- What is a “neutron star”? – what is called a neutron star is what’s left over when a star goes nova and essentially burns itself out. All that is left are the heavy elements from its core that have condensed into a mass that is – in these cases – 20-30 times the mass of our sun. The nova explosion blew away essentially all the lighter elements, so what’s left is VERY dense. How dense? Well, these stars were on the order of 20-30 times the mass of our sun today, and the volume the cores take up were around the volume of the city of Chicago. These are some of the most dense things in the Universe.
- How did the collision ever occur? – the two neutron stars were attracted to each other by gravity attraction. They got closer and started doing a death spiral dance, and the culmination of the “dance” was when the two collided.
- How did we find out this was going to happen? – there are some very smart people who work as astrologists, and some of these folks found the pair of neutron stars already doing their dance. They informed all their “friends and neighbours” so virtually everybody in the science was watching when this happened. The actual collision only lasted about 30 seconds and there was a massive emittance of light and other types of radiation.
I will stop here because I am no expert, and the experts have done wonderful jobs of clarifying and simplifying the explanations so that even not so intelligent or trained people like me can understand it. Here’s a first link:
Once you are there, there are a large number of additional videos and talks and explanations for those of you who are interested.