M1 - Crab Nebula

From the author of Welcome to the Universe in 3D

Click here to return to the single image from 2006.

Here's an animated gif showing two images of the Crab Nebula, one taken on October 27, 2006, and the other taken on March 26, 2019.

There are two interesting things to observe in the animation above:

The Crab Nebula's size varies. It's bigger in the 2019 image.
The bright star in the upper right part of the image seems to be moving.

Let's focus on the varying size of the nebula. It's expanding because this nebula is the remnant of a supernova explosion that took place in the year 1054 (almost one thousand years ago).

After a careful analysis, it appears that the nebula in 2019 is 1.288% larger than it was back in 2006. Here's an animated gif in which the 2006 picture has been enlarged by a factor of 1.288%. The stars appear to move but the nebula doesn't vary.

There were \(4533\) days between the two exposures. If we denote the expansion factor by \(x\) and we assume a constant linear rate of expansion, then the formula for computing the date at which the supernova explosion took place is

date = \( 2019 - \frac{4533}{365.25} \cdot \frac{1}{1-1/(1+x)} \)

Plugging in the value \(x = 0.01288\), we get an estimate of the date for the supernova:

\(x = 0.01288\): date = \( 1045 \)

I recomputed the estimate by subsampling the measurements 34 different ways. Here's the histogram showing the range of dates obtained:

Final comment: The moving star is TYC-2 1309-1640-1. It is a K dwarf star known to have a large proper motion.

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