Pulse aquí si desea leer esta página en castellano

Pulsars are the results of a supernova explosion

Pulsars come from supernovae

Back in 1967, a 24-year-old Irish girl was at Cambridge University, doing her Ph.D. in Physics. She was called Jocelyn Bell.

Shortly before she had joined a team made up of five other researchers, who, led by Anthony Hewish, were building a radio telescope.

One fine day this young woman detected radio signals too regular and fast to come from quasars.

The sound of these signals is reproduced by her in a lecture she gave years later.

Joselyn Bell and pulsars
Young Jocelyn Bell in June 1967. Credit: Wikipedia, web “en.wikipedia.org/wiki/Jocelyn_Bell_Burnell”.

Every member of the team realized that these were extraordinary signs. They began to study the data and were discarding one after another the possible sources of terrestrial origin or artificial satellites.

Chart Jocelyn. pulsars
he chart examined by Jocelyn Burnell in August 1967. Credit: web “en.wikipedia.org/wiki/PSR_B1919%2B21”.

This chart with data from the “4 Acre Array radio telescope”, showed the trace of the first identified pulsar, subsequently designated PSR B1919+21.

Then they fantasized a bit about the possibility that the signals were emitted by extraterrestrial civilizations.

They finally deduced that these strange signals came from a very massive star rotating at high speed. They call it “pulsar” (Pulsating star).

The first pulsar was called, among themselves, LGM (Little Green Men, little green men, don’t lack a sense of humor); today it is known as CP 1919 and also PSR 1919, although it should be called Star Bell.

Pulsar Cab
The Crab Nebula is a pulsar wind nebula associated with the 1054 supernova. Credit: Wikipedia

In the 40 years since that day, other pulsars have been detected and they are known to be neutron stars that rotate very rapidly, circling several times per second, produce regular pulsations with radio frequency wavelengths.

As the star rotates, a beam of radio waves sweeps across the Earth, the pulse then being observed, similar to light from a lighthouse.

Pulse periods are typically 1 second, but range from 1.56 milliseconds to 4.3 seconds. The periods of the pulses gradually lengthen as neutron stars lose rotational energy.

The formation of a pulsar begins when a supernova explodes, which is a star that has almost twice the mass of the Sun and a diameter of about 2,000,000 kilometers.

The mass that remains after the explosion is only subjected to the force of gravity and by compression is reduced to a body of only 20 or 30 km in diameter and at temperatures exceeding 1012 ºK.

The atoms of the star are subjected to such brutal pressure that the electrons join with the protons, generating neutrons. This is how a neutron star turns out.

The generated neutrons move at speeds close to that of light, and collide violently with each other until they stop the gravitational effect that cannot continue to compress the star, which is converted into a neutron star with such a dense mass , that a teaspoon of it would weigh billions of tons.

The neutron star that results from this process comes to life rotating with incredible speed, several hundred times per second, and creating a huge magnetic field (around 108 Teslas).

The combined effect of the great density of neutron stars and their intense magnetic field causes particles from outside that approach the star to be accelerated to extreme speeds, creating intense jets of radiation: radio waves, X-rays and gamma rays.

For some reason, still unknown, the magnetic poles of many neutron stars do not coincide with their axis of spin.

This means that the radiation jets from the magnetic poles do not always point in the same direction, but rotate with the star.

The result is that the human observer detects bursts of radiation that last a brief moment, each time the star’s magnetic pole points toward its position.

Radiation pulses are perceived with a very exact period, repeated over and over again, as if it were a powerful and extremely fast lighthouse. The chosen name “pulsating star” is well suited.

This phenomenon has inspired some scientists at the Paris observatory to use the signals emitted by pulsars as a gigantic interstellar GPS system intended to serve as a guide in space travel.

The proposed system, called PPS, instead of using a satellite system like GPS does, would use radio signals from 4 pulsars. Any spacecraft could calculate its position in space with an accuracy of about one meter, thus having a totally safe system for navigation.

In fact, the Voyager probes carry a gold disk with the position of our Sun relative to that of several nearby pulsars. A kind of cosmic map that would allow the location of the Sun to possible intelligent extraterrestrial beings.

Voyager Badge. pulsars
Voyager Badge

The top image represents the gold plate attached to the Pioneer X and XI space probes of NASA’s space exploration program. They were released in 1972 and 1973, respectively.

Carl Sagan persuaded NASA to have the probes carry this plate designed by him and Frank Drake.

The plates carry a symbolic message that would inform a possible extraterrestrial civilization that could intercept the probes, about the human being and his place of origin: the Earth.

In them they appear: to the right, the image of the probe, with the sole purpose of giving proportion to the two human figures drawn in front, one female and the other male.

On the left, a bundle of lines starting radially from the same point. That reference point is the Sun, the lines indicate the direction of the most significant pulsars close to our solar system and in each one, in a binary numbering system, the sequence of pulses of each one.

A technically advanced civilization, with knowledge of pulsars, could interpret the plates.

The diagram located in the upper left part of the plate, represents an inversion in the direction of spin of the electron, in a hydrogen atom, the most abundant element in the universe.

At the bottom is a diagram of the solar system, with the planets arranged according to their distance from the Sun and with an indication of the initial path of the Pioneers.

Recently, using the Fermi Space Telescope, which scans the entire sky every 3 hours, 16 new pulsars emitting frequency of gamma rays have been detected. Joined to the 8 similar pulsars already known, there is a map of 24 gamma ray pulsars, aligned in our Milky Way.

The vast majority of known pulsars are in the Milky Way and it is estimated that there may be as many as 100,000 pulsars in it.

The theory of how pulsars generate their radiation needs to be revised. There are many models, but no accepted theory.

5-minute VIDEO in English, interview with Jocelyn Bell.

29 minute English VIDEO, Pulsars, by Jocelyn Bell .