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I didn't have time to watch both videos all the way through, but:- The first video is about Betelgeuse, a red supergiant star that will probably go supernova in the next million years (and may even have gone supernova already - but we don't know it yet!). Because it's only 700 light-years from Earth, it would be brighter than the full Moon. A much closer supernova could damage life on Earth.- The second video is about supermassive black holes at the center of galaxies; it is not about supernovae. The nearest supermassive black hole is about 25,000 light years away, and is fairly quiet at present, so this is likely to pose less of a risk in the near future than Betelgeuse (or pollution, which is even closer).Astronomers are always on the watch for new supernovas, as it tells much about:- What sorts of stars can go supernova, and at what stage of their lives (this has only recently become feasible to model on our very largest supercomputers, at immense cost)- Understanding why there are far fewer visible supernovas in our galaxy than theory predicts- What is the brightness of different types of supernova- Imaging a supernova using neutrinos- Refining the distance to distant galaxies- Measuring Dark Energy- Supernovas can be discovered by amateur astronomers, giving them their 15 minutes of fame.- Close supernovas are visible to the naked eye, which is of interest to the general public Some specialist telescopes scan the night sky on a daily basis, looking for supernovas in other galaxies.https://en.wikipedia.org/wiki/All_Sky_Automated_Survey_for_SuperNovae
If you want to hear some impressive science knowledge, answering questions without notice, listen to:- http://www.abc.net.au/triplej/dr-karl/- http://www.capetalk.co.za/podcasts/115/the-naked-scientist/78148/naked-scientist-dr-chris-smithI have the luxury of checking my vague recollections on Wikipedia before I post them.