Here is a graphic comparing the sizes of four of the well-known Super Massive Black Holes (SMBHs), in relationship to the size of the solar system
Sgr A*, the SMBH at the center of our galaxy and the SMBH in galaxy M87 have both been imaged by the Event Horizon Telescope (EHT); their images are used as background in the graphic below. The image of M87 is also used in the graphic for the Andromeda galaxy and for TON 618, the most massive SMBH observed to date.
NASA states the mass of TON 618 as 60+ billion solar masses, which I think is based on an earlier estimate. Newer estimates put the mass at 40 billion solar masses.
The theoretical limit for SMBHs is stated as 50 billion solar masses.
Under certain unlikely conditions, they can grow to 270 billion solar masses.
The smallest known black hole, V723 Mon, nicknamed "The Unicorn" clocks in at just 3 solar masses. Discovered in 2021, it is also the closest black hole, located 1,500 ly from Earth. EH diameter < 18 km.
Follow-up work in 2022 argued that V723 Monocerotis does not contain a black hole, but is a mass-transfer binary containing a red giant and a subgiant star that has been stripped of much of its mass.
The paper titled "Unicorns and Giraffes in the binary zoo: stripped giants with subgiant companions", explains, based on new observations, why V723 Mon is not a black hole. https://arxiv.org/abs/2203.06348
Look closely at this spiral galaxy to spot a circled, blue dot. It marks the location of what could be a black hole weighing 20,000 Suns. Its color is the result of light from both an accretion disk and a surrounding cluster of young stars: https://bit.ly/3A9mFSb#BlackHoleWeek#BlackHole#astronomy#space
To celebrate, Hubble has new images to share featuring active galactic nuclei, or AGNs. Some galaxies contain AGNs, which are extremely bright central regions that host a supermassive black hole!