APOD: The Cartwheel Galaxy from Hubble (2016 Dec 18)

Comments and questions about the APOD on the main view screen.
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APOD: The Cartwheel Galaxy from Hubble (2016 Dec 18)

Postby APOD Robot » Sun Dec 18, 2016 5:05 am

Image The Cartwheel Galaxy from Hubble

Explanation: To some, it looks like the wheel of a cart. In fact, because of its outward oval appearance, the presence of a central galaxy, and their connection with what looks like the spokes of a wheel, the galaxy on the right is known as the Cartwheel Galaxy. To others, however, it looks like a complicated interaction between galaxies awaiting explanation. Along with the two galaxies on the left, the Cartwheel is part of a group of galaxies about 400 million light years away in the constellation Sculptor. The large galaxy's rim spans over 100,000 light years and is composed of star forming regions filled with extremely bright and massive stars. Pictured, the Cartwheel's ring-like shape is the result of gravitational disruption caused by a smaller galaxy passing through a large one, compressing the interstellar gas and dust and causing a star formation wave to move out like a ripple across the surface of a pond.

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heehaw

Re: APOD: The Cartwheel Galaxy from Hubble (2016 Dec 18)

Postby heehaw » Sun Dec 18, 2016 6:57 am

Am up for a 2 AM snack, and I am flabbergasted by this spectacular galaxy!

heehaw

Re: APOD: The Cartwheel Galaxy from Hubble (2016 Dec 18)

Postby heehaw » Sun Dec 18, 2016 10:13 am

heehaw wrote:Am up for a 2 AM snack, and I am flabbergasted by this spectacular galaxy!

And now I'm up for the day, at 5:10 am, and I want to add some obvious words: what we see in the photo is just the froth on the wave: most of the matter is dark matter, and we still don't know, despite my own best efforts and those of thousands of others, just what the dark matter actually is! It is supposed to be highly structured in blobs of various sizes. Mapping it is a work in progress. But, just as with our own oceans, the froth is the most complex and visible!

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Re: APOD: The Cartwheel Galaxy from Hubble (2016 Dec 18)

Postby bls0326 » Sun Dec 18, 2016 2:10 pm

+1 Spectacular galaxy!

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Re: APOD: The Cartwheel Galaxy from Hubble (2016 Dec 18)

Postby Wadsworth » Sun Dec 18, 2016 3:38 pm

+2 Awesome!

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Re: APOD: The Cartwheel Galaxy from Hubble (2016 Dec 18)

Postby Jim Leff » Sun Dec 18, 2016 3:57 pm

What are those two structures on the left? Photo bombers?

P Maisonpierre

Re: APOD: The Cartwheel Galaxy from Hubble (2016 Dec 18)

Postby P Maisonpierre » Sun Dec 18, 2016 7:53 pm

I was trying to imagine what the night-sky-view might look like if you were on a planet located toward the center but still some distance from the "hub", on a spoke of the Cartwheel Galaxy. Looking toward the hub you'd get a riot of stars, but then looking out toward the rim you'd also get a Milky Way like band -- maybe ? Whatever you might see, though, what an astounding celestial object: the CG.

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Re: APOD: The Cartwheel Galaxy from Hubble (2016 Dec 18)

Postby Ann » Sun Dec 18, 2016 8:51 pm

Jim Leff wrote:What are those two structures on the left? Photo bombers?


They are dwarf galaxies, and it has been surmised that one of them is the galaxy that scored a bulls-eye on its big brother, plunging right through the center of the Cartwheel Galaxy and setting off tremendous breakers that rippled through all the thousands of light-years of the galactic disk. In other words, one of them is prime suspect of, well, turning an ordinary spiral galaxy into the Cartwheel in the first place!

There is a problem with this scenario, however. A small galaxy plunging straight through the central parts of a large galaxy like the Cartwheel ought to lose all of its gas, and the small blue galaxy appears to be very gas-rich. The small yellow galaxy contains no visible gas, but on the other hand it is extremely well-ordered, and the ordeal of plunging through the center of another galaxy ought to throw the interloper into a state of chaos.

But it is not absolutely certain that one of the two bright dwarf galaxies is the one that cartwheeled the Cartwheel. If you check out this (large, 1.5 Mb!) picture of the Cartwheel and its surroundings, you can see a faint, beige dwarf galaxy to the lower right of the Cartwheel. This could perhaps be the galaxy that scored a bulls-eye on the Wheel of wheels galaxy.

Ann
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Re: APOD: The Cartwheel Galaxy from Hubble (2016 Dec 18)

Postby neufer » Mon Dec 19, 2016 4:02 am

Ann wrote:
Jim Leff wrote:
What are those two structures on the left? Photo bombers?

They are dwarf galaxies, and it has been surmised that one of them is the galaxy that scored a bulls-eye on its big brother, plunging right through the center of the Cartwheel Galaxy and setting off tremendous breakers that rippled through all the thousands of light-years of the galactic disk. In other words, one of them is prime suspect of, well, turning an ordinary spiral galaxy into the Cartwheel in the first place!

There is a problem with this scenario, however. A small galaxy plunging straight through the central parts of a large galaxy like the Cartwheel ought to lose all of its gas, and the small blue galaxy appears to be very gas-rich. The small yellow galaxy contains no visible gas, but on the other hand it is extremely well-ordered, and the ordeal of plunging through the center of another galaxy ought to throw the interloper into a state of chaos.

But it is not absolutely certain that one of the two bright dwarf galaxies is the one that cartwheeled the Cartwheel. If you check out this (large, 1.5 Mb!) picture of the Cartwheel and its surroundings, you can see a faint, beige dwarf galaxy to the lower right of the Cartwheel. This could perhaps be the galaxy that scored a bulls-eye on the Wheel of wheels galaxy.

The connecting band of X-rays from (Charlie?) Chandra pretty clearly points to
that "small blue (gas-rich) galaxy" as being the likely hit & run driver.

(Perhaps, the "small blue galaxy" merely skipped off the other like a rock.)
...........................................................................................
Hugh Drake: ...it's like finding a needle in a haystack.

Charlie Chan: Needle can be found when correct thread located.

https://en.wikipedia.org/wiki/Cartwheel_Galaxy wrote:
<<The Cartwheel galaxy shows non-thermal radio and optical spokes, but they are not the same spokes.

The unusual shape of the Cartwheel Galaxy may be due to a collision with a smaller galaxy such as those in the lower left of the image. The most recent star burst (star formation due to compression waves) has lit up the Cartwheel rim, which has a diameter larger than the Milky Way. Star formation via starburst galaxies, such as the Cartwheel Galaxy, results in the formation of large and extremely luminous stars. When massive stars explode as supernovas, they leave behind neutron stars and black holes. Some of these neutron stars and black holes have nearby companion stars, and become powerful sources of X-rays as they pull matter off their companions (also known as ultra and hyperluminous X-ray sources). The brightest X-ray sources are likely black holes with companion stars, and appear as the white dots that lie along the rim of the X-ray image. The Cartwheel contains an exceptionally large number of these black hole binary X-ray sources, because many massive stars formed in the ring.>>
Art Neuendorffer

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Ann
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Re: APOD: The Cartwheel Galaxy from Hubble (2016 Dec 18)

Postby Ann » Mon Dec 19, 2016 5:14 am

I think you're right, Art.

On a different note, the Cartwheel galaxy is a quite suitable choice for the Astronomy Picture of the Day at this time of year. At least it is suitable for those of us who live in Sweden!

Jul, noun, Swedish. Meaning: Christmas. Pronunciation: yool.

Hjul, noun, Swedish. Meaning: Wheel. Pronunciation: yool.

God Jul, noun phrase, Swedish. Meaning: Merry Christmas. Pronunciation: good yool.

So, God Jul and God Hjul to everyone here!

Ann
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Scotch7

Re: APOD: The Cartwheel Galaxy from Hubble (2016 Dec 18)

Postby Scotch7 » Sun Mar 19, 2017 6:14 pm

Supercomputer animations posted by Chris Mihos of Case Western Reserve University show some interesting theories about how the Cartwheel Galaxy came to be so... photogenic and mysterious:

http://burro.astr.cwru.edu/SSAnims/

Thanks to https://www.quora.com/profile/Romeel-Dav%C3%A9 for the link

luna-tick

Re: APOD: The Cartwheel Galaxy from Hubble (2016 Dec 18)

Postby luna-tick » Wed Mar 22, 2017 8:44 am

discussion on cartwheel galaxy is well presented. the cartwheel phenomenon being on the right and the two other galaxies appearing on left of screen. the discussion was important because it established nomenclature of reference on computer screen - the object on the right and the object on the left of a computer screen. i really did have a problem working out what is left and right on the computer screen. thank you for making that clarification.

the cartwheel galaxy.

image of the cartwheel galaxy.

discussion says that the cartwheel galaxy (on the right) and the two objects on the left are distinctly separate.

is there any possibility that the cartwheel galaxy and the two objects on the left are one and the same ??

and related by a before and after event ??

what cosmic event could possibly cause a before and after scene on an astronomical screen ??

the before being the two objects on the left - and the after being the cartwheel galaxy.

in probing such a possibility the individual ojbects must be examined. a convenient explanation would hold that the cartwheel galaxy and the two objects on the left are separate and unrelated. even so, the blue and yellow of each of the objects occur in such an arrangement that they summon a before and after explanation.

how could four objects - two yellow and two blue - appear so similar to each other and be so placed that they appear as neighbors in a cosmic portrait.

the convenient thing to do is to accept the explanation that the cartwheel galaxy and the two objects on left are physically separate bodies.

because the possibility of them being one and the same defies explanation.

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Re: APOD: The Cartwheel Galaxy from Hubble (2016 Dec 18)

Postby Ann » Thu Mar 23, 2017 12:42 am

luna-tick wrote:discussion on cartwheel galaxy is well presented. the cartwheel phenomenon being on the right and the two other galaxies appearing on left of screen. the discussion was important because it established nomenclature of reference on computer screen - the object on the right and the object on the left of a computer screen. i really did have a problem working out what is left and right on the computer screen. thank you for making that clarification.

the cartwheel galaxy.

image of the cartwheel galaxy.

discussion says that the cartwheel galaxy (on the right) and the two objects on the left are distinctly separate.

is there any possibility that the cartwheel galaxy and the two objects on the left are one and the same ??

and related by a before and after event ??


how could four objects - two yellow and two blue - appear so similar to each other and be so placed that they appear as neighbors in a cosmic portrait.

the convenient thing to do is to accept the explanation that the cartwheel galaxy and the two objects on left are physically separate bodies.

because the possibility of them being one and the same defies explanation.


You didn't get a lot of response to your question, so I'll chime in with some thoughts.

Yes, the galaxies are separate entities. They are separate in that their constituent stars are in orbit around the centers of the three different galaxies. The stars of the Cartwheel galaxy are in orbit around the center of mass of the Cartwheel galaxy, the stars of the small blue galaxy are in orbit around the center of the small blue galaxy, and the stars of the small yellow galaxy are in orbit around the center of the small yellow galaxy.

Mostly! Because it is possible that the galaxies have exchanged some stars, when they passed very close to each other. It is also possible that some of the stars have been flung into extremely elongated orbits when the galaxies passed close to one another.

We may also assume that the galaxies have dark matter halos that are in contact with one another, if the galaxies are located sufficiently close to one another.

A post that Art (neufer) made in this thread shows that the Cartwheel galaxy and the small blue galaxy seem to be connected by a stream of hot, X-ray emitting gas. So in a sense, the galaxies are connected. But the optical outlines of the galaxies are very clearly separated, which means that the stars of these two galaxies are in orbit around the centers of each separate galaxy.

NGC 2276 and NGC 3200.
Photo: Carlos and Crystal Acosta/Adam Block/NOAO/AURA/NSF
Finally, how can the two small galaxies next to the Cartwheel galaxy look so different (and be so different)?

I can only say that galaxies that are located close to one another sometimes look completely different. A prime example is the the spiral galaxy NGC 2276 and the elliptical galaxy NGC 2300. How can these two galaxies be so close together, yet have evolved so differently?

One possibility is that they were not born close together, but have gradually approached one another. If so, during the time when they were too widely separated to influence one another, they may have had very different "life histories". For example, the elliptical galaxy is likely to have undergone multiple collisions with smaller galaxies, which were then incorporated into the main body of NGC 2300. This may have messed up the spiral pattern of NGC 2300 and destroyed it. At the same time, multiple collisions may have fed the central black hole of NGC 2300, which may have heated and stirred up the gas of NGC 2300, making it unfit for star formation.

But NGC 2276 may have evolved slowly, undergoing few or no mergers and hanging on to most of its gas. When NGC 2276 then approached NGC 2300, the tidal forces acting on NGC 2276 compressed its gas and made it ripe for star formation.

What I'm suggesting is that the two small galaxies next to the Cartwheel galaxy may not have been born close to one another, so they may have evolved quite differently. But another possibility is that the small blue galaxy is undergoing a galaxy-wide burst of star formation due to its close interaction with the Cartwheel galaxy. Perhaps the small blue galaxy picked up a lot of gas from the Cartwheel somehow, and at the same time (or soon afterwards) this gas was compressed into perfect star forming conditions. The small yellow galaxy may be entirely devoid of gas. It looks like it.

Ann
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