APOD: The Magellanic Stream (2010 Jan 25)

[APOD Robot]

The Magellanic Stream

Explanation: Spanning the sky toward the majestic Clouds of Magellan is an unusual stream of gas: the Magellanic Stream. The origin of this gas remains unknown but likely hold a clue to origin and fate of our Milky Way's most famous satellite galaxies: the LMC and the SMC. Until recently, two leading genesis hypotheses have been considered: that the stream was created by gas stripped off these galaxies as they passed through the halo of our Milky Way, or that the stream was created by the differential gravitational tug of the Milky Way. Recently, however, wide angle radio images -- including those from the Byrd Green Bank Telescope -- have shown that the Magellanic Stream is longer and older than previously thought, perhaps as old as 2.5 billion years. These observations bolster a third possible origin for the stream -- that the Large and Small Magellanic Cloud galaxies once passed so close to each other that gravitational tides triggered a burst of star formation that left the stream. Pictured above digitally superposed on a recently-completed all-sky image in visible light, the radio emission of Magellanic stream is shown in false color pink extending across the sky and ending at the two Magellanic galaxies on the lower right.

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[peter_from_nyc]

Hi:

I assume the "halo" of the Milky Way is a sphere the surrounds the flattened, spiral disk that is the Milky Way. As opposed to a 2-dimensional halo around the spiral.

It would be good if we could see the image projected upon a solid sphere (or upon a transparent sphere that showed where the sun was).

I understand that some programs have been written for planetariums and other museums to project earth data upon a sphere so you can see it in 3-D.

Can that be done for this picture, which I take is a flat representation of a spherical view, much like a 2-D map is a representation of a 3-D earth?

Here's an example of showing the earth in 3-D:
http://www.earth3d.org/

and here's a video (as opposed to a user controlled image) of a 3-D Milky Way:

Click to play embedded YouTube video.

If the Milky Way were in 3-D under user control, one could see it from the point of view of Earth, and from that of an intergalactic visitor.

Peter

[DonAVP]

Hi:

I assume the "halo" of the Milky Way is a sphere the surrounds the flattened, spiral disk that is the Milky Way. As opposed to a 2-dimensional halo around the spiral.

It would be good if we could see the image projected upon a solid sphere (or upon a transparent sphere that showed where the sun was).

I understand that some programs have been written for planetariums and other museums to project earth data upon a sphere so you can see it in 3-D.

Can that be done for this picture, which I take is a flat representation of a spherical view, much like a 2-D map is a representation of a 3-D earth?

Here's an example of showing the earth in 3-D:
http://www.earth3d.org/

and here's a video (as opposed to a user controlled image) of a 3-D Milky Way:

Click to play embedded YouTube video.

If the Milky Way were in 3-D under user control, one could see it from the point of view of Earth, and from that of an intergalactic visitor.

Peter

You can see the same thing and much more with Google Earth. Google earth include Mars and the Moon. Other planets maybe in the future. I mentioned a program called Celestia http://www.shatters.net/celestia/ last week on another thread this will let you view our galaxy as well as a couple of hundred other galaxies and several hundred thousand stars and all of the it in 3D.

Don

[neufer]

CAUGHT RED-HANDED: OUR GALAXY IS DESTROYING ITS NEIGHBOURS

<<Astronomers using CSIRO's Parkes radio telescope have made a picture that shows our Galaxy ripping apart its nearest neighbours.

The two nearest neighbouring galaxies, the Large and Small Magellanic Clouds, are less than a tenth of our Galaxy in size. They are close by, only twice as far from the starry edge of our Galaxy as that edge is from the Galaxy's centre. And they orbit our Galaxy, in thrall to its gravitational pull. That pull is now tearing them apart, by tugging harder on their near side than on their far side. Hydrogen gas stripped from the Clouds by this process is now streaming out ahead and behind them. The dismemberment was imaged by the new 'multibeam' instrument on the Parkes telescope, which detects the hydrogen gas in galaxies - the 'bones' underlying their starry 'flesh'.

Developed by CSIRO, it is the most powerful instrument of its kind in the world. Most of its work is searching for faint and hidden galaxies that can't be detected any other way. The new picture has settled a long-standing controversy sparked by a much earlier finding made with the Parkes telescope. In 1973 Dr (later Professor) Don Mathewson from Mount Stromlo Observatory used the Parkes telescope to discover a trail of gas flowing behind the Magellanic Clouds. This trail, called the Magellanic Stream, is more than twice as long as the diameter of our Galaxy. Astronomers have argued for decades about the Stream's origin. "But over the years we've whittled it down to two choices," said CSIRO's Dr Lister Staveley-Smith, lead scientist on the multibeam project.

"One was a process called ram-pressure stripping - gas being swept out of the Magellanic Clouds as the Clouds travelled through our Galaxy's outskirts."

"The other was so-called tidal forces from our Galaxy. That idea predicted we'd find material coming off the leading edge of the Clouds - and we have," said Dr Staveley-Smith.

"People have looked before for this stuff but haven't found it because they sampled the sky rather coarsely, whereas we've been searching with a fine-toothed comb," said Ms Mary Putman, the PhD student at Mount Stromlo Observatory who made the key picture. "We are interested in how galaxies interact, because it's an important aspect of how they evolve over time. We are still trying to understand how important interactions are in creating new stars, for instance," said Mt Stromlo Observatory's Dr Brad Gibson, Ms Putman's thesis supervisor.>>

<<Barack Obama stated that his health care plan has “run into a bit of a buzz saw.”>>

Artist's impression: our Galaxy's gravity claws at the fabric of two neighbouring galaxies,
the Large and Small Magellanic Clouds, pulling out streams of hydrogen gas.
The letters X, Y and Z label the axes, to indicate positions in 3D space.
Picture: Dallas Parr, CSIRO.>>

[peter_from_nyc]

This is some thanks to Art Neuendorffer for the illustration http://www.csiro.au/news/mediarel/mr1998/mr98194.html
which shows that the "halo" is 2-D, and that it is perpendicular to the plane of our spiral galaxy.

It is not what I expected.

It's also interesting that the two (LMC and SMC) Megellanic Clouds are near each other, and are in the same plane (the plane of the 'halo').

Peter

[Chris Peterson]

This is some thanks to Art Neuendorffer for the illustration which shows that the "halo" is 2-D, and that it is perpendicular to the plane of our spiral galaxy.

I believe you have misunderstood the illustration. The galaxy actually has two halos- one is the approximately spherical dark matter halo (recently reported to be somewhat distorted), and the other is an approximately spherical halo consisting of stars, clusters, and dwarf galaxies. The latter is not at all uniform in density, but appears to be made up of streams of material ripped out of tiny galaxies that have interacted with our own. I like this report that describes the halo as a bunch of spaghetti around the meatball of our galaxy.

Neither halo is 2D, or otherwise disc-like.

[DonAVP]

I was reading another thread in "The Asterisk Cafe" and found this link http://www.skyandtelescope.com/news/81035932.html. It sure seems to be the same thing.

[The Code]

I was reading another thread in "The Asterisk Cafe" and found this link http://www.skyandtelescope.com/news/81035932.html. It sure seems to be the same thing.

Yes it is. but the topic is different. There is no mention of DE/DM on this thread.

[Chris Peterson]

Yes it is. but the topic is different. There is no mention of DE/DM on this thread.

Dark energy is not discussed and is irrelevant to the topic. Dark matter is very relevant to the discussion, and is mentioned if you follow some of the links. That's because the halo of our (or any) galaxy consists primarily of dark matter. So if you are discussing the way in which our galaxy's halo disrupts material passing through it, you have to consider dark matter.

[The Code]

Yes it is. but the topic is different. There is no mention of DE/DM on this thread.

Dark energy is not discussed and is irrelevant to the topic. Dark matter is very relevant to the discussion, and is mentioned if you follow some of the links.

Until now you mean.

[Chris Peterson]

Until now you mean.

Not sure what you mean. My point was that dark matter has previously been discussed, and is very relevant to the thread. Dark energy is not. The S&T article discusses both, and is interesting and topical even though its discussion of dark energy really has nothing to do with this particular discussion.

[The Code]

Until now you mean.

Not sure what you mean. My point was that dark matter has previously been discussed, and is very relevant to the thread. Dark energy is not. The S&T article discusses both, and is interesting and topical even though its discussion of dark energy really has nothing to do with this particular discussion.

What part of this do you not understand mate? :

A key to this revelation was the ability to measure the distances of far galaxies by the apparent brightnesses of Type-Ia supernovae within them, independently of a galaxy's redshift. This distance can then be matched with the redshift — which tells how much the universe expanded while the light was in transit. In this way, astronomers were able to see how the expansion rate has changed over long stretches of cosmic time.

Since then, astronomers have found a wealth of other evidence that some force is causing the expansion to speed up — and how much of it there is, and the crucial fact that it seems to be neither weakening nor strengthening as space enlarges. It was named "dark energy" for lack of anything better.

Now an international team has teased out the effects of dark energy in our own Local Group of galaxies. The Local Group includes the Milky Way, the Andromeda Galaxy, M33, and about 50 dwarf galaxies identified so far.

The team analyzed recent Hubble Space Telescope observations of Local Group galaxy motions (radial velocities), made by a team led by Russian astronomer Igor Karachentsev. By studying how galaxies move with respect to the gravitational center of the Local Group, they could find the boundary where the Local Group’s gravity gives way to dark energy’s “antigravity” effect on larger scales. Dwarf galaxies beyond this boundary are moving outward and will be lost.

Its all in the links?

[bystander]

What part of this do you not understand mate?

DE has absolutely nothing to do with the Milky Way Halo nor the Magellanic Stream, which is what this thread is about.

[The Code]

If you say so mate. I totally agree.

The End

Mark

[Chris Peterson]

What part of this do you not understand mate?

I understand the S&T article perfectly. But the stuff about dark energy is not relevant to how our galaxy's halo interacts with material passing through it. The article points out that the smallest scale where dark energy's effects show up in data is at the level of clusters of galaxies- in this case, the Local Group. That's far larger than the subject of this particular APOD.

[bystander]

Mark

You need to reread the last paragraph of your quote above. DE only affects things outside our local group. Inside DM and gravity hold sway.

By studying how galaxies move with respect to the gravitational center of the Local Group, they could find the boundary where the Local Group’s gravity gives way to dark energy’s “antigravity” effect on larger scales. Dwarf galaxies beyond this boundary are moving outward and will be lost.

[The Code]

Its been highlighted . Job done.

I,m out.

I made no quotes. I am very careful.

[peter_from_nyc]

This is Peter, who started the question (and thanks for all your replies):

It would be good if we could see the image [as] a transparent sphere that showed where the sun was ....

Can that be done for this picture [of The Magellanic Stream], which I take is a flat representation of a spherical view, much like a 2-D map is a representation of a 3-D earth?

What I liked is the phrase:

The model can be visualized as a big meatball in a bowl of spaghetti. The meatball is the Milky Way, and spaghetti strands winding away in all different directions represent ripped apart small galaxies.

http://uanews.org/node/25687

which had this image, which (again) would be nice to see in 3-D.

[theTonster]

This picture appears to be on a Sinusoidal Projection, which has pointy Poles, instead of, say, the Hammer Projection, in which the whole sky (or a planet...) fits into a 2:1 ellipse, which has less distortion than the former. The Stream appears to have a kink because of the projection. Perhaps using an oblique Hammer could split the difference between the MWG and the Stream, to clarify this point. Reprojection used to be tedious, but is easy now.
I also note the discussion drifted slightly off topic, invoking Lambda-CDM when Newtonian gravity is sufficient. The Stream might in fact, be a useful test for the application of Modified Newtonian Dynamics (MOND). I wonder what Professor Stacy McGaugh and his colleagues might have to say on this matter. The Stream is certainly distant enough to be in the realm of very low acceleration, for which MOND was proposed.

[Juanko]

I'm happy with this forum. I entered the astrology world few weeks ago and every time i learn something new, it just blows me away. Seeing more of the galaxy photos makes one think what if we could go up there and see stuff like these closely! would be amazing.

[bystander]

I entered the astrology world few weeks ago

This isn't astrology, it's astronomy. Science not superstition. Quite a difference.

[Beyond]

Hmmm....seems to me that Astrology & Astronomy both deal with the same thing(space)but in two different ways. They both, to some extent, deal with trying to find out what is really going on with everything. However, because of the "forces" at work in the Universe, both physical and otherwise, everything is out of whack to varying degrees and can not be relied on much for meaningful answers. But that doesn't stop people from trying. Even a broken clock is right twice a day.

[Chris Peterson]

Hmmm....seems to me that Astrology & Astronomy both deal with the same thing(space)but in two different ways.

Astrology has no interest in space. Astrology is a kind of religion, which seeks to explain events and behavior in terms of the positions of planets. That isn't remotely what astronomy seeks to do.

[Ann]

I'm happy with this forum. I entered the astrology world few weeks ago and every time i learn something new, it just blows me away. Seeing more of the galaxy photos makes one think what if we could go up there and see stuff like these closely! would be amazing.

Right, Juanko, some of us astronomy people don't like it too much when others mix up astronomy and astrology. Astronomy is the scientific study of stars, planets, galaxies and the universe. Astrology is, basically, about predicting a person's future by studying the position of the planets. Like bystander said, that is not what this forum is about.

So please understand that you can't read about astrology here. You can't even discuss astrology here, sorry.

But I hope you will feel welcome here anyway! As long as you like to read about our amazing fantastic universe and look at splendid images of galaxies and other cool stuff, this is the right place for you!

Ann

[bystander]

Milky Way Sidelined in Galactic Tug of War
http://asterisk.apod.com/vie ... 31&t=21327