The FAST radio telescope has detected a new millisecond pulsar. Credit & Copyright: Pei Wang / NAOC.
A pulsar is a space object that emits powerful electromagnetic radiation in the radio range, characterized by a strict periodicity. The energy released in such pulses is a small fraction of the total energy of the pulsar. The vast majority of discovered pulsars are in Milky Way. Each pulsar emits pulses at a certain frequency, which ranges from 640 pulsations per second to one every five seconds. The periods of the main part of such objects are in the range from 0.5 to 1 second. Studies have shown that the frequency of pulses increases by one billionth of a second every day, which in turn is explained by the slowing down of rotation as a result of the energy emitted by the star.
The first pulsar was discovered by Jocelyn Bell and Anthony Hewish in June 1967. The discovery of such objects was not theoretically predicted and came as a big surprise to scientists. In the course of research, astrophysicists have found that such objects must consist of a very dense substance. Only massive bodies, such as stars, have such a gigantic density of matter. Due to the enormous density, nuclear reactions taking place inside the star turn particles into neutrons, which is why these objects are called neutron stars.
Most stars have a density slightly higher than that of water, a prominent representative here is our Sun, the main substance in which is gas. White dwarfs are equal in mass to the Sun, but have a smaller diameter, as a result of which their density is approximately 40 t/cm 3 . Pulsars are comparable in mass to the Sun, but their dimensions are very tiny - about 30,000 meters, which in turn increases their density to 190 million tons/cm 3 . With this density, the Earth would have a diameter of about 300 meters. Most likely, pulsars appear after a supernova explosion, when the shell of a star disappears, and the core shrinks into a neutron star.
The best studied pulsar to date is PSR 0531+21, which is located in the Crab Nebula. This pulsar makes 30 revolutions per second, its induction magnetic field is one thousand gauss. The energy of this neutron star is one hundred thousand times greater than the energy of our star. All energy is divided into: radio pulses (0.01%), optical pulses (1%), x-rays(10%) and low frequency radio emission / cosmic rays(rest).
The pulsar PSR B1957+20 is in a binary system. Credit & Copyright: Dr. Mark A. Garlick; Dunlap Institute for Astronomy & Astrophysics, University of Toronto. The duration of a radio pulse in a standard neutron star is a thirtieth of the time between pulsations. All pulses of a pulsar differ significantly from each other, however, the general shape of the pulse of a particular pulsar is peculiar only to it and is the same for decades. This form can tell a lot of interesting things. Most often, any impulse is divided into several subpulses, which in turn are divided into micropulses. The size of such micropulses can reach up to three hundred meters, and the energy emitted by them is equal to that of the sun.
At the moment, the pulsar is represented by scientists as a rotating neutron star, which has a powerful magnetic field that captures nuclear particles emitted from the surface of the star and then accelerates them to tremendous speeds.
Pulsars consist of a core (liquid) and a crust whose thickness is approximately one kilometer. As a result, neutron stars are more like planets than stars. Due to the speed of rotation, the pulsar has an oblate shape. During the pulse, the neutron star loses some of its energy, and as a result, its rotation slows down. Due to this deceleration, stress builds up in the crust and then the crust breaks, the star becomes a little more round - the radius decreases, and the speed of rotation (due to conservation of momentum) increases.
Distances to pulsars discovered to date range from 100 light-years to 20,000.
Predicted by theorists, in particular, academician L. A. Landau in 1932.
Star transformations
The stars are not forever. Depending on what the star was like and how its existence proceeded, the star will turn or in white dwarf, or in neutron star. Neutron star pulsar. If a star collapses, it forms black hole in space.
Black hole. These are the ideas about the "death" of stars, developed by Academician Ya. B. Zeldovich and his students. White dwarfs have been known for a very long time. For three decades, there has been controversy around this prediction. Disputes, but not searches. It was pointless to search for neutron stars using ground-based observatories: they probably do not emit visible rays, and the rays of other parts of the electromagnetic spectrum are powerless to overcome the armored shield of the earth's atmosphere. universe from outer space
The search began only when it became possible to look at universe from outer space. At the end of 1967, astronomers made sensational discovery. At a certain point in the sky, it suddenly lit up and went out after hundredths of a second point source of radio beams. About a second later, the flash was repeated. These repetitions followed each other with the precision of a ship's chronometer. It seemed that through the black night of the Universe a distant lighthouse was winking at the observers. Then quite a lot of such lighthouses became known. Turned out they were different. periodicity of ray pulses, radiation composition. Majority pulsars- as these newly discovered stars were called - had a total duration of a period from a quarter of a second to four seconds. Today, the number of pulsars known to science is about 2000. And the possibilities of new discoveries are far from being exhausted. Pulsars are neutron stars. It is difficult to imagine any other mechanism, with iron precision, igniting and extinguishing the flash of a pulsar than the rotation of the star itself. On one side of the star, a source of radiation is "installed", and with each revolution around its axis, the ejected beam falls for a moment on our Earth. But what kind of stars are able to rotate at a speed of several revolutions per second? Neutron - and no others. Ours, for example, makes one revolution in almost 25 days; speed up and centrifugal forces simply tear it apart, smash it to pieces.
Sunrise. However, on neutron stars, the matter is compressed to a density unimaginable in normal conditions. Each cubic centimeter of the matter of a neutron star under terrestrial conditions would weigh from 100 thousand to 10 billion tons! Fatal compression sharply reduces the diameter of the star. If in their radiant life stars have diameters of hundreds of thousands and millions of kilometers, then the radii of neutron stars rarely exceed 20-30 kilometers. Such a small "flywheel", and also firmly riveted by the forces of universal gravitation, can be untwisted at a speed of several revolutions per second - it will not fall apart. A neutron star must spin very fast. Have you seen how the ballerina spins, standing up on one toe and holding her hands tightly to her body? But then she spread her arms - her rotation immediately slowed down. The physicist will say: the moment of inertia has increased. In a neutron star, as its radius decreases, the moment of inertia, on the contrary, decreases, it sort of “presses its hands” closer and closer to the body. At the same time, its rotation speed increases rapidly. And when the diameter of the star decreases to the value indicated above, the number of its revolutions around the axis should be exactly the same as the “pulsar effect” provides. Physicists would love to be on the surface of a neutron star and perform some experiments. After all, conditions must exist there, similar to which are nowhere else: a fantastic value of the gravitational field and a fantastic strength of the magnetic field. According to scientists, if a contracting star had a magnetic field of a very modest magnitude - one oersted (the Earth's magnetic field, dutifully turning the blue compass needle to the north, is equal to about half an oersted), then a neutron star's field strength can reach 100 million and trillion oersteds ! In the 1920s, during his work in the laboratory of E. Rutherford, the famous Soviet physicist Academician P. L. Kapitsa put the experience of obtaining superstrong magnetic fields. He managed to obtain a magnetic field of unprecedented strength in the volume of two cubic centimeters - up to 320 thousand oersteds. Of course, this record has now been surpassed. Through the most complicated tricks, having brought down a whole electric niagara on a single coil of a solenoid - a power of a million kilowatts - and exploding an auxiliary powder charge at the same time, they manage to obtain a magnetic field strength of up to 25 million oersteds. There is this field several millionths of a second. And on a neutron star, a constant field thousands of times greater is possible! The structure of a neutron star
Soviet scientist academician V. L. Ginzburg painted a pretty detailed picture structures of a neutron star. Its surface layers should be in a solid state, and already at a depth of a kilometer, with an increase in temperature, the solid crust should be replaced by a neutron liquid containing some admixture of protons and electrons, a liquid of amazing properties, superfluid and superconducting.
The structure of a neutron star pulsar. Under terrestrial conditions, the only example of a superfluid liquid is the behavior of the so-called helium-2, liquid helium, at temperatures close to absolute zero. Helium-2 is able to instantly flow out of the vessel through the smallest hole, is able, neglecting the force of gravity, to climb up the wall of the test tube. Superconductivity is also known under terrestrial conditions only at very low temperatures. Like superfluidity, it is a manifestation in our conditions of the laws of the world of elementary particles. In the very center of a neutron star, according to Academician VL Ginzburg, there may be a non-superfluid and non-superconducting core. Two giant fields - gravitational and magnetic - create a kind of crown around the neutron star. The axis of rotation of the star does not coincide with the magnetic axis, and this causes the "pulsar effect". If we imagine that the magnetic pole of the Earth, (more: Astronomers have studied the sky since time immemorial. However, only with a significant leap in the development of technology, scientists were able to discover objects that previous generations of astronomers did not even have in their imagination. Some of them are quasars and pulsars.
Despite the enormous distances to these objects, scientists managed to study some of their properties. But despite this, they still hide a lot of unsolved secrets.
What are pulsars and quasars
The pulsar, as it turned out, is a neutron star. Its pioneers were E. Huish and his graduate student D. Bell. They were able to detect pulses, which are streams of radiation of a narrow direction, which become visible after certain time intervals, since this effect occurs due to the rotation of neutron stars.
A significant compaction of the star's magnetic field and its very density occurs during its compression. It can be reduced to a size of several tens of kilometers, and at such moments the rotation occurs at an incredibly high speed. This speed in some cases reaches thousandths of a second. This is where electromagnetic radiation waves come from.
Quasars and pulsars can be called the most unusual and mysterious discoveries of astronomy. The surface of a neutron star (pulsar) has less pressure than its center, for this reason neutrons decay into electrons and protons. Electrons are accelerated to incredible speeds due to the presence of a powerful magnetic field. Sometimes this speed reaches the speed of light, resulting in the release of electrons from magnetic poles stars. Two narrow beams of electromagnetic waves - this is exactly what the movement of charged particles looks like. That is, electrons emit radiation in the direction of their direction.
Continuing the enumeration of unusual phenomena associated with neutron stars, it should be noted their outer layer. In this sphere, there are spaces in which the core cannot be destroyed due to insufficient density of the substance. The consequence of this is that the densest crust is covered by the formation of a crystalline structure. As a result, stress accumulates and at a certain moment this dense surface begins to crack. Scientists call this phenomenon "starquake".
Pulsars and quasars remain completely unexplored. But if amazing studies have told us about pulsars or the so-called. neutron stars have a lot of new things, quasars keep astronomers in the suspense of the unknown.
The world first learned about quasars in 1960. The discovery said that these are objects with small angular dimensions, which are characterized by high luminosity, and by class they belong to extragalactic objects. Because they have a rather small angular size, for many years it was thought that they were just stars.
The exact number of discovered quasars is unknown, but in 2005, studies were carried out, in which there were 195 thousand quasars. So far, nothing available to explain about them is known. There are many assumptions, but none of them has any evidence.
Astronomers have found out only that for a time interval of less than 24 hours, their brightness marks sufficient variability. According to these data, one can note their relatively small size of the radiation region, which is comparable to the size solar system. Found quasars exist at a distance of up to 10 billion light years. We managed to see them because of their the highest level luminosity.
The closest such object to our planet is located approximately at around 2 billion light years. Perhaps future research and the Newest technologies will provide humanity with new knowledge about the white spots of outer space.
Supernova remnant Korma-A, at the center of which is a neutron star
Neutron stars are the remnants of massive stars that have reached the end of their evolutionary path in time and space.
These interesting objects are born from once massive giants that are four to eight times the size of our Sun. It happens in a supernova explosion.
After such an explosion, the outer layers are ejected into space, the core remains, but it is no longer able to support nuclear fusion. Without external pressure from the overlying layers, it collapses and shrinks catastrophically.
Despite their small diameter - about 20 km, neutron stars boast 1.5 times the mass of our Sun. Thus, they are incredibly dense.
A small spoonful of star matter on Earth would weigh about a hundred million tons. In it, protons and electrons are combined into neutrons - this process is called neutronization.
Compound
Their composition is unknown; it is assumed that they may consist of a superfluid neutron liquid. They have an extremely strong gravitational pull, much stronger than that of the Earth and even the Sun. This gravitational force is especially impressive because it has a small size.
All of them rotate around an axis. During compression, the angular momentum of rotation is preserved, and due to a decrease in size, the rotation speed increases.
Due to the huge speed of rotation, the outer surface, which is a solid “crust”, periodically cracks and “starquakes” occur, which slow down the rotation speed and dump “excess” energy into space.
The overwhelming pressure that exists in the core may be similar to that which existed at the moment big bang, but unfortunately, it cannot be simulated on Earth. Therefore, these objects are ideal natural laboratories where we can observe energies inaccessible on Earth.
radio pulsars
Radio pulsars were discovered in late 1967 by graduate student Jocelyn Bell Burnell as radio sources that pulsate at a constant frequency.
The radiation emitted by the star is visible as a pulsating radiation source or pulsar.
Schematic representation of the rotation of a neutron star
Radio pulsars (or simply a pulsar) are spinning neutron stars whose jets of particles move at nearly the speed of light, like a spinning beacon beam.
After continuous rotation, for several million years, pulsars lose their energy and become normal neutron stars. Only about 1,000 pulsars are known today, although there may be hundreds of them in the galaxy.
Radio pulsar in the Crab Nebula
Some neutron stars emit X-rays. The famous Crab Nebula is a good example of such an object, formed during a supernova explosion. This supernova explosion was observed in 1054 AD.
Pulsar wind, Chandra video
A radio pulsar in the Crab Nebula photographed by the Hubble Space Telescope through a 547nm filter (green light) from August 7, 2000 to April 17, 2001.
magnetars
Neutron stars have a magnetic field millions of times stronger than the strongest magnetic field produced on Earth. They are also known as magnetars.
Planets near neutron stars
So far, four are known to have planets. When it is in a binary system, it is possible to measure its mass. Of these binary systems in the radio or X-ray range, the measured masses of neutron stars were about 1.4 times the mass of the Sun.
Double systems
A completely different type of pulsar is seen in some X-ray binaries. In these cases, a neutron star and an ordinary one form a binary system. A strong gravitational field pulls material from an ordinary star. Material falling on it during the accretion process heats up so much that it produces X-rays. Pulsed X-rays are visible when hot spots on a spinning pulsar pass through the line of sight from Earth.
For binary systems containing an unknown object, this information helps to distinguish whether it is a neutron star, or, for example, a black hole, because black holes are much more massive.
A neutron star is a very strange object with a diameter of 20 kilometers, this body has a mass comparable to that of the sun, one gram of a neutron star would weigh more than 500 million tons under terrestrial conditions! What are these objects? They will be discussed in the article.
Composition of neutron stars
The composition of these objects (for obvious reasons) has been studied so far only in theory and mathematical calculations. However, much is already known. As the name implies, they consist mainly of densely packed neutrons.
The atmosphere of a neutron star is only a few centimeters thick, but all of its thermal radiation is concentrated in it. Behind the atmosphere is a crust composed of densely packed ions and electrons. In the middle is the nucleus, which is made up of neutrons. Closer to the center, the maximum density of matter is reached, which is 15 times greater than the nuclear one. Neutron stars are the densest objects in the universe. If you try to further increase the density of matter, it will collapse into a black hole, or a quark star will form.
A magnetic field
Neutron stars have rotation speeds up to 1000 revolutions per second. In this case, electrically conductive plasma and nuclear matter generate magnetic fields of gigantic magnitudes. For example, the magnetic field of the Earth is 1 gauss, a neutron star is 10,000,000,000,000 gauss. The strongest field created by man will be billions of times weaker.
Pulsars
This is a generic name for all neutron stars. Pulsars have a well-defined rotation period that does not change for a very long time. Due to this property, they are called "beacons of the universe."
Particles fly out through the poles in a narrow stream at very high speeds, becoming a source of radio emission. Due to the mismatch of the axes of rotation, the direction of the flow is constantly changing, creating a beacon effect. And, like every lighthouse, pulsars have their own signal frequency, by which it can be identified.
Virtually all discovered neutron stars exist in double X-ray systems or as single pulsars.
Exoplanets near neutron stars
The first exoplanet was discovered during the study of a radio pulsar. Since neutron stars are very stable, it is possible to very accurately track nearby planets with masses much smaller than that of Jupiter.
It was very easy to find a planetary system near the pulsar PSR 1257 + 12, 1000 light years away from the Sun. Near the star are three planets with masses of 0.2, 4.3 and 3.6 Earth masses with periods of revolution of 25, 67 and 98 days. Later, another planet was found with the mass of Saturn and a period of revolution of 170 years. A pulsar with a planet slightly more massive than Jupiter is also known.
In fact, it is paradoxical that there are planets near the pulsar. A neutron star is born as a result of a supernova explosion, and it loses most of its mass. The rest no longer has enough gravity to hold the satellites. Probably, the found planets were formed after the cataclysm.
Research
The number of known neutron stars is about 1200. Of these, 1000 are considered radio pulsars, and the rest are identified as X-ray sources. It is impossible to study these objects by sending any apparatus to them. In the Pioneer ships, messages were sent to sentient beings. And the location of our solar system is indicated precisely with an orientation to the pulsars closest to the Earth. From the Sun, the lines show the directions to these pulsars and the distances to them. And the discontinuity of the line indicates the period of their circulation.
Our nearest neutron neighbor is 450 light years away. This is a binary system - a neutron star and white dwarf, the period of its pulsation is 5.75 milliseconds.
It is hardly possible to be close to a neutron star and stay alive. One can only fantasize about this topic. And how can one imagine the magnitudes of temperature, magnetic field and pressure that go beyond the boundaries of reason? But pulsars will still help us in the development of interstellar space. Any, even the most distant galactic journey, will not be disastrous if stable beacons, visible in all corners of the Universe, work.
