Researcher models black hole collision

The merging of two black holes is one of the strangest occurrences expected in modern astronomy. But now Yale researcher Priyamvada Natarajan, an assistant astronomy professor, is helping to solve the mystery behind the merging of these galactic phenomena.

Natarajan found that these mergers complete themselves with a massive release of energy, possibly powering the bright lights known as quasars. As seen in the night sky, a quasar is an extremely distant, and thus old, celestial object with a power output of several thousand times that of our entire galaxy.

“Ours is the first detailed calculations of how the merger of these two supermassive black holes proceeds,” Natarajan said. “There is a huge outflow of gas, and the quasar shines very brightly. It’s a violent, very high energy event.”

Along with Philip Armitage, an assistant professor at the University of Colorado, Natarajan used a supercomputer to test her theoretical models.

In the past, modeling this fatal dance between two black holes, which can sometimes occur over a ten-million-year time frame, has proved problematic.

Deep inside a black hole there lurks a “singularity,” a place where gravity greatly intensifies. Computer simulations have had difficulty modeling the waves both inside and outside the hole at the same time. In this case, the supercomputer helped clarify how the configuration of the two black holes changed over a span of time as long as ten million years.

In the center of every galaxy, there lies a black hole millions of times the size of our own sun. This massive sink slowly draws stellar gases into its center from what is known as an accretion disc — a ring of material that winds its way around the black hole.

Before these gases become completely engulfed, they emit X-rays. This energy release powers quasars, but what Natarajan and her partner hoped to discern was how the merging of two gigantic black holes would affect these quasars.

As two supermassive black holes take root in the accretion disc, their orbits slowly shrink to bring them close enough together that “all the gas trapped between them immediately rushes to the more massive black hole, leading to a brief increase in brightness coupled with an energetic outflow of gas at very high speeds,” Natarajan said.

Natarajan said that the next step in this line of research will be exploring the final “hiss” observed when there is an outflow of energy following the merger of two black holes.

The article detailing these results will appear in an upcoming issue of the Astrophysical Journal Letters.