Home Radio waves When galaxies collide: UConn astrophysicist investigates supermassive black hole mergers

When galaxies collide: UConn astrophysicist investigates supermassive black hole mergers

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All over the universe, galaxies are merging. This process creates supermassive black holes a billion times the mass of our sun – or at least scientists suspect it.

Scientists have yet to prove the existence of these supermassive, or binary, black hole fusions. Chiara Mingarelli, assistant professor of physics, was the principal investigator of a $ 650,000 National Science Foundation collaborative research grant, half of which goes to UConn, to conduct an experiment to prove the existence of binaries of supermassive black holes.

Researchers at the Laser Interferometer Gravitational Wave Observatory (LIGO) have detected high-frequency gravitational waves indicating the existence of small black hole binaries. These frequencies are of the order of 100 hertz. Mingarelli searches for waves in the nanohertz frequency range – more than a billion times lower than the waves LIGO can detect.

These smaller black holes can move closer to each other before merging, and scientists can usually see the merging for a fraction of a second. The black holes of interest to Mingarelli create gravitational waves so strong that mergers can be observed millions of years before they occur, and occur at much lower frequencies.

“At very high frequencies, you see the very last jolt in the life of these tiny black hole fusions,” says Mingarelli. “With NANOGrav – a Pulsar Timing Array experiment – you see the last 25 million years of their life because gravitational waves are so big.”

Currently, there is no evidence that supermassive black holes merge, or, if they do, how they merge, what makes them merge, and what their gravitational waves look like.

Mingarelli’s experiment will address these questions through “multi-messenger science,” an approach that uses both light signals and gravitational wave signals to understand the full picture of these epic events.

“We’re really spoiled in a way, because supermassive black holes are in massive galaxies and these can be very bright, so we know where to look,” says Mingarelli. “The more data you can get from systems as rare as fusing supermassive black holes, the better.”

This light information will come from the observation of active galactic nuclei (AGN). AGNs are the centers of black holes that gain mass and project bright jets of light. The combination of AGN data and gravitational waves will allow Mingarelli and his team at UConn to estimate how many supermassive black holes merge and contribute to the gravitational wave background.

This grant will combine, for the first time, traditional astronomy with gravitational wave astronomy, putting Mingarelli and the students in his laboratory at the forefront of astrophysics.

“UConn students are really going to be at the forefront of gravitational wave research around the world,” Mingarelli said. “It could really transform our knowledge of supermassive black hole mergers.”

This new approach will allow Mingarelli to reverse engineer a complete model of the supermassive binaries of black holes in the universe.

Traditionally, scientists have linked the background of gravitational waves to theoretical fusion rates of galaxies. Mingarelli’s approach provides a much more grounded set of measurements to the extent that actual galaxy mergers produce observable AGNs.

Jenny Greene, professor of astrophysical sciences at Princeton University and co-PI of the grant, will be responsible for identifying other AGNs. With these new data, Mingarelli’s group will make new predictions about the background amplitude of gravitational waves.

Through this work, Mingarelli will produce a ranking of galaxies from most to least likely to have a supermassive black hole binary.

“This project really sets up a whole new way of thinking about low-frequency gravitational waves and extragalactic astronomy,” Mingarelli said. “With our new method, not only can we make predictions about the background amplitude of gravitational waves, but we can also make predictions about where the most likely and closest supermassive black hole systems are located. . “

Mingarelli and his students will work with high school students in Connecticut, New Jersey and New York on this project.

Students will contribute to research by identifying new pulsars with the Pulsar Search Collaboratory. Pulsars are cosmic “beacons”. They rotate and send flashes of radio waves towards the earth at regular intervals. Gravitational waves, like those produced by supermassive binaries in black holes, change the distance between objects. So if a gravitational wave moves through a galaxy, it will bring pulsars closer to Earth and then pull them back.

“It causes this oscillation in space-time,” says Mingarelli. “So the pulsar pulses come early, then late… and that’s how we can search for gravitational wave signals from supermassive black holes. “

Students will research radio astronomy data for pulsars. The more pulsars we include in our Pulsar Timing Array experiment, the more information it will be able to detect about gravitational waves, meaning that these students will make a significant contribution to this cutting-edge scientific effort.

“Sometimes in some marginalized communities, students don’t even know they can be scientists, they don’t know they can think of black holes for a living,” says Mingarelli. “Exposing them to the possibility of participating in basic research is really important, in my opinion, just as helping students understand science as a career is a possibility.”

Mingarelli holds a doctorate. from the University of Birmingham. She is also a research scientist at the Center for Computational Astrophysics at the Flatiron Institute.

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