According to the search results, the biggest black hole in the universe is TON 618, which weighs roughly 66 billion solar masses. However, there are other massive black holes that have been discovered, such as the ultramassive black hole in the galaxy cluster Abell 1201, which has a mass of 30 billion suns. The largest directly observed black hole with a confirmed mass is also around the theoretical limit to the size of black holes, and it is TON 618. The following are some of the most massive black holes discovered so far, according to:

• TON 618: 4.07×10¹⁰ M☉
• SDSS J010013.02+280225.8: 2.7×10¹⁰ M☉
• S5 0014+81: 4.0×10¹⁰ M☉
• NGC 3842: 9.7×10⁹ M☉
• NGC 4889: 2.1×10¹⁰ M☉

It is worth noting that there may be even larger black holes that have not been discovered yet.