BLACK HOLES

Of all the powerful and destructive forces in the universe, black holes remain some of the most mysterious. In recent years, astronomers have studied far more of them and discovered that not only do they come in all shapes and sizes, but rather than being stationary in space, some are actually moving, and some even travel at incredible speeds. But what are the consequences of this, and how does it affect the surrounding regions? We’re only just starting to find out.

When stars that are more than three times the size of our own reach the end of their lives, they can undergo extreme gravitational collapse, which sucks all the remaining material into an incredibly confined space. Here, the force of gravity is so strong that conventional rules of how atoms interact are overridden, and the result is a black hole. They are so dense, and the gravity is so powerful, that even the fastest-moving particles, such as photons of light, are unable to escape the event horizon that surrounds it. So, apparently, photons of light are not as powerful as Matthew McConaughey.

If the Sun were to be suddenly compacted into an area to such an extent that it would become a black hole, it would have a diameter of just four miles across, although it would still have the same mass as the Sun. This means that the gravity exerted on the rest of the solar system would be the same; the planets would still orbit the way they do now. This means that black holes interact with other objects beyond the grasp of the event horizon just like anything else.

For a long time, black holes were just theoretical, but as researchers have developed technology to look into the sky, it’s now believed that they are actually quite common. All galaxies are thought to contain supermassive black holes at their centers, and images have been taken that show the universe to be full of them. While the black holes themselves aren’t visible, the disks of matter that surround them show the telltale signs of a massive gravitational anomaly within. There are instances where the phenomenon can actually expel material, such as when they collide with one another or through a process discovered by Stephen Hawking known as Hawking radiation.

What’s even more fascinating is that studies examining supermassive black holes at galaxy cores have found that they also spin, just like other objects in space, but the rate at which they rotate is almost unbelievable. So, let’s talk about these spinning black holes.

NASA’s Chandra X-ray Observatory is a space telescope that detects X-rays more than a hundred times as sensitively as any other system. Astronomers have used its capabilities to look at five different quasars, which are gigantic galactic nuclei with supermassive black holes that have the mass of many hundreds of millions of our Sun and are surrounded by large disks of gas and material. Quasars are incredibly bright in the sky compared to surrounding objects, but at distances of between 10 and 11 billion light-years away from us, they are extremely difficult to examine in detail. To do this effectively, astronomers take advantage of a range of effects that happen to the light as it travels towards us to help sharpen the image.

The first effect is called gravitational lensing, which occurs because any object with a sufficiently large mass, such as a galaxy, warps space-time in a way that magnifies images from behind. All five quasars they looked at were perfectly positioned to be gravitationally lensed, giving greater clarity. This also causes a phenomenon predicted by Einstein, where the light has been bent to such an extent that multiple images of an object are seen at the same time. One of these images, which shows four versions in a closed configuration, is known as the Einstein Cross. In this case, the galaxy used to magnify the image is ten times closer to us than it is to the quasars.

Stars also cause warping of space-time, although to a much lesser extent. This can be used to further refine any magnification in a process called microlensing. It’s how scientists managed to gain such clear images of the quasars, much better than has ever been done before. When they did, they could hardly believe what the images showed. They expected the accretion disks of material around the black holes to be superheated, which is why they’re so bright in the sky, but they also found that these disks were orbiting the black holes much closer to the event horizon than would be expected if they were static. This means they had to be spinning at super high speeds. In one case, the spin had reached around 70% of the speed of light. For this to be possible, the black holes themselves would have to be spinning at even greater speeds. It’s not that one of them has an event horizon moving at very near the speed of light; it’s believed that this happens because material is usually added to a black hole from the same direction as it approaches from an already spinning disk. Over billions of years, each addition adds momentum to the whole spin, and eventually, it can reach such huge speeds. For example, the Einstein Cross has been measured with a spin of 670 million miles per hour.

Not only does this have consequences for the disk of material around it but also for the fabric of space-time itself. There’s currently no way of detecting quite how far the ripples spread, but with the mass and speeds involved, it likely has distortive effects throughout the whole of its host galaxy. Basically, the more we learn about black holes, the more we realize how truly powerful and destructive they can be. Future probes and research projects are still being planned that will further explore these phenomena, so who knows what we might find out next and what that means for our fundamental understanding of the universe.

Thank you so much for reading!