The Physics of Black Holes: Exploring the Mysteries of Spacetime

Written by Sarya Gulec

Our universe contains secrets, from galaxies to stars, but perhaps the most fascinating and mysterious phenomena are black holes. Black holes are regions in spacetime with gravitational forces so powerful that nothing can be drawn out from there, not even light.

We can say that black holes are where matter is squashed into an incredibly small area, generating a gravitational pull so impossible. Outside of this point is the region known as the event horizon; once crossed, return is not possible. Inside the event horizon lies the singularity, where gravity tears itself apart and existing laws of physics break down.

According to Albert Einstein's general theory of relativity, gravity is spacetime bending caused by mass and energy. Black holes provide a spectacular demonstration of this bending. Their enormous masses warp spacetime so much that all directions necessarily bend inward of the event horizon. This curvature also affects the trajectories of nearby objects and even the trajectory of light, creating such effects as gravitational lensing, wherein the light of background objects is warped around the black hole to produce multiple or skewed images.

In 1974, physicist Stephen Hawking also proposed black holes are not black but emit due to quantum phenomena on the event horizon—a phenomenon that was subsequently named Hawking radiation. Hawking radiation is a prediction that black holes evaporate as they lose mass. But this raises the black hole information paradox: if the black hole completely evaporates, where does the information regarding the matter it devoured go? Quantum theory preaches that information cannot be lost, yet Hawking's equations say otherwise, threatening the very fabric of physics. New research has provided plausible answers to the paradox. Computations indicate that information is not lost but is stored as weak correlations within the Hawking radiation itself. This complies with quantum mechanical rules, i.e., although the information is grossly jumbled and in practice unrecoverable, it is not lost.

Black holes are difficult to observe directly, yet, it is possible to conclude their presence based on the effects they have on the surrounding matter. The matter is, for example, being heated as it proceeds into a black hole, and X-rays that can be measured by space telescopes are given off. Moreover, the effect that black holes have on the surrounding stars and clouds of gas provides indirect evidence of their existence.

In 2019, a milestone in the subject was achieved with the imaging of the supermassive black hole at the center of galaxy M87, M87*, by the Event Horizon Telescope. The image showed the first visual proof of a black hole's shadow and provided us with unprecedented views of these entities.

Later on, the view of NASA via the James Webb Space Telescope in the early universe unveiled supermassive black holes, deviating from previous theories on their formation and evolution.

One example is the lifespan of LID-568, a supermassive black hole estimated to have formed around 1.5 billion years after the Big Bang, with a mass of approximately 10 million Suns. This explanation supports the theory of the spontaneous creation of primordial black holes on a large scale, which are believed to have undergone a period of rapid growth. Beyond their enigmatic nature, black holes play a crucial role in shaping the universe.

Supermassive black holes, which reside at the center of most galaxies, including our Milky Way, are claimed to determine the formation and evolution of galaxies. Gravitational interactions between them may set the pace for star formation and determine matter distribution in galaxies. Also, active black hole jets and outflows deposit energy in adjacent interstellar gas, impacting galaxy thermal equilibrium and dynamics. In conclusion, black holes are the natural laboratory for probing the laws of physics under extreme conditions as scientists experiment. From their dramatic warp of spacetime to the enigmatic effect of Hawking radiation, they challenge and tease the estimated. Ongoing observation and theory will only continue to shed light on these cosmic enigmas and perhaps uncover new aspects of the underlying nature of the universe.

References:

1. Dunham, W. (2024, November 6). Webb telescope reveals rapid growth of primordial black hole. reuters.com. https://www.reuters.com/technology/space/webb-telescope-reveals-rapid-growth-primordial-black-hole-2024-11-05/

2. Dunham, W. (2024, September 18). Faraway black hole unleashes record-setting energetic jets. reuters.com. https://www.reuters.com/technology/space/faraway-black-hole-unleashes-record-setting-energetic-jets-2024-09-18/

3. Dunham, W. (2025, January 14). Intrepid white dwarf has a close encounter with a massive black hole. reuters.com. https://www.reuters.com/science/intrepid-white-dwarf-has-close-encounter-with-massive-black-hole-2025-01-14/

4. Musser, G. (2023, June 30). The Most Famous Paradox in Physics Nears Its End. Quanta Magazine. https://www.quantamagazine.org/the-most-famous-paradox-in-physics-nears-its-end-20201029/

5. Sutter, P. (2024, June 26). Black holes, explained by an astrophysicist. Astronomy Magazine. https://www.astronomy.com/science/black-holes-explained-by-an-astrophysicist/