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Depends on the number of civs per galaxy, and whether they are
checking for black hole binaries. A rough calculation suggests that
this could wipe out biospheres across a galaxy:<br>
<br>
If we assume the energy release was around 10^50 J over a second,
then the power per square meter at distance d is 10^50/(4 pi r^2)
Watts. So the criticial distance if the danger power is P is
r=sqrt(10^50/4 pi P). If we assume a megawatt/m^2 is enough to cause
biosphere damage, then the distance is 298,000 lightyears. To wipe
out more advanced civilizations I would expect a much higher P; for
a gigawatt the range is 9,400 lightyears - bad in the central part
of a galaxy, but not even covering it.<br>
<br>
So if you are an optimist about civilizations, then you should
expect a fair number to have at least had to flee over long
distances from this. <br>
<br>
I wonder if one can make a gravity wave powered sail? I doubt it,
since most matter is too transparent to the gravity waves to get any
decent coupling. But black holes sometimes get a 1000 km/s kick from
mergers. <br>
<br>
<br>
<div class="moz-cite-prefix">On 2016-02-11 16:34, Giulio Prisco
wrote:<br>
</div>
<blockquote
cite="mid:9C49E0D5-9FDD-4F14-877C-23A26AD77806@gmail.com"
type="cite">
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<div>I'm wondering how many zillions of sentient beings died as a
result of the black hole fusion event.</div>
<div><br>
On Feb 11, 2016, at 5:13 PM, John Clark <<a
moz-do-not-send="true" href="mailto:johnkclark@gmail.com"><a class="moz-txt-link-abbreviated" href="mailto:johnkclark@gmail.com">johnkclark@gmail.com</a></a>>
wrote:<br>
<br>
</div>
<blockquote type="cite">
<div>
<div dir="ltr"><font size="4">On Sept. 14
<div class="gmail_default"
style="font-family:arial,helvetica,sans-serif;display:inline">
</div>
at 4am the LIGO
<div class="gmail_default"
style="font-family:arial,helvetica,sans-serif;display:inline">
detector in </div>
Livingston
<div class="gmail_default"
style="font-family:arial,helvetica,sans-serif;display:inline">
Louisiana </div>
detected <font face="arial, helvetica, sans-serif">a burst
</font>
<div class="gmail_default" style="display:inline"><font
face="arial, helvetica, sans-serif">
of gravitational waves, 7 milliseconds later the LIGO
detector in Hanford Washington detected the same
thing. The possibility of this being due to chance is </font></div>
vanishingly small
<div class="gmail_default"
style="font-family:arial,helvetica,sans-serif;display:inline">
. What they detected was 2 black holes circling each
other at 250 times a second, one was 36 times the mass
of the sun and the other 29 times. The entire signal
only lasted for a fifth of a second. </div>
</font>
<div><font face="arial, helvetica, sans-serif"><br>
</font></div>
<div><font face="arial, helvetica, sans-serif"><a
moz-do-not-send="true"
href="http://www.nytimes.com/2016/02/12/science/ligo-gravitational-waves-black-holes-einstein.html"><a class="moz-txt-link-freetext" href="http://www.nytimes.com/2016/02/12/science/ligo-gravitational-waves-black-holes-einstein.html">http://www.nytimes.com/2016/02/12/science/ligo-gravitational-waves-black-holes-einstein.html</a></a>
<div class="gmail_default"
style="font-family:arial,helvetica,sans-serif;display:inline">
</div>
</font></div>
<div><font face="arial, helvetica, sans-serif">
<div class="gmail_default"
style="font-family:arial,helvetica,sans-serif;display:inline"><br>
</div>
</font></div>
<div><font size="4" face="arial, helvetica, sans-serif">
<div class="gmail_default"
style="font-family:arial,helvetica,sans-serif;display:inline">J
ohn K Clark</div>
</font></div>
<div><font face="arial, helvetica, sans-serif"><br>
</font></div>
</div>
</div>
</blockquote>
<blockquote type="cite">
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<pre class="moz-signature" cols="72">--
Anders Sandberg
Future of Humanity Institute
Oxford Martin School
Oxford University</pre>
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