Universities here in our Canadian Province of Ontario have been making a name for themselves in cosmology over the past few weeks. A couple of hours down Highway 401 from us is the University of Western Ontario (Western for short). Shantanu Basu and and Arpan Das are researchers in Western’s Department of Physics & Astronomy. They have made some important discoveries about black holes. Astrophysical Journal Letters has published their findings.
Most of us have heard of black holes and have a mental image of what they are. Science fiction writers love them. A black hole is a zone in space with such strong gravity that nothing can escape from it. This isn’t limited to material objects. It includes all types of particles and even electromagnetic radiation. That’s why not even light can get out of a black hole. We can’t see them, so we call them black. We call them holes but that doesn’t mean they are empty in any way. They are full of unimaginably dense mass.
Black holes started appearing in popular culture in the 1980s. This was in response to the Disney film The Black Hole starring Maximillian Schell and Anthony Perkins. They’ve come back into the news this year as a result of the release of the first photograph of a black hole last April. People have the impression that black holes are a recent discovery. In fact, the idea of black holes goes much further back in history from a scientific perspective.
The first inkling that there could be objects in space that had gravitational fields so strong they do not let light escape came from John Michell and Pierre-Simone Laplace in the 18th Century. After Einstein released his Theory of General Relativity in 1915, Karl Schwarzschild shared a mathematical solution that showed that black holes could exist.
Einstein himself was lukewarm on the theory for a long time. In 1939, he released a paper called “On a Stationary System With Spherical Symmetry Consisting of ManyGravitating Masses” in the Annals of Mathematics. In it, he argued that “this argument however, is not convincing”. In the conclusion of the paper, he wrote “The Schartzschild singularities do not exist in physical reality”. Black holes are one kind of singularity.
Einstein was often right, as shown by Relativity and the Electromagnetic Effect. Even so, he was also often wrong, including about black holes. In the 1960s, scientists confirmed that the theory of relativity confirmed the existence of black holes. Then, Jocelyn Bell Burnell discovered neutron stars, which proved that stars do collapse under their own gravity into something much more dense.
The standard theory since then has been that black holes come from the remnants of collapsed stars, following the same process as neutron stars. That’s where this new discovery from Western University comes in. The researchers have found evidence that black holes can form without coming out of the remnants of a star.
Cosmologists have been puzzled by the existence of supermassive black holes near the beginning of the universe. Stars would not have been old enough to collapse so soon after the Big Bang. Basuand Das have used mathematical modeling to show that super-massive black holes form far more swiftly than cosmologists had thought. Then, they abruptly stop.
As Dr. Basu explains, “Supermassive black holes only had a short time period where they were able to grow fast and then at some point, because of all the radiation in the universe created by other black holes and stars, their production came to a halt. That’s the direct-collapse scenario.”
Since around 2010, astronomers have been discovering black holes that are a billion times more massive than our sun. These objects have high red shifts. This means that, based on the Doppler Effect, they already existed within 800 million years after the Big Bang. Since the universe is 13.8 billion years old, scientists consider this to be near the beginning of time as we know it.
This new explanation, that super-massive black holes collapse directly, rather than forming out of star remnants, is apparently at least part of the explanation for such primordial, super-massive black holes. A better understanding of supermassive black holes is important for understanding the universe and its origins.
For example, astronomers believe that supermassive black holes exist in the centre of certain galaxies, including our own Milky Way galaxy. Knowing how they form can help us discover how galaxies and galaxy clusters take shape.
This discovery and the surrounding context reminds me how awe-inspiring our universe is. One of the most remarkable patterns we see repeated everywhere is how the universe is self-organizing.
Cosmology offers us a profound story that is still not fully told. We owe a debt of gratitude to Shantanu Basu and Arpan Das for adding the latest chapter.
Sources:
https://news.westernu.ca/2019/06/western-black-hole-research-unise-origins/
Shantanu Basu, Arpan Das. The Mass Functionof SupermassiveBlack Holes in the Direct-collapse Scenario. The Astrophysical Journal, 2019; 879 (1): L3 DOI: 10.3847/2041-8213/ab2646
Not All Black Holes Emerge From Collapsed Stars
