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.
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.
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.
This month brings the excitement of a comet hunt, as Wirtanen 46P reaches closest approach on December 16th. This is a relatively small comet (1.5km across) with a period of just over 5 years. However Wirtanen is known to produce a relatively large tail for its stature, so it’s definitely one to look out for. In mid December it’ll be positioned between the Pleiades star cluster and red giant star Aldebaran in Taurus, so will be relatively easy to locate in the night sky.
Reports of naked eye sightings and some photographs are already emerging online despite the current low altitude of the comet at high norther latitudes. However its vantage will steadily improve as we head into mid December, although Moon conditions will become less favourable then, so time your hunt well.
Wirtanen should be observable in a wide-field telescope or binocular view, and possibly naked eye under very dark conditions. You could also try locating it by taking a 10-30 second exposure in your DSLR camera.
I’ve put together a short video to help you locate it over December. Clear skies!
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.
You can see three excellent examples of open star clusters within the Orion and Taurus constellations, all in one convenient direction during winter skies (looking south or south east) and in a rough line drawn out by Orion’s belt.
Start with the Orion nebula (M42), below the three belt stars in Orion. This star forming region contains a very young open cluster called the Trapezium which is surrounded by glowing clouds of ionised hydrogen gas. You can see this nebula in binoculars but it looks best in a low or medium power telescope eyepiece.
Moving up into the eye of Taurus to the red giant star Aldebaran, we find the Hyades cluster. Aldebaran is like a premonition of the fate that awaits out own sun. A red giant around 7 billion years old, bloated and shuddering in its final gasps before it collapses down to a white dwarf. Shining brightly all around Aldebaran are the members of the Hyades open cluster (although they are much further away) – quite a mature cluster at around 500 millions years old. Best viewed in binoculars.
And finally moving higher and to the right we find the Pleiades, a lovely jewel box of middle age hot stars (and many less bright members) slowly drifting apart to join the general distribution of stars. When the dinosaurs roamed the earth this cluster would have resembled the Orion nebula – bright and nebulous, its hot infant stars lighting up the surrounding hydrogen gas clouds.