Oooh, I can do another back of the envelope calculation here! (cf <a href="https:&#x2F;&#x2F;news.ycombinator.com&#x2F;item?id=11081838" rel="nofollow">https:&#x2F;&#x2F;news.ycombinator.com&#x2F;item?id=11081838</a> )<p>If this happened in the centre of the Milky Way, we&#x27;re about 25k light years away.<p>Let&#x27;s say 2 1 million solar masses black holes merged there... and they also gave off about 3&#x2F;60 of their mass as radiation, that&#x27;s about 100&#x27;000 solar masses being radiated 25k light years away.<p>Using my calculation in the other post, we&#x27;re talking 10^52 Joules. Across a distance of 25&#x27;000 light years, or about 10^20 metres, that&#x27;s then decreased by 10^40 (inverse square) so we&#x27;re left with about 10^12 Joules...<p>Which is good news! If that happened in the Milky Way, we would probably survive it - though we&#x27;d definitely notice some strange atmospheric effects...