What are black holes? Sure, we can identify them. We know the closest black hole, Gaia BH1, and the projected farthest, in galaxy QSO J0313-1806. We know the biggest, TON 618 with a mass 66 billion times larger than the Sun, and the smallest, XTE J1650-500 with a mass only 3.8 times larger than the Sun.³ We know that they spin, and we know they exist. We know that they are not wormholes or “cosmic vacuum cleaners.”³ But what are black holes? 

Let us begin with what we do know about black holes. They are astronomical objects with incredibly powerful gravitational pulls. Over their lifetime, they continue to grow through accumulating matter, such as gas from nearby stars. They can even overtake neighboring black holes, allowing them to grow in size. The event horizon, the apparent boundary of black holes, is the location where the velocity of any object pulled in would have to surpass the speed of light to escape–in other words, matter and radiation beyond the event horizon would have to defy the laws of the cosmos to escape the gravitational pull of the black hole. Therefore, since not even light has enough velocity to escape this gravitational pull, the black hole serves as an indefinite prison sentence, locking away the secrets of the cosmos within its event horizon.³

In the core of stars, a process called nuclear fusion occurs in which hydrogen atoms are crushed into helium. This process releases tremendous amounts of energy, which pushes against the outer gravitational force of the star.⁶ This creates a delicate balance in the star, which allows it to hold its shape. For stars with greater mass, the heat and pressure at the core allow them to fuse heavier elements until they reach iron. Since the fusion process that forms iron does not generate any energy–unlike the elements that came before it–iron builds up at the star’s center until there is a critical amount and the balance between radiation and gravity is broken. This allows the core of the star to collapse in on itself, causing the star to die in a supernova explosion, often forming a black hole or neutron star. The residue from this explosion creates all the heavier elements found on Earth. 

Scientists can only theorize the vast properties of these mysterious cosmic objects and what truly happens to the matter they suck up. Though light cannot reach a speed that surpasses the gravitational pull of a black hole, vast tidal forces in close proximity cause matter nearby the black hole to rise to temperatures reaching millions of degrees, emitting X-rays and radio waves that scientists study.³ Furthermore, matter that orbits near the surface of the black hole is sometimes launched out as well; this particulate matter’s emittance of gamma rays, X-rays, and radio waves can be further analyzed to gain a better understanding of the underlying nature of black holes. So, to better understand the incredible properties, components, and secrets of the black holes–our neighbors in the vast cosmos–we must further study the insights of the particulate matter that they provide.

References

1. NASA STEM Team. (2014, June 4). What Is a Black Hole? (Grades 5-8) – NASA. NASA. https://www.nasa.gov/learning-resources/for-kids-and-students/what-is-a-black-hole-grades-5-8/
2. NASA. (2023, September 9). First Image of a Black Hole – NASA Science. Science.nasa.gov. https://science.nasa.gov/resource/first-image-of-a-black-hole/
3. NASA. (2024). Black Holes – NASA Science. Science.nasa.gov; NASA. https://science.nasa.gov/universe/black-holes/ 
4. Reddy, F. (2020, September 8). What Are Black Holes? NASA; NASA. https://www.nasa.gov/universe/what-are-black-holes/ 
5. Lerner, L. (2022, October 13). What is a black hole? News.uchicago.edu. https://news.uchicago.edu/explainer/black-holes-explained 
6. Nuclear Fusion Energy: the energy of the Stars. (n.d.). Fusion for Energy. https://fusionforenergy.europa.eu/what-is-fusion/ 

Image References 

Figure 1: Information@eso.org. (2024). ESOblog: A DIY guide to supermassive black holes. www.eso.org. https://www.eso.org/public/blog/diy-guide-black-holes/ 

Figure 2: Palma, C. (2018). The Evolution of Massive Stars and Type II Supernovae | Astronomy 801: Planets, Stars, Galaxies, and the Universe. Psu.edu. https://www.e-education.psu.edu/astro801/content/l6_p5.html