Starship Asterisk*

Exploring the Antennae

Explanation: Some 60 million light-years away in the southerly constellation Corvus, two large galaxies are colliding. The stars in the two galaxies, cataloged as NGC 4038 and NGC 4039, very rarely collide in the course of the ponderous cataclysm, lasting hundreds of millions of years. But their large clouds of molecular gas and dust often do, triggering furious episodes of star formation near the center of the cosmic wreckage. Spanning about 500 thousand light-years, this stunning composited view also reveals new star clusters and matter flung far from the scene of the accident by gravitational tidal forces. The remarkable collaborative image is a mosaic constructed using data from small and large ground-based telescopes to bring out large-scale and faint tidal streams, composited with the bright cores imaged in extreme detail by the Hubble Space Telescope. Of course, the suggestive visual appearance of the extended arcing structures gives the galaxy pair its popular name - The Antennae.

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The Antennae seems to have better reception this time around.

Oh, I love it!

Note how one of the galaxies, NGC 4039, the one on the left in this image, is surrounded by a large yellowish halo of stars. The other galaxy, NGC 4038, has a smaller halo which is also more bluish. Of course, NGC 4038 is the galaxy that is forming most of the brilliant clusters of stars. The colors of the halos of the galaxies tell us that NGC 4039 was probably a relatively gas-poor galaxy before collision with NGC 4038, and it had a large population of old yellow stars. NGC 4038, by contrast, was gas-rich and had a relatively young and blue population.

Ann

The date on apod page needs correction from Feb 8 to Feb 12

Looking at this image, it seems more like 2 eels swimming around each other in a 3 dimensional pool rather than a collision in 2 dimensions (in directional vectors). Looking at the tails that have formed, it made me wonder if after the central cores of the galaxies merge, are we seeing the birth of spiral arms for the ultimate composite galaxy? Has this been modeled anywhere?

Looking at the expanded picture it appears another collision at 11:00. Then several other potential collisions. It appears as if two sections of the universe collided? Any Ideas?

Since they broached the subject, where IS the "scene of the accident" in this field? At the lower end of larger left star trail, or at end of smaller right trail? I cannot make sense why there are two antipodal star trails. The Newton in me knows they cannot reverse course on their own.
The scene of a two-car collision can show divergent tire skid tracks as the drivers brake, anticipating collision beforehand. But if the cars become locked/entangles, there should be only ONE debris trail AFTER collision. What gives?
And why was my first entry deleted? No religion or politicss in this legit question....

tomatoherd wrote:Since they broached the subject, where IS the "scene of the accident" in this field? At the lower end of larger left star trail, or at end of smaller right trail? I cannot make sense why there are two antipodal star trails. The Newton in me knows they cannot reverse course on their own.
The scene of a two-car collision can show divergent tire skid tracks as the drivers brake, anticipating collision beforehand. But if the cars become locked/entangles, there should be only ONE debris trail AFTER collision. What gives?
And why was my first entry deleted? No religion or politicss in this legit question....

We're seeing the effects of tidal forces acting on gravitationally bound particle systems. Galaxies don't behave as rigid bodies. What happens when a pair of galaxies pass near each other, or through each other (there's really no difference) is that angular momentum is transferred between particles (stars). That changes their orbits, in many cases converting their closed elliptical orbits to open hyperbolic ones. Stars in open orbits or highly eccentric elliptical orbits form tails like we see here.

tomatoherd wrote:
And why was my first entry deleted? No religion or politicss in this legit question....

First of all, moderator actions are NOT discussed in the open forum.
Secondly, your post was not deleted; you posted it in the wrong place.

Chris,
oh!, so, they were orbiting each other, spiraling closer before 'collision', not strangers passing in the night from opposite directions. If so, it helps me some to visualize it.

Bystander,
sorry...and okay.

The rare stellar collisions do occur and I'm sure it’s a bang even though there seems a question about the "Big" one.

http://www.space.com/28507-doomed-stars ... birth.html

If true, as far as the old theory goes, maybe we can say, "The cat ate it!"
Talk about ponderous cataclysms

tomatoherd wrote:Chris,
oh!, so, they were orbiting each other, spiraling closer before 'collision', not strangers passing in the night from opposite directions. If so, it helps me some to visualize it.

They were almost certainly members of the same cluster, which means they were in orbit around each other. But there was no "spiral" involved. There's nothing preventing a pair of extended bodies which are in orbit around each other from coming very close, or even intersecting. That's what's going on now with the Milky Way and Andromeda. We orbit each other, and in a few billion years will come close enough together that parts of each will pass through one another- even though the centers of mass won't intersect.

Maybe I'm under the influence of the coming holiday, but my first thought was that it looks like a heart!

Rolf Olsen is crazy! What the hell is he going to do next?!!

I absolutely love this approach of combining wider ground based data that shows the whole galaxy and its surrounding environment and professional observatory data for the central parts! I think people like Rob Gendler and Judy Schmidt are amazing! I love the whole world! I have a wonderful feeling in my heart right now!

Chris Peterson wrote:

tomatoherd wrote:Since they broached the subject, where IS the "scene of the accident" in this field? At the lower end of larger left star trail, or at end of smaller right trail? I cannot make sense why there are two antipodal star trails. The Newton in me knows they cannot reverse course on their own.
The scene of a two-car collision can show divergent tire skid tracks as the drivers brake, anticipating collision beforehand. But if the cars become locked/entangles, there should be only ONE debris trail AFTER collision. What gives?
And why was my first entry deleted? No religion or politicss in this legit question....

We're seeing the effects of tidal forces acting on gravitationally bound particle systems. Galaxies don't behave as rigid bodies. What happens when a pair of galaxies pass near each other, or through each other (there's really no difference) is that angular momentum is transferred between particles (stars). That changes their orbits, in many cases converting their closed elliptical orbits to open hyperbolic ones. Stars in open orbits or highly eccentric elliptical orbits form tails like we see here.

The "blueness" of the antennae confuse me. I associate the blueness with star formation and star formation is associated with gas and dust. Can that much dusty gas be projected into a hyperbolic orbit that way? I would assume that the tidal slingshot effect is restricted to the heavier objects and only small amounts of gas dust would be carried along.... Am I misinterpreting the blue or misunderstanding basic physics?

FloridaMike wrote:The "blueness" of the antennae confuse me. I associate the blueness with star formation and star formation is associated with gas and dust. Can that much dusty gas be projected into a hyperbolic orbit that way? I would assume that the tidal slingshot effect is restricted to the heavier objects and only small amounts of gas dust would be carried along.... Am I misinterpreting the blue or misunderstanding basic physics?

Gas clouds can have their orbits modified just like stars can. I think we sometimes see actual structures like spiral arms perturbed by tidal forces, so we end up with tight tails rather than big blobs. That also stirs things up, forming shocks and regions of high density, and that often results in star formation- something commonly seen in colliding or otherwise strongly interacting galaxies.

I read somewhere that even if two galaxies collide there is no actual collision of stars. Just too much empty space between stars.

I've observed these galaxies several times, but so far I have not been able to see the 'tails' - they are exceedingly faint. The galactic cores themselves appear as two commas.

I see that the antenna on the left
it corresponds to right Galaxy and vs.

I Google searched "computer model of galaxy collision ngc 4038" and got a number of hits.

The ifa.hawaii.edu hit had, as its last model, a movie from one computer simulation which, in the middle, shows a fairly good comparison to the NGC 4038/4039 we see in our sky.

It is fun to watch.

Craig Willford

Chris Peterson wrote:
Gas clouds can have their orbits modified just like stars can. I think we sometimes see actual structures like spiral arms perturbed by tidal forces, so we end up with tight tails rather than big blobs. That also stirs things up, forming shocks and regions of high density, and that often results in star formation- something commonly seen in colliding or otherwise strongly interacting galaxies.

Yes, I was confusing myself by imagining that the tidal streams where composed of gas clouds + the stars that were ejected along the same trajectory. The stars that were ejected with the gas are no longer part of the tidal stream having taken a different path through intergalactic space.

FloridaMike wrote:
The "blueness" of the antennae confuse me. I associate the blueness with star formation and star formation is associated with gas and dust. Can that much dusty gas be projected into a hyperbolic orbit that way? I would assume that the tidal slingshot effect is restricted to the heavier objects and only small amounts of gas dust would be carried along.... Am I misinterpreting the blue or misunderstanding basic physics?

I can't tell you about the basic physics, but I'll comment on the color of the tails.

There is clearly gas in the long tail on the left, which originates in the gas-rich galaxy on the right, NGC 4038. There are certainly a lot of pre-existing stars in that tail too, but the "squiggliness" of that tail tells us that there is also gas in it and that there has been "internal dynamics" when the gas and stars interacted. Star clusters have formed in that tail, mostly at the end of it, where the gas from the tail interacts with the surrounding intergalactic medium. To me the blue color of this tail makes very good sense. The tail contains many relatively young stars that were born already when tidal forces threw them out of their galaxy, and also it contains a good number of even younger stars that were born in the tail.

The tail that originates in the gas-poor galaxy on the left, NGC 4039, is shorter, is "elegantly shaped" with no kinks in it and it contains no clusters. Also the tail gets fainter at the end. I'd say this tail contains almost no gas at all. To me, the color of this tail seems bluer than I would have expected. But if the stars that are found in this tail were originally located in the other parts of this galaxy, then they may be younger and bluer than than the rest of the galaxy.

Take a look at Adam Block's excellent image of galaxy NGC 6340. (There are several satellite galaxies and background galaxies in the picture as well.) The large bulge of this galaxy is yellow, but the bulge is surrounded by faint spiral arms that are bluer than the bulge. If this galaxy had been affected by tidal forces that made the galaxy "throw out" a tail of stars, then this tail would be bluer than the galactic bulge, if most of the stars in the tail came from the outer parts of the galaxy.

But I still suspect that the blue color of the tail of NGC 4039 has been somewhat enhanced.

Ann

The timing on this one was great - in class today I was talking about how disk galaxies and ellipticals produce different kinds of tidal debris, because the stars in the disk (and gas clouds in the disk) share very nearly the same velocity at a given point. (Put this APOD up on a big screen and turned the room lights off). So when given a quick impulse by external tides, they sail out together. Having a common velocity, they will stay together and only disperse very slowly, in contrast to stars in ellipticals, which disperse rather quickly into broad fans and bowtie shapes instead of thing, long tails.

In the Antennae, there are identified star-forming regions well out in the tails, with stars so young that they must have formed well after the material left the galaxies. There are also HI clouds seen at 21 cm; in fact, because the cold hydrogen disks often extend well beyond the bright stellar disk, the gas can be in even more extended tails. John Hibbard's H I Rogues Gallery has an amazing collection of these HI tidal features, some from galaxies which ordinary optical images barely show disturbance in.

Today's APOD shows something I never noticed before - for the longer tail, additional faint material which in projection curves somewhat back toward the main galaxy. More grist for simulations trying to unravel the history of the Antennae.

OK,
Time for Political Correctness to step in.... This a a beautiful shot, of a wonderful event...the MERGER of two galaxies, and the CREATION of new stars, and systems...planets...water...maybe even life....The Miracle that is The Universe.
It is not a COLLISION, or "Car Accident"...it is a Marriage of Galaxies...the making of a new "family of stars", a new Island Universe.
Not "galaxies in collision"....Galaxies in Merger...Not "violence"...But LOVE....the Gravitational "attraction"...they FELL FOR EACH OTHER.....(falling into each others gravitational influence)...
John saw Marsha across the vastness of Spacetime, and was struck by her beauty, and gravitated towards her. Marsha, in the same instance, felt the same, and fell head long and willingly towards John, accepting her fate to merge herself with him.....
SEE???? FALLING IN LOVE!!!!!!!

Happy Valentine's Day...
:---[===] *

Boomer12k wrote:OK,
Time for Political Correctness to step in.... This a a beautiful shot, of a wonderful event...the MERGER of two galaxies, and the CREATION of new stars, and systems...planets...water...maybe even life....The Miracle that is The Universe.
It is not a COLLISION, or "Car Accident"...it is a Marriage of Galaxies...the making of a new "family of stars", a new Island Universe.
Not "galaxies in collision"....Galaxies in Merger...Not "violence"...But LOVE....the Gravitational "attraction"...they FELL FOR EACH OTHER.....(falling into each others gravitational influence)...
John saw Marsha across the vastness of Spacetime, and was struck by her beauty, and gravitated towards her. Marsha, in the same instance, felt the same, and fell head long and willingly towards John, accepting her fate to merge herself with him.....
SEE???? FALLING IN LOVE!!!!!!!

Happy Valentine's Day...
:---[===] *

I find that pleasantly poetic Boomer. I too prefer merger over collision when speaking of galactic encounters.

Bruce