# The largest black hole ever discovered can fit 30 billion suns. We found it with gravity and bent light.

#### Dale H

A mass of 30 billion Suns definitely is very massive. However, its not close to the mass of Ton 618 which is 66 billion solar masses or Phoenix A which is 100 billion solar masses.

I was going to comment on Ton 6-1-8, but the Phoenix A you mentioned, holy 100 billion Solar Masses Batman!, I was not aware of it's discovery, thank you so much for dropping that info, I must go quench my knowledge of Phoenix A

#### Always Curious

I'm not very good at this - can somebody please help? I'm trying to calculate the Schwarzschild radius of a black hole of 30 billion solar masses. The result I get is on the order of 10 light years! That seems high. Does anyone have a simple formula?

#### Unclear Engineer

See https://www.e-education.psu.edu/astro801/book/export/html/1836 .

So 30 solar masses has an event horizon radius of 90 Km, and a 30 billion solar mass black hole would have an event horizon radius of 90 billion kilometers. A light year is 9,460,730,777,119.56 km (see https://www.metric-conversions.org/length/lightyears-to-kilometers.htm ), so that event horizon becomes 90,000,000,000 / 9,460,000,000,000 = 9 / 946 = 0.0095 light year = ~ 1/100 light-year.

Pluto's average distance from the sun is 5.9 billion kilometers. (See https://www.metric-conversions.org/length/lightyears-to-kilometers.htm ) So, that event horizon is 90,000,000,000 / 5,900,000,000 = about 15 times the orbital radius of Pluto.

#### Always Curious

So I was off by only three orders of magnitude - a trivial error! Thanks, Engineer, for the correction and for putting that still-huge radius into context.

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