...Neutron stars are the smallest, densest stars known to exist: about 12 miles wide, with a teaspoon of neutron star material having a mass of about a billion tons. The core is a soup of pure neutrons, while the crust is smooth, solid and 10 billion times
stronger than steel.
The 100-second hum picked up by Ligo told the story of how the two stars, each slightly heavier than the sun, approached their death. Initially separated by 200 miles, they circled each other 30 times a second. As they whirled inwards, accelerating to 2,000 orbits each second, the signal rose in pitch like a slide whistle.
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