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Two faces of Saturn
by Spektrum der Wissenschaft
A quarter of a century of stellar history
8.4.2026
Translation: machine translated
It is usually impossible to follow the development of an astronomical object directly due to the enormous distances involved. Decades of observation with the Hubble Space Telescope have nevertheless made it possible to visualise the progressive expansion of the famous Crab Nebula.
It is the first entry in French astronomer Charles Messier's famous list of 110 stationary astronomical objects. The Crab Nebula (Messier 1, M 1) is the remnant of a massive star that exploded in a massive supernova almost 1000 years ago. The event, known as SN 1054, was observed worldwide in the year 1054. Since then, the remaining material has been continuously expanding and changing its structure. While astronomical objects usually appear static due to the enormous distances involved, NASA's Hubble Space Telescope, which has been in operation for more than 36 years, has been able to document these changes over a quarter of a century. A team led by astronomer William Blair from Johns Hopkins University analysed the development between 1999 and 2024 and published the results in the scientific journal «The Astrophysical Journal».
The Crab Nebula is located around 6500 light years from Earth in the constellation Taurus. Comprehensive observation with Hubble began back in 1999 - at that time with the Wide Field and Planetary Camera 2 (WFPC2). During the last maintenance mission in 2009, astronauts replaced it with the Wide Field Camera 3 (WFC3), which has a higher resolution, a larger detection range and extended filters. In 2024, Hubble was pointed at M 1 again for a detailed follow-up examination.
The comparison of the two data sets clearly reveals the expansion of the nebula. From the distance and the time offset, an outward speed of some filaments of around 15.3 kilometres per second (5.5 million kilometres per hour) can be determined. The team found that such filaments move significantly more in the outer areas than in the centre of the nebula. In fact, they move outwards as a whole instead of stretching out as is usually observed.
Because unlike many supernova remnants, the expansion here is not only driven by the original expansion: At the centre of the Crab Nebula is a pulsar - the extremely dense and rapidly rotating core of the original star. This generates a strong magnetic field that interacts with the very energetic and charged particles in the ejected material. The resulting synchrotron radiation drives the gas apart.
Messier 1 is one of the closest supernova remnants of this type to Earth. It is therefore invaluable to astronomers - even today. By comparing the Hubble data with observations at other wavelengths, such as the infrared images from the James Webb Space Telescope, a comprehensive picture of the ongoing evolution of a supernova «can be created at close range».
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Header image: NASA, ESA, STScI, William Blair (JHU); Image Processing: Joseph DePasquale (STScI)
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