APOD: Simulation: A Disk Galaxy Forms (2012 Jul 17)

[APOD Robot]

Simulation: A Disk Galaxy Forms

Explanation: How do galaxies like our Milky Way form? Since our universe moves too slowly to watch, faster-moving computer simulations are created to help find out. Green depicts (mostly) hydrogen gas in the above movie, while time is shown in billions of years since the Big Bang on the lower right. Pervasive dark matter is present but not shown. As the simulation begins, ambient gas falls into and accumulates in regions of relatively high gravity. Soon numerous proto-galaxies form, spin, and begin to merge. After about four billion years, a well-defined center materializes that dominates a region about 100,000 light-years across and starts looking like a modern disk galaxy. After a few billion more years, however, this early galaxy collides with another, all while streams of gas from other mergers rain down on this strange and fascinating cosmic dance. As the simulation reaches half the current age of the universe, a single larger disk develops. Even so, gas blobs -- some representing small satellite galaxies -- fall into and become absorbed by the rotating galaxy as the present epoch is reached and the movie ends. For our Milky Way Galaxy, however, big mergers may not be over -- recent evidence indicates that our large spiral disk Galaxy will collide and coalesce with the slightly larger Andromeda spiral disk galaxy in the next few billion years.

<< Previous APOD

This Day in APOD

Next APOD >>

[/b]

[Beyond]

Aw man.... i wish he coulda gone a few more billion years with it. I was really enjoying it, then it stopped. Bummer! Kinda reminds me of Disco.
Do a little dance, spin a lotta dust, become alive-become alive.

[Case]

Pervasive dark matter is present but not shown.

Yet, in this simulation, the center rotates much faster than the outer regions , even at t=13.6.

[neufer]

Pervasive dark matter is present but not shown.

Yet, in this simulation, the center rotates much faster than the outer regions , even at t=13.6.

Velocities should be roughly constant regardless of distance from the center.

[Vincent Pinto]

while time is shown in billions of years since

None of us who read this or those who posted the original quote were there then to so professorially say it took that much time. More importantly, the assumptions used to make the statement in the quote are non-verifiable assumptions, and therefore to posit the notion it took that long is certainly not science. It would however most emphatically constitute a belief. Since the same vein, there are some people, I'm told, who believe in a flat earth.

[Guest]

This video was a good example of an optical illusion. The clouds seem to keep moving well after the movie stopped.

[ThePiper]

Velocities should be roughly constant regardless of distance from the center.

@neufer
Are you sure? In this case we would have a homogenous disk. But We have spirals because of the speed-gradients between the center and the outer areas.

[Boomer12k]

One...reminds me of how cotton candy is formed. Forming around the central slim cone.

Two...Dark Matter is supposed to be what makes a galaxy appear to rotate as a single unit..as the Gravity is supposed to be very much beyond the mere edge of a galaxy, and caused by 90% dark matter, (that you cannot detect, so far)...as discovered by Carolyn Shoemaker, (she was examining the spectroscopy of galaxies)...I have observed that this is basically an illusion as our own galaxy has stars of various speeds, both apparently approaching and receding from us, so not all are swirling in the same manner. Also we bob up and down in the galaxy, (gravity wave?), as on Dec. 21st, 2012 we are going to cross the galactic equator. Hope to see you all the next day.

Three...The simulation does not run out of material...more and more material seems to just generate and fall into the galaxy, was Fred Hoyle correct? --- I am assuming that the simulation is much larger than just this one area. (As I see other material go by)...But in the real universe, in our own galactic area, while we do have smaller satellite galaxies and such, I don't see them coming in and joining like cotton candy, at the edges like it appears to be here...our galaxy seems more...constant....I think is the word I am looking for...we don't see "extra galactic material" falling into M31, from the sides, for instance...maybe it just represents dust and gas, and not star formation...lot of things the article does not explain, but hey, pressed for space, I guess.

Four...Galaxy formation here seems to be VERY clumpy. I realize this is only one type of galaxy, very much like M63. But there are VERY SMOOTH galaxies like M104.

Still, interesting and thought provoking.

:---[===] *

[winstond]

Why does it start to spin and what keeps it spinning?

[neufer]

[url=http://en.wikipedia.org/wiki/Galaxy_rotation_curve]Rotation curve[/url][b] of a typical spiral galaxy: [color=#0000FF]predicted (A)[/color] and [color=#FF0000]observed (B)[/color]. The discrepancy between the curves can be accounted for by adding a dark matter component to the galaxy.[/b]

---

Velocities should be roughly constant regardless of distance from the center.

Are you sure? In this case we would have a homogenous disk.
But We have spirals because of the speed-gradients between the center and the outer areas.

We have spirals due to some sort of
dynamic (quasi-)standing gravitational wave.

[Tszabeau]

I'll never again look at dust bunnies the same.

[neufer]

Click to play embedded YouTube video.

Why does it start to spin and what keeps it spinning?

• Conservation of angular momentum

[Virgin Islands]

Better keep this simulation away from that vacuum cleaner fella - Dyson or we will be watching it in his commercials.

[neufer]

while time is shown in billions of years since

None of us who read this or those who posted the original quote were there then to so professorially say it took that much time.

• Orin possibly

More importantly, the assumptions used to make the statement in the quote are non-verifiable assumptions, and therefore to posit the notion it took that long is certainly not science. It would however most emphatically constitute a belief. Since the same vein, there are some people, I'm told, who believe in a flat earth.

In point of fact, the only galaxies that we are able to observe are from the past...mostly from billions of years in the past:

[b][color=#0000FF]Oldest Known Galaxy Detected[/color][/b]

---

<<Astronomers using the Hubble Space Telescope have discovered what scientists think is the oldest galaxy so far detected, a galaxy so far away that the light from it has taken 13.2 billion light years to reach us, here on earth. It is so old that it is thought to be one of the earliest galaxies ever formed, just 480 million years after the Big Bang.

Scientists believe that galaxies started to form 200 to 300 million years after the Big Bang as new stars clustered together, then evolved into baby galaxies then eventually into large galaxies that we see today.

The newly detected galaxy was discovered using Hubbles’s recently installed Wide Field Planetary Camera 3 combined with Hubble’s eight feet wide mirror. The galaxy is calculated to be small compared to our own galaxy, the milky way, at one hundredth its size.

Astronomers and scientists are looking forward to the launch of NASA’s James Webb telescope sometime after 2014. This will enable observers to look back even further in time to when the galaxies were just forming.>>

[eltodesukane]

Velocities should be roughly constant regardless of distance from the center.

@neufer
Are you sure? In this case we would have a homogenous disk. But We have spirals because of the speed-gradients between the center and the outer areas.

constant velocities still implies non-constant angular velocities, so there is no contradiction

[orin stepanek]

Orin possibly

Not that I remember!

[Margaretta]

Fantastic simulation. Thank you. Do the particles of two merged galaxies speed up, maintain speed or slow down?

[ems57fcva]

I'm not very impressed by this simulation. No central bulge (and at least an insignificant one), no dust lanes, and no bridges between the centers of the galaxies after a close encounter. So I see there as being a long ways to go here.

[neufer]

I'm not very impressed by this simulation. No central bulge (and at least an insignificant one), no dust lanes, and no bridges between the centers of the galaxies after a close encounter. So I see there as being a long ways to go here.

No bars or spiral arms to speak of for that matter.

Personally, I think that it is really neat that there is still a long ways to go here.

[neufer]

Do the particles of two merged galaxies speed up, maintain speed or slow down?

The kinetic energy of the individual stars can only increase
as they feed off of the potential energy of unmerged galaxies.

[FloridaMike]

I have done this simulation dozens of times, with cream and a cup of coffee....

[Chris Peterson]

Two...Dark Matter is supposed to be what makes a galaxy appear to rotate as a single unit..as the Gravity is supposed to be very much beyond the mere edge of a galaxy, and caused by 90% dark matter, (that you cannot detect, so far)...as discovered by Carolyn Shoemaker, (she was examining the spectroscopy of galaxies)...

It was Vera Rubin, not Carolyn Shoemaker, who first noted the peculiarities in galactic rotation curves that were suggestive of dark matter halos (dark matter itself had already been inferred from earlier observations of the motions of galaxies in clusters).

Also we bob up and down in the galaxy, (gravity wave?), as on Dec. 21st, 2012 we are going to cross the galactic equator.

We don't bob up and down, but rather, orbit on a plane slightly inclined to the nominal galactic plane. We won't be on the galactic equator on Dec 21, however.

Three...The simulation does not run out of material...more and more material seems to just generate and fall into the galaxy, was Fred Hoyle correct?

No, Hoyle was wrong. No new material is being created in this simulation, it's just falling in from outside the volume that is being rendered. The simulation correctly considers that the Universe is bigger than just the region visualized.

--- I am assuming that the simulation is much larger than just this one area. (As I see other material go by)...But in the real universe, in our own galactic area, while we do have smaller satellite galaxies and such, I don't see them coming in and joining like cotton candy, at the edges like it appears to be here...our galaxy seems more...constant....I think is the word I am looking for...we don't see "extra galactic material" falling into M31, from the sides, for instance...maybe it just represents dust and gas, and not star formation...lot of things the article does not explain, but hey, pressed for space, I guess.

This is a simple simulation in some respects. It's just modeling gas and allowing stars to form from the gas. I don't think the elemental evolution of the galaxy is being considered at all- there's nothing here but hydrogen and maybe helium. No dust, no metals. I'm not at all sure this doesn't reasonably simulate how our galaxy formed, as well. The small cluster we're a part of strongly suggests a period of infall very like what the simulation shows.

[ddale51]

Wow. Fascinating stuff. It seems to me that I detect a bit of a bar that forms in the center of the later galaxy. It's not very prominent but it kind of shows how maybe the bar can form on a larger scale, something I've been puzzled about ever since I first saw the bars in photos of spiral galaxies (though I'm hardly an expert in such matters). Is this a valid observation?

[Chris Peterson]

Wow. Fascinating stuff. It seems to me that I detect a bit of a bar that forms in the center of the later galaxy. It's not very prominent but it kind of shows how maybe the bar can form on a larger scale, something I've been puzzled about ever since I first saw the bars in photos of spiral galaxies (though I'm hardly an expert in such matters). Is this a valid observation?

I agree. We're seeing a barred spiral galaxy form.

[richiem]

Sim doesn't run for me -- and they always have before. Is there something different about this one?