This is how the Crab Nebula was born: in 1054 A.D, a new, very bright star has appeared in Earth’s sky, in the constellation Taurus. Chinese, Japanese, Korean, and Arab astronomers observed the event and noted: “a new bright star emerged in the heavens”. The star was so bright: for nearly three weeks, it was visible even during the daytime, under the hot, shiny summer sun, and remained visible for around two years (653 days to be exact). Today, we know that that “heavenly star” was actually a supernova (SN 1054, see notes 1), and its remnant is what we now know as the Crab Nebula today (catalog designations M1, NGC 1952, Taurus A).
The Crab Nebula was observed later by English astronomer John Bevis (1695-1771) in 1731, long before its true nature was understood and identified. It was identified as the supernova remnant of SN 1054 between 1921 and 1942, at first speculatively (the 1920s), with some plausibility by 1939, and beyond a reasonable doubt by the Dutch astronomer Jan Oort (see notes 2) in 1942. With that identification, the Crab Nebula became the first astronomical object identified with a historical supernova explosion. Today, it is not visible to the naked eye but can be made out using binoculars under favorable conditions. It lies in the Perseus Arm of the Milky Way galaxy, at a distance of about 6,500 light-years from Earth.
The core of the exploding star formed a pulsar, called the Crab Pulsar (or PSR B0531+21).
Time-lapse of the Crab Nebula
Amateur astronomer Detlef Hartmann created this amazing animation of the Crab Nebula expanding, using observations he made over a decade with a home-built telescope. Today, the Crab Nebula has a diameter of 3.4 parsecs (11 light-years) and is expanding at a rate of about 1,500 kilometers per second (930 mi/s) or 0.5% of the speed of light. Here is the one-decade (from 2008 to 2017) time-lapse animation of the Crab Nebula below.
Several studies suggested that the expanding cloud of the stellar debris is expanding much too fast to be associated with a supernova explosion in 1054. This dilemma led astronomers to the idea that the remnant’s central pulsar (the Crab Pulsar, a young, rapidly spinning and extremely dense neutron star, 28-30 kilometers or 17-19 miles across with a spin rate of 30.2 times per second) leftover from the 1054 supernova, emitted such copious amounts of energy that it actually accelerated the expanding cloud of debris, making it move faster with time.
- The exact date of the event has been disputed, but most accounts accept the Chinese date of July 4. Between 532 B.C. and A.D. 1064, Chinese astronomers recorded at least 75 supernovas (they called them as “guest stars”, as they have no idea what they actually were). The 1054 supernova was the brightest.
- Jaan Oort (28 April 1900 – 5 November 1992) was a Dutch astronomer who made significant contributions to the understanding of the Milky Way and who was a pioneer in the field of radio astronomy. The Oort cloud, the Oort constants, and the Asteroid, 1691 Oort, were all named after Jan Oort.