Factsheet: The Crab Nebula – perhaps most the interesting object in our night sky

The Crab Nebula is arguably the single most interesting object in our night sky. It is the remnant of one of Nature’s most violent processes – a supernova explosion. In 1054 Chinese astronomers observed a new and very bright star that continued to be visible for the next 2 years. A supernova is produced at the end of the life of a massive star when the nuclear processes in the interior of the star can no longer persist. The star collapses, triggering an extreme explosion releasing, at its peak, more energy than an entire galaxy. Shockwaves from supernova explosions can trigger the formation of new stars and solar systems such as our own.

The incredibly filamentary structure seen throughout the entire image consists of remnant material from interior of the original star – a violent testimony of the explosion that ripped the star apart.

The Crab Nebula provides one of Nature’s finest laboratories, where studies of the effects of a supernova explosion can be undertaken. These explosions are crucial for our understanding of how the composition of matter in the Universe evolves.

At the core of a star is the nuclear furnace where lighter elements are combined to produce heavier elements accompanied by the release of energy. This process of nucleosynthesis generates all the heavier atoms that make up ‘normal’ matter in the Universe, including the atoms that build the carbon-based life we find on Earth. The very heaviest elements need conditions even more extreme than the cores of ‘normal’ stars - conditions that prevail in the very explosion of a massive star, and are thus another by-product of supernovas. Supernova remnants like the Crab Nebula, impelled out into the surrounding interstellar medium, will eventually disperse the processed elements that may then become part of new stars. There is no star yet observed that contains only the original hydrogen and helium components of the Universe that were produced in the first three minutes after the Big Bang.

At the heart of the Crab Nebula lies a dense object known as a neutron star or pulsar. This is an extremely compact object with a mass of 1.5 times that of the Sun and a diameter of only 10 km. Neutron stars are fascinating objects that display some of the most extreme high energy physics we are able to observe in Nature. The Crab pulsar is only barely visible in this Hubble image, since the image was taken to highlight the gas in the filaments. The pulsar has a very strong magnetic field and is spinning very fast - approximately 30 times every second. From the magnetic poles it emits a beam of synchrotron radiation - much like the sweeping beam of a lighthouse - and the characteristic pulsed signal is best observed with X-ray telescopes such as the European Space Agency’s XMM-Newton or NASA’s Chandra X-ray Observatory. It is in fact the energy from the slowing down of the pulsar that keeps the entire Crab nebula shining.