Starship Asterisk*

The Antennae

Explanation: Some 60 million light-years away in the southerly constellation Corvus, two large galaxies collided. But the stars in the two galaxies cataloged as NGC 4038 and NGC 4039 don't collide in the course of the ponderous, billion year or so long event. Instead, their large clouds of molecular gas and dust do, triggering furious episodes of star formation near the center of the cosmic wreckage. Spanning about 500 thousand light-years, this stunning view also reveals new star clusters and matter flung far from the scene of the accident by gravitational tidal forces. Of course, the visual appearance of the far-flung arcing structures gives the galaxy pair its popular name - The Antennae.

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I love this image!

I really love this image! It's a great example for how galaxies merge.!!!
How is it that the inner structure is not as blurred as the outher edge?

Another collision in Wild Space. Where's a Cosmic Cop when you need one??
Actually this is the only Space picture that i have ever seen that could be used for Valentines Day.
To me, it looks like a "jellyfish" Heart with a couple of Tendricles floating off to the side and maybe another one or more off to the rear.
Antennae? - not really.

Can I ask some basic questions?
If this really is the photo of 2 galaxies that have collided, why do the curvatures in the tails become sharper as they collide? It seems the opposite would happen. Since we suppose that the galaxies are attracted to each other due to gravitational forces, the curvature lines should become more straight as they get closer to each other, but in fact it looks like the opposite.

Astronut wrote:Antennae? - not really.

I cannot agree with you. If you rotate the image 180°, the tidal tales look like old TV-antennas (although one is bend a little bit). Of course you need a little bit of creativity to see it.

verk wrote:If this really is the photo of 2 galaxies that have collided, why do the curvatures in the tails become sharper as they collide? It seems the opposite would happen. Since we suppose that the galaxies are attracted to each other due to gravitational forces, the curvature lines should become more straight as they get closer to each other, but in fact it looks like the opposite.

Good question!
I don't know whether my answere is correct. My theory is that the gas is spread away due to the increasing speed of rotation that is caused by the gravitational force which depends on the radius. The galaxies are not flying right into each other but rotate and pass by each other what desturbs them.

verk wrote:Can I ask some basic questions?

Please don't stop asking!

I'm with Astronut: looks like a heart to me, too, and a very pretty one at that!

Astronut, the Rosetta Nebula shows up on Valentine's Day some years in different pics (some below) and there are other suitable images for the day, too:
http://antwrp.gsfc.nasa.gov/apod/ap090214.html
http://antwrp.gsfc.nasa.gov/apod/ap080214.html
http://antwrp.gsfc.nasa.gov/apod/ap070214.html
http://antwrp.gsfc.nasa.gov/apod/ap030214.html
http://antwrp.gsfc.nasa.gov/apod/ap000214.html

Lets get down to it!
When I showed my wife this photo and explained what was happening she said;
'So they are having 'Nukie' (sex) and producing lots of babies'

As an Astronomy Neophyte,
This series has sparked my interest in Astonomy again. What happens when two spiral galaxies with presumptive central black holes colide? I realize that the galaxies are primarily empty space, but do we know if the black holes merge or the gravitational forces are counterbalanced by net forces that repulse? You talk about new star formation by merger of dust clouds, but the central black hole interaction must create huge and measurable changes also. What about the large amount of "Dark Matter" and "Dark Energy" that permeates and surrounds the galaxies? Do they become measurable in some way during this galactic "accident"?

A very non-technical WOW!! What a great picture. So many questions - I was wondering also how the two galaxies' central core/black holes could possibly not interact with each other and even pull together.

Imagine if somehow two black holes were aligned in opposite directions/spins/forces and would just null each other out.

But then what if they were aligned in the same orientation - would they become so powerful that they could pull in most, if not all, of the matter in each of the original galaxies.

I know, I know - more imagination than technical expertise ........

The thing that impresses me is the bridge of gas and stars between the cores of the galaxies. To get a better look at it, click on the photo or go to http://apod.nasa.gov/apod/image/1005/NGC4038_ssro.jpg and zoom in on the cores of the galaxies. The impression I have is that the material is being funneled into a concentration of mass on the left side of the bridge. I assume that this concentration is newly forming galactic center which is in front of the galactic core on the left. (The other possibility is that the material is being funneled into the center of the galaxy on the left, but I don't expect that to be the case unless the left galaxy is much more massive than the one on the right.)

JMM wrote:What happens when two spiral galaxies with presumptive central black holes colide? I realize that the galaxies are primarily empty space, but do we know if the black holes merge or the gravitational forces are counterbalanced by net forces that repulse?

In terms of their impact on galaxies, even supermassive black holes are rather minor and boring. They typically only have the mass of some millions of stars- a tiny fraction of the entire galaxy. When two galaxies collide, the dynamics are pretty much the same whether or not there are central black holes, because the gravity fields of the galaxies are pretty much the same either way. Only in a tiny region very close to the black hole is the gravity field sufficiently distorted to get interesting effects.

You talk about new star formation by merger of dust clouds, but the central black hole interaction must create huge and measurable changes also.

Only in the very rare case where two galaxies collide in such a way that their central black holes pass very close to each other. In that case, the two black holes may enter a tight orbit around each other, and may even merge after some time.

What about the large amount of "Dark Matter" and "Dark Energy" that permeates and surrounds the galaxies? Do they become measurable in some way during this galactic "accident"?

There is no dark energy around galaxies. But the structure of galactic collisions does reveal much about their dark matter halos, and is part of the evidence supporting the existence of dark matter.

biddie67 wrote:A very non-technical WOW!! What a great picture. So many questions - I was wondering also how the two galaxies' central core/black holes could possibly not interact with each other and even pull together.

The gravitational effect of the central black holes is small compared with the galaxies as a whole. And the galaxies have been interacting for billions of years- orbiting each other in a complex way that has led up to a collision (possibly not for the first time). Black holes don't pull together any more than any other objects operating under the influence of gravity. They were in orbit around each other when the galaxies were distant, and the only difference when the galaxies are colliding is that they are nearer each other in that orbit.

I do like the image. I am new to learning astronomy. Are the individual stars (foreground stars) in the Milky Way? Byran

Byran wrote:I do like the image. I am new to learning astronomy. Are the individual stars (foreground stars) in the Milky Way? :?

Yes, all of the stars are in the foreground, and in the Milky Way. Except... if you look closely you'll see that some of those "stars" are actually distant galaxies.

verk wrote:Can I ask some basic questions?
If this really is the photo of 2 galaxies that have collided, why do the curvatures in the tails become sharper as they collide? It seems the opposite would happen. Since we suppose that the galaxies are attracted to each other due to gravitational forces, the curvature lines should become more straight as they get closer to each other, but in fact it looks like the opposite.

verk,
Loads of simulations on internet video, like this: http://www.youtube.com/watch?v=RBFc1ldP_Ps
I presume they are based on basic physics and they look very like the APOD.
OR, this one is IDENTICAL! http://www.youtube.com/watch?v=P8S-RW9Veks

No one has asked: What would it be like to be on a planet in thos galaxies?
No stellar collisions, but lots of star forming, energy all over the place.
COULD there be life on such a planet. or would that whole region of space be sterilised?

John

Last year, there was an eppisode of "Hubble's Universe Unfiltered" which discussed the topic of merging galaxies. There was also an animation which, in my opinion, was quite good.
You can find it here. Hope it helps.

JohnD wrote: Loads of simulations on internet video, like this: http://www.youtube.com/watch?v=RBFc1ldP_Ps
I presume they are based on basic physics and they look very like the APOD.
OR, this one is IDENTICAL! http://www.youtube.com/watch?v=P8S-RW9Veks

Neither one of those simulations shows a bridge developing between the galaxies as is seen in this image! Furthermore, the second simulation (which you claim to be "IDENTICAL") has two secondary tidal tails appearing on the opposite sides of the galactic cores from the primary tails. No such tails are present in this image! Instead, the "X" shape is created by the crossing of the tidal tails after the galaxies have passed.

To top it off, there is another You Tube video show comparing galaxy collisions and actual photos as http://www.youtube.com/watch?v=lXy3B2K4 ... re=related. In the third comparison, the simulation shows two disconnected tidal tails, while the comparison photo shows a unified bridge between the galaxies, and some evidence for large chunks of matter starting to move into that bridge.

Let's just say that I see these simulations as doing a very poor job of reflecting reality. There is something missing from them. Whether it is dark matter, colliding gas being left in the middle, or what I cannot say.

Thnak you, ems! I liked that very much, esp. the CGI rotates between actual photos, demonstrating I hope to verks how the tails do look.

I still think the scond video is very, very similar to the origianl APOD, stop it at 6 seconsd and see.

John

JohnD wrote:Thank you, ems! I liked that very much, esp. the CGI rotates between actual photos, demonstrating I hope to verks how the tails do look.

I still think the second video is very, very similar to the original APOD, stop it at 6 seconds and see. [sp. corrected]

I'm not going to deny the similarity, especially at low resolution. Certainly the simulations of the early parts of the interactions are more-or-less correct, based on their correctly generating long tidal tails coming off of the trailing sides of the interacting galaxies. However, at 6 seconds the colliding galaxies are tearing each other up, and turning into an elliptical mass. There is no bridge, just chaos. On the other hand, NGC 4038 (on the right) seems to me to be fairly intact, and remains distinct from NGC 4039 (on the left and behind the left end of the bridge). Also, at 6 seconds into the simulation the secondary tidal tails (which are collinear with the primary tidal tails) are still being reabsorbed, but in the Antennae there is no sign of them. Instead there is this bridge which joins the interacting galaxies and does so in each case at a substantial angle from the orientation of the tidal tails as they join their parent galaxies.

This may impress you as just a bunch of details, but do recall that "the devil is in the details".

BTW - With the video I posted, I really suspect that the most developed collision is actually the third one shown, since none of the others had developed a connecting bridge yet.

I will stand corrected. I was looking at the Hubblesite picture of these galaxies (http://hubblesite.org/newscenter/archiv ... rmat/zoom/), and found that they do have short, stubby secondary tidal tales. Still, they are nothing like the secondary tidal tales in the simulations. Furthermore, they are distinct from the bridge of gas and starts joining the galaxies, making that bridge even more inconsistent with the simulations.

From the Big Bang onward, it would seem to me that all significant mass (ie galaxies) would be travelling outward spherically from the point of the explosion with that sphere having an ever-expanding radius. I can see how individual nova could send mass in different directions, but as far as galaxy size aggregates are concerned it seems they should be travelling along non-intersecting vectors. Plus, without friction, shouldnt they all be travelling at the same velocity, therefore no rear-end collisions? What caused this deviation from the initially expanding sphere?

Thanks,
Osage

Osage wrote:From the Big Bang onward, it would seem to me that all significant mass (ie galaxies) would be travelling outward spherically from the point of the explosion with that sphere having an ever-expanding radius. I can see how individual nova could send mass in different directions, but as far as galaxy size aggregates are concerned it seems they should be travelling along non-intersecting vectors. Plus, without friction, shouldnt they all be travelling at the same velocity, therefore no rear-end collisions? What caused this deviation from the initially expanding sphere?

The Big Bang describes an "explosion" in four dimensions, not three. So there is no sphere of expansion, and never was. The expansion we see is taking place on the three-dimensional surface of a four-dimensional hypersphere. The center is at t=0 - a direction we can't see. There is no three-dimensional center of expansion, which is why it appears everything is moving away from everything else, and why objects with greater separation are moving apart faster.