Scientists 'astonished' as Crab nebula dims

While the swirling cloud of neutrons and light elements that forms the Crab nebula may look chaotic, scientists have long held it as a reliable source of energy.

Over the course of many years, the output from the nebula has been used to calibrate instrumentation in the belief that it remains relatively constant.

However, Louisiana State University claims to have "astonished" scientists with the news that the nebula is steadily dimming.

Researchers working at NASA's Fermi gamma-ray space telescope have detected a sizeable decrease of about seven per cent in the gamma radiation emitted by the nebula since summer 2008.

The finding was so shocking that the team initially blamed the instrumentation - and have now confirmed the result on four separate platforms.

It means the nebula - which reaches its 1,000th anniversary in 2054 - may not be the "standard candle" that it has long been perceived to be, but may actually flicker like a real flame.