APOD: Rotation of the Large Magellanic Cloud (2018 May 16)

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APOD: Rotation of the Large Magellanic Cloud (2018 May 16)

Post by APOD Robot » Wed May 16, 2018 4:07 am

Image Rotation of the Large Magellanic Cloud

Explanation: This image is not blurry. It shows in clear detail that the largest satellite galaxy to our Milky Way, the Large Cloud of Magellan (LMC), rotates. First determined with Hubble, the rotation of the LMC is presented here with fine data from the Sun-orbiting Gaia satellite. Gaia measures the positions of stars so accurately that subsequent measurements can reveal slight proper motions of stars not previously detectable. The featured image shows, effectively, exaggerated star trails for millions of faint LMC stars. Inspection of the image also shows the center of the clockwise rotation: near the top of the LMC's central bar. The LMC, prominent in southern skies, is a small spiral galaxy that has been distorted by encounters with the greater Milky Way Galaxy and the lesser Small Magellanic Cloud (SMC).

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Re: APOD: Rotation of the Large Magellanic Cloud (2018 May 16)

Post by blastoff » Wed May 16, 2018 4:26 am

Why would it have that lobe above the center? Binary centers of gravity?

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Re: APOD: Rotation of the Large Magellanic Cloud (2018 May 16)

Post by Ann » Wed May 16, 2018 5:09 am

Gaia is such a great instrument! :D

But because it doesn't show bright stars the way "pixel bleeding" images do, it is sometimes a bit hard to make head or tail of Gaia's pictures. So the Tarantula Nebula is near the top of today's APOD, right? Near the center of rotation of the Large Magellanic Cloud?

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Re: APOD: Rotation of the Large Magellanic Cloud (2018 May 16)

Post by Chris Peterson » Wed May 16, 2018 5:22 am

blastoff wrote:
Wed May 16, 2018 4:26 am
Why would it have that lobe above the center? Binary centers of gravity?
No. It's what orbits look like when you have what is essentially a moving center of gravity caused by tidal interactions. Effectively, all of these stars see somewhat different centers of gravity, determined not just by the combined (and moving) mass of the LMC, but by the moving mass of the Milky Way, as well.
Chris

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Re: APOD: Rotation of the Large Magellanic Cloud (2018 May 16)

Post by Adriano » Wed May 16, 2018 5:54 am

Superb picture. Is there a black hole at the centre of LMC?

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Re: APOD: Rotation of the Large Magellanic Cloud (2018 May 16)

Post by edgardine » Wed May 16, 2018 6:16 am

So glad about gaia's data.

However, one of the sentences seems to be outdated information "The LMC [...] is a spiral galaxy that has been distorted by encounters with the greater Milky Way Galaxy and the lesser Small Magellanic Cloud."
Recently, I read some articles about the past encounters of Andromeda, in which they said that the LMC has been distorted then.
I may be wrong

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Re: APOD: Rotation of the Large Magellanic Cloud (2018 May 16)

Post by APODFORIST » Wed May 16, 2018 7:38 am

Which time span is displayed or extrapolated in this picture?

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Re: APOD: Rotation of the Large Magellanic Cloud (2018 May 16)

Post by BillT » Wed May 16, 2018 8:22 am

Adriano wrote:
Wed May 16, 2018 5:54 am
Superb picture. Is there a black hole at the centre of LMC?
Some evidence:

https://arxiv.org/abs/1804.10197

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Re: APOD: Rotation of the Large Magellanic Cloud (2018 May 16)

Post by Ann » Wed May 16, 2018 8:55 am

edgardine wrote:
Wed May 16, 2018 6:16 am
So glad about gaia's data.

However, one of the sentences seems to be outdated information "The LMC [...] is a spiral galaxy that has been distorted by encounters with the greater Milky Way Galaxy and the lesser Small Magellanic Cloud."
Recently, I read some articles about the past encounters of Andromeda, in which they said that the LMC has been distorted then.
I may be wrong
This Wikipedia article about the Hubble sequence identifies the Large Magellanic Cloud as an irregular galaxy. However, I think it could be argued that the LMC might also be classified as an SBd galaxy:
Sd (SBd) – very loosely wound, fragmentary arms; most of the luminosity is in the arms and not the bulge.
If you take a look at this picture of the Large Magellanic cloud, you might perhaps agree that the scattered regions of star formation surrounding the bar of the LMC do show some slight simiarities to spiral arms.

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Re: APOD: Rotation of the Large Magellanic Cloud (2018 May 16)

Post by JohnD » Wed May 16, 2018 8:57 am

Fingerprint!

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Re: APOD: Rotation of the Large Magellanic Cloud (2018 May 16)

Post by heehaw » Wed May 16, 2018 9:07 am

Chris Peterson wrote:
Wed May 16, 2018 5:22 am
blastoff wrote:
Wed May 16, 2018 4:26 am
Why would it have that lobe above the center? Binary centers of gravity?
No. It's what orbits look like when you have what is essentially a moving center of gravity caused by tidal interactions. Effectively, all of these stars see somewhat different centers of gravity, determined not just by the combined (and moving) mass of the LMC, but by the moving mass of the Milky Way, as well.
Surely the motion is influenced by the distribution of "the ghost in the room," the dark matter? Can we find out about dark matter locations from Gaia?

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Re: APOD: Rotation of the Large Magellanic Cloud (2018 May 16)

Post by RocketRon » Wed May 16, 2018 9:55 am

APODFORIST wrote:
Wed May 16, 2018 7:38 am
Which time span is displayed or extrapolated in this picture?
Good question. Very good question...

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Re: APOD: Rotation of the Large Magellanic Cloud (2018 May 16)

Post by De58te » Wed May 16, 2018 10:31 am

APODFORIST wrote:
Wed May 16, 2018 7:38 am
Which time span is displayed or extrapolated in this picture?
I heard that Gaia's mission is to take up to 70 snapshots of its targets over 5 years [Wikipedia], and the elapsed time since Gaia's launch is 4 years, 4 months, and 27 days, I'd say the time period is around 4 years and 4 months. (Just my unofficial guess.)

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Re: APOD: Rotation of the Large Magellanic Cloud (2018 May 16)

Post by BillT » Wed May 16, 2018 10:55 am

De58te wrote:
Wed May 16, 2018 10:31 am
ata
APODFORIST wrote:
Wed May 16, 2018 7:38 am
Which time span is displayed or extrapolated in this picture?
I heard that Gaia's mission is to take up to 70 snapshots of its targets over 5 years [Wikipedia], and the elapsed time since Gaia's launch is 4 years, 4 months, and 27 days, I'd say the time period is around 4 years and 4 months. (Just my unofficial guess.)
DR2 covers the first 22 months of data collection. DR1 was the first 14 months. It takes a lot of work before the data can be released in a usable form. The diagram is extrapolated from that. 22 months of proper motion would be sub pixel and invisible on a rendering like that.

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Re: APOD: Rotation of the Large Magellanic Cloud (2018 May 16)

Post by neufer » Wed May 16, 2018 11:59 am

BillT wrote:
Wed May 16, 2018 10:55 am
De58te wrote:
Wed May 16, 2018 10:31 am
APODFORIST wrote:
Wed May 16, 2018 7:38 am

Which time span is displayed or extrapolated in this picture?
I heard that Gaia's mission is to take up to 70 snapshots of its targets over 5 years [Wikipedia], and the elapsed time since Gaia's launch is 4 years, 4 months, and 27 days, I'd say the time period is around 4 years and 4 months. (Just my unofficial guess.)
DR2 covers the first 22 months of data collection. DR1 was the first 14 months. It takes a lot of work before the data can be released in a usable form. The diagram is extrapolated from that. 22 months of proper motion would be sub pixel and invisible on a rendering like that.
I wouldn't be too concerned with "sub pixel."

Multiple pixels are involved with each spinning Gaia "snapshot" and

the center of each "snapshot" Airy disk can be determined to high "sub pixel" precision.
Art Neuendorffer

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Re: APOD: Rotation of the Large Magellanic Cloud (2018 May 16)

Post by neufer » Wed May 16, 2018 12:05 pm

Chris Peterson wrote:
Wed May 16, 2018 5:22 am
blastoff wrote:
Wed May 16, 2018 4:26 am

Why would it have that lobe above the center? Binary centers of gravity?
No. It's what orbits look like when you have what is essentially a moving center of gravity caused by tidal interactions. Effectively, all of these stars see somewhat different centers of gravity, determined not just by the combined (and moving) mass of the LMC, but by the moving mass of the Milky Way, as well.
You lost me there, Chris. I would have said: Yes, binary centers of gravity.

How can you be so sure that it isn't primarily binary centers of gravity?
Art Neuendorffer

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Re: APOD: Rotation of the Large Magellanic Cloud (2018 May 16)

Post by edgardine » Wed May 16, 2018 12:21 pm

Ann wrote:
Wed May 16, 2018 8:55 am
edgardine wrote:
Wed May 16, 2018 6:16 am
So glad about gaia's data.

However, one of the sentences seems to be outdated information "The LMC [...] is a spiral galaxy that has been distorted by encounters with the greater Milky Way Galaxy and the lesser Small Magellanic Cloud."
Recently, I read some articles about the past encounters of Andromeda, in which they said that the LMC has been distorted then.
I may be wrong
This Wikipedia article about the Hubble sequence identifies the Large Magellanic Cloud as an irregular galaxy. However, I think it could be argued that the LMC might also be classified as an SBd galaxy:
Sd (SBd) – very loosely wound, fragmentary arms; most of the luminosity is in the arms and not the bulge.
If you take a look at this picture of the Large Magellanic cloud, you might perhaps agree that the scattered regions of star formation surrounding the bar of the LMC do show some slight simiarities to spiral arms.

Ann
Thank you for your answer, Ann. (I really appreciate your work on color, there are so many inconsistencies about it)

English is not my native language, I probably did not express myself clearly. What I consider potentially outdated is that the LMC has been distorted by the Milky Way rather than by Andromeda.
I read a recent article about it, but I can not retrieve it.
Here are two
http://iopscience.iop.org/article/10.10 ... 2/924/meta
https://arxiv.org/abs/1010.2748

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Re: APOD: Rotation of the Large Magellanic Cloud (2018 May 16)

Post by orin stepanek » Wed May 16, 2018 12:29 pm

Elongated star trails make it look fuzzy wuzzy 1 8-)
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Re: APOD: Rotation of the Large Magellanic Cloud (2018 May 16)

Post by tmcdanel » Wed May 16, 2018 1:01 pm

neufer wrote:
Wed May 16, 2018 12:05 pm
Chris Peterson wrote:
Wed May 16, 2018 5:22 am
blastoff wrote:
Wed May 16, 2018 4:26 am

Why would it have that lobe above the center? Binary centers of gravity?
No. It's what orbits look like when you have what is essentially a moving center of gravity caused by tidal interactions. Effectively, all of these stars see somewhat different centers of gravity, determined not just by the combined (and moving) mass of the LMC, but by the moving mass of the Milky Way, as well.
You lost me there, Chris. I would have said: Yes, binary centers of gravity.

How can you be so sure that it isn't primarily binary centers of gravity?
I had the same question as the OP, Blastoff, which is why I came to the discussion. I do not understand what looks like "eddies" on the outer edges. A really good example of that is the upper left corner. I am not certain I understand Chris' response, except that it should be looked at "4 dimensionally" over time? with center's of gravity of binary and more complex systems moving?
Perhaps it would be easier to understand as an animated video.
Thank you all.

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Re: APOD: Rotation of the Large Magellanic Cloud (2018 May 16)

Post by Chris Peterson » Wed May 16, 2018 1:08 pm

APODFORIST wrote:
Wed May 16, 2018 7:38 am
Which time span is displayed or extrapolated in this picture?
I don't think we can quite look at it like that. The convolution technique used on the data creates the appearance of flow in order to visualize the field, but a long exposure (that is, thousands of years) wouldn't look just like this image.
Chris

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Re: APOD: Rotation of the Large Magellanic Cloud (2018 May 16)

Post by Chris Peterson » Wed May 16, 2018 1:10 pm

neufer wrote:
Wed May 16, 2018 11:59 am
BillT wrote:
Wed May 16, 2018 10:55 am
De58te wrote:
Wed May 16, 2018 10:31 am


I heard that Gaia's mission is to take up to 70 snapshots of its targets over 5 years [Wikipedia], and the elapsed time since Gaia's launch is 4 years, 4 months, and 27 days, I'd say the time period is around 4 years and 4 months. (Just my unofficial guess.)
DR2 covers the first 22 months of data collection. DR1 was the first 14 months. It takes a lot of work before the data can be released in a usable form. The diagram is extrapolated from that. 22 months of proper motion would be sub pixel and invisible on a rendering like that.
I wouldn't be too concerned with "sub pixel."

Multiple pixels are involved with each spinning Gaia "snapshot" and

the center of each "snapshot" Airy disk can be determined to high "sub pixel" precision.
Yes. But that's not the point. At the scale of today's image, all the motion is subpixel, and since today's image contains no stellar images, there wouldn't even be centroids that could be calculated.
Chris

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Re: APOD: Rotation of the Large Magellanic Cloud (2018 May 16)

Post by Chris Peterson » Wed May 16, 2018 1:14 pm

neufer wrote:
Wed May 16, 2018 12:05 pm
Chris Peterson wrote:
Wed May 16, 2018 5:22 am
blastoff wrote:
Wed May 16, 2018 4:26 am

Why would it have that lobe above the center? Binary centers of gravity?
No. It's what orbits look like when you have what is essentially a moving center of gravity caused by tidal interactions. Effectively, all of these stars see somewhat different centers of gravity, determined not just by the combined (and moving) mass of the LMC, but by the moving mass of the Milky Way, as well.
You lost me there, Chris. I would have said: Yes, binary centers of gravity.

How can you be so sure that it isn't primarily binary centers of gravity?
I don't even know what a "binary center of gravity" is. A system only has one center of gravity. But in a system like this, there is a complex gravitational field, and there are long lasting tidal effects, as well. So the motion of the system is not uniformly around some clearly defined center of gravity.
Chris

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Re: APOD: Rotation of the Large Magellanic Cloud (2018 May 16)

Post by E Fish » Wed May 16, 2018 1:26 pm

JohnD wrote:
Wed May 16, 2018 8:57 am
Fingerprint!
That was my first thought, too! Before I read the description, I was thinking it looked like a cosmic fingerprint.

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Re: APOD: Rotation of the Large Magellanic Cloud (2018 May 16)

Post by Steve Dutch » Wed May 16, 2018 1:43 pm

Every so often something comes along that makes me shake my head in disbelief. Seeing proper motions of stars in the Large Magellanic Cloud is it for today.

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Re: APOD: Rotation of the Large Magellanic Cloud (2018 May 16)

Post by Chris Peterson » Wed May 16, 2018 1:46 pm

Steve Dutch wrote:
Wed May 16, 2018 1:43 pm
Every so often something comes along that makes me shake my head in disbelief. Seeing proper motions of stars in the Large Magellanic Cloud is it for today.
For me, it's not just seeing the information that this image presents, but appreciating the elegance of our visualization techniques given rich data sets. Because that's all we're looking at here: a huge table of numbers, converted to an image which instantly and without complex visual analysis gives us the underlying meaning of all those numbers in a very intuitive way.
Chris

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