How did Hubble confirm the widespread presence of supermassive black holes in centers like M87?

By measuring the velocities of stars and gas swirling violently around galactic centers

Hubble provided observational proof for the theoretical concept that supermassive black holes reside at the core of nearly every large galaxy. The confirmation technique relied on the telescope's superior resolution to accurately measure the speeds of stars and gas orbiting the galactic center, specifically mentioning the galaxy M87 as an example. By analyzing the orbital velocities—which can reach millions of miles per hour—scientists could apply Keplerian principles to calculate the immense mass required to hold that material in such tight, high-speed orbits within a very small spatial region. This calculation definitively proved the existence of singularities containing the gravity equivalent of millions or billions of suns, cementing their role in galactic structure and evolution.