It was July 1967 when the large radio-telescope of Cambridge, Massachusetts, began to receive strange signals from space. They were very rapid pulses which greatly irritated scientists since their research about the nature of the radio sources in space were being disturbed by what they considered to be interference: the use of radio bands by an increasing number of persons was a real disaster for radio astronomers around the world. Soon however the Cambridge group discovered that the signals were not coming from the Earth, but from a region located in the Crab Nebula, between the stars Altair and Vega, and they were very regular: they lasted exactly one third of a second and were separated by an "empty" space of one second and a third. Thus, irritation was soon replaced by amazement and then great excitement: what was producing what seemed to be the ticking of an interstellar clock? It was the astronomer Jocelyn Bell, who was also the first one to identify the mysterious signal, to develop the theory, and not totally so far fetched, that this was a real message sent by "someone". The source was christened LGM 1, with the initials which stood for Little Green Men, as the extraterrestrials were commonly called in science-fiction slang. However, the scientists soon had to reject the idea of extraterrestrial intelligence. First, the signals seemed to be a rather wasteful use of energy: ten billion times the total power that can be produced on the Earth only to transmit some ticking was just too much. And then, those signals were not as regular as first thought. There must be another explanation. But what? Since it was not an artificial origin, it had to be a new real phenomenon that had never been detected before. After much discussion, the astronomers concluded that those signals were transmitted by a star which, rotating rapidly around itself, emitted radio pulses like a lighthouse sweeps the sky with its intermittent light. It was called a pulsar (i.e. pulsating star) and it was a very special star: a star formed only of neutrons. These particles in the nucleus of atoms have no electric charge (that's why they are called neutrons), they do not repel each other and are therefore very compact: and so much so that a neutron star with the same mass as our Sun would have a diameter of less than 10 kilometers! These superdense stars, which are probably the remains of the explosion of a supernova, i.e. a giant red star, are so small that they are practically invisible, and one of the ways to identify them is through the emission of radio pulses such as those detected by the Cambridge group.
It was July 1967 when the large radio-telescope of Cambridge, Massachusetts, began to receive strange signals from space. They were very rapid pulses which greatly irritated scientists since their research about the nature of the radio sources in space were being disturbed by what they considered to be interference: the use of radio bands by an increasing number of persons was a real disaster for radio astronomers around the world. Soon however the Cambridge group discovered that the signals were not coming from the Earth, but from a region located in the Crab Nebula, between the stars Altair and Vega, and they were very regular: they lasted exactly one third of a second and were separated by an "empty" space of one second and a third. Thus, irritation was soon replaced by amazement and then great excitement: what was producing what seemed to be the ticking of an interstellar clock? It was the astronomer Jocelyn Bell, who was also the first one to identify the mysterious signal, to develop the theory, and not totally so far fetched, that this was a real message sent by "someone". The source was christened LGM 1, with the initials which stood for Little Green Men, as the extraterrestrials were commonly called in science-fiction slang. However, the scientists soon had to reject the idea of extraterrestrial intelligence. First, the signals seemed to be a rather wasteful use of energy: ten billion times the total power that can be produced on the Earth only to transmit some ticking was just too much. And then, those signals were not as regular as first thought. There must be another explanation. But what? Since it was not an artificial origin, it had to be a new real phenomenon that had never been detected before. After much discussion, the astronomers concluded that those signals were transmitted by a star which, rotating rapidly around itself, emitted radio pulses like a lighthouse sweeps the sky with its intermittent light. It was called a pulsar (i.e. pulsating star) and it was a very special star: a star formed only of neutrons. These particles in the nucleus of atoms have no electric charge (that's why they are called neutrons), they do not repel each other and are therefore very compact: and so much so that a neutron star with the same mass as our Sun would have a diameter of less than 10 kilometers! These superdense stars, which are probably the remains of the explosion of a supernova, i.e. a giant red star, are so small that they are practically invisible, and one of the ways to identify them is through the emission of radio pulses such as those detected by the Cambridge group.
