What are Black Holes? 

Black holes are defined by NASA as “an astronomical object with a gravitational pull so strong that nothing, not even light, can escape it”. They have been found in most galaxies, including our own. There are two kinds of black holes, Stellar-mass black holes, which can be found all throughout our Milky Way Galaxy and be up to a dozen times bigger than the Sun, and Supermassive Monsters, which are found in the center of most big galaxies and can weigh billions of solar masses. With this information in mind, we can better discuss the recent discoveries made by NASA. 

September 2015: Gravitational Waves Are Detected

100 years after Albert Einstein made his important prediction regarding relativity, the twin Interferometer Gravitational-wave Observatory (LIGO) detectors in Livingston, Louisiana and Hanford, Washington detected signals indicating a collision that occurred approximately 1.3 billion years ago. According to Einstein’s general relativity theory, each of these black holes would have lost energy due to the gravitational waves they were emitting; this slowly brought them closer together over the course of billions of years. They approached each other more and more rapidly in their last few minutes, and finally at about half the speed of light in the final seconds before they collided to create one massive black hole. Once they collided, it emitted one last large burst of waves. These were the waves detected by LIGO and reported to the rest of the world. 

 2019: Historic Photo is Taken 

In April of 2019, NASA’s Event Horizon Telescope (EHT) captured an image of a black hole that was reportedly 6.5 billion times bigger than the sun. This photo was absolutely ground-breaking, as black holes are dense and no light can escape from them. Because of this, black holes cannot be seen, but in this historic photo it is outlined by a hot ring of material, making it possible to capture the incredible phenomenon. This photo was taken by eight separate radio telescopes placed in different areas around the globe, all working together to capture one high quality image. This coordination of technology greatly exceeded the expectations of NASA experts such as Paul Hertz, the director of the astrophysics department. When asked about the historic event, he said: “Years ago, we thought we would have to build a very large space telescope to image a black hole. By getting radio telescopes around the world to work in concert like one instrument, the EHT team achieved this, decades ahead of time.”

2022: Eerie Sound is Recorded

(Video Credit: 11Alive on YouTube, Aug. 24th 2022, Sound Of A Black Hole, https://www.youtube.com/watch?v=Z13SgTvq5Yc)

Most recently, NASA had another historic breakthrough when they were able to intercept sound waves from the Perseus galaxy cluster. However, it wasn’t as simple as recording the sound as it would have been on Earth. The black hole emitted such a low octave sound that human ears cannot perceive it. NASA had to put it through a process called “sonification”, in which astronomical data is manipulated to produce the sound. The original sound was not within the range of human hearing, so the sound produced by the sonification process had to be further manipulated. The signals were pitched up almost 57 octaves and greatly amplified in order for the human ear to hear it, and it’s still an incredibly low tone. These low-frequency waves are created by the jets created from the energy emitted from the black hole. NASA promises that when they released the recording their intention was not to scare the general public, just to make us aware of the important and interesting discovery they had made.