Gravitational waves come from a number of sources. We will focus on the two major ones: black holes and neutron stars.
What are Black Holes?
Black holes are massive (around more than 30 times heavier than our sun) collapsed stars. At the end of their lifetime, the star has no more fuel to burn to counteract the force of gravity pushing on its surface (which is very strong as the star is massive). The star collapses in on itself, creating an exploding star known as a supernova and what’s left behind forms a singularity and a black hole. They are called black holes because even light cannot escape from them and so, they appear black to any light-based observations.
Singularities
A singularity occurs when an infinite amount of mass is compressed into an infinitely small space and all of our known laws of physics completely break down. A singularity is the ‘heart’ of a black hole and something we know hardly anything about.
Binary Black Hole Merger
A binary black hole system describes a system in which two black holes orbit closely to each other. As they orbit, gravitational waves are created, taking energy away from the system. This causes the two black holes to spiral into each other, eventually colliding and forming a larger single object, releasing massive amounts of energy in the form of gravitational waves.
What are Neutron Stars?
Neutron stars are the final form of slightly less massive stars (around 10 – 20 times the mass of our sun) and are incredibly dense objects. The atoms that once made up the original star are stripped into their building blocks (neutrons, protons and electrons) and the immense pressure exerted crushes the protons and electrons into neutrons (hence the name neutron star!). These stars are the most dense objects known to us.