How often do stars explode in the universe? Are there so many stars that there are millions exploding all of the time?
There are probably about 1,000 supernovas every second.
It has been estimated that in our Milky Way galaxy there is a supernova explosion every 50 years.
Given that the Hubble telescope has detected some 150 billion galaxies, this means that on average there are 30 billion supernova explosions in visible galaxies every year. That brings the average to just under 1,000 supernova explosions every second.
Many of the galaxies will be so distant that it might not be possible to detect a supernova.