Archive for September 25th, 2021

The Crab Nebula

September 25, 2021

We live only a few conscious decades, and we fret ourselves enough for several lifetimes.

(Christopher Hitchens)

I recently gave a 5 minute talk to a non-technical group about the Crab Nebula (M1, the first object in Charles Messier’s catalog) that related to a sense of wonder in Science. I thought the brief content was worth sharing here.

Chinese astronomers in 1054 witnessed a “guest star”, an explosion that gave rise to a remnant several light years wide called the Crab Nebula.

The object is several thousand light-years distant from earth, yet visible in a small telescope, although with nothing like the detail shown in the Hubble Space Telescope image of Figure 1!

Figure 1: The Crab Nebula, a Hubble Space Telescope image mosaic (source: NASA)

At the heart of the nebula is an object composed only of neutrons, a spoonful of which would weigh a billion tonnes, spinning 30 times per second, energising the nebula, wave-like rings expanding outward from the centre like ripples in a pond (Figure 2).

The original star ran out of the elements that had sustained its nuclear fusion for millions of years, its core collapsing then rebounding in a fraction of a second, ending as a supernova explosion.

Figure 2: The central region of the Crab Nebula (source: NASA)

The event synthesised elements heavier than iron that spread out into the space between the stars, to be incorporated into new stars and their planetary systems, some perhaps going on to develop life.

The iron in our blood, along with trace elements like zinc and iodine, come from such stars.

So, not only are we star-stuff, as Carl Sagan liked to say, but in fact we owe our existence to massive stars that burned bright and lived short lives (millions vs the billions of years our sun will last) then died, so that we could live for just a few decades.