Why can the Crab Nebula not keep shining in X-rays without energy from its pulsar?
This nebula is the product of a supernova explosion; in this section, the blast wave has encountered an area of dense interstellar gas, creating turbulence in the wave and causing it to glow. The picture is a composite of three images taken by the Hubble Space Telescope.
The Crab Nebula cannot continue to shine in X-rays without its pulsar because the high-energy electrons responsible for this synchrotron radiation have a very short lifespan.1
Calculations indicate that these electrons should lose their energy and decay in approximately 30 years—a duration significantly shorter than the nebula's age of nearly 1,000 years. Because the nebula continues to emit vast amounts of energy, it requires a constant, external power source to replenish these electrons.1
This energy is supplied by the Crab pulsar, a rotating neutron star located at the center of the nebula. As the pulsar gradually slows its rotation, it releases energy that is transferred to the nebula, effectively fueling its ongoing nonthermal emission across the electromagnetic spectrum, including X-rays and gamma rays.231