Messier 1, The Exploding Crab Nebula!
Optics:   Ritchey–Chrétien 20" F/8.2 (4166mm FL) Processing:   PixInsight, Photoshop
Camera:   SBIG STXL-11000 with Adaptive Optics Date:   October 29-30 2021
11 Megapixel (4008 x 2672 16-bit sensor) Location:   Columbus, Texas
Exposure:   LRGB = 320:90:80:110 minutes Imager:   Kent E. Biggs
1000 years ago, ancient Chinese astronomers witnessed a star exploding catastrophically; the Crab Nebula is what remains of that explosive supernova. The images on this page explore the Crab Nebula including its original star, now a pulsar, and its continued expanding shell of material seen in the below animated image* or video as well as a close by star with visible proper motion.
Details: The Crab Nebula (also called Messier 1, M1, or NGC 1952) lies in the direction of the constellation Taurus and was one of the first pulsars ever identified. It is also the first object ever associated with an historical supernova. The Earl of Rosse William Parsons drew the nebula in 1842 using a 36 inch telescope; the drawing resembled a crab, giving it its name. While it was discovered by English astronomer John Bevis in 1731, it wasn’t until the early 20th century that astronomers discovered that it seemed to be expanding which you can see below. That indicated a relatively recent supernova, and indeed it was, because, on July 4th, in the year 1054, Chinese astronomers recorded a new star in the same part of the sky as the Crab Nebula. That new star was bright enough to be seen during the day. A sudden new “star” recorded in ancient history, usually meant either a comet or a nova. In fact, the word “nova” means new star. A nova happens whenever an old star suddenly brightens as it throws off material into space, often a result of collecting this material over time from a nearby younger star. A nova does not usually destroy the star.

A supernova, however, occurs when a star reaches the end of its life and explodes in one of the most violent events in the universe. A supernova’s original star (called its progenitor) is then greatly changed or even destroyed in the process. Most supernova become a neutron star or if massive enough, a black hole. A neutron star is a gigantic atomic nucleus, tens of kilometers across. It is held together by gravity since it contains only neutrons, many formed from protons and electrons combining during the supernova in such extreme pressures of the explosion. Neutron stars are therefore so dense that a teaspoon of their material weighs several billion tons.

The Crab Nebula is very close to the ecliptic (the plane in which the earth, moon, and all planets orbit our sun). Consequently, many solar system objects come visually close to this nebula during their orbits as seen from earth. On January 4, 2003, Saturn passed in front of the Crab. In the image above, another solar system object is visible*; it even came very close to transiting M1, a day or so after this image. The object identifies as Asteroid 3409 Abramov, a stony Koronian asteroid about 11 kilometers in diameter. Its orbits between Mars and Jupiter in the outer asteroid belt once every 5 years. Ironically, the asteroid is not much smaller than the Crab Pulsar. However, at an average of 400 million kilometers away from us, 3409 Abramov is quite close compared to the Crab Nebual at 6500 light years away or 150 million times further away. Click on the above image, zoom into the asteroid line caused by it moving during many exposures. Note the gaps in the line caused by both processing and a delay of about 1 minute between each exposure.

It is rare and exciting to see any changes, even movements in astronomical objects outside of our solar system. Most objects, even in our own galaxy, are so far away, they move or change too slowly to see any difference during our entire lives. However, incredibly, the above time lapse video is two images taken exactly 13 years apart - the first in October 2008 and the second in October 2021, a long time lapse indeed! Several things are noteworthy in the video. First, the gas and dust in the explosion can be seen expanding considerably*, in fact, the shell is moving outwards at nearly 1000 miles per second or 0.5 percent the speed of light. The nebula has, therefore, expanded nearly 1 trillion miles in the 13 years between images. Reversing this rate gives a nice calculation of the explosion origin at about 1000 years ago as seen by the ancient Chinese. Second, note the blue-white cloudy material inside and throughout the nebula moving during its expansion. Third, note the movement of the yellow-orange star in the lower left corner of the image. The star is Tycho 1309-1640-1 and exhibits what is called proper motion since it is relatively nearby to us compared to all the other stars in this image. Proper motion is the movement of stars, each in their own path around our galaxy. Every star has its own proper motion; we can see this ones clearly over 13 years due to both its and our sun’s movement. Looking forward to the next timelapse image in a decade or so!

* Hover mouse over an image to animate or see annotations.

M1 Compare
The Living, Expanding Crab Nebula

When stars collapse to form neutron stars they often spin faster and faster, like a figure skater pulling their arms in during a spinning performance. This collapse and fast spin may form a pulsar in which charged particles, accelerated to relativistic speeds, cause a kind of wind and a standing shock wave. The Crab Nebula contains such a pulsar as indicated in the above and below images. It was originally a normal star with a size of over a million kilometers in diameter, however, now, due to its catastrophic supernova, what remains of the star is only 28-30 kilometers in diameter, yet spins at over 30 times each second. In the image below you can more clearly see this pulsar and the surrounding shock waves caused by the pulsar’s wind. The shock waves appear elongated, but are actually  more circular since the pulsar spin is at an angle to us. This pulsar lights up the crab nebula with a ghostly bluish-white color, and the red filaments are the remnants of the original star’s atmosphere containing ionized helium and hydrogen along with some heavier elements. Also visible below is a mysterious jet of material creating a tail of sorts. What causes the jet is still a mystery as it is not related to the pulsar spin or shock waves.

M1 Zoomed
The Pulsar and Shock Waves Up Close

Finally, the below image is a zoomed out version of the above to show more of the surrounding stars. It also shows the expanding materail by hovingering a mouse pointer over the image.

M1 Compare
Zoomed out Explosion