Ask Ethan: How many black holes are there in the Universe?
You know what a black hole is, and we’ve found a few so far. But oh, are there ever so many more out there!
“Black holes are the seductive dragons of the universe, outwardly quiescent yet violent at the heart, uncanny, hostile, primeval, emitting a negative radiance that draws all toward them, gobbling up all who come too close…these strange galactic monsters, for whom creation is destruction, death life, chaos order.” -Robert Coover
For the third time in history, we’ve directly detected an unmistakable signature of black holes: gravitational waves resulting from their merger. Combine that with what we know from stellar orbits around the galactic center, X-ray and radio observations of other galaxies, and gas infall/velocity measurements, and the evidence for black holes in a variety of situations is undeniable. But is there enough information, from these and other sources, to teach us what the number and distribution of black holes in the Universe truly is? That’s the topic of this week’s Ask Ethan, as John Methot inquires:
The most recent LIGO event made me wonder how numerous black holes are, and that made me wonder what the sky would look like if we could see them (and, for clarity, see *only* black holes)… what is the…
