Astro Weekly: The birth of a black hole

When the very concept of a black hole first emerged around 1915 from the theory of general relativity, Albert Einstein suspected that his math was flawed. Subsequent theoretical work suggesting the existence of a gravitational singularity (a place where the laws of physics don’t exist) resulted in more skepticism. How could something so absurd exist in nature? It took over half a century for most physicists to accept the existence of these objects, but today they thrive at the forefront of astrophysical research. In 2019, Homo sapiens obtained the first image of a black hole—one of the most inspiring scientific achievements of the 21st century. Thanks to those images, humanity now has a solid understanding of how black holes form. The process is rather simple.

The process is rather simple. A large star (greater than 8 solar masses) will remain in stellar equilibrium. This means that the energy generated by fusion reactions are sufficient to counter the force of gravity until it reaches the fusion of iron. The fusion of iron produces no net energy output because iron has a binding energy so high that all the energy is absorbed during fusion rather than released. This absorption of energy lowers the core temperature of the star and no further fusion can take place. The equilibrium of energy output and gravity exists no more, and the star collapses in on itself at speeds up to 23 percent that of light. The crushing weight of collapsing matter compresses the star into a point of zero volume and infinite density called the singularity. During this compression, the temperature and pressure become so high that a cataclysmic explosion blows most of the remaining stellar material into space in a type II supernova. Left in the nebulous aftermath of this titanic explosion lies the singularity. A black hole is born.

Just like biological organisms, black holes need to be fed to grow. They feed themselves by consuming surrounding mass (stars, interstellar gas, etc.) and/or merging with other black holes to grow progressively larger. Over time, some become supermassive, reaching a mass millions or billions times greater than their original mass.

Let’s begin the semester by recognizing how fortunate we are to have access to education and the freedom to quench our intellectual thirst.