The biggest single object (not counting galaxies, universe, etc.) ever discovered is S5 0014+81. Prepare to have your mind blown.

S5 0014+81 is a quasar. Upon further inspection they found out that a black hole resides at the center of the quasar. Scientists were expecting an average sized black hole… but were surprised to find out that the mass of the black hole was a massive 40,000,000,000 (40 Billion) Solar Masses.

*Waits 5 seconds to let that sink in*

The Schwarzschild radius of that superheavy black hole is 118.35 Billion Kilometers.

Doesn’t sound like much, eh? Well, here is the thing: If our sun were the size of a soccer ball, “big bro’s” diameter is 37.42km.

Here is another picture to help you deal with the size of this object:

Since the question is what is the biggest single object in the observable universe, galaxies, galactic filaments or clustres, etc. shouldn’t be included.

In that case, the largest single object would be the quasar named TON 6–18.

This is the biggest blackhole known. It is classified as an ultramassive blackhole. It’s mass is equal to the mass of 66 billion Suns. That is, 66 followed by nine zeros (66,000,000,000). And the mass of one Sun, is approximately 2×10302×1030.

This is how massive the black hole is.

The diameter of TON 6–18 is 390 billion km(390,000,000,000 kilometres). That’s larger than our Solar System! If it were to replace our sun, it would engulf ALL the planets, and even the dwarf planets like Pluto.

This is how big, TON 6–18 is. Our brain can’t grasp objects that are this big.