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

[neufer]

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

I had to patiently wait for three to four minutes.

[neufer]

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.

I think that a binary black hole formed during the major merger event
and it picked up angular momentum with the later inflow.

A true bar would be a gravitational wave not a binary black hole.

[southofblock]

Click to play embedded YouTube video.

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

• Conservation of angular momentum

Fine. What though causes the initial spin? That is, the center of mass of a clump of gas particles is vectored directly towards the center of mass of the larger, denser collection of particles. Where is the moment arm?

[Chris Peterson]

I think that a binary black hole formed during the major merger event
and it picked up angular momentum with the later inflow.

That's possible, too.

[Chris Peterson]

Fine. What though causes the initial spin? That is, the center of mass of a clump of gas particles is vectored directly towards the center of mass of the larger, denser collection of particles. Where is the moment arm?

The center of mass of a clump of gas particles isn't vectored towards the center of mass of another particle collection. The two collections are in orbit about their common center of mass. That's the source of the spin.

[neufer]

[b][color=#0000FF]Artist’s rendering of galaxy BX442 & its companion dwarf galaxy (upper left).[/color] [color=#FF0000]More typical galaxy from this period:[/color][/b]

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<<Ancient starlight traveling for 10.7 billion years has brought a surprise – evidence of a spiral galaxy long before other spiral galaxies are known to have formed.

“As you go back in time to the early universe, galaxies look really strange, clumpy and irregular, not symmetric,” said Alice Shapley, a UCLA associate professor of physics and astronomy, and co-author of a study reported in today’s journal Nature. “The vast majority of old galaxies look like train wrecks. Our first thought was, why is this one so different, and so beautiful?”

Galaxies today come in a variety of unique shapes and sizes. Some, like our Milky Way Galaxy, are rotating disks of stars and gas called spiral galaxies. Other galaxies, called elliptical galaxies, resemble giant orbs of older reddish stars moving in random directions. Then there are a host of smaller irregular shaped galaxies bound together by gravity but lacking in any visible structure. A great, diverse population of these types of irregular galaxies dominated the early Universe, says Shapely.

Light from this incredibly distant spiral galaxy, traveling at nearly six trillion miles per year, took 10.7 billion years to reach Earth; just 3 billion years after the Universe was created in an event called the Big Bang.

According to a press release from UCLA, astronomers used the sharp eyes of the Hubble Space Telescope to spy on 300 very distant galaxies in the early Universe. The scientists originally thought their galaxy, one of the most massive in their survey going by the unglamorous name of BX442, was an illusion, perhaps two galaxies superimposed on each other.

“The fact that this galaxy exists is astounding,” said David Law, lead author of the study and Dunlap Institute postdoctoral fellow at the University of Toronto’s Dunlap Institute for Astronomy & Astrophysics. “Current wisdom holds that such ‘grand-design’ spiral galaxies simply didn’t exist at such an early time in the history of the universe.” A ‘grand design’ galaxy has prominent, well-formed spiral arms.

To understand their image further, astronomers used a unique, state-of-the-art instrument called the OSIRIS spectrograph at the W.M. Keck Observatory atop Hawaii’s dormant Mauna Kea volcano. The instrument, built by UCLA professor James Larkin, allowed them to study light from about 3,600 locations in and around BX442. This spectra gave them the clues they needed to show they were indeed looking at a single, rotating spiral galaxy.>>

http://asterisk.apod.com/viewtopic.php?f=31&t=29114

[southofblock]

Fine. What though causes the initial spin? That is, the center of mass of a clump of gas particles is vectored directly towards the center of mass of the larger, denser collection of particles. Where is the moment arm?

The center of mass of a clump of gas particles isn't vectored towards the center of mass of another particle collection. The two collections are in orbit about their common center of mass. That's the source of the spin.

Well, don't really get it. How did the two collections start orbiting? (It is easy to ask questions, and have done little research). If the big bang was spherical, then all of the particles moved out radially(yes?), how did one particle start moving tangential to the others?

[therodly1]

This simulation is very good. I am curious just how it was done.

When watching it, one has to keep in mind that the time factor is greatly distorted, and 'rapidly spinning' is really just an artifact of the simulation.

That the way we currently believe a galaxy spins may be a posit made from insufficient data, in my opinion. I don't see a need yet for dark matter to hold a galaxy together, having run my own simulations. This doesn't mean that I don't think dark matter exists, I'm sure it does. Given the size of a galaxy, for example, the Milky Way galaxy, how can we be sure that the measured velocities, and directions are going to be relatively consistent over the next hundred years, let alone the light years that it will take for a galaxy to complete a rotation, if it indeed rotates?

But I am digressing. I sure cannot find fault with this simulation. It is a great show!

[neufer]

[img3="Crab Nebula supernova remnant/big bang remnant "analogy""]http://upload.wikimedia.org/wikipedia/c ... Nebula.jpg[/img3]

Well, don't really get it. How did the two collections start orbiting? (It is easy to ask questions, and have done little research). If the big bang was spherical, then all of the particles moved out radially(yes?), how did one particle start moving tangential to the others?

The big bang remnant is sort of analogous to the Crab Nebula supernova remnant in that everything is fundamentally flying apart while at the same time local inhomogeneities are "condensing."

Unlike both the early inflation period and the late dark energy expansion, the big bang expansion canNOT effectively "do work" by separating gravitationally bound inhomogeneities. Local gravity always trumps local big bang expansion. (The same holds for electromagnetically bound particles: 13 billion year old hydrogen atoms are identical to modern hydrogen atoms; it is only the unbound photons which they emit whose wavelengths "get expanded" by the big bang expansion.)

[Chris Peterson]

Well, don't really get it. How did the two collections start orbiting? (It is easy to ask questions, and have done little research). If the big bang was spherical, then all of the particles moved out radially(yes?), how did one particle start moving tangential to the others?

Any two causally connected particles in the Universe are orbiting each other. If their relative speeds are low enough, their orbit is closed (elliptical); it it is high, the orbit is open (hyperbolic).

The Big Bang wasn't spherical, and particles aren't moving radially from any single point. When the Universe had evolved to the point where matter first appeared, its contents were a soup of particles with random velocities, all in an expanding matrix of spacetime.

BTW, even if you imagine a spherical expansion of debris, as in a perfect explosion, all of the material is moving tangentially with respect to other material, right?

[ThePiper]

The evolution of a vortex/cyclone and a spiral galaxy: What's the common and what's the difference in the dynamic processes?
There must be some commons because of the similarity in the results.

[Chris Peterson]

The evolution of a vortex/cyclone and a spiral galaxy: What's the common and what's the difference in the dynamic processes?
There must be some commons because of the similarity in the results.

Just because two processes produce results that appear (superficially, at least) similar, that doesn't mean that those processes have anything in common.

[neufer]

The evolution of a vortex/cyclone and a spiral galaxy: What's the common and what's the difference in the dynamic processes?
There must be some commons because of the similarity in the results.

A logarithmic or equiangular spiral is indicative of something being
fundamentally dimensionless... perhaps, say, orbital velocity:

[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]

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[b][color=#0000FF][size=115]Cutaway of a nautilus shell showing a logarithmic spiral[/size][/color][/b]

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<<A logarithmic spiral, equiangular spiral or growth spiral is a special kind of spiral curve which often appears in nature. The logarithmic spiral was first described by Descartes and later extensively investigated by Jacob Bernoulli, who called it Spira mirabilis, "the marvelous spiral".

In several natural phenomena one may find curves that are close to being logarithmic spirals. Here follows some examples and reasons:

1) The arms of spiral galaxies. Our own galaxy, the Milky Way, has several spiral arms, each of which is roughly a logarithmic spiral with pitch of about 12 degrees.

2) The bands of tropical cyclones, such as hurricanes.

3) Many biological structures including the shells of mollusks. In these cases, the reason may be construction from expanding similar shapes, as shown for polygonal figures in the accompanying graphic.

4) The approach of a hawk to its prey. Their sharpest view is at an angle to their direction of flight; this angle is the same as the spiral's pitch.

5) The approach of an insect to a light source. They are used to having the light source at a constant angle to their flight path. Usually the sun (or moon for nocturnal species) is the only light source and flying that way will result in a practically straight line.

6) The nerves of the cornea (this is, corneal nerves of the subepithelial layer terminate near superficial epithelial layer of the cornea in a logarithmic spiral pattern).

7) Logarithmic spiral beaches can form as the result of wave refraction and diffraction by the coast. Half Moon Bay, California is an example of such a type of beach.>>