with the rest of the non-dark matter in the milky way?

Related question: do we know if the dark matter cloud that the milky way is embedded in is uniformly distributed in a spherical shape, or is it more concentrated where the non-dark matter is concentrated? I would highly suspect the latter.
It is orbiting with the rest of the non-dark matter in the Milky Way.

Models most consistent with observation suggest that dark matter halos are ellipsoidal (although they can be spherical... a special case) and have a density profile described by a power law, with the highest density in the center (which in the case of galactic halos would lie close to the ordinary matter center of the galaxy).
Thanks. Then my suspicion was correct for a change!
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VictorBorun
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Re: APOD: M104: The Sombrero Galaxy (2021 May 14)

Post by VictorBorun » Mon May 17, 2021 9:53 am

Chris Peterson wrote:
Sun May 16, 2021 7:54 pm
It is orbiting with the rest of the non-dark matter in the Milky Way.
Wow.
Still it's not so well aligned with gas and stellar orbits and so a dark sail would catch some dark wind if such a sail happens to be possible.