By Katharine Santiago
We have all heard of black holes being referenced in one way or another, whether it be through well known astrophysicists or pop culture, people like Niel Degrasse Tyson or the movie Interstellar. This year, scientists were not only able to see a black hole for the first time, but they were also able to take the first picture of one as well. This was previously thought to be impossible, since the gravitational pull of black holes is so strong that not even light can escape, which makes them virtually invisible, or so we thought. There are forces around black holes that heat up matter to such a degree that it emits radio waves and X-rays. Some matter gets so hot that it will be propelled out at almost the speed of light and create jets that emit gamma rays as well (NASA, 2019).
So how did scientists figure out how to capture an image of an otherwise invisible object? Some might say they actually didn’t. Rather, they took a picture of that hot matter surrounding the black hole’s event horizon, or the point where nothing can escape the gravitational pull of the black hole once crossed, commonly referred to as the “point of no return” (NASA, ). The Event Horizon telescope (EHT) was built to capture images of the radiation emitted by the M87 galaxy’s black hole. Separate telescopes that make up the EHT simultaneously measure the radiation emitted by photons, or light particles, surrounding the event horizon in a location named the last photon orbit, or the furthest light can go before getting sucked into the black hole (EHT Collaboration, 2019). Essentially, as matter approaches the event horizon, the particles rub against each other to create friction. This friction emits light in a ring shape, which is what the EHT captured. The data was then reconstructed in the form of images. The same emissions discussed above form a shadow around a black hole, and this is what makes the M87 black hole visible. The images created from the EHT’s data were consistent with what researchers predicted based on the theory of general relativity.
The general theory of relativity comes from Albert Einstein, and to this day is considered one of the most important theories in physics. He theorized that space and time were intertwined into one continuum, and that larger objects cause a greater distortion in space-time (citation here). A common metaphor here is imagining a blanket stretched out at all four corners, and then imagining how far it would go down if you dropped a golf ball in the middle vs. a bowling ball. The bowling ball would make a bigger indent in the blanket because it has more mass. When we talk about black holes, they have such a great mass that they bend space-time to such an extent that a singular point is created, known as a singularity. One of the biggest things to come from this image is the vindication of Einstein’s theory. With this image we now know that how he described space and time was accurate (Reuell, 2019).
What this research does is make black holes a real, physical phenomenon rather than a theory established by math. Before this image, we had no way of knowing indefinitely if black holes truly existed. Now there is undeniable proof. The Next step for these researchers is to use the EHT to capture an image of the black hole sitting in the center of our galaxy, the Milky Way, called Sagittarius A. They plan to go much bigger than that, too. By continuing to use and improve the EHT, researchers hope to continue to prove different parts of Einstein’s theory of relativity, as well as how black holes affect the geography of a galaxy, which has big implications for us in the Milky Way, where we have our very own black hole. Knowing if and how it will alter our solar system is of relevance to all of us.
References:
NASA. (2019). What Are Black Holes?. [online] Available at: https://www.nasa.gov/vision/universe/starsgalaxies/black_hole_description.html [Accessed 4 Nov. 2019].
The Event Horizon Telescope Collaboration et al.(2019). First M87 Event Horizon Telescope Results. I. The Shadow of the Supermassive Black Hole. The Astrophysical Journal Letters, 875 (L1). https://doi.org/10.3847/2041-8213/ab0ec7
Reuell, P. (2019) Seeing The Unseeable. The Harvard Gazette. Retrieved from https://news.harvard.edu/gazette/story/2019/04/harvard-scientists-lead-team-revealing-black-hole/
Volume 6: The Berlin Years: Writings, 1914-1917 (English translation supplement) page 146. (n.d.). Retrieved from https://einsteinpapers.press.princeton.edu/vol6-trans/158.
Picture of black hole can be found here: https://eventhorizontelescope.org/blog/first-ever-image-black-hole-published-event-horizon-telescope-collaboration