Final answer:
Pulsars emit two narrow beams of energy from their magnetic poles due to the misalignment between their magnetic and rotational axes, creating a pulse of radiation observable from Earth when a beam intersects with our line of sight, analogous to a lighthouse. The model is supported by the correspondence between rotational energy loss and energy output of surrounding nebulae, such as the Crab Nebula.
Step-by-step explanation:
Astronomers suggest there must be two beams of energy coming from a pulsar because the rotational axis is misaligned with the magnetic axis, which is a critical aspect of the pulsar model. At each of the magnetic poles, particles from the neutron star are accelerated and emit energy in the form of a narrow beam over a broad range of the electromagnetic spectrum as the star rotates. As a result, each time one of the magnetic poles sweeps across our line of sight, we detect a pulse of radiation, providing evidence that supports the lighthouse model of pulsar behavior. This is further confirmed by the significant energy output of the Crab Nebula, which receives its energy from the pulsar beams, generated by the loss of rotational energy of the neutron star. Only when the beam of the pulsar is directed towards Earth can we observe the pulsar, and since space allows for a three-dimensional arrangement, many pulsar beams do not intersect with our planet, hence why we can detect only a fraction of them.