The Crab Nebula, the most famous galactic supernova relic: a very special sequence.

Everyone familiar with the sky knows Messier 1, the legendary “Crab” nebula: it is the remnant of the most famous galactic supernova, SN 1054. We managed to create a very special sequence, with a bonus, showing how much time matters in our Universe. Enjoy!

The Crab Nebula: 2011 vs 2021 images. Click on the image for the HD version.

The Crab Nebula: 2011 vs 2021 images. Click on the image for the HD version.

One of the most famous astronomical events in human history has been the explosion of a supernova in 1054, in the Taurus constellation, quite obviously named SN 1054. It was recorded at least by Chinese astronomers and if we point our modern telescopes where once there was that bright star, now we find a complex gas structure and an exotic astrophysical treasure: a neutron star, pulsating about 30 times per second, something we call pulsar.

This object has been of vital importance in modern astrophysics and it is simply impossible to fully cover it here. For our purposes, it is enough to remind you that, as an effect of the violent supernova explosion, the original stellar structure is mainly blown away and forms the gas cloud we mentioned: the so-called supernova remnant. Typical expansion velocities after the supernova event are of the order of 10000 km/s. This is a significant fraction of the speed of light. Of course, the supernova remnant continues to expand well after the explosion and its size increases over the time. As a result, we see these objects getting larger and larger in the sky.

The "Crab" nebula's pulsar.

The “Crab” nebula’s pulsar.

These arguments apply to the SN 1054 remnant, which is expanding at about 1500km/s. Messier 1 (one of the official names of this object, as well as NGC 1952) lies at about 6500 light years from us and its physical size is estimated to be around 10 light years. It was discovered in 1731 by J. Bevis and rediscovered in 1758 by C. Messier.

Considering the current expansion rate, in 10 years the “Crab” nebula expands of 473.364.000.000 km, about 80 times the Pluto-Sun distance. Considering the estimated distance of the object, the mentioned value is measurable with a good telescope. Here it is a great activity for students: measuring the nebula anugularnexpansion and using the rates coming from spectroscopy, find the distance of the object.

This quick introduction was essential to present the animation above, where we put together two images captured 9.1 years apart (Dec. 2011 and Feb. 2021), remotely taken with the “Elena” (PlaneWave 17″+Paramount ME+SBIG STL-6303E) robotic unit available at Virtual Telescope. The two pictures were properly aligned and, once blinked, they clearly show the expansion of the gas structure.

I must say I’ve been looking forward to capture such a document for a long time and these nights I decided to capture the “Crab” again, to compare it with a 2011 shot I had in my archives. I believe the resulting animation is mind blowing. Not only the expansion is clearly visible, but also changes in the structure are quite obvious.

While the evolving nebula is the main actor here, if you look carefully you will find a bonus in the image. On the upper left side, there is a star clearly moving. It is G 100-20, an high proper motion (0.24″/year) star. From its paralax, we find it to be at 58 light years from us.

The High Proper Motion star G 100-20.

The High Proper Motion star G 100-20.

After such a great experience, here it is the lesson learned: time matters, all around the Universe.

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