By Heather Hamilton, contributing writer
As gravitational-wave detectors enable a more penetrating view into the furthest reaches of the cosmos, we’re treated to images of some of the most colossal machinations of known reality: super massive black hole mergers. LIGO — the world’s largest gravitational wave observatory — has already counted three and a half, all larger than expected. For scientists, this raises an important question: Are these large black holes the result of previous mergers? Are they cannibalizing themselves?
According to a paper published by Cornell University Libraries, we’re now able to tell.
Researchers at the University of New Mexico say they’ve observed and measured the orbital motion between two large black holes more than 750 million light years away from Earth. Karishma Bansal, Department of Physics & Astronomy graduate student, is the first author of the paper, and she worked alongside UNM Professor Greg Taylor and colleagues at Stanford, the U.S. Naval Observatory, and the Gemini Observatory.
The black holes were confirmed as a visual binary system after researchers recorded their radio emissions using the Very Long Baseline Array (VLBA) — a radio telescope array comprised of 10 separate units — and plotted the trajectories over time.
In a press release, Bansal said, “When Dr. Taylor gave me this data, I was at the very beginning of learning how to image and understand it. And, as I learned there was data going back to 2003, we plotted it and determined [that] they are orbiting one another. It’s very exciting.”
Part of the excitement lies in the fact that the supermassive black holes have a mass that is 15 billion times that of the sun, with orbital periods lasting 24,000 years. “What we’ve been able to do is a true technical achievement over this 12-year period using the VLBA to achieve sufficient resolution and precision in the astrometry to actually see the orbit happening,” said Taylor. “It’s a bit of triumph in technology to have been able to do this.”
Black holes are formed when the star’s outer mass becomes too much for the core to bear, causing the star to collapse in on itself and ignite fusion. If the ensuing energy cannot counterbalance the downward pressure because all core elements have burned, leaving behind an iron core, then fusion stops, and gravity takes over, causing the star to implode.
When the mass is small, the star becomes a white dwarf. But if the mass is large, the star explodes and turns into a neutron star, or if it is dense enough, a black hole. Neutron stars and black holes may even consume each other, gradually allowing neutron stars to become black holes or black holes to expand in size.
The team of researchers examined black holes with up to 50 solar masses, noting how larger black holes arose from those in close proximity. They discovered that the mass ratio of black holes involved in mergers changes based on how many black holes each has essentially consumed. They also studied the spin of black holes, though the measurements don’t have great resolution yet. First-generation black holes are composed of dying stars, which merge to become second-generation holes. Then, second-generation and first-generation black holes can merge or two second-generation holes join.
By using calculations derived from mass, spinning, and merger-mass ratios, researchers can determine the distribution of second-generation black holes and predict how far in the past they occurred. Ars Technica reports that second-generation mergers are more likely to occur closer to us than first-generation mergers.
The team believes that continued study may reveal information beyond the interaction of black holes and reveal the future of our galaxy. Taylor explained: “Supermassive black holes have a lot of influence on the stars around them and the growth and evolution of the galaxy. So understanding more about them and what happens when they merge with one another could be important for our understanding of the universe.”
Sources: Cornell University Libraries, Eurekalert, Ars Technica
Image Source: Wikimedia
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