Monsters within the Universe
Black holes are some of the strangest and most fascinating objects in the Universe. They are known to be extremely dense, with an incredibly strong gravitational attraction that nothing can escape from—including all particles and electromagnetic radiation. Even visible light cannot escape a black hole's grasp, which is where they get their name.
When gas, dust and other stellar debris come close to a black hole but not quite close enough to fall in, they form a flattened disk of spinning material around something called an event horizon. An event horizon is essentially the point of no return for these particles because the escape velocity surpasses the speed of light, the fastest speed in the Universe.
The National Research Council of Canada's (NRC) Herzberg Astronomy and Astrophysics Research Centre is home to some of Canada's leading experts in black hole research. Experts from the research centre are working on understanding supermassive black holes (SBHs), primordial "monsters" in the centres of galaxies that have grown to be millions or even billions of times more massive than our Sun, way before the Universe as we know it was even a billion years old.
Looking into the abyss and debunking myths
Throughout the years, black holes have been depicted in several movies and television shows as large and mysterious masses that can swallow up an individual or cause natural disasters. It is important to understand that these movies are fictional and are meant to entertain rather than educate. Some questions, however, do come to mind when thinking of black holes and we asked one of our experts, Tyrone Woods, Plaskett Fellow at the Herzberg Astronomy and Astrophysics Research Centre, to debunk some of the most common myths about them.
First, the question on everyone's mind: Are all black holes actually black? Surprisingly, no! In and around black holes, gravity is so strong that nothing can escape from them, not even light. This means that black holes emit no light and do not have a colour. We are able to monitor them because of the astronomical bodies surrounding them and when moving away from us, they actually appear red.
Another common myth about black holes is that they are said to suck in everything. Black holes are known to be denser than most astronomical objects but they exert gravity just as any other object in space does, like the planet Earth. The main difference is that they occupy a way smaller volume of space while being incredibly massive. This creates a region near them where the curvature of space-time is so strong that nothing can escape it, and once the event horizon is crossed, anything trapped inside will never get out. The real question is, where does everything go? To this day, researchers still don't know. Perhaps that is one of the reasons why black holes are such a fascinating mystery to be solved.
Is it possible for a black hole to cause hurricanes and tidal waves on Earth? If Earth were to get too close to V616 Monocerotis, the closest known black hole, the weather would be affected. But, if a black hole got close enough to Earth, it would disastrous!
How many black holes are there? Well, for now we know of 3 different types of black hole: stellar-mass, intermediate-mass, and supermassive. For now, we know of about 10 to 100 stellar-mass black holes, about 100 intermediate-mass black holes and maybe 5 million to 80 million supermassive ones.
Recent discoveries have led astronomers to conclude that each galaxy has at least one supermassive black hole in its centre and several stellar black holes. This means that there are billions upon billions of black holes in the Universe.
Into the unknown
Even though Einstein predicted their existence back in 1916, the first possible black hole was not actually detected until 1971 and the first actual image of one wasn't obtained until 2019. For years now, we've known that these big black holes were formed in the early Universe. The NRC's own Dr. Chris Willott, Senior Research Officer, played a key part in this discovery. One big question remains: How did they get so big, so quickly?
One idea is that these very early, very massive black holes might have been born in the collapse of supermassive stars, formed when a dense cluster of some of the first stars ever merged into a single object. Dr. Woods wrote a paper on what these objects would look like and how they would collapse to form big black holes. The paper was featured in the magazine New Scientist earlier this year.
There has also been a lot of related work on how researchers might find these objects with the James Webb Space Telescope and other facilities, in which the NRC is playing a strong role. This research is also strongly connected to the broader problem of understanding how the growth of SBHs over the history of the Universe relates to the evolution of the galaxies in which they reside, something Dr. Ferrarese has done a lot of foundational work on at the NRC.