The largest known galaxy in the universe is IC 1101, which is estimated to have a diameter of 5.5 million light-years.
It is estimated that there are between 100 billion to 200 billion galaxies in the observable universe, with each galaxy containing an average of 100 billion stars. This means there are roughly 10 sextillion (10^22) stars in the observable universe.
Scientists use various methods to measure the distance between galaxies, including redshift measurements, standard candles such as Type Ia supernovae, and the cosmic distance ladder which relies on the properties of specific objects like Cepheid variable stars.
No, we cannot see the edge of the universe as it is constantly expanding and there is no definitive edge. The observable universe is limited by the distance light can travel in the 13.8 billion years since the Big Bang, which is estimated to be around 93 billion light-years in diameter.
Yes, there are estimated to be billions of other galaxies in the universe, many of which may have planets capable of supporting life. The search for extraterrestrial life is ongoing and has focused on potential habitable planets within our own galaxy and beyond.