APOD: 21st Century M101 (2019 Nov 06)

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APOD: 21st Century M101 (2019 Nov 06)

Post by APOD Robot » Wed Nov 06, 2019 5:06 am

Image 21st Century M101

Explanation: One of the last entries in Charles Messier's famous catalog, big, beautiful spiral galaxy M101 is definitely not one of the least. About 170,000 light-years across, this galaxy is enormous, almost twice the size of our own Milky Way Galaxy. M101 was also one of the original spiral nebulae observed with Lord Rosse's large 19th century telescope, the Leviathan of Parsonstown. In contrast, this multiwavelength view of the large island universe is a composite of images recorded by space-based telescopes in the 21st century. Color coded from X-rays to infrared wavelengths (high to low energies), the image data was taken from the Chandra X-ray Observatory (purple), the Galaxy Evolution Explorer (blue), Hubble Space Telescope(yellow), and the Spitzer Space Telescope(red). While the X-ray data trace the location of multimillion degree gas around M101's exploded stars and neutron star and black hole binary star systems, the lower energy data follow the stars and dust that define M101's grand spiral arms. Also known as the Pinwheel Galaxy, M101 lies within the boundaries of the northern constellation Ursa Major, about 25 million light-years away.

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Ann
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Re: APOD: 21st Century M101 (2019 Nov 06)

Post by Ann » Wed Nov 06, 2019 6:06 am

Some Pinwheel galaxy facts:

1) It is HUGE. It is estimated to be 170,000 light-years in diameter. Wikipedia claims that the diameter of the Milky Way is much wider, 258,000 light-years. Don't believe Wikipedia! The diameters of the Milky Way and M101 have been estimated using different methods. NASA, by contrast, wrote that the diameter of M101 is nearly twice the diameter of the Milky Way.

2) M101 contains stars like all the grains of sand of the Earth. Both Wikipedia and NASA agrees that M101 contains over a trillion stars, twice the number of the Milky Way, according to Wikipedia.

3) It is lopsided. Tidal forces are tugging at it.

4) It is BLUE!!! Its B-V index, +0.45, is amazingly blue for a large, let alone ultra-large galaxy!

5) It is chock full of emission nebulas! My word!

6) So M101 is like a galaxy out of the Universe's youth, when galaxies went bananas and formed stars like crazy. The only galaxy that I can think of that is a little bit like it is M99, but I do know that M99 is less blue than M101, and I'm almost certain that it is smaller than M101 and contains fewer stars. I agree that M99 is lopsided just like M101, however!

M101. Photo: Adam Block/Mount Lemmon SkyCenter.
M99. Photo: Adam Block/Mount Lemmon SkyCenter.


















Ann
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Wes K

Re: APOD: 21st Century M101 (2019 Nov 06)

Post by Wes K » Wed Nov 06, 2019 9:22 am

Seeing M101 reminded me of a question I've had for some time. While we see this galaxy nearly face on, the spiral structure of the galaxy seems quite ordered and familiar. But how is the force of gravity and conservation of angular momentum 'communicated' to the outer most perimeter of the galaxy? Given that gravity waves or changes in its field propagate at the speed of light, any change at the center of the galaxy would presumably take 85,000 years to be felt at the farthest edges.
I realize dark matter flattens the rotation curves of galaxies, but is it also responsible for communicating changes to the gravitational field across the galaxy in some super-luminal way? I know this last point violates special relativity, but I'm confused as to how a galaxy remains intact.

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Re: APOD: 21st Century M101 (2019 Nov 06)

Post by orin stepanek » Wed Nov 06, 2019 12:55 pm

Huge galaxy; being larger than the Milky Way! 8-)

Seems I remember some pinwheels as Cracker Jacks toys! :mrgreen:
6801cjtinx10.jpg
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Re: APOD: 21st Century M101 (2019 Nov 06)

Post by Ann » Wed Nov 06, 2019 1:09 pm

Wes K wrote:
Wed Nov 06, 2019 9:22 am
Seeing M101 reminded me of a question I've had for some time. While we see this galaxy nearly face on, the spiral structure of the galaxy seems quite ordered and familiar. But how is the force of gravity and conservation of angular momentum 'communicated' to the outer most perimeter of the galaxy? Given that gravity waves or changes in its field propagate at the speed of light, any change at the center of the galaxy would presumably take 85,000 years to be felt at the farthest edges.
I realize dark matter flattens the rotation curves of galaxies, but is it also responsible for communicating changes to the gravitational field across the galaxy in some super-luminal way? I know this last point violates special relativity, but I'm confused as to how a galaxy remains intact.
I don't think that forces that make M101 irregular emanate from within, but from without.
Wikipedia wrote:

M101 is asymmetrical due to the tidal forces from interactions with its companion galaxies. These gravitational interactions compress interstellar hydrogen gas, which then triggers strong star formation activity in M101's spiral arms that can be detected in ultraviolet images.
Explanation of spiral galaxy arms.
User:Dbenbenn / User:Mysid - Image:Spiral galaxy arms diagram.png recreated
as SVG by Mysid.
But perhaps you are asking why M101 is a spiral galaxy at all, and why its arms display an overall spiral shape?
Wikipedia wrote:

Density wave theory or the Lin–Shu density wave theory is a theory[1][2] proposed by C.C. Lin and Frank Shu in the mid-1960s to explain the spiral arm structure of spiral galaxies. The Lin–Shu theory introduces the idea of long-lived quasistatic spiral structure[1] (QSSS hypothesis). In this hypothesis, the spiral pattern rotates in a particular angular frequency (pattern speed), whereas the stars in the galactic disk are orbiting at a different speed depending on their distance to the galaxy center. The presence of spiral density waves in galaxies has implications on the star formation, since the gas orbiting around the galaxy may be compressed and form shock periodically.[3] Theoretically, the formation of global spiral pattern is treated as an instability of the stellar disk caused by the self-gravity, as opposed to tidal interactions.[4] The mathematical formulation of the theory has also been extended to other astrophysical disk systems,[5] such as Saturn's rings.
Click to play embedded YouTube video.
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Re: APOD: 21st Century M101 (2019 Nov 06)

Post by Chris Peterson » Wed Nov 06, 2019 2:13 pm

Wes K wrote:
Wed Nov 06, 2019 9:22 am
Seeing M101 reminded me of a question I've had for some time. While we see this galaxy nearly face on, the spiral structure of the galaxy seems quite ordered and familiar. But how is the force of gravity and conservation of angular momentum 'communicated' to the outer most perimeter of the galaxy? Given that gravity waves or changes in its field propagate at the speed of light, any change at the center of the galaxy would presumably take 85,000 years to be felt at the farthest edges.
I realize dark matter flattens the rotation curves of galaxies, but is it also responsible for communicating changes to the gravitational field across the galaxy in some super-luminal way? I know this last point violates special relativity, but I'm confused as to how a galaxy remains intact.
It is better to think of this as a static structure influenced by fixed gravitational fields. The propagation time doesn't matter, because nothing is really changing fast enough to matter. Keep in mind that the temporal gradient caused by the speed of light is only on the order of a hundred thousand years, while the orbital period of the stars and arm structures are on the order of a hundred million years.
Chris

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RooM101

Post by neufer » Wed Nov 06, 2019 2:14 pm

https://en.wikipedia.org/wiki/Ministries_of_Nineteen_Eighty-Four#Room_101 wrote:
<<RooM 101, introduced in the climax of George Orwell's novel Nineteen Eighty-Four, is the basement torture chamber in the Ministry of Love, in which the Party attempts to subject a prisoner to his or her own worst nightmare, fear or phobia, with the object of breaking down their resistance.
  • You asked me once, what was in Room 101. I told you that you knew the answer already. Everyone knows it. The thing that is in Room 101 is the worst thing in the world.
    — O'Brien, Part III, Chapter V
Such is the purported omniscience of the state in the society of Nineteen Eighty-Four that even a citizen's nightmares are known to the Party. The nightmare, and therefore the threatened punishment, of the protagonist Winston Smith is to be attacked by rats. This is manifested in Room 101 by confronting Smith with a wire cage that contains two large rats. The front of the cage is shaped so that it can fit over a person's face. A trap-door is then opened, allowing the rats to devour the victim's face. This cage is fitted over Smith's face, but he saves himself by begging the authorities to let his lover, Julia, suffer this torture instead of him. The threatened torture, and what Winston does to escape it, breaks his last promise to himself and to Julia: never to betray her. (Even though he had confessed to their actions, he still loved her until this point.) The book suggests that Julia is likewise subjected to her own worst fear (although it is not revealed what that fear is), and when she and Winston later meet in a park, he notices a scar on her forehead. The intent of threatening Winston with the rats was to force him into betraying the only person he loved and therefore to break his spirit.

Orwell named Room 101 after a conference room at Broadcasting House where he used to sit through tedious meetings.>>
https://en.wikipedia.org/wiki/101_(topic) wrote:
<<101 is a topic for beginners in any area. It has all the basic principles and concepts that are expected in a particular field.

In American university course numbering systems, the number 101 is often used for an introductory course at a beginner's level in a department's subject area. This common numbering system was designed to make transfer between colleges easier. In theory, any numbered course in one academic institution should bring a student to the same standard as a similarly numbered course at other institutions. The term was first introduced by the University of Buffalo in 1929. It was used as a course catalog, the first known usage of the term by Oxford English Dictionary. Based on this usage, the term "101" has been extended to mean an introductory level of learning or a collection of introductory materials to a topic.>>
Art Neuendorffer

khh

Re: APOD: 21st Century M101 (2019 Nov 06)

Post by khh » Wed Nov 06, 2019 8:48 pm

OMG, it's full of stars!

sillyworm 2

Re: APOD: 21st Century M101 (2019 Nov 06)

Post by sillyworm 2 » Wed Nov 06, 2019 10:38 pm

Enjoyed watching the density wave theory video...I know it's a virtual rendering..I was noticing that stars seem to migrate from one spiral arm to the next adjacent arm. Is this one of the outcomes this video meant to reveal?

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Re: APOD: 21st Century M101 (2019 Nov 06)

Post by Ann » Thu Nov 07, 2019 4:27 am

sillyworm 2 wrote:
Wed Nov 06, 2019 10:38 pm
Enjoyed watching the density wave theory video...I know it's a virtual rendering..I was noticing that stars seem to migrate from one spiral arm to the next adjacent arm. Is this one of the outcomes this video meant to reveal?
I think so. Note that the stars almost seem to get "stuck" for a while in the higher density of the spiral arm before they can move on to the next arm.

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