Researchers Model Immense Galactic Flares From Feeding Black Holes

Brett Smith for redOrbit.com – Your Universe Online

When a star orbits too close to a galaxy’s central supermassive black hole, it gets torn apart and sucked in by gravitational forces – a phenomenon known as an a tidal disruption.

In a new study, researchers from Georgia Institute of Technology and the Max Planck Institute in Germany have used computational and theoretical models to describe the dynamics of these cosmic events that cause massive flares of light and energy.

“Black holes by themselves do not emit light,” said study author Tamara Bogdanovic, an assistant professor of physics at the Georgia Tech. “Our best chance to discover them in distant galaxies is if they interact with the stars and gas that are around them.”

Technological and observational advancements in recent decades have allowed scientists to observe a few dozen of these flares shooting out from the centers of galaxies.

“This flare of light was found to have a characteristic behavior as a function of time. It starts very bright and its luminosity then decreases in time in a particular way,” Bogdanovic explained. “Astronomers have identified those as galaxies where a central black hole just disrupted and ‘ate’ a star. It’s like a black hole putting up a sign that says ‘Here I am.’”

In the study, which has been submitted to the Astrophysical Journal, the researchers ran simulations on several supercomputers to construct the sequence of events through which a stellar core might be affected by the gravity of an immense black hole.

“Calculating the messy interplay between hydrodynamics and gravity is feasible on a human timescale only with a supercomputer,” said study author Roseanne Cheng, from the Center for Relativistic Astrophysics at Georgia Tech. “Because we have control over this virtual experiment and can repeat it, fast forward, or rewind as needed, we can examine the tidal disruption process from many perspectives. This in turn allows us to determine and quantify the most important physical processes at play.”

The researchers found that their computer model was able to replicate both theory and observational data.

“There are many situations in astrophysics where we cannot get insight into a sequence of events that played out without simulations,” Bogdanovic said. “We cannot stand next to the black hole and look at how it accretes gas. So we use simulations to learn about these distant and extreme environments.”

Bogdanovic said her next goal is to decode the hallmarks of observed tidal disruption events.

“The most recent data on tidal disruption events is already outpacing theoretical understanding and calling for the development of a new generation of models,” she explained. “The new, better quality data indicates that there is a great diversity among the tidal disruption candidates. This is contrary to our perception, based on earlier epochs of observation, that they are a relatively uniform class of events.”

“We have yet to understand what causes these differences in observational appearance, and computer simulations are guaranteed to be an important part of this journey,” Bogdanovic concluded.