The Cat’s Eye Halo

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Image Credit: R. Corradi, Nordic Optical Telescope

I recently stumbled across this stunning image of the famous Cat’s Eye nebula. It’s a false colour enhancement showing the extended ejecta from the dying star, imaged by the Nordic Optical Telescope on the Canary islands..

The cat’s eye is dubbed a ‘planetary nebula’. An erroneous label as this has nothing to do with planets whatsoever. Rather these nebulae are the beautiful symmetries left behind when stars of similar mass to our Sun enter their final gasps of life. Before collapsing down to a white dwarf (a compact star held in place by electron pressure), the star sheds its atmosphere is great puffs, producing these ghostly but beautiful clouds of ionised gas.

I made a video about Planetary nebulae you can watch here:
https://modulouniverse.com/2019/03/03/planetary-nebulae-video/

The outer gaseous tendrils seen in this image extend almost 3 light years across and probably represent earlier and more transient episodes of stellar influenza, before the star began its collapse in earnest.

Image Credit: R. Corradi, Nordic Optical Telescope

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.

Planetary Nebula

The term planetary nebula is highly erroneous, as these emission nebula have nothing whatsoever to do with planets.  Perhaps the most famous of these is the beautiful ring nebula in Lyra, not far from the brilliant star Vega, although many other planetary nebula are scattered around our night skies, and can be observed comfortably in larger telescopes.

The following video by ESA is a fantastic 3D model of the Ring nebula. In essence the ring nebula is the remnants of a dying Sun like star beyond its red giant phase. As the star enters its final stages its outer layers are shed in great expanding waves, and the residual hot white dwarf star at the centre ionises these gases into beautiful coloured shells.

This ionisation process is very similar to the mechanism that produces Earth based aurora. Electrons are recaptured within the host atoms (often hydrogen, helium, oxygen and nitrogen) and the drop to lower energy levels releases light of a specific frequency, governed by the simple equation we all learn in physics, E = hf.