Believe it or not, this is the Crab Nebula, one of the most famous cosmic objects. Except that this image – 9.8 light years across – doesn’t look like the Crab Nebula at all, but the Electric Blue Puff Puff Jellyfish.
You don’t recognise it because that’s the X-ray image taken by NASA’s Chandra X-ray Observatory. And it’s precisely its x-ray signature that has astronomers puzzled.
For decades, the Crab Nebula – the remains of a nova that reached our planet in 1054 – has been considered the steadiest known high-energy source in the universe. Spinning at 30 times per second, the super dense neutron star nebula core was used to calibrate instruments.
Not anymore. A team of astrophysicists have discovered that the nebula’s X-ray energy has been steadily declining “at four different “hard” X-ray energies, from 12,000 to 500,000 electron volts (eV)”. Combining measurements from several X-ray observatories, they have been able to establish a 7 per cent energy decrease in just two years. This means that astronomers need to find a new way to calibrate their gear. [NASA]