![]() Those with periods of a few milliseconds and whose periods are changing very slowly are called the millisecond pulsars. The period of PSR J1603-7202 increases by just 0.0000005 seconds every million years! There are two main types of pulsar. However the periods of all radio pulsars are increasing extremely slowly. For example, a pulsar called PSR J1603-7202 is known to have a period of 0.0148419520154668 seconds. The time between pulses is incredibly regular and can be measured very precisely. Periods of one second are typical although pulsars have been discovered with periods from a few milliseconds (one millisecond equals 0.001 seconds) up to eight seconds. The time interval between consecutive pulses is called the pulsar's period. No wonder they were first thought to be extra-terrestrials trying to communicate with us! (More sounds of pulsars are available at the Jodrell Bank pulsar webpage) ![]() If the telescope was plugged into a suitable loud-speaker (instead of recording the data on to a computer system) and a bright enough pulsar was being observed then you would actually hear the signal. Later, the data are searched for periodic signals of the type found by Jocelyn Bell which, if found, confirm the presence of a pulsar. The output of the telescope is continuously recorded by a computer that needs plenty of storage space - a recent survey at Parkes stored the equivalent of 8000 CDs worth of data. The Parkes radio telescope in Australia has found more than twice as many pulsars as the rest of the world's telescopes put together.Īn astronomer who is searching for a pulsar will position the radio telescope at an area of sky for between a few minutes and twelve hours (longer observations allow the astronomer to detect weaker pulsars, but it requires the drinking of lots of strong coffee to stay awake!). Even though pulsars were first discovered as radio sources they have now been observed using optical, X-ray and gamma-ray telescopes. The pulsar discovered by Bell and Hewish is now called PSR B1919+21: PSR stands for Pulsating Source of Radio and B1919+21 indicates the position of the pulsar in the sky. Once established that the signals were not of this origin (and also not caused by people on Earth), the unidentified object they were coming from was called a "pulsar" because the emission was pulsed. In fact the source of these pulses were initially referred to as LGM1, Little Green Man 1. Jocelyn Bell noticed small pulses of radiation when their telescope was looking at a particular position in the sky and for a short time scientists thought they might be coming from an extra-terrestrial civilisation. The first pulsar was discovered by chance by Jocelyn Bell and Anthony Hewish in 1967 who were actually studying distant galaxies at the time. We finish by providing links to other webpages for those of you who would like to read more about pulsars. We explain how these pulsars are actually studied today and what we can learn from these amazing objects. ![]() We continue with a section on the theory of pulsars where we explain why pulsars are thought to be neutron stars (the collapsed core of a star that underwent a supernova explosion). We start by describing how astronomers discover and subsequently observe pulsars. This webpage has been designed to give you an understanding of pulsar astronomy.
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