How Big is a Supermassive Black Hole Compared to Earth?

The size of a supermassive black hole can vary significantly, depending on the specific black hole in question. While some black holes might be smaller, others can be much larger. For instance, a supermassive black hole may range from roughly four times the diameter of our entire Solar System to over 50 billion times the mass of the Sun. This variance is influenced by the specific characteristics of the black hole and its environment.

Theoretical Limits and Growth Patterns

Ultramassive black holes, which are at least ten times the mass of most supermassive black holes, can reach sizes of up to 10 billion solar masses before growth begins to slow down. This slowdown is due to the coalescence of an unstable accretion disk into stars that orbit the black hole. However, there appears to be a theoretical upper limit, with anything above 50 billion solar masses experiencing an almost halted growth rate.

Familiar Black Holes: One Example

Let's consider a moderate example known as the supermassive black hole at Ton 618. This hyperluminous broad-absorption-line radio-loud quasar and Lyman-alpha blob is located in the constellations Canes Venatici and Coma Berenices, approximately 18.2 billion light-years away from Earth. With a mass of 66 billion solar masses, the Schwarzschild radius of this black hole is an impressive 1300 Astronomical Units (AU), or about 390 billion kilometers in diameter. This makes it more than 40 times the distance from Neptune to the Sun.

Understanding Schwarzschild Radius

To better understand the scale, the Schwarzschild radius is a key concept. It is the boundary within which the escape velocity exceeds the speed of light, effectively defining the event horizon of a black hole. For a black hole with a mass of 66 billion solar masses, the Schwarzschild radius would be approximately 1300 AU. This immense size highlights the immense gravitational pull of such a massive black hole.

The significance of comparing the size of a black hole to Earth or other celestial objects provides a better visualization of the scale and impact such celestial phenomena have on the universe. Understanding these relationships can help explain the dynamics of galaxies and their evolution over time.