Quasar Answers

Credit: Aaron Smith/TACC/UT-Austin

Many supermassive black holes like the one found at the center of the Milky Way are believed to form from the collapse of a star much more massive than our sun. This creates a “seed” black hole that then grows by merging with other black holes and sucking in more matter. What remains a mystery, though, is how supermassive black holes called quasars form. These shoot large streams of hot gas and formed in the early universe, even before there was surrounding gas for a seed black hole to feed on.

Using the Stampede supercomputer at UT Austin’s Texas Advanced Computing Center, astronomers Volker Bromm, Aaron Smith and Avi Loeb tested a theory of quasar formation that Loeb (now at Harvard University) and Bromm had developed in 2003. The theory: a black hole at the center of the emerging quasar forms when a hot, primordial gas cloud is compressed by the gravity of a surrounding halo of dark matter. This process, called direct collapse, needs gas so hot it can’t cool enough to form a star.

Data collected both by the Hubble Space Telescope and by telescopes on the ground suggested that a galaxy called CR7 was either a cluster of young stars or a quasar formed by direct collapse. The researchers developed a new computational model to simulate both possible scenarios. 

The star cluster scenario “spectacularly failed,” Smith says, but the direct collapse black hole model performed well. The implication is quasars do, in fact, form where gas interacts with dark matter and is too hot to allow for a star.