Artwork of a pulsar as seen by a nearby planet. Current models suggest that pulsars are neutron stars with a diameter of about 10km and a mass in the range between 1.5-3 solar masses. They have strong magnetic fields and also rotate very quickly around their axes. The main feature of a pulsar is the emission of a flash of energy, detected from radio up to X-ray wavelengths, with periods ranging from a few milliseconds up to a few seconds. This flash of energy is concentrated into a narrow beam and, like the flashing of a lighthouse, is detected every time it crosses the Earth's path.