APOD: M81 versus M82 (2013 Sep 25)

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APOD: M81 versus M82 (2013 Sep 25)

Post by APOD Robot » Wed Sep 25, 2013 4:05 am

Image M81 versus M82

Explanation: Here in the Milky Way galaxy we have astronomical front row seats as M81 and M82 face-off, a mere 12 million light-years away. Locked in a gravitational struggle for the past billion years or so, the two bright galaxies are captured in this deep telescopic snapshot, constructed from 25 hours of image data. Their most recent close encounter likely resulted in the enhanced spiral arms of M81 (left) and violent star forming regions in M82 so energetic the galaxy glows in X-rays. After repeated passes, in a few billion years only one galaxy will remain. From our perspective, this cosmic moment is seen through a foreground veil of the Milky Way's stars and clouds of dust. Faintly reflecting the foreground starlight, the pervasive dust clouds are relatively unexplored galactic cirrus, or integrated flux nebulae, only a few hundred light-years above the plane of the Milky Way.

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Re: APOD: M81 versus M82 (2013 Sep 25)

Post by Ann » Wed Sep 25, 2013 4:49 am

Oh, that's a brilliant image! Look at the smooth,non-starforming envelope of M82 and the red ribbons poking out of the center of it from the violent star formation going on in there! Look look at the brilliantly blue dwarf galaxy, Holmberg XII (as I think it is called) bursting with hot young stars that were born because of gas-rich Holmberg's interaction with large galaxy M81. And look at all that local fluff and all those tendrils of gas that mill around everywhere like an unruly ensemble of stage hands!

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Re: APOD: M81 versus M82 (2013 Sep 25)

Post by deathfleer » Wed Sep 25, 2013 5:45 am

Beautiful photo. Am I not right if I say that the M81 's core is spinning anti clockwise?

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Re: APOD: M81 versus M82 (2013 Sep 25)

Post by starsurfer » Wed Sep 25, 2013 6:51 am

This is often described as an interacting galaxy pair in the overall astronomical media but in fact it is a triplet along with the strange galaxy NGC 3077. An interesting paper: http://arxiv.org/abs/1101.4023

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Re: APOD: M81 versus M82 (2013 Sep 25)

Post by Boomer12k » Wed Sep 25, 2013 7:06 am

Always spectacular!!

At the moment, I think M81 is winning....

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Re: APOD: M81 versus M82 (2013 Sep 25)

Post by whowho » Wed Sep 25, 2013 9:07 am

After all these years, I just noticed that the date at the top is formatted 2013 September 25. I think that order is international standard? It is so much better than our custom of writing dates as, e.g., 3/3/03 or March 3, 2003. I have dropped into the habit of writing 2013 Set 25 Wed, myself. Adding the day of the week, which one often wants to know, is also an error check feature.

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Re: APOD: M81 versus M82 (2013 Sep 25)

Post by neufer » Wed Sep 25, 2013 11:23 am

http://en.wiktionary.org/wiki/str%C3%B8#Danish wrote:
strø (past tense strøede): sprinkle, scatter, strew
  • http://www.astroeder.com/en.htm : Ivan Eder's astrophotography page
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Re: APOD: M81 versus M82 (2013 Sep 25)

Post by rstevenson » Wed Sep 25, 2013 12:14 pm

Ann wrote:... Look look at the brilliantly blue dwarf galaxy, Holmberg XII (as I think it is called) bursting with hot young stars that were born because of gas-rich Holmberg's interaction with large galaxy M81.
I think there are only 9 Holmberg galaxies. I can't at the moment discover which one that is. I think it's Holmberg IX.

Rob

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Re: APOD: M81 versus M82 (2013 Sep 25)

Post by Ann » Wed Sep 25, 2013 3:12 pm

rstevenson wrote:
Ann wrote:... Look look at the brilliantly blue dwarf galaxy, Holmberg XII (as I think it is called) bursting with hot young stars that were born because of gas-rich Holmberg's interaction with large galaxy M81.
I think there are only 9 Holmberg galaxies. I can't at the moment discover which one that is. I think it's Holmberg IX.

Rob
Right you are, Rob! :clap: :clap: :clap:

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Bottom's Up

Re: APOD: M81 versus M82 (2013 Sep 25)

Post by Bottom's Up » Wed Sep 25, 2013 4:10 pm

deathfleer wrote:Am I not right if I say that the M81 's core is spinning anti clockwise?
Yes! and No! - depends on which side you're calling "up".

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Re: APOD: M81 versus M82 (2013 Sep 25)

Post by WallyBalls » Wed Sep 25, 2013 8:31 pm

M81 is going to kick ass!

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Re: APOD: M81 versus M82 (2013 Sep 25)

Post by neufer » Wed Sep 25, 2013 9:59 pm

deathfleer wrote:
Am I not right if I say that the M81 's core is spinning anti clockwise?
  • You are indeed not right :!:
http://messier.seds.org/m/m081.html wrote:
<<Investigations performed in 1994 have indicated that M81 has probably only little dark matter, as its rotation curve was found to fall off in the outer regions; this is in contrast to many galaxies, including our own Milky Way, for which the rotation curve increases outward. To explain the velocity of the stars in these regions, the galaxy must have a certain amount of mass. However, the total mass observed in luminous matter - stars and nebulae - is typically insufficient to explain this behaviour; thus it is assumed that there is a significant portion of mass in galaxies is non-luminous, dark matter (or at least low-luminosity matter). For M81, the percentage of dark matter is now estimated to be lower than average.>>
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Re: APOD: M81 versus M82 (2013 Sep 25)

Post by Anthony Barreiro » Wed Sep 25, 2013 11:50 pm

deathfleer wrote:Beautiful photo. Am I not right if I say that the M81 's core is spinning anti clockwise?
As Neufer pointed out the stars are rotating clockwise from our perspective. I often have trouble figuring out which way a spiral galaxy is rotating just from looking at a picture. It helps me to remember that the stars are not spiraling in toward the center of the galaxy like water running down a drain. Rather the stars are following elliptical paths around the center of the galaxy. The spiral arms that we see are areas where the gas is more dense, so there is more star formation in those areas, thus most of the young, hot, bright stars are seen along the leading edges of the spiral arms.

A useful analogy is to think of a traffic jam on the freeway. The traffic jam may last for a long time, but any individual car will move through the traffic jam in a shorter period of time. The traffic jam is like the spiral arm, and the cars are like stars.

Hope this helps.

By the way, this is an awesomely beautiful picture. Even better than what I see through my little telescope! :ssmile:
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Re: APOD: M81 versus M82 (2013 Sep 25)

Post by Beyond » Thu Sep 26, 2013 12:23 am

The way neufer shows it, is like how a circular saw blade works. The forward edge of the teeth rotate into what is being cut, which in this case is clockwise.
But if you see it from the other side, it would appear counter clockwise.
However, i don't know if all galaxy's rotate in the direction their arms point.
That's the way i sawed it. :yes:
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Re: APOD: M81 versus M82 (2013 Sep 25)

Post by neufer » Thu Sep 26, 2013 1:17 am

Image
Beyond wrote:
The way neufer shows it, is like how a circular saw blade works.

The forward edge of the teeth rotate into what is being cut, which in this case is clockwise.

However, i don't know if all galaxy's rotate in the direction their arms point.

That's the way i sawed it. :yes:
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Re: APOD: M81 versus M82 (2013 Sep 25)

Post by neufer » Thu Sep 26, 2013 1:24 am

http://www.cosmosportal.org/view/article/138223/ wrote:

A side-by-side comparison shows the nearby galaxy Messier 81, which is similar to our own Milky Way, in both visible (left) and ultraviolet light (right). While visible-light images of galaxies reveal the distribution of stars, ultraviolet-light images highlight the most active, young stars. The ultraviolet image of Messier 81 shows that the galaxy's spiral arms are dotted with pockets of violent star-forming activity. Note the prominent groups of young stars tracing out the spiral pattern, as well as the bulge's deficit of this population in the UV image.

The visible-light image is from the National Optical Astronomy Observatory. The ultraviolet-light image was taken by the Galaxy Evolution Explorer. (Source: NASA/JPL. Image credit: NASA/JPL-Caltech/NOAO.)>>
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Re: APOD: M81 versus M82 (2013 Sep 25)

Post by Beyond » Thu Sep 26, 2013 1:30 am

neufer wrote:
Image
Beyond wrote:
The way neufer shows it, is like how a circular saw blade works.

The forward edge of the teeth rotate into what is being cut, which in this case is clockwise.

However, i don't know if all galaxy's rotate in the direction their arms point.

That's the way i sawed it. :yes:
So... the milky way is rotating the opposite way of M81 :?: Like a saw blade cutting backwards (which is used that way to cut plastics and the like).
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Re: APOD: M81 versus M82 (2013 Sep 25)

Post by alter-ego » Thu Sep 26, 2013 4:42 am

neufer wrote:
deathfleer wrote:
Am I not right if I say that the M81 's core is spinning anti clockwise?
  • You are indeed not right :!:
http://messier.seds.org/m/m081.html wrote:
<<Investigations performed in 1994 have indicated that M81 has probably only little dark matter, as its rotation curve was found to fall off in the outer regions; this is in contrast to many galaxies, including our own Milky Way, for which the rotation curve increases outward. To explain the velocity of the stars in these regions, the galaxy must have a certain amount of mass. However, the total mass observed in luminous matter - stars and nebulae - is typically insufficient to explain this behaviour; thus it is assumed that there is a significant portion of mass in galaxies is non-luminous, dark matter (or at least low-luminosity matter). For M81, the percentage of dark matter is now estimated to be lower than average.>>
For the most part, spiral galaxies have trailing arms. All grand design spiral arms are trailing. Statistically, the vast majority most spiral galaxies have trailing arms. The source of leading-edge arms is believed to be the result from collisions causing retrograde perturbations. It's also been observed that only parts of the galaxy may be affected, i.e outer arms may be leading while the inner arms are trailing. NGC 4622 is an example, and possibly M81.

http://articles.adsabs.harvard.edu/full ... 3.000.html
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Re: APOD: M81 versus M82 (2013 Sep 25)

Post by Nitpicker » Thu Sep 26, 2013 6:16 am

Thanks for the education: neufer, Anthony and alter-ego. I especially like the explanation of leading/trailing and front/back.

As someone who is inclined towards a mathematical understanding of things, but who is otherwise quite ignorant of how gravitational forces create and maintain spiral galaxies, would it be a fair thing to say that:

The faster orbital motion of the more massive objects (stars) around the centre of a spiral galaxy is a first-order gravitational effect, while the formation and slower motion of the dusty/gassy/fluffy/nebulous spiral arms is more of a second-order, resonant effect.

... or is it way, way more complicated than that?

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Spiral arms are self-perpetuating, persistent and long-lived

Post by Ann » Thu Sep 26, 2013 7:53 am

http://www.cfa.harvard.edu/news/2013/pr201310.html wrote:

The new results fall somewhere in between the two theories and suggest that the arms arise in the first place as a result of the influence of giant molecular clouds - star forming regions or nurseries common in galaxies. Introduced into the simulation, the clouds act as "perturbers" and are enough to not only initiate the formation of spiral arms but to sustain them indefinitely.

"We find they are forming spiral arms," explains D'Onghia. "Past theory held the arms would go away with the perturbations removed, but we see that (once formed) the arms self-perpetuate, even when the perturbations are removed. It proves that once the arms are generated through these clouds, they can exist on their own through (the influence of) gravity, even in the extreme when the perturbations are no longer there."
So once spiral arms have formed, they are hard to get rid of - except through galactic collisions that kick the stars in all directions and leave an elliptical galaxy behind.

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Re: APOD: M81 versus M82 (2013 Sep 25)

Post by rstevenson » Thu Sep 26, 2013 11:31 am

Beyond wrote:So... the milky way is rotating the opposite way of M81 :?: Like a saw blade cutting backwards (which is used that way to cut plastics and the like).
The correct way to cut plastics, as with any other material, is to use the right kind of saw blade and run it forwards as usual.

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Re: APOD: M81 versus M82 (2013 Sep 25)

Post by Beyond » Thu Sep 26, 2013 12:05 pm

rstevenson wrote:
Beyond wrote:So... the milky way is rotating the opposite way of M81 :?: Like a saw blade cutting backwards (which is used that way to cut plastics and the like).
The correct way to cut plastics, as with any other material, is to use the right kind of saw blade and run it forwards as usual.

Rob
Actually, i was thinking more of fiberglass, but just couldn't think of the word. It's been a really long time :!:
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Re: APOD: M81 versus M82 (2013 Sep 25)

Post by neufer » Thu Sep 26, 2013 12:26 pm

neufer wrote:
deathfleer wrote:
Am I not right if I say
that the M81 's core is spinning anti clockwise?
  • You are indeed not right :!: ... :arrow:
alter-ego wrote:
<<For the most part, spiral galaxies have trailing arms. All grand design spiral arms are trailing. Statistically, the vast majority most spiral galaxies have trailing arms. The source of leading-edge arms is believed to be the result from collisions causing retrograde perturbations. It's also been observed that only parts of the galaxy may be affected, i.e outer arms may be leading while the inner arms are trailing. NGC 4622 is an example, and possibly M81.>>
I should point out that M81 is 12 Mly away such that 0.1 arcsec ~ 6 lyr.

[c]Therefore Adriaan van Maanen was "observing"
relativistic orbital proper motions :!: ... :arrow:[/c]
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deathfleer

Re: APOD: M81 versus M82 (2013 Sep 25)

Post by deathfleer » Thu Sep 26, 2013 4:31 pm

alter-ego wrote:
neufer wrote:
deathfleer wrote:
Am I not right if I say that the M81 's core is spinning anti clockwise?
  • You are indeed not right :!:
http://messier.seds.org/m/m081.html wrote:
<<Investigations performed in 1994 have indicated that M81 has probably only little dark matter, as its rotation curve was found to fall off in the outer regions; this is in contrast to many galaxies, including our own Milky Way, for which the rotation curve increases outward. To explain the velocity of the stars in these regions, the galaxy must have a certain amount of mass. However, the total mass observed in luminous matter - stars and nebulae - is typically insufficient to explain this behaviour; thus it is assumed that there is a significant portion of mass in galaxies is non-luminous, dark matter (or at least low-luminosity matter). For M81, the percentage of dark matter is now estimated to be lower than average.>>
For the most part, spiral galaxies have trailing arms. All grand design spiral arms are trailing. Statistically, the vast majority most spiral galaxies have trailing arms. The source of leading-edge arms is believed to be the result from collisions causing retrograde perturbations. It's also been observed that only parts of the galaxy may be affected, i.e outer arms may be leading while the inner arms are trailing. NGC 4622 is an example, and possibly M81.

http://articles.adsabs.harvard.edu/full ... 3.000.html

I thought it was like the water spraying out of a water sprinkler

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Re: APOD: M81 versus M82 (2013 Sep 25)

Post by neufer » Thu Sep 26, 2013 6:21 pm

deathfleer wrote:
alter-ego wrote: <<For the most part, spiral galaxies have trailing arms. All grand design spiral arms are trailing. Statistically, the vast majority most spiral galaxies have trailing arms. The source of leading-edge arms is believed to be the result from collisions causing retrograde perturbations. It's also been observed that only parts of the galaxy may be affected, i.e outer arms may be leading while the inner arms are trailing. NGC 4622 is an example.

http://articles.adsabs.harvard.edu/full ... 3.000.html
I thought it was like the water spraying out of a water sprinkler
Definitely NOT like the water spraying out of Henry Winkler a water sprinkler
http://en.wikipedia.org/wiki/Spiral_galaxy#Historical_theory_of_Lin_and_Shu wrote:
Image
<<The first acceptable theory for the spiral structure was devised by C. C. Lin and Frank Shu in 1964, attempting to explain the large-scale structure of spirals in terms of a small-amplitude wave propagating with fixed angular velocity, that revolves around the galaxy at a speed different from that of the galaxy's gas and stars. They suggested that the spiral arms were manifestations of spiral density waves - they assumed that the stars travel in slightly elliptical orbits, and that the orientations of their orbits is correlated i.e. the ellipses vary in their orientation (one to another) in a smooth way with increasing distance from the galactic center. This is illustrated in the diagram. It is clear that the elliptical orbits come close together in certain areas to give the effect of arms. Stars therefore do not remain forever in the position that we now see them in, but pass through the arms as they travel in their orbits.>>
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