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Why do the Crab Nebula’s red filaments and blue inner region look different?
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Supernova remnant
Detail of the Cygnus Loop.
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 distinct appearance of the Crab Nebula’s red filaments and its blue inner region is due to the different physical processes generating their light:
- Red Filaments: These consist of glowing gas that emits a spectrum characteristic of a diffuse nebula. This light is produced by the material ejected during the supernova explosion, which forms a lacy network of hydrogen-rich gas.1
- Blue Inner Region: This amorphous, structureless area radiates synchrotron radiation. This nonthermal emission is produced by high-energy electrons spiraling through the intense magnetic field surrounding the Crab pulsar. Because this radiation is generated by charged particles moving at speeds close to that of light, it is highly polarized and spans a broad range of frequencies, extending from visible light up to X-rays and gamma rays.21
The pulsar at the center of the nebula acts as the engine for this process, continuously supplying the energy required for the nebula to glow by losing its own rotational energy.31