Space & astronomy · the experiment
Find the missing mergers
Two neutron stars that collided in 2017, a galaxy of very old stars, and a waiting time the standard picture did not expect. Four questions, from beginner to expert.
1 · Date the collision
Beginner
What did Foley measure to estimate how long the pair behind GW170817 waited before merging?
2 · Apply the canonical rule
Canonical distribution: the number of mergers per unit of delay falls as 1 divided by the delay, from a minimum delay of about 10 million years.
Intermediate
With this rule alone, how many mergers per unit of delay at 1 billion years for each one at 10 billion years?
3 · Count the detections needed
Under the canonical distribution, the chance that a detected merger is as old as GW170817 is 1.8%.
Expert
About how many detections would it take before expecting one such old merger?
4 · Look into the distance
Suppose no pair merges before a delay of 10 billion years. Looking far away means looking back in time.
Expert
What would future detectors see at great distances?
Mergers tracked down
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