Harvard Smithsonian Center for Astrophysics | 2020 Jun 01
Scientists at the Center for Astrophysics | Harvard & Smithsonian, and the Black Hole Initiative (BHI), have shed light on how black holes grow over time by developing a new model to predict if growth by accretion or by mergers is dominant, according to the results of a study ...Artist's conception depicting the growth channels of black holes in the nearby and
distant universe. In the nearby universe, smaller black holes grow by accretion while
larger black holes grow by mergers. In the distant universe, the opposite is true.
Credit: M. Weiss
Dr. Avi Loeb, Frank B. Baird Jr. ..., and Dr. Fabio Pacucci ... have developed a theoretical model to determine the main channel for the growth of black holes. The model is valid from the local universe up to redshift 10, or roughly from the present day to about 13 billion years ago.
The study suggests that the main growth channel depends on the mass of the black hole and on redshift. In the nearby universe small black holes grow mostly by accretion, while very big black holes grow mostly via mergers. In the very-far-away universe there is a reversal: small black holes grow mostly by mergers, big black holes by accretion.
"Black holes can grow in two ways. They can accrete mass from the space around them or they can merge with each other, forming one more massive black hole,” said Pacucci. "We currently believe that the first black holes started to form approximately with the first population of stars, over 13.5 billion years ago." The question is: how did these "seeds" grow to form the very broad population of black holes that scientists now detect in the universe, from small ones up to the very large monsters that we observe shining from the other side of the cosmos? Loeb added, "We can constrain their history not just by detecting light but also through gravitational waves, the ripples in spacetime that their mergers produce." ...
Separating Accretion and Mergers in the Cosmic Growth of Black Holes
with X-ray and Gravitational Wave Observations ~ Fabio Pacucci, Abraham Loeb
- arXiv.org > astro-ph > arXiv:2004.07246 > 15 Apr 2020 (v1), 30 Apr 2020 (v2)