APOD: The Andromeda Galaxy in Ultraviolet (2021 Jul 18)

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APOD: The Andromeda Galaxy in Ultraviolet (2021 Jul 18)

Post by APOD Robot » Sun Jul 18, 2021 4:05 am

Image The Andromeda Galaxy in Ultraviolet

Explanation: What does the Andromeda galaxy look like in ultraviolet light? Young blue stars circling the galactic center dominate. A mere 2.5 million light-years away, the Andromeda Galaxy, also known as M31, really is just next door as large galaxies go. Spanning about 230,000 light-years, it took 11 different image fields from NASA's Galaxy Evolution Explorer (GALEX) satellite telescope to produce this gorgeous portrait of the spiral galaxy in ultraviolet light in 2003. While its spiral arms stand out in visible light images, Andromeda's arms look more like rings in ultraviolet. The rings are sites of intense star formation and have been interpreted as evidence that Andromeda collided with its smaller neighboring elliptical galaxy M32 more than 200 million years ago. The Andromeda galaxy and our own comparable Milky Way galaxy are the most massive members of the Local Group of galaxies and are projected to collide in several billion years -- perhaps around the time that our Sun's atmosphere will expand to engulf the Earth.

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Re: APOD: The Andromeda Galaxy in Ultraviolet (2021 Jul 18)

Post by De58te » Sun Jul 18, 2021 10:52 am

Curious. The Andromeda galaxy in ultraviolet seems to be surrounded on all sides by more yellow stars than blue. All except for a portion near the central top frame of the photo where there appears to be a large void of stars. If Andromeda is twice as big as the Milky Way, this void seems to approach the size of the Milky Way. Could this be because the stars there don't shine in the ultraviolet, are blocked by a really dark cloud of dust, or that really is an area void of stars?

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Re: APOD: The Andromeda Galaxy in Ultraviolet (2021 Jul 18)

Post by orin stepanek » Sun Jul 18, 2021 11:50 am

m31_gendler_1080.jpg
M31_Galex_6000.jpg
Just beautiful; either way you view it; visible or ultraviolet light! :D
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Re: APOD: The Andromeda Galaxy in Ultraviolet (2021 Jul 18)

Post by johnnydeep » Sun Jul 18, 2021 12:51 pm

De58te wrote:
Sun Jul 18, 2021 10:52 am
Curious. The Andromeda galaxy in ultraviolet seems to be surrounded on all sides by more yellow stars than blue. All except for a portion near the central top frame of the photo where there appears to be a large void of stars. If Andromeda is twice as big as the Milky Way, this void seems to approach the size of the Milky Way. Could this be because the stars there don't shine in the ultraviolet, are blocked by a really dark cloud of dust, or that really is an area void of stars?
Not sure about the prevalence of yellow stars, but I'd guess it's because most stars simply appear yellow in this ultraviolet image? But the "void" you noticed is some sort of instrument or image processing artifact. Here are the voids exposed by edge detection in GIMP:

Edge Detection on Ultravoilet Andromeda Image.JPG

[ EDIT: on second thought, I think the voids reveal the image to be a composite of several smaller images. ]
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Re: APOD: The Andromeda Galaxy in Ultraviolet (2021 Jul 18)

Post by ryzrx-100 » Sun Jul 18, 2021 1:01 pm

Are we (meaning Milky Way Galaxy) in Andromeda Galaxy's gravity well at this point? I would think so even at 2.5 million light-years distance. I would expect the galaxies to show evidence of this and perhaps the start of orbits depending on the vectors of the galaxies. As an astronomy project, I would find two other galaxies with similar masses and distance to determine their effects on each other.

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Re: APOD: The Andromeda Galaxy in Ultraviolet (2021 Jul 18)

Post by johnnydeep » Sun Jul 18, 2021 1:09 pm

Interesting fact: the "projected to collide" link in the description is to a paper coauthored by Abraham Loeb, a.k.a. Avi Loeb, who happens to be the same Avi Loeb who recently published a book about the evidence that the solar system interloper 'Oumuamua - https://en.wikipedia.org/wiki/ʻOumuamua - is an alien spacecraft. His "evidence" is debatable at best but he is evidently a highly accomplished Harvard astrophysicist nonetheless.
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Re: APOD: The Andromeda Galaxy in Ultraviolet (2021 Jul 18)

Post by Chris Peterson » Sun Jul 18, 2021 1:19 pm

ryzrx-100 wrote:
Sun Jul 18, 2021 1:01 pm
Are we (meaning Milky Way Galaxy) in Andromeda Galaxy's gravity well at this point? I would think so even at 2.5 million light-years distance. I would expect the galaxies to show evidence of this and perhaps the start of orbits depending on the vectors of the galaxies. As an astronomy project, I would find two other galaxies with similar masses and distance to determine their effects on each other.
Our two galaxies are in closed orbits around each other.
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Re: APOD: The Andromeda Galaxy in Ultraviolet (2021 Jul 18)

Post by neufer » Sun Jul 18, 2021 2:36 pm

Click to play embedded YouTube video.
Chris Peterson wrote:
Sun Jul 18, 2021 1:19 pm
ryzrx-100 wrote:
Sun Jul 18, 2021 1:01 pm


I would expect the galaxies to show evidence of this and perhaps the start of orbits depending on the vectors of the galaxies.
Our two galaxies are in closed orbits around each other.
  • Closed orbits :?:
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Re: APOD: The Andromeda Galaxy in Ultraviolet (2021 Jul 18)

Post by Chris Peterson » Sun Jul 18, 2021 2:57 pm

neufer wrote:
Sun Jul 18, 2021 2:36 pm
Chris Peterson wrote:
Sun Jul 18, 2021 1:19 pm
ryzrx-100 wrote:
Sun Jul 18, 2021 1:01 pm
I would expect the galaxies to show evidence of this and perhaps the start of orbits depending on the vectors of the galaxies.
Our two galaxies are in closed orbits around each other.
  • Closed orbits :?:
Yes, most certainly closed orbits. That does not preclude a collision. They are extended objects.
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Re: APOD: The Andromeda Galaxy in Ultraviolet (2021 Jul 18)

Post by neufer » Sun Jul 18, 2021 3:37 pm

Chris Peterson wrote:
Sun Jul 18, 2021 2:57 pm
neufer wrote:
Sun Jul 18, 2021 2:36 pm
Chris Peterson wrote:
Sun Jul 18, 2021 1:19 pm

Our two galaxies are in closed orbits around each other.
  • Closed orbits :?:
Click to play embedded YouTube video.
  • Closed orbits :?:
Yes, most certainly closed orbits. That does not preclude a collision. They are extended objects.
1) It begins as a three body (i.e., M31, M33, Milky Way) situation
  • all orbiting their common center of mass.
2) The collision involves both broad dark matter gravitational fields & gas interactions.
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Re: APOD: The Andromeda Galaxy in Ultraviolet (2021 Jul 18)

Post by Chris Peterson » Sun Jul 18, 2021 3:56 pm

neufer wrote:
Sun Jul 18, 2021 3:37 pm
Chris Peterson wrote:
Sun Jul 18, 2021 2:57 pm
neufer wrote:
Sun Jul 18, 2021 2:36 pm
  • Closed orbits :?:
  • Closed orbits :?:
Yes, most certainly closed orbits. That does not preclude a collision. They are extended objects.
1) It begins as a three body (i.e., M31, M33, Milky Way) situation
  • all orbiting their common center of mass.
2) The collision involves both broad dark matter gravitational fields & gas interactions.
Yes. The important concept, IMO, is that all of the members of the local group are in closed (Keplerian) orbits around each other. Of course, the orbital elements are in constant flux because it's a multiple body system with a shifting center of gravity (and shifting local centers of gravity). But none of the members have eccentricities greater than one with respect to any of the other members.
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Re: APOD: The Andromeda Galaxy in Ultraviolet (2021 Jul 18)

Post by neufer » Sun Jul 18, 2021 5:16 pm

Chris Peterson wrote:
Sun Jul 18, 2021 2:57 pm
neufer wrote:
Sun Jul 18, 2021 2:36 pm
Click to play embedded YouTube video.
  • Closed orbits :?:
Yes, most certainly closed orbits. That does not preclude a collision. They are extended objects.
Chris Peterson wrote:
Sun Jul 18, 2021 3:56 pm
neufer wrote:
Sun Jul 18, 2021 2:36 pm

1) It begins as a three body situation (i.e., M31, M33 & Milky Way):
  • all orbiting their common center of mass.

2) The collision involves both broad dark matter gravitational fields & gas interactions.
Yes. The important concept, IMO, is that all of the members of the local group are in closed (Keplerian) orbits around each other. Of course, the orbital elements are in constant flux because it's a multiple body system with a shifting center of gravity (and shifting local centers of gravity). But none of the members have eccentricities greater than one with respect to any of the other members.
None of the members are in closed Keplerian orbits.

:arrow: However, all of the members are in BOUND non-Keplerian orbits.
https://en.wikipedia.org/wiki/Bertrand%27s_theorem wrote:
<<In classical mechanics, Bertrand's theorem states that among central-force potentials with bound orbits, there are only two types of central-force (radial) scalar potentials with the property that all BOUND orbits are also closed orbits. The theorem is named after its discoverer, Joseph Bertrand.>>
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Re: APOD: The Andromeda Galaxy in Ultraviolet (2021 Jul 18)

Post by Chris Peterson » Sun Jul 18, 2021 5:26 pm

neufer wrote:
Sun Jul 18, 2021 5:16 pm

None of the members are in closed Keplerian orbits.

:arrow: However, all of the members are in BOUND non-Keplerian orbits.
No. They are all in closed, Keplerian orbits.
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Re: APOD: The Andromeda Galaxy in Ultraviolet (2021 Jul 18)

Post by neufer » Sun Jul 18, 2021 6:10 pm

Chris Peterson wrote:
Sun Jul 18, 2021 5:26 pm
neufer wrote:
Sun Jul 18, 2021 5:16 pm

None of the members are in closed Keplerian orbits.

:arrow: However, all of the members are in BOUND non-Keplerian orbits.
No. They are all in closed, Keplerian orbits.
  • Why would an N-body problem ever really involve "closed, Keplerian orbits" :?:
https://en.wikipedia.org/wiki/Kepler_problem wrote:
<<In classical mechanics, the Kepler problem is a special case of the two-body problem, in which the two bodies interact by a central force F that varies in strength as the inverse square of the distance r between them. The force may be either attractive or repulsive. The problem is to find the position or speed of the two bodies over time given their masses, positions, and velocities. Using classical mechanics, the solution can be expressed as a Kepler orbit using six orbital elements.>>
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Re: APOD: The Andromeda Galaxy in Ultraviolet (2021 Jul 18)

Post by Ann » Sun Jul 18, 2021 6:48 pm

johnnydeep wrote:
Sun Jul 18, 2021 12:51 pm
De58te wrote:
Sun Jul 18, 2021 10:52 am
Curious. The Andromeda galaxy in ultraviolet seems to be surrounded on all sides by more yellow stars than blue. All except for a portion near the central top frame of the photo where there appears to be a large void of stars. If Andromeda is twice as big as the Milky Way, this void seems to approach the size of the Milky Way. Could this be because the stars there don't shine in the ultraviolet, are blocked by a really dark cloud of dust, or that really is an area void of stars?
Not sure about the prevalence of yellow stars, but I'd guess it's because most stars simply appear yellow in this ultraviolet image? But the "void" you noticed is some sort of instrument or image processing artifact. Here are the voids exposed by edge detection in GIMP:


Andromeda is a very yellow galaxy!


The U-B index of Andromeda is +0.500, and the B-V index is +0.920. That's very yellow. And it means that there is an amazing abundance of red and yellow stars in our big sister galaxy and rather few blue stars there. The superb image by u/_bar gives you an idea of how yellowish it is.

Andromeda is seen in a part of the sky which corresponds, I'd say, to the thick disk of the Milky Way. The thick disk is dominated by old yellow stars. Young blue star Nu Andromeda, located very close to where we see Andromeda in the sky, is an exception to the rule (and it belongs to the thin disk, too).

But the Milky Way itself is dominated by old yellow stars in the part of the sky where we see Andromeda. (And in my opinion, the Milky Way is probably a quite red galaxy too, although not as red as Andromeda.)



The ultraviolet image of Andromeda shows our sister galaxy to be a ring galaxy, which means it may have some similarities with the Cartwheel galaxy. IN the case of the Cartwheel, one of its satellite galaxies passed violently right through the disk of the larger galaxy, causing it to ripple like the waves of a pond. The outer ring of the Cartwheel is very active in star formation.

Andromeda, by contrast, is low in star formation, which is why it is so yellow in visible light. So why is it so blue in ultraviolet? The way I understand it, the far ultraviolet filter in the now-defunct GALEX telescope reacted to even modest A-type stars like Vega och Sirius. So you should probable think of the blue rings of Andromeda as conglomerates of hobbit stars like Sirius rather than brilliant clusters of O- and B-type giants like Rigel and the three mighty stars in Orion's Belt.

Ann
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Re: APOD: The Andromeda Galaxy in Ultraviolet (2021 Jul 18)

Post by neufer » Sun Jul 18, 2021 9:09 pm

Ann wrote:
Sun Jul 18, 2021 6:48 pm
De58te wrote:
Sun Jul 18, 2021 10:52 am

The Andromeda galaxy in ultraviolet seems to be surrounded on all sides by more yellow stars than blue. All except for a portion near the central top frame of the photo where there appears to be a large void of stars.
johnnydeep wrote:
Sun Jul 18, 2021 12:51 pm

Not sure about the prevalence of yellow stars, but I'd guess it's because most stars simply appear yellow in this ultraviolet image?
  • Andromeda is a very yellow galaxy!
Last edited by neufer on Sun Jul 18, 2021 10:15 pm, edited 1 time in total.
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Re: APOD: The Andromeda Galaxy in Ultraviolet (2021 Jul 18)

Post by Chris Peterson » Sun Jul 18, 2021 9:14 pm

neufer wrote:
Sun Jul 18, 2021 6:10 pm
Chris Peterson wrote:
Sun Jul 18, 2021 5:26 pm
neufer wrote:
Sun Jul 18, 2021 5:16 pm

None of the members are in closed Keplerian orbits.

:arrow: However, all of the members are in BOUND non-Keplerian orbits.
No. They are all in closed, Keplerian orbits.
  • Why would an N-body problem ever really involve "closed, Keplerian orbits" :?:
Because there's always a center of gravity, at any instant of time. We model n-body systems using purely Keplerian elements, re-evaluated at fine intervals. That is, every body in the system has a set of Keplerian elements with respect to every other element. There's a dominant closed orbit (unless the body is escaping the system) and a large number of elements that may or may not be closed.
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Re: APOD: The Andromeda Galaxy in Ultraviolet (2021 Jul 18)

Post by neufer » Sun Jul 18, 2021 9:38 pm

neufer wrote:
Sun Jul 18, 2021 9:09 pm
Ann wrote:
Sun Jul 18, 2021 6:48 pm
De58te wrote:
Sun Jul 18, 2021 10:52 am

The Andromeda galaxy in ultraviolet seems to be surrounded on all sides by more yellow stars than blue. All except for a portion near the central top frame of the photo where there appears to be a large void of stars.
johnnydeep wrote:
Sun Jul 18, 2021 12:51 pm

Not sure about the prevalence of yellow stars, but I'd guess it's because most stars simply appear yellow in this ultraviolet image?
  • Andromeda is a very yellow galaxy!
Andromeda is low in star formation, which is why it is so yellow in visible light. So why is it so blue in ultraviolet? The way I understand it, the far ultraviolet filter in the now-defunct GAKEX telescope reacted to even modest A-type stars like Vega och Sirius. So you should probable think of the blue rings of Andromeda as conglomerates of hobbit stars like Sirius rather than brilliant clusters of O- and B-type giants like Rigel and the three mighty stars in Orion's Belt.
Click to play embedded YouTube video.
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Re: APOD: The Andromeda Galaxy in Ultraviolet (2021 Jul 18)

Post by neufer » Sun Jul 18, 2021 10:12 pm

neufer wrote:
Sun Jul 18, 2021 6:10 pm
Chris Peterson wrote:
Sun Jul 18, 2021 5:26 pm
neufer wrote:
Sun Jul 18, 2021 5:16 pm

None of the members are in closed Keplerian orbits.

:arrow: However, all of the members are in BOUND non-Keplerian orbits.
No. They are all in closed, Keplerian orbits.
  • Why would an N-body problem ever really involve "closed, Keplerian orbits" :?:
Chris Peterson wrote:
Sun Jul 18, 2021 9:14 pm

Because there's always a center of gravity, at any instant of time. We model n-body systems using purely Keplerian elements, re-evaluated at fine intervals. That is, every body in the system has a set of Keplerian elements with respect to every other element. There's a dominant closed orbit (unless the body is escaping the system) and a large number of elements that may or may not be closed.
Perhaps if you are Ernest Rutherford analysing alpha particle scattering in the Geiger–Marsden gold foil experiment.

But if you are analyzing the Big Picture of galactic collisions taking into account both gas & dark matter interactions then I doubt that the name Kepler ever comes up
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Re: APOD: The Andromeda Galaxy in Ultraviolet (2021 Jul 18)

Post by Chris Peterson » Sun Jul 18, 2021 10:19 pm

neufer wrote:
Sun Jul 18, 2021 10:12 pm
neufer wrote:
Sun Jul 18, 2021 6:10 pm
Chris Peterson wrote:
Sun Jul 18, 2021 5:26 pm


No. They are all in closed, Keplerian orbits.
  • Why would an N-body problem ever really involve "closed, Keplerian orbits" :?:
Chris Peterson wrote:
Sun Jul 18, 2021 9:14 pm

Because there's always a center of gravity, at any instant of time. We model n-body systems using purely Keplerian elements, re-evaluated at fine intervals. That is, every body in the system has a set of Keplerian elements with respect to every other element. There's a dominant closed orbit (unless the body is escaping the system) and a large number of elements that may or may not be closed.
Perhaps if you are Ernest Rutherford analysing alpha particle scattering in the Geiger–Marsden gold foil experiment.

But if you are analyzing the Big Picture of galactic collisions taking into account both gas & dark matter interactions then I doubt that the name Kepler ever comes up
Well, like I said, it's central to the n-body integration tools I use.
Chris

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Re: APOD: The Andromeda Galaxy in Ultraviolet (2021 Jul 18)

Post by VictorBorun » Mon Jul 19, 2021 3:08 pm

Ann wrote:
Sun Jul 18, 2021 6:48 pm

The ultraviolet image of Andromeda shows our sister galaxy to be a ring galaxy, which means it may have some similarities with the Cartwheel galaxy. IN the case of the Cartwheel, one of its satellite galaxies passed violently right through the disk of the larger galaxy, causing it to ripple like the waves of a pond. The outer ring of the Cartwheel is very active in star formation.

Ann
Stretching by cos(77°), estmated almost edge-on angle between our line of sight and Andromeda spin vector, I don't see neither a large perfect ring nor a small symmetric pair of arms inside.
Andromeda UV.jpg
Andromeda 24-micron.jpg
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Re: APOD: The Andromeda Galaxy in Ultraviolet (2021 Jul 18)

Post by Ann » Mon Jul 19, 2021 7:15 pm

VictorBorun wrote:
Mon Jul 19, 2021 3:08 pm
Ann wrote:
Sun Jul 18, 2021 6:48 pm

The ultraviolet image of Andromeda shows our sister galaxy to be a ring galaxy, which means it may have some similarities with the Cartwheel galaxy. IN the case of the Cartwheel, one of its satellite galaxies passed violently right through the disk of the larger galaxy, causing it to ripple like the waves of a pond. The outer ring of the Cartwheel is very active in star formation.

Ann
Stretching by cos(77°), estmated almost edge-on angle between our line of sight and Andromeda spin vector, I don't see neither a large perfect ring nor a small symmetric pair of arms inside.
Andromeda doesn't have a large perfect ring, and it doesn't have spiral arms, either.

I'm just saying that there are some similarities between Andromeda and the Cartwheel galaxy, and some suggestions that Andromeda is a ring galaxy.

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Re: APOD: The Andromeda Galaxy in Ultraviolet (2021 Jul 18)

Post by VictorBorun » Tue Jul 20, 2021 3:31 am

I wish we could map Milky Way this good…
Discover an IR+UF gap 10 thousands ly wide and 40 thousands ly wide long…
A distinct ring containing Sun and small arms hugging the core…

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Re: APOD: The Andromeda Galaxy in Ultraviolet (2021 Jul 18)

Post by Ann » Tue Jul 20, 2021 4:05 am

By the way, is there a reason for Andromeda to be a ring galaxy? Yes, there is!!

M32 (NGC 221) is a tiny, extremely compact dwarf elliptical satellite of Andromeda. Most likely M32 started out as a disk galaxy, but because it regularly passes right through the disk of Andromeda, the disk of M32 was stripped away by tidal forces, leaving only the very compact tiny bulge.

And what about Andromeda itself? How does it react to having a compact 3 billion ⊙ mass of stars regularly plunge through its disk? Don't you think it would set up some ripples in the pond that is the disk of our large sister galaxy?

I think it would!

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Re: APOD: The Andromeda Galaxy in Ultraviolet (2021 Jul 18)

Post by alter-ego » Tue Jul 20, 2021 4:38 am

Ann wrote:
Tue Jul 20, 2021 4:05 am
By the way, is there a reason for Andromeda to be a ring galaxy? Yes, there is!!

M32 (NGC 221) is a tiny, extremely compact dwarf elliptical satellite of Andromeda. Most likely M32 started out as a disk galaxy, but because it regularly passes right through the disk of Andromeda, the disk of M32 was stripped away by tidal forces, leaving only the very compact tiny bulge.

And what about Andromeda itself? How does it react to having a compact 3 billion ⊙ mass of stars regularly plunge through its disk? Don't you think it would set up some ripples in the pond that is the disk of our large sister galaxy?

I think it would!

Ann
And you are not alone with this thinking:
An almost head-on collision as the origin of two off-centre rings in the Andromeda galaxy (2006) wrote: Abstract.The unusual morphology of the Andromeda Spiral (Messier 31, the closest spiral galaxy to the Milky
Way) has long been an enigma. Although regarded for decades as showing little evidence of a violent history,
M 31 has a well-known outer ring of star formation at a radius of 10 kpc whose center is offset from the
galaxy nucleus. In addition, the outer galaxy disk is warped as seen at both opticaland radio
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