11/24/2019
The Crab Supernova Remnant (M1)
On July 4, 1054 astronomers of the northern Song Dynasty in China wrote of a spectacular "guest star" that suddenly appeared in the constellation we call Ta**us. It was
4 times as bright as the planet Venus (!) and was easily visible in daytime for about 3 weeks!
The star exploded around 5300 BCE, at the time of the earliest cities on Earth, but the light took 6300 years to get here. After running out of thermonuclear fuel to hold itself up against gravity, the star (whose mass was around 10x that of our Sun) collapsed and the resulting shock wave spewed its atmosphere into interstellar space.
Nearly 1000 years later, the filamentary remnants of the blast are still spreading across our sky, expanding at almost 1000 miles per second. The remnant appears to be about 13 light-years across, around 3x as wide as the distance from the Sun to Alpha Centauri. Images taken a few years apart clearly show the changes as it continues to expand.
At the center of the nebula is a tiny neutron star no more than 20 miles in diameter but whose mass is greater than that of our Sun. This incredible object is all that's left of the star whose guts are spreading across space. It's composed entirely of tightly packed neutrons, essentially a colossal atomic nucleus. It spins like crazy, about 30x every second, and its powerful magnetic field sweeps past Earth like a psychedelic searchlight with blasts of radiation from radio to gamma rays. In radio it sounds like tick-tick-tick, only super fast -- 30 ticks/second! It's one of the brightest sources of gamma rays in the sky.
This image is a composite of 160 x 5-minute shots from my back yard with special narrow-band filters that only let through the light emitted by ionized hydrogen (red), oxygen (blue), and sulfur (yellow). Using these narrow filters blocks out all the other light from the city and the Moon, plus it's cool to know what the filaments are made of. The focal length was 1510 mm, and this is a bit more than 13 hours of exposure taken over a bunch of nights in October and November.
The diffuse blue glow in the center is called "synchrotron radiation." It's emitted by free electrons being flung around and around at nearly the speed of light by the insanely strong magnetic field of the supernova remnant.
