The element with the greatest atomic mass in the universe is currently oganesson (Og), which is also known as element 118. Oganesson is an extremely heavy and highly unstable element. It was first synthesized in a laboratory in 2002 by a team of Russian and American scientists.
Oganesson belongs to the category of superheavy elements, which are characterized by having atomic numbers higher than 104. Due to their high atomic numbers, these elements have very short half-lives, making them highly unstable and difficult to study. Oganesson, in particular, has an extremely short half-life of a few milliseconds.
The atomic mass of oganesson is not precisely known, as it is challenging to measure due to its fleeting existence. However, it is expected to have a very high atomic mass, potentially exceeding 300 atomic mass units (amu).