Crab Nebula Composite

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This is an amazing composite image of the Crab Nebula supernova remnant. It shows the neutron star at the center, superimposed over the shockwave nebula (whose outline can be observed dimly in a decent telescope).

This is what happens to high mass stars when they run out of fuel. The atmosphere of the star suddenly collapses inward and dramatically rebounds off the compressed neutron core.

Conservation of angular momentum makes the neutron star spin rapidly (a pulsar) and the rest of the star’s atmosphere expands into space releasing huge quantities of energy (a supernova).

This particular supernova was observed and recorded by Chinese astronomers in 1054 AD as a ‘guest star’, in the constellation Taurus.  It remained visible as a naked eye star for over a year before fading.

Betelgeuse visibly dimmer

I can’t get over how much dimmer Betelgeuse in Orion appears at the moment. To my eye Aldebaran (a red giant) in Taurus now appears obviously brighter.

This was an image taken last winter.

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Orion image from winter 2019

Many click bait astronomy articles have surfaced claiming the star might be dimming due to its impending collapse and rebound as a supernova, but Betelgeuse is a known variable star and similar changes in its brightness have been noted in the past, although recent changes appear to deviate from established patterns.

Unusual gravitational waves have also been detected in the vicinity of the red supergiant, adding to the sense of mystery.  It’s important to note that these waves are merely in the vicinity, so could easily be generated by countless other sources behind Betelgeuse.

Still, it’s fun to speculate about the possibility of witnessing a relatively close supernova event in our lifetime.  The last two major naked eye supernovas were recorded in 1572 and and 1054, in Taurus (the Crab nebula) and Cassiopeia (Tycho Brahe supernova).  Both generated enough luminosity to be visible in daylight for several weeks, and shone as new ‘guest stars’ for around a year or so before fading.

Some work published by Dolan in 2016 estimated the impact of a Betelgeuse supernova on Earth and found it to be negligible.  At 500 light years distance the residual energy of the vastly expanded shockwave would be exponentially diminished as it passed Earth.  However the brightness predicted would be magnitude -12.4,  making such an event more luminous than a full Moon!

For the mathematically motivated I enclose an extract from his calculations below.

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The Crab Nebula

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In 1054AD Chinese astronomers recorded a bright new star suddenly appear in the constellation Taurus the bull. It brilliantly out shone all other stars and was visible in broad daylight. After a year or so its light faded and it vanished.

The event was a supernova explosion – the dramatic explosion of a massive star. Today we can see the remnants left behind from this violent event – the Crab Nebula. An expanding shockwave of recycled stellar material. The above amazing image is from the Hubble space telescope.

You can see the Crab Nebula in a modestly sized amateur telescope, and as always the darker the skies the more detail you’ll see.  With a 150mm scope or larger you should be able to trace out the overall mottled shape of the nebula.  Use averted vision and see if you can pick out extra detail and structure.

Finding the Crab is relatively straightforward as it sits just beside the lowest horn of the constellation Taurus the bull, which sits above and right of Orion during evening skies at the moment.

 

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