APOD: Spiral Galaxies in Collision (2014 Jan 19)

[APOD Robot]

Spiral Galaxies in Collision

Explanation: Billions of years from now, only one of these two galaxies will remain. Until then, spiral galaxies NGC 2207 and IC 2163 will slowly pull each other apart, creating tides of matter, sheets of shocked gas, lanes of dark dust, bursts of star formation, and streams of cast-away stars. Astronomers predict that NGC 2207, the larger galaxy on the left, will eventually incorporate IC 2163, the smaller galaxy on the right. In the most recent encounter that about peaked 40 million years ago, the smaller galaxy is swinging around counter-clockwise, and is now slightly behind the larger galaxy. The space between stars is so vast that when galaxies collide, the stars in them usually do not collide.

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[Boomer12k]

Awesome detail...very clear picture...

Two throwing stars colliding...

If two galaxies collide, and no one takes a picture.....

One observation...to me, it appears where the collision takes place, 2207's arms are pushed up and away from IC2163...some stars from 2207 trail through and behind IC2163...but the DUST TRAILS seem not to be disturbed...are they more massive??? The stars in the second arm from the right, appear to be pushed back, like a wave hitting a shore rock at the beach. I would think, they would "fall" towards IC2163...the first arm from the right, appears broken up...the second seems pushed away....Dark Matter? Dark Energy? A same charge Field of some type???
As I continue to look at this...I am thinking IC2163 is CHOPPING DOWN into 2207...and that area in collision is being splayed out as the mass of IC2163 slices into it, and it "peels" it back somewhat....as the mass of IC2163's stars PASS 2207's stars, they warp spacetime from their momentum, and it disrupts the area...and as they mix, they influence each others paths as they pass, and so the distinction of "ARMS" is dissolved,....kind of like two weather fronts, and how they influence each other....hmmmmm.....

It is really hard not to use inaccurate and outdated terms like "Attract" and "Pull"....and "force" when talking about Gravity....

Wouldn't it be cool to see a wide angle shot with the Star Streams?
OH....

http://cav-sfo.com/M51ccd.html

In the wide shot, you can see another disruption on the other side of 2207....a previous pass? Also, in the wide shot you don't see the "chopping" of IC2163....the shapes of the two also look more elongated in today's APOD and more circular in the wide shot...

:---[===] *

[michaelwaltrip2]

Hey. Enjoy APOD, its my home page on all my devices. Really enjoyed the Scale of the Universe the other day.
About the Galaxy Collision, I saw a recent show about super-massive black holes being the center of all galaxies. I wonder about what happens to the super massive black holes in such a collision? What would happen if the centers would actually collide?

Thanks. I am Michael Waltrip, I hope this gets to the editors of APOD?

[Ann]

About the Galaxy Collision, I saw a recent show about super-massive black holes being the center of all galaxies. I wonder about what happens to the super massive black holes in such a collision? What would happen if the centers would actually collide?

Jonathan O'Callaghan wrote:
Scientists believe that the interaction of two black holes could have one of two outcomes. The first is that they merge together to form one, much more massive black hole. The second is that due to spin, the two black holes could interact and recoil from each other sending one hurtling away.

We do now have evidence that the second option has happened. We believe that at the centre of large galaxies there resides a supermassive black hole containing hundreds of millions of times the mass of our Sun. These supermassive black holes are thought to be spinning at phenomenal rates, and so as two galaxies collide, their black holes will eventually interact. And scientists at the Max Planck Institute for extraterrestrial Physics have observed a black hole being ‘kicked out’ of its parent galaxy through interacting with a bigger black hole. We can effectively think of it as two spinning tops. Depending on the rate of their spin, their size and the angle at which they collide, they could come together, or one can get spun out of the way of the other. While both options are possible, we thus far only have evidence of the second, more extreme of these options.

- See more at: http://www.spaceanswers.com/deep-space/ ... ASS1W.dpuf

You can watch two computer-generated animations about what happens when black holes collide here. The animations make the assumption that the black holes are going to merge, or at least that is how I interpret them.

Ann

[Nitpicker]

Interesting stuff. I suppose it is possible that right at the moment, a smaller galaxy is similarly colliding with the Milky Way, on the other side of the galactic centre from us, in the observation shadow. We'll probably never know.

[michaelwaltrip]

Do all super massive black holes spin? (Do all black holes spin? or is this theory). I am trying to imagine the energy of the momentum or such a thing. This must (my speculation) a contributing factor to the "black" gravity of it all. Are black holes every destroyed? Do they have a life cycle? I'm sorry, perhaps these are better questions for another place. I remember reading about Einstein being fascinated with the idea of black hold collision. Thanks.

[DanS1]

Is there any possibility that the two galaxies are different distances from this view point? That is, 2207 could be closer and they just appear to be merging? If you look closely at 2207's lighter arms on the right side, it doesn't look as if it's distorted or effected by the merge. Just a thought.

[Shayna]

I wonder why the galaxies will collide and the stars don't. Aren't the stars part of the galaxy?

[geckzilla]

Is there any possibility that the two galaxies are different distances from this view point? That is, 2207 could be closer and they just appear to be merging? If you look closely at 2207's lighter arms on the right side, it doesn't look as if it's distorted or effected by the merge. Just a thought.

There are wider views of the two galaxies showing tidal streams which indicate they are undergoing some sort of interaction. It must be in an early stage because both galaxies are otherwise fairly normal looking.

I wonder why the galaxies will collide and the stars don't. Aren't the stars part of the galaxy?

Galaxies look solid and stars seem huge but in reality stars are very tiny compared to the space between them so the stars just pass by one another. It's really hard to make them collide. It's something like throwing a cloud of marbles at another cloud of marbles but all the marbles are kilometers apart from one another. Anyway, it's easy to look at a distant galaxy and not realize just how far apart everything within it really is.

[neufer]

Do all super massive black holes spin? (Do all black holes spin? or is this theory).

Almost all things spin.

(However, the Higgs boson, mesons, helium-4, and Carbon-12 all have zero spin.)

Black holes have only three properties: mass, spin, & electrical charge.
Of these three, probably only the electrical charge is close to zero.

I am trying to imagine the energy of the momentum or such a thing.

Good luck with THAT!

This must (my speculation) a contributing factor to the "black" gravity of it all.

<<Early theories of dark matter concentrated on hidden heavy normal objects, such as black holes, neutron stars, faint old white dwarfs, brown dwarfs, as the possible candidates for dark matter, collectively known as massive compact halo objects or MACHOs. Astronomical surveys for gravitational microlensing, including the MACHO, EROS and OGLE projects, along with Hubble telescope searches for ultra-faint stars, have not found enough of these hidden MACHOs.>>

Are black holes every destroyed? Do they have a life cycle?

A miniscule black hole of mass of 228 tonnes will self-destruct in 1 second into a violent burst of gamma rays.

A tiny black hole of mass of 72 kilotonnes (~ Yamato-class battleship)will self-destruct in 1 year.

A small black hole of mass of 72 megatonnes will self-destruct in a billion years.

However, all stellar mass black holes that we know about will survive for around a googol years.

[HellCat]

Good pic - always a fan.

There's a chance to make this sentence in the description a bit clearer.

"In the most recent encounter that about peaked 40 million years ago, the smaller galaxy is swinging around counter-clockwise, and is now slightly behind the larger galaxy."

I suggest moving it to the end of the paragraph, and splitting it into two sentences because it's stating two separate points.

Keep up the great work!

[BDanielMayfield]

Is there any possibility that the two galaxies are different distances from this view point? That is, 2207 could be closer and they just appear to be merging? If you look closely at 2207's lighter arms on the right side, it doesn't look as if it's distorted or effected by the merge. Just a thought.

Not according to Bruce, and his wife agrees, so it must be true.

The two spiral galaxies (in figure 1) IC 2163 (on the right) and NGC 2207 (on the left), have narrowly missed a collision in the constellation Canis Major, where they are located about 6 degrees southwest of the Dog Star, Sirius. Imaged by the Wide Field and Planetary Camera 2 on NASA's Hubble Space Telescope, these beautiful hurricane worlds can now be more closely examined to survey the damage.
IC 2163 has an unusual eye-shaped structure formed by fast-moving gas and star streams in the eyelids and a bright galactic nucleus in the pupil. The bright oval streams extend on either side to form long tidal arms that fling out stars and gas for 100 thousand light years. The tidal arm on the left is partially hidden by the foreground dust in NGC 2207. Computer simulations indicate that ovals like this are very short-lived features that appear when a companion galaxy orbits in the direction of rotation. This proved to be a valuable clue for reconstructing the past history of this pair.

Seven astronomers led by the husband and wife team of Bruce and Debra Elmegreen have been observing these galaxies and others like it for the last ten years. Neutral hydrogen velocities that were obtained by Elias Brinks, Michele Kaufman and Debra Elmegreen with the Very Large Array Radio Telescope in New Mexico were meticulously compared to computer models of the orbits, structures, and motions, made by Maria Sundin, Magnus Thomasson, and Bruce Elmegreen. By matching the models with the observations, they could determine that IC 2163 orbited around NGC 2207 from the left to the right, going behind NGC 2207 200 million years ago and making its closest approach 40 million years ago. The main response in IC 2163 to the tidal forces was the eye-shaped oval and tidal tails, while the disk of NGC 2207 developed a large warp.

How nice that Bruce & Debra Elmegreen can collaborate. In any event, Bruces agree, these galaxies are close and will collide.

Bruce

[hoohaw]

Good pic - always a fan.

There's a chance to make this sentence in the description a bit clearer.

"In the most recent encounter that about peaked 40 million years ago, the smaller galaxy is swinging around counter-clockwise, and is now slightly behind the larger galaxy."

I suggest moving it to the end of the paragraph, and splitting it into two sentences because it's stating two separate points.

Keep up the great work!

Also: "Billions of years from now, only one of these two galaxies will remain." That is wrong! The two galaxies will merge into one.

[Chris Peterson]

Almost all things spin.

(However, the Higgs boson, mesons, helium-4, and Carbon-12 all have zero spin.)

That should read an atom of H-4 or C-12, and it is probably a mistake to confound classical spin and quantum spin. Classical spin refers to physical rotation; quantum spin refers to a form of angular momentum. There's no reason to believe that quantum particles rotate in any physical way.

Black holes are an interesting case. They may behave like particles, not like any sort of extended bodies. Indeed, they may be particles. Black holes certainly have spin; whether they rotate is open to question. But they do appear to cause spacetime around them to rotate.

[Chris Peterson]

I wonder why the galaxies will collide and the stars don't. Aren't the stars part of the galaxy?

Galaxies look solid and stars seem huge but in reality stars are very tiny compared to the space between them so the stars just pass by one another. It's really hard to make them collide. It's something like throwing a cloud of marbles at another cloud of marbles but all the marbles are kilometers apart from one another. Anyway, it's easy to look at a distant galaxy and not realize just how far apart everything within it really is.

A quick, back-of-the-envelope analysis.

The smallest thing we can see on our computer screen is the size of a single pixel. In an image of a galaxy, the faintest observable star will be that size (and diffraction will make many larger than that). If your screen is 1000 pixels across, and you're looking at the image of a galaxy that is 100,000 ly across, the image scale is 100 ly/pixel. That's 10¹⁵ km/pixel. A real star is around 10⁶ km across. So the stars we're seeing on our screen are bloated in size by a factor of a billion. Put another way, you'd need a computer screen the size of the Sun (a million kilometers across) to get a true sense of the size of stars compared with their actual separations.

[ta152h0]

it appears the arms are moving in the same direction like two spur gears meshing in space

[neufer]

it appears the arms are moving in the same direction like two spur gears meshing in space

• Well... this is another fine mesh you've gotten us into

---

<<In the history of science, the clockwork universe compares the universe to a mechanical clock. It continues ticking along, as a perfect machine, with its gears governed by the laws of physics, making every aspect of the machine predictable.

This idea was very popular among deists during the Enlightenment, when Isaac Newton derived his laws of motion, and showed that alongside the law of universal gravitation, they could explain the behaviour of both terrestrial objects and the solar system.

A similar concept goes back, to John of Sacrobosco's early 13th-century introduction to astronomy: On the Sphere of the World. In this widely popular medieval text, Sacrobosco spoke of the universe as the machina mundi, the machine of the world, suggesting that the reported eclipse of the Sun at the crucifixion of Jesus was a disturbance of the order of that machine.

Responding to Gottfried Leibniz, a prominent supporter of the theory, in the Leibniz–Clarke correspondence, Samuel Clarke wrote: "The Notion of the World's being a great Machine, going on without the Interposition of God, as a Clock continues to go without the Assistance of a Clockmaker; is the Notion of Materialism and Fate, and tends, (under pretence of making God a Supra-mundane Intelligence,) to exclude Providence and God's Government in reality out of the World."

In 2009 artist Tim Wetherell created a large wall piece for Questacon (The National Science and Technology centre in Canberra, Australia) representing the concept of the clockwork universe. This steel artwork contains moving gears, a working clock, and a movie of the lunar terminator.

[bactame]

Chris wrote:"A quick, back-of-the-envelope analysis."

Now there is a handsome nuts and bolts of the situation.

[Ron-Astro Pharmacist]

Very Owlish !!

[Guest]

Do all super massive black holes spin? (Do all black holes spin? or is this theory). I am trying to imagine the energy of the momentum or such a thing. This must (my speculation) a contributing factor to the "black" gravity of it all.

Black holes are a theorem of general relativity. So on one level, they are just theory, but it is an accepted theory. The thing that makes a black hole what it is in having become so collapsed that the gravitational field has become so strong the light itself cannot escape from the object. There is something call an event horizon that defines the area of spacetime from within which light cannot escape.

To the question of spin: There is no requirement that a black hole must spin. However, as an object collapses it retains its angular momentum as it becomes a black hole. So if the star was spinning at all as it collapses (and there almost all stars have spin if not all stars), then the resultant black hole will also spin.

Are black holes every destroyed? Do they have a life cycle? I'm sorry, perhaps these are better questions for another place. I remember reading about Einstein being fascinated with the idea of black hole collision. Thanks.

Black holes can evaporate, but ironically the bigger a black hole is the less it is able to evaporate. (Small ones OTOH can self-destruct on a fairly short timescale.) It is much more likely that large black holes will grow bigger as they absorb more matter. There are also people who study black hole collisions, but you are best off googling that topic for more information.

[ems57fcva]

Awesome detail...very clear picture...

Two throwing stars colliding...

If two galaxies collide, and no one takes a picture.....

One observation...to me, it appears where the collision takes place, 2207's arms are pushed up and away from IC2163...some stars from 2207 trail through and behind IC2163...but the DUST TRAILS seem not to be disturbed...are they more massive??? The stars in the second arm from the right, appear to be pushed back, like a wave hitting a shore rock at the beach. I would think, they would "fall" towards IC2163...the first arm from the right, appears broken up...the second seems pushed away....Dark Matter? Dark Energy? A same charge Field of some type???
As I continue to look at this...I am thinking IC2163 is CHOPPING DOWN into 2207...and that area in collision is being splayed out as the mass of IC2163 slices into it, and it "peels" it back somewhat....as the mass of IC2163's stars PASS 2207's stars, they warp spacetime from their momentum, and it disrupts the area...and as they mix, they influence each others paths as they pass, and so the distinction of "ARMS" is dissolved,....kind of like two weather fronts, and how they influence each other....hmmmmm.....

I think that arms of 2207 being pushed up are due to tidal effects from early in the collision.

As for IC2163 "chopping down" into 2207, what I see is a somewhat diffuse bridge between the nuclei of the two galaxies. It is hard to see because it is first behind the spiral arms of 2207 and then is against the left spiral arm of IC2163. However, the gas and just lanes do a very good job of outlining it. It is possible that the smaller galaxy is being drained of material through this bridge. However, other outcomes are possible. If IC 2163 has been caught by 2207, then it may either become a satellite galaxy that is slowly cannibalized bu 2207. Otherwise it is possible that both galaxies may be disrupted and a new combined galaxy appear in their place.

No one seems to be able to explain the bridges. So there is something about galaxy mergers that is not yet well understood.

[JohnD]

Click to play embedded YouTube video.

We havea personal interest in this. Andromeda and the Milky Way will collide ina few mega-millenia. There are several videos online that purport to show wht will happen. This one happens to be especially smooth and '3D'.

John

[Nitpicker]

We havea personal interest in this. Andromeda and the Milky Way will collide ina few mega-millenia. There are several videos online that purport to show wht will happen. This one happens to be especially smooth and '3D'.

John

One potentially possible outcome selected from an almost infinite number of possible outcomes. I won't be staying up for it.

[Ann]

That's a fine video, JohnD. It does show - or seems to show - that the galaxy that remains after the merger will be somewhat less massive than the two individual galaxies that merged, since some of their material will be flung into space and lost to both of them.

Ann

[rstevenson]

That's a fine video, JohnD. It does show - or seems to show - that the galaxy that remains after the merger will be somewhat less massive than the two individual galaxies that merged, since some of their material will be flung into space and lost to both of them.

I recall reading somewhere (but can't find it now) an estimate that in a "typical" galaxy collision there might be just one star to star collision, and perhaps not even that. Of course, there will be many close encounters which change the velocity of both stars, but would any of those close encounters cause the resulting velocity of one or both stars to exceed the escape velocity of the merged galaxy? I suspect not, though quite a few stars will be sent off on long vacations before their new orbits can bring them back.

Rob