Oooh, I can do another back of the envelope calculation here! (cf https://news.ycombinator.com/item?id=11081838 https://news.ycombinator.com/item?id=11081838 )

Oooh, I can do another back of the envelope calculation here! (cf https://news.ycombinator.com/item?id=11081838 https://news.ycombinator.com/item?id=11081838 ) If this happened in the centre of the Milky Way, we're about 25k light years away. Let's say 2 1 million solar masses black holes merged there... and they also gave off about 3/60 of their mass as radiation, that's about 100'000 solar masses being radiated 25k light years away. Using my calculation in the other post, we're talking 10^52 Joules. Across a distance of 25'000 light years, or about 10^20 metres, that's then decreased by 10^40 (inverse square) so we're left with about 10^12 Joules... Which is good news! If that happened in the Milky Way, we would probably survive it - though we'd definitely notice some strange atmospheric effects...