Carnegie Mellon University theoretical cosmologist Tiziana Di Matteo and colleagues have for the first time included black holes and the quasars that they spawn in a large-scale simulation of the evolution of the universe using a Cray XT3 supercomputer. From data analysed so far a very different picture, from the all-consuming hungry monster, is emerging of black holes.

Cray XT3 Supercomputer

The Cray XT3 supercomputer, used to perform the calculations required for the simulation, is comprised of 2,000 XT3 processors interconnected by exceptionally high-speed, high bandwidth internal communications links capable of delivering the necessary large chunks of data among the 2,000 processors.

The XT3 really was the key to the success of the high-resolution simulation, which tracked 230 million hydrodynamic particles scattered over a representative chunk of the universe containing more than a million galaxies.

The simulation occupied four weeks of run time, which tracked the evolution of galactic super clusters (the largest known structures in the universe) while resolving the growth of black holes at the centers of galaxies simultaneously.

Figure 1: 450 Million Years after Big Bang Universe has a relatively uniform structure. The first black hole is the yellow spot at the bottom of the picture.

Figure 2: 6 billion years after the big bang the universe has many black holes and a pronounced filamentary structure. The yellow circles are black holes with the diameter of the circle proportional to the mass of the black hole. Hotter areas are brighter.

Di Matteo and colleagues started with the GADGET-2 software that Volker Springel of the Max Planck Institute for Astrophysics developed and then factored in “seed” black holes at the center of galaxies.

Next, an equation that describes how black holes “accrete” (swallow) gas had to be included into the mix. After which calculations describing the heating of surrounding galactic gas by the quasar radiation produced at the lip of the black hole completed the picture.

Preliminary Analysis

Preliminary analysis of the data they obtained shows that black holes play a much larger role in the scheme of things than was previously thought. It seems that black holes play a galactic moderating role.

While travelling on its inward spiral path the matter drawn into black holes becomes very hot and emits large quantities of radiation. This radiation is detectable using both earthbound and earth-orbiting telescopes. We observe this as a quasar. Because of their high luminosity, quasars are visible over vast distances.

Another notable characteristic of quasars is that they emit across the electromagnetic spectrum. Strong emissions in the UV, X-ray and gamma ray sector mean that quasars are visible through dust and gas clouds. Some Quasars (15% or more) also produce powerful radio frequency emissions.

Then over the millennia, as the black hole absorbs more and more matter, it emits more and more radiation. Eventually, it begins to radiate so much energy that it begins to affect its surroundings and stops more gas from flowing in.

The first result of this blowback effect is that the quasar associated with the black hole is shutdown. Because gas is no longer falling into the black hole, the gas at the lip of the black hole cools and eventually stops radiating energy.

At the same time, it expels most of the galaxy’s interstellar gas into intergalactic space. Because of this new star formation within that galaxy slows massively and eventually stops.

Although virtually every galaxy had a quasar when it was young, only about one galaxy in 10,000 does today. All of the galaxies without quasars are most likely old galaxies with their interstellar gases expelled into intergalactic space so no new stars are forming. This explains the “red and dead” phenomenon that has puzzled astronomers. Old galaxies are red due to the predominance of old stars.

Di Matteo and her colleagues simulation shows that there is very little interstellar gas left in these older galaxies.

Central Black Hole Mass / Host Galaxy Mass Ratio

This simulation also confirmed the findings of precise measurements taken using the Hubble Space Telescope and other instruments that the mass of the central black hole is 1/1000TH the mass of the stars in that galaxy. This helped to validate the simulation using Di Matteo’s model but did not tell us why.

Figure 3: Approximately 600 million years after the big bang.

Simulation snapshots Figure 3 and Figure 4 zoom-in on the galaxy that hosts the most massive black hole in the universe today. This massive elliptical galaxy is at the center of a large galaxy cluster. At about 600 million years after the big bang (Figure 3), matter is more diffuse than it is about 4.5 billion years later. Gas density increases from blue to red, and arrows indicate black holes (arrow-size relative to mass).

The simulation showed the universe over its 14 billion years of existence. Very early on the universe is virtually uniform, with matter dispersed rather evenly, and just small perturbations in this background – corresponding well with the picture provided by cosmic microwave background studies. The first black holes appear (Fig.1) when the universe is 300 million years old – just a child.

As the movie proceeds, matter in the universe clumps together in a filamentary fashion (Fig. 2). Empty regions tend to become even emptier over time while the dense regions become ever denser. By the end, supermassive black holes are lurking in the center of most galaxies, quasars shine bright and then blow out, and galaxies change colors from blue to red as they age.