Guests crowded into the Sunflower Theatre Friday night to learn about a pair of dark, hungry monsters lurking at the center of a distant galaxy.
As part of the theater’s ongoing “Ideas, Education and Exploration” series, University of New Mexico doctoral student Karishma Bansal presented her recent discoveries on a pair of orbiting supermassive black holes in a galaxy about 750 million light years from Earth, the most compact orbiting system ever detected. She explained how black holes form, how scientists detect them and what the most recent advances in detection have told astronomers about the objects. Speaking to a packed house during the free event, Bansal often waxed poetic as she talked about the black holes she has studied, comparing their motion around one another to a “dance.”
Black holes are celestial objects so dense and massive that nothing, not even light, can escape their gravitational force. Most are formed when massive stars, several times the mass of the sun, die and collapse under their own weight. But as Bansal explained, supermassive black holes are much too big to have formed from collapsing stars, and scientists still aren’t sure how they are created. They do believe that most large galaxies, including the Milky Way, have a supermassive black hole at the center. When galaxies collide, their black holes often begin orbiting one another, and eventually merge to form an even larger black hole.
“They are hungry monsters,” Bansal said. “They just eat and eat all the material around them.”
But despite their size, it’s not easy to detect faraway objects that don’t emit light. Scientists confirm the existence of black holes through a variety of methods, Bansal said, such as tracking the way light from other objects bends around them, and by looking for quasars, huge jets of plasma spewed out by the material around most supermassive black holes. In 2016, a group of scientists working on a giant telescope called the Laser Interferometer Gravitational-Wave Observatory found a new way to learn about the objects, by detecting gravitational waves from the collision of a pair of supermassive black holes.
Bansal said she used about 12 years of data from the Very Long Baseline Array, a collection of radio telescopes located all over North America, to confirm that two supermassive black holes in a galaxy called 0402+379 are moving around one another. She said that discovery, finalized earlier this year, was important because most orbiting black holes scientists have been able to detect in the past are thousands of light years away from each other, and no one has ever actually measured their motion. The two black holes she studied are separated by just 24 light years.
She said her discovery is an example of what scientists can detect with larger telescopes and better resolution. But there’s still much to be learned. Right now she and other scientists have mapped out several possible orbit patterns for the black holes, but they need more data to know which pattern the pair is following. They also want to find more compact systems like this, she said, which will require more high-resolution telescopes and technology that can detect gravitational waves.
While supermassive black holes in distant galaxies might not seem to affect everyday life, Bansal said she believes it’s worthwhile to try and unravel their mysteries, especially since many astronomers believe they are a picture of what the Milky Way may look like in the far distant future.
“You are sitting on Earth, and you get to look up at the dark skies all night,” Bansal said. “Why not enjoy the show?”
Most of her audience seemed to agree, as they applauded many of the telescope images she showed during the presentation, and peppered her with questions afterward.
The Sunflower’s next free event will be a screening of the documentary “The Mask You Live In” on Sept. 14.