Galaxy Formation

A 220 kilo parsec wide view of a galaxy being formed in a cosmological context. Watch as the blue gas gradually turns into red stars. One fundamental questions in astronomy is whether stars in the Milky Way formed in little objects that accrete onto the disk or if they form from gas swirling around the disk. In this simulation, after an intense merging phase which forms the stellar bulge, gas gently accretes to form a rotating stellar disk. Several satellites are destroyed by the galaxy tidal field and leave streams of stars along their past orbits. (Encoded using Quicktime's mpeg4 codec.)

Octavio Valenzuela, Greg Stinson, Beth Willman (NYU)

This movie shows a bar forming and the changes that it brings about in a disk galaxy. Disk galaxies are often inherently unstable to forming a bar. Since it forms out of material that was rotating, the bar itself will be rotating. The bar therefore acts somewhat like a blender, pushing disk material around and producing spiral arms. This pushing by the bar (and the bar-induced spirals) is strong enough to alter the density distribution of disk galaxies. This video follows this evolution out to larger radii than has previously been possible. The material being pushed out by the bar piles up at large radii and leads to a characteristic sharp drop in the density beyond that. Observations find similar drops in real galaxies. Detailed analysis of simulations such as this, which for the first time could use large enough numbers of particles to properly resolve the low density outer regions, show that the density drops in the simulations match the type of sharp drops seen by observers. (189 MB)

Victor Debattista

This video shows how bars produce bulge-like structures. Roughly 70% of disk galaxies have a bar, an elongated stellar structure through their center. Bars are efficient at driving evolution of disk galaxies. Amongst other things, bars can help a central mass concentration to form, resembling the bulges of galaxies. One way this can happen is for the bar to bend vertically. This bending is known as the firehose instability because the cause is similar to the pressure imbalance that causes a firehose to swing violently when it is turned on. In the big panel of this video, we view the bar in its rotating frame, with the colors indicating the average positions of particles above or below the mid-plane of the disk. The top-right panel shows how the bar is rotating. Two side panels show the disk edge-on. During the firehose instability, the outer ends of the bar bend downwards and the central part bends upwards. In this case, the system goes through three phases of strong bending, during which time the disk thickens and the center gets rounder and more bulge-like (bottom-right panel). When the bar is viewed from its side (top-left panel), it appears peanut-shaped. Such peanut-shaped bulges have been observed in about 45% of edge-on galaxies; as the bottom-right panel shows, the true fraction is likely to be even higher since a peanut bulge cannot always be recognized. Once the disk thickens, the pressure imbalance is reduced and the firehose instability quenches. (285 MB)

Victor Debattista

This movie shows the effect that a new recipe for star formation has on a disk galaxy 1/100th the size of our own Milky Way. As white stars form out of red gas, the convulsive supernovae explosions of the young stars drive gas out of the galaxy. This effect is intended to mimic what must happen early in the history of the universe to eliminate small galaxies that are predicted in a Cold Dark Matter universe, but which are unseen in the vicinity of the Milky Way.

Greg Stinson

Here the energy of the simulated supernovae explosions deposited in the same mass galaxy is increased and the outflow of red gas is much more dramatic.

Greg Stinson

As a stable disk of red gas and white stars spin, we see that spiral arm structures naturally form and survive for many billions of years.