An unknown source has been sending radio blasts towards Earth since at least 1988, scientists say. For 35 years, the source has been sending out regular 20-minute blasts of energy that vary considerably in their brightness, researchers say. The emissions appear something like the blasts that come out of pulsars or fast radio bursts, which last for milliseconds to several seconds. But the newly discovered source sends radio signals that pulsate on a period of 21 minutes something previously thought impossible by expected explanations. Pulsars are neutron stars that spin around quickly, throwing out radio blasts as they do. When one crosses Earth, the emissions can be picked up very briefly and brightly, like being in the path of the light from a rotating lighthouse. Scientists believe that process can only work if the magnetic field of the pulsar is strong, and it is rotating quickly enough " if not, there would not be enough energy to see the pulsar from Earth. That has led to the development of the "pulsar death line", which suggests that sources must be spinning fast and strong enough to be detected. The newly discovered object named GPMJ1839-10, however, is way beyond that death line. If it is a pulsar, then it seems to be operating in ways that scientists thought impossible. It could also be a highly magnetised white dwarf or magnetar, an extra kind of neutron star with incredibly strong magnetic fields. But they do not tend to send out emissions of this kind, researchers believe.