Since Einstein turned physics on its head over a century ago with his theory of general relativity, scientists have repeatedly set out to prove its implications. General relativity, in a nutshell, works as follows: all objects exist in a sort of four-dimensional fabric known as space-time, and their very existence in this fabric distorts it proportionally to their mass. When space-time becomes distorted by mass, a pull on all other existing objects in the nearby space-time is created. We refer to this as gravity. The higher an object’s mass, the stronger gravitational pull it exerts on nearby objects.
This relationship is often likened to placing a bowling ball and a marble on a trampoline. The heavy bowling ball will cause a dimple in the trampoline, which represents “space-time,” and the marble will roll towards the bowling ball as if it were drawn to it by gravity.
In 1916, Einstein’s contemporary Karl Schwarzschild published a bizarre idea he arrived at using Einstein’s work. This work used Einstein’s theory to outline a relationship between mass, radius, and the velocity required to escape an object’s gravitational field. He found that an object with enough mass would collapse under its own weight into an incredibly-dense and infinitesimally‑small point called a singularity. A singularity, he proposed, would distort space-time so much that its intense gravity would produce a region surrounding it called an event horizon from which not even light would be able to escape.
Thus, black holes became an integral part of the scientific discussion. As more people scrutinized them, the more they began to realize that understanding a black hole’s extreme conditions would help us probe into some of the universe’s greatest mysteries.
No one ever expected, however, to see a photograph of one. After all, how could it be possible to photograph something so totally black?
As it turns out, black holes, while dark themselves, are surrounded by light. Further research has allowed us to define more parts of their anatomy than originally laid out. A “black hole,” as we know it today, is comprised of the following:
- Singularity: An infinitely-dense point of mass with no volume at the center of a black hole.
- Event Horizon: The region of gravity surrounding the black hole that is too great for even light to escape. The radius of a black hole’s event horizon is one Schwarzschild-Radius (1rs)
- Photon Sphere: 1.5rs away from the singularity is a shell of light photons that’s in an unstable orbit around the black hole.
- Shadow: Black holes distort space-time so heavily that they bend the path of light back over on itself. This effect creates a difficult to comprehend “shadow” that is 2.6rs large. This shadow would appear to us as an image comprised of the event horizon and photon sphere pressed into a flat disc. The entire “surface area” of the event horizon surrounded by a ring of the proton sphere would be visible to an observer. Try to imagine looking at our planet from the moon and seeing its entire surface at once flattened onto a disc with clouds encircling it. This “part” of the black hole doesn’t correspond to anything physically distinct from the previous two parts, but it is important for understanding the photo and the way light drastically bends around a black hole.
- Stable Orbit: The innermost edge of the accretion disc just beyond the rim of the shadow is a stable orbit of matter 3rs from the singularity.
- Accretion Disc: There is a large disc of hot gas and matter around a black hole spinning rapidly enough to give off light.
- Jets: Spinning supermassive black holes can compress and expel light-years long jets of bright, hot matter.
The videos below from Veritasium (one of my favorite science educators) explains the image better than I could ever hope to. The first video explains the components above and was released before the picture debuted, making its accuracy a testament to science’s mathematical predictions and simulations of black holes. The second video explains the image in further detail and includes detailed simulated graphics.
How, you might ask, were scientists able to take this picture? Despite its immense size (6.5 billion times as massive as the sun), the black hole is still 55 million light-years away, making it a very small target. According to EHT project director Sheperd Doeleman, taking this photo was “equivalent to being able to read the date on a quarter in Los Angeles, when [standing] in Washington, DC.”
To get the resolution necessary, the team calculated that the they would need a telescope roughly the size of the Earth. Since this is physically impossible, the team decided to use a process called interferometry. With this technology, they created an extremely large virtual telescope made up of a network of separate telescopes on eight different sites across the globe synced together by atomic clocks and focusing on the same point in the sky. As the Earth rotated while the picture was being taken, each telescope across the globe recorded a slightly different angle of the same object. This produced 5,000 terabytes of data for the team of scientist to stitch together into the resulting image. Just to put the sheer amount of data they collected into perspective, the internet would have been incapable of transferring it all to a central location in any reasonable time frame. Instead, all data needed to be written onto hard drives and shipped via airplane from each site to be processed into the final image.
This photo was a project that I have been eagerly anticipating for years. It astounds me that this blurry wonder of astronomy has finally been captured. Looking at it leaves me feeling both in awe of the great scientific minds that have brought us here and humbled by the sheer scope and strangeness of what our universe has to offer.
What are your thoughts on this monumental achievement? Share them in the comments below.
Written By: Jacob Monash