Answer to Question 1
The blue glow of the Crab Nebula is produced by synchrotron radiation. This form of electromagnetic radiation, unlike blackbody radiation, is produced by rapidly moving electrons spiraling through magnetic fields and is common in the nebulae produced by supernovae. In the case of the Crab Nebula, the electrons travel so fast they emit visual wavelengths. In most such nebulae, the electrons move slower, and the synchrotron radiation is at radio wavelengths.
Answer to Question 2
Because a pulsar's period is so precise, astronomers can detect tiny variations by comparison with atomic clocks. When astronomers checked pulsar PSR B1257+12, they found variations in the period of pulsation analogous to the variations caused by the orbital motion of the binary pulsar but much smaller. When these variations were interpreted as Doppler shifts, it became evident that the pulsar was being orbited by at least two objects with planetlike masses of about 4 and 3 Earth masses. The gravitational tugs of the planets make the pulsar wobble about the center of mass of the system by about 800 km, and that produces the tiny changes in period that are observed.
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