Astronomers find black holes created by mergers carry information about their progenitors

Astronomers believe that at the center of many, if not all, galaxies is a titanic black hole with a mass millions or even billions of times that of our sun. These supermassive black holes cannot be created directly through the collapse of a massive star, as is the case with black holes from stars tens of times the mass of the Sun, as no star is large enough to give birth to such a massive object.

This means that there must be processes that allow a black hole to grow to such a mass. Although the consumption of gas and dust and even stars around black holes can facilitate this growth, the fastest way to accumulate mass is a series of mergers of larger and larger black holes.

Paper published in Astroparticle Physics and Imre Bartos and Oscar Barrera from the Department of Physics at the University of Florida for details on how some of the “daughter” black holes created in such mergers could carry information about the “parent” black holes that collided to create them.

“We find that black holes that are born from the collision of other black holes carry information about the properties of their progenitors, including the spin of the progenitors as well as their masses,” Bartos says. “A major new focus of our research is the reconstruction of progenitor black hole cycles, building on previous work that focused on progenitor masses.”

Black holes have very few characteristics that can be used to distinguish them, only differences in mass, angular momentum, or “spin,” and electrical charge. Theoretical physicist John Wheeler of Princeton University, USA explained this by saying “black holes have no hair.” Bartos adds that even in the face of these few properties and “hairless theory,” it is still possible to use the spin of a black hole to reveal details about its origin.

“For example, black holes emerging from the swirling gas, or primordial collisions of ‘parent’ black holes, can result in high spin, while during birth through the death and collapse of stars, black holes often have low spin,” Bartos continues.

To conduct their research, Bartos and Barrera used a mathematical technique called Bayesian inference, taking the measured properties of black holes and their prior expectations as input and generating an inferred distribution of the properties of progenitor black holes. The research is useful because physicists are using tiny waves in time called gravitational waves to learn more about black hole collisions and mergers.

“Recent observations of black hole mergers suggest the possibility that black hole merger lines – places where many black holes merge in a row, thus forming denser and denser black holes – may be common in the universe.

“This raises the question of how we can recover the properties of progenitor black holes from measurements of the new generation,” Bartos says. “I’m fascinated by the detective story of uncovering what happened in these black holes in the past and finding the fingerprints of generations past there.”