When was the first pulsar discovered? Pulsar

The content of the article

PULSAR, an astronomical object that emits powerful, strictly periodic pulses of electromagnetic radiation, mainly in the radio range. The energy emitted in pulses is only a small fraction of its total energy. Almost all known pulsars are located in our Galaxy. Each pulsar has its own pulsation period; they range from 640 pulses per second to one pulse every 5 s. The periods of most pulsars range from 0.5 to 1 s. Accurate measurements show that typically the period between pulses increases by one billionth of a second per day; this is exactly what should be expected when the rotation of a star slows down, losing energy in the process of radiation.

The discovery of pulsars in 1967 was a big surprise, since such phenomena had not been predicted before. It soon became clear that this phenomenon was associated either with radial pulsations or with the rotation of stars. But neither ordinary stars nor even white dwarfs can naturally pulsate at such a high frequency. They can't rotate that fast either - the centrifugal force will tear them apart. This can only be a very dense body, consisting of a substance predicted by L.D. Landau and R. Oppenheimer in 1939. In this substance, the nuclei of atoms are pressed closely together. Only the gigantic force of gravity, which is possessed only by very massive bodies such as stars, can compress matter to such an extent. At enormous densities, nuclear reactions convert most particles into neutrons, which is why such bodies are called neutron stars.

The powerful pulsar PSR 0531+21, located in the Crab Nebula, has been studied in the most detail. This neutron star makes 30 revolutions per second and its rotating magnetic field with an induction of 10 12 G “works” like a giant accelerator of charged particles, giving them energy up to 10 20 eV, which is 100 million times more than in the most powerful accelerator on Earth . The total radiation power of this pulsar is 100,000 times higher than that of the Sun. Less than 0.01% of this power comes from radio pulses, approx. 1% is emitted as optical pulses and approx. 10% – in the form of x-rays. The remaining power probably comes from low-frequency radio emission and high-energy elementary particles - cosmic rays.

The duration of a radio pulse in a typical pulsar is only 3% of the time interval between pulses. Consistently arriving pulses are very different from each other, but the average (generalized) shape of the pulse is different for each pulsar and is preserved for many years. Analysis of the pulse shape showed many interesting things. Typically, each pulse consists of several subpulses that "drift" along the average pulse profile. For some pulsars, the shape of the average profile can suddenly change, moving from one stable shape to another; each of them persists for many hundreds of pulses. Sometimes the pulse power drops and then recovers. This “freezing” can last from a few seconds to several days.

Upon detailed analysis, subpulses reveal a fine structure: each pulse consists of hundreds of micropulses. The emission region of such a micropulse on the surface of the pulsar is less than 300 m in size. In this case, the emission power is comparable to that of the sun.

The mechanism of action of a pulsar.

So far, there is only an approximate picture of the action of a pulsar. It is based on a rotating neutron star with a powerful magnetic field. The rotating magnetic field captures nuclear particles escaping from the surface of the star and accelerates them to very high energies. These particles emit electromagnetic quanta in the direction of their movement, forming rotating beams of radiation. When the beam is directed towards the Earth, we receive a radiation pulse. It is not entirely clear why these impulses have such a clear structure; perhaps only small areas of the neutron star's surface eject particles into the magnetic field. Particles of maximum energy cannot be accelerated individually; they appear to form beams containing perhaps 10 12 particles, which are accelerated as a single particle. This also helps to understand the sharp boundaries of the pulses, each of which is probably associated with a separate particle beam.

Opening.

The first pulsar was discovered by accident in 1967 by Cambridge University astronomers J. Bell and E. Hewish. While testing a new radio telescope with equipment for recording rapidly varying cosmic radiation, they unexpectedly discovered chains of pulses arriving with a clear periodicity. The first pulsar had a period of 1.3373 s and a pulse duration of 0.037 s. Scientists named it CP 1919, which means “Cambridge Pulsar”, which has a right ascension of 19 hours 19 minutes. By 1997, more than 700 pulsars had been discovered through the efforts of all radio astronomers around the world. Pulsar research is carried out using the largest telescopes, since high sensitivity is required to detect short pulses.

The structure of a pulsar.

Neutron stars have a liquid core and a solid crust approx. 1 km. Therefore, the structure of pulsars is more reminiscent of planets than stars. Rapid rotation leads to some oblateness of the pulsar. The radiation carries away energy and angular momentum, which causes rotation deceleration. However, the hard crust prevents the pulsar from gradually becoming spherical. As the rotation slows down, stress accumulates in the crust and finally it breaks: the star abruptly becomes slightly more spherical, its equatorial radius decreases (by only 0.01 mm), and the rotation speed (as a result of conservation of momentum) increases slightly. Then again there follows a gradual slowdown in rotation and a new “starquake”, leading to a jump in the rotation speed. Thus, by studying changes in the periods of pulsars, it is possible to learn a lot about the physics of the solid crust of neutron stars. Tectonic processes occur in it, like in the crust of planets, and, possibly, their own microscopic mountains are formed.

Double pulsars.

The pulsar PSR 1913+16 was the first to be discovered in a binary system. Its orbit is very elongated, so it comes very close to its neighbor, which can only be a compact object - a white dwarf, a neutron star or a black hole. The high stability of pulsar pulses makes it possible to very accurately study its orbital motion using the Doppler shift of their arrival frequency. Therefore, the binary pulsar was used to test the conclusions of general relativity, according to which the major axis of its orbit should rotate about 4° per year; This is exactly what is observed.

Several dozen double pulsars are known. Discovered in 1988, the pulsar in the binary system rotates 622 times per second. Its neighbor, with only 2% the mass of the Sun, was probably once a normal star. But the pulsar made it “lose weight”, pulling part of the mass onto itself, and part of it by evaporating and “blowing away” into outer space. Soon the pulsar will completely destroy its neighbor and will be left alone. Apparently, this can explain the fact that the overwhelming majority of pulsars are single, while at least half of normal stars are included in binary and more complex systems.

Distance to pulsars.

Passing from the pulsar to Earth, radio waves overcome the interstellar medium; interacting with free electrons in it, they slow down - the longer the wavelength, the stronger the slowdown. By measuring the delay of a long-wavelength pulse relative to a short-wavelength one (which reaches several minutes) and knowing the density of the interstellar medium, it is possible to determine the distance to the pulsar.

As observations show, on average in the interstellar medium there are approx. 0.03 electrons per cubic centimeter. Based on this value, the distances to pulsars average several hundred light years. years. But there are also more distant objects: the double pulsar PSR 1913+16 mentioned above is 18,000 light years away. years.

The FAST radio telescope has discovered a new millisecond pulsar. Credit: Pei Wang/NAOC.

A pulsar is a space object that emits powerful electromagnetic radiation in the radio range, characterized by 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 located in the 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 range from 0.5 to 1 second. Research has shown that the periodicity of the pulses increases by one billionth of a second every day, which in turn is explained by the slowdown in rotation due to the energy emitted by the star.

The first pulsar was discovered by Jocelyn Bell and Anthony Hewish in June 1967. The discovery of this kind of object was not predicted theoretically and came as a big surprise to scientists. During research, astrophysicists discovered that such objects must consist of very dense matter. 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 transform particles into neutrons, which is why these objects are called neutron stars.

Most stars have a density slightly greater than that of water; a prominent example here is our Sun, the main substance of 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 miniature - approximately 30,000 meters, which in turn increases their density to 190 million tons / cm 3. At this density, the Earth would have a diameter of approximately 300 meters. Most likely, pulsars appear after a supernova explosion, when the shell of the star disappears and the core collapses 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 magnetic field induction 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/cosmic rays (the rest).

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, but the general shape of a pulse of a particular pulsar is unique to it and is the same for decades. This form can tell you 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 they emit is equal to solar energy.

At the moment, scientists think of a pulsar as a rotating neutron star with a powerful magnetic field that captures nuclear particles escaping from the surface of the star and then accelerates them to colossal 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. Because of this deceleration, tension builds up in the crust and then the crust breaks, the star becomes a little more round - the radius decreases, and the rotation speed (due to conservation of torque) increases.

Distances to pulsars discovered to date range from 100 light years to 20 thousand.

A pulsar (pink) can be seen at the center of the M82 galaxy.

Explore pulsars and neutron stars The Universe: description and characteristics with photos and videos, structure, rotation, density, composition, mass, temperature, search.

Pulsars

Pulsars They are spherical compact objects, the dimensions of which do not extend beyond the boundaries of a large city. The surprising thing is that with such a volume they exceed the solar mass in terms of mass. They are used to study extreme states of matter, detect planets beyond our system, and measure cosmic distances. In addition, they helped find gravitational waves that indicate energetic events, such as supermassive collisions. First discovered in 1967.

What is a pulsar?

If you look for a pulsar in the sky, it appears to be an ordinary twinkling star following a certain rhythm. In fact, their light does not flicker or pulsate, and they do not appear as stars.

The pulsar produces two persistent, narrow beams of light in opposite directions. The flickering effect is created because they rotate (beacon principle). At this moment, the beam hits the Earth and then turns again. Why is this happening? The fact is that the light beam of a pulsar is usually not aligned with its rotation axis.

If the blinking is generated by rotation, then the speed of the pulses reflects the speed at which the pulsar is spinning. A total of 2,000 pulsars were found, most of which rotate once per second. But there are approximately 200 objects that manage to make a hundred revolutions in the same time. The fastest ones are called millisecond ones, because their number of revolutions per second is equal to 700.

Pulsars cannot be considered stars, at least not “living”. Rather, they are neutron stars, formed after a massive star runs out of fuel and collapses. As a result, a strong explosion is created - a supernova, and the remaining dense material is transformed into a neutron star.

The diameter of pulsars in the Universe reaches 20-24 km, and their mass is twice that of the Sun. To give you an idea, a piece of such an object the size of a sugar cube will weigh 1 billion tons. That is, something as heavy as Mount Everest fits in your hand! True, there is an even denser object - a black hole. The most massive reaches 2.04 solar masses.

Pulsars have a strong magnetic field, which is 100 million to 1 quadrillion times stronger than Earth's. For a neutron star to start emitting light like a pulsar, it must have the right ratio of magnetic field strength and rotation speed. It happens that a beam of radio waves may not pass through the field of view of a ground-based telescope and remain invisible.

Radio pulsars

Astrophysicist Anton Biryukov on the physics of neutron stars, slowing down rotation and the discovery of gravitational waves:

Why do pulsars rotate?

The slowness of a pulsar is one rotation per second. The fastest ones accelerate to hundreds of revolutions per second and are called millisecond. The rotation process occurs because the stars from which they were formed also rotated. But to get to that speed, you need an additional source.

Researchers believe that millisecond pulsars were formed by stealing energy from a neighbor. You may notice the presence of a foreign substance that increases the rotation speed. And that's not a good thing for the injured companion, which could one day be completely consumed by the pulsar. Such systems are called black widows (after a dangerous type of spider).

Pulsars are capable of emitting light in several wavelengths (from radio to gamma rays). But how do they do it? Scientists cannot yet find an exact answer. It is believed that a separate mechanism is responsible for each wavelength. Beacon-like beams are made of radio waves. They are bright and narrow and resemble coherent light, where the particles form a focused beam.

The faster the rotation, the weaker the magnetic field. But the rotation speed is enough for them to emit rays as bright as slow ones.

During rotation, the magnetic field creates an electric field, which can bring charged particles into a mobile state (electric current). The area above the surface where the magnetic field dominates is called the magnetosphere. Here, charged particles are accelerated to incredibly high speeds due to a strong electric field. Each time they accelerate, they emit light. It is displayed in optical and x-ray ranges.

What about gamma rays? Research suggests that their source should be sought elsewhere near the pulsar. And they will resemble a fan.

Search for pulsars

Radio telescopes remain the main method for searching for pulsars in space. They are small and faint compared to other objects, so you have to scan the entire sky and gradually these objects fall into the lens. Most were found using the Parkes Observatory in Australia. Much new data will be available from the Square Kilometer Array Antenna (SKA) starting in 2018.

In 2008, the GLAST telescope was launched, which found 2050 gamma-ray emitting pulsars, of which 93 were millisecond. This telescope is incredibly useful because it scans the entire sky, while others highlight only small areas along the plane.

Finding different wavelengths can be challenging. The fact is that radio waves are incredibly powerful, but they may simply not fall into the telescope lens. But gamma radiation spreads across more of the sky, but is inferior in brightness.

Scientists now know of the existence of 2,300 pulsars, found through radio waves and 160 through gamma rays. There are also 240 millisecond pulsars, of which 60 produce gamma rays.

Use of pulsars

Pulsars are not just amazing space objects, but also useful tools. The emitted light can tell a lot about internal processes. That is, researchers are able to understand the physics of neutron stars. These objects have such high pressure that the behavior of matter differs from the usual. The strange content of neutron stars is called “nuclear paste.”

Pulsars bring many benefits due to the precision of their pulses. Scientists know specific objects and perceive them as cosmic clocks. This is how speculation about the presence of other planets began to appear. In fact, the first exoplanet found was orbiting a pulsar.

Don’t forget that pulsars continue to move while they “blink”, which means they can be used to measure cosmic distances. They were also involved in testing Einstein's theory of relativity, like moments with gravity. But the regularity of the pulsation can be disrupted by gravitational waves. This was noticed in February 2016.

Pulsar Cemeteries

Gradually, all pulsars slow down. The radiation is powered by the magnetic field created by the rotation. As a result, it also loses its power and stops sending beams. Scientists have drawn a special line where gamma rays can still be detected in front of radio waves. As soon as the pulsar falls below, it is written off in the pulsar graveyard.

If a pulsar was formed from the remnants of a supernova, then it has a huge energy reserve and a fast rotation speed. Examples include the young object PSR B0531+21. It can remain in this phase for several hundred thousand years, after which it will begin to lose speed. Middle-aged pulsars make up the majority of the population and produce only radio waves.

However, a pulsar can extend its life if there is a satellite nearby. Then it will pull out its material and increase the rotation speed. Such changes can occur at any time, which is why the pulsar is capable of rebirth. Such a contact is called a low-mass X-ray binary system. The oldest pulsars are millisecond ones. Some reach billions of years of age.

Neutron stars

Neutron stars- rather mysterious objects, exceeding the solar mass by 1.4 times. They are born after the explosion of larger stars. Let's get to know these formations better.

When a star 4-8 times more massive than the Sun explodes, a high-density core remains and continues to collapse. Gravity pushes so hard on a material that it causes protons and electrons to fuse together to become neutrons. This is how a high-density neutron star is born.

These massive objects can reach a diameter of only 20 km. To give you an idea of ​​density, just one scoop of neutron star material would weigh a billion tons. The gravity on such an object is 2 billion times stronger than Earth's, and the power is enough for gravitational lensing, allowing scientists to view the back of the star.

The shock from the explosion leaves a pulse that causes the neutron star to spin, reaching several revolutions per second. Although they can accelerate up to 43,000 times per minute.

Boundary layers near compact objects

Astrophysicist Valery Suleymanov on the emergence of accretion disks, stellar wind and matter around neutron stars:

The interior of neutron stars

Astrophysicist Sergei Popov on extreme states of matter, the composition of neutron stars and methods for studying the interior:

When a neutron star is part of a binary system where a supernova has exploded, the picture is even more impressive. If the second star is inferior in mass to the Sun, then it pulls the mass of the companion into the “Roche lobe”. This is a spherical cloud of material orbiting a neutron star. If the satellite was 10 times larger than the solar mass, then the mass transfer is also adjusted, but not so stable. The material flows along the magnetic poles, heats up and creates X-ray pulsations.

By 2010, 1,800 pulsars had been found using radio detection and 70 using gamma rays. Some specimens even had planets.

Types of Neutron Stars

Some representatives of neutron stars have jets of material flowing almost at the speed of light. When they fly past us, they flash like the light of a beacon. Because of this, they are called pulsars.

When X-ray pulsars sample material from their more massive neighbors, it comes into contact with a magnetic field and produces powerful beams visible in the radio, X-ray, gamma-ray and optical spectrum. Since the source is located in the companion, they are called accretion pulsars.

Rotating pulsars in the sky are driven by the rotation of stars because high-energy electrons interact with the pulsar's magnetic field above the poles. As the material inside the pulsar's magnetosphere accelerates, it causes it to produce gamma rays. The release of energy slows down the rotation.

The magnetic fields of magnetars are 1000 times stronger than those of neutron stars. Because of this, the star is forced to rotate much longer.

Evolution of neutron stars

Astrophysicist Sergei Popov on the birth, radiation and diversity of neutron stars:

Shock waves near compact objects

Astrophysicist Valery Suleymanov about neutron stars, gravity on spacecraft and the Newtonian limit:

Compact stars

Astrophysicist Alexander Potekhin about white dwarfs, the density paradox and neutron stars:

It was too unusual. Its main feature, for which it received its name, is periodic bursts of radiation, with a strictly defined period. A sort of radio beacon in space. At first it was assumed that it was a pulsating star that changes its size - such things have been known for a long time. And it was discovered by Jocelyn Bell, a graduate student at Cambridge University, using a radio telescope.
Interestingly, the first pulsar was named LGM-1, which means “little green men” in English. However, it gradually became clear that pulsars are natural objects of our Universe, and quite a lot of them have already been discovered—nearly two thousand. The closest one to us is 390 light years away.

So what is a pulsar? This is a very small but very dense neutron star. Such stars are formed after the explosion of a giant star, much larger than our Sun, a dwarf. As a result of the cessation of the thermonuclear reaction, the matter of the star is compressed into a very dense object - this is called collapse, and during this, electrons - negative particles, are pressed into the nuclei and combine with protons - positive particles. In the end, all the matter of the star turns out to consist of only neutrons, which gives a huge density - neutrons have no charge and can be located very closely, almost on top of each other.

So, all the matter of a huge star fits into one neutron star, which is only a few kilometers in size. Its density is such that a teaspoon of the substance of this star weighs a billion tons.

The first pulsar, discovered by Jocelyn Bell, sent electromagnetic bursts into space with a frequency of 1.33733 seconds. Other pulsars have different periods, but the frequency of their radiation remains constant, although it can lie in different ranges - from radio waves to X-rays. Why is this happening?

The fact is that a neutron star the size of a city rotates very quickly. It can make a thousand revolutions around its axis in one second. Moreover, it has a very powerful magnetic field. Protons and electrons move along the force fields of this field, and near the poles, where the magnetic field is especially strong and where these particles reach very high speeds, they release energy quanta in various ranges. It turns out like a natural synchrophasotron - a particle accelerator, only in nature. This is how two regions are formed on the surface of the star, from which very powerful radiation comes.

Place a flashlight on the table and start rotating it. The beam of light rotates with it, illuminating everything in a circle. Likewise, a pulsar, when rotating, sends out its radiation with the period of its rotation, and it is very fast. When the Earth is in the path of the beam, we see a burst of radio emission. Moreover, this ray comes from a spot on a star, the size of which is only 250 meters! What power is this if we can detect a signal hundreds and thousands of light years away! The magnetic poles and rotation axis of the pulsar do not coincide, so the emitting spots rotate and do not stand still.

When the first pulsar was discovered in June 1967, it was taken seriously as an artificial space object. It was too unusual. Its main feature, for which it received its name, is periodic bursts of radiation, with a strictly defined period. A sort of radio beacon in space. At first it was assumed that it was a pulsating star that changes its size - such things have been known for a long time. And it was discovered by Jocelyn Bell, a graduate student at Cambridge University, using a radio telescope.

Interestingly, the first pulsar was named LGM-1, which means “little green men” in English. However, it gradually became clear that pulsars are natural objects of our Universe, and quite a lot of them have already been discovered—nearly two thousand. The closest one to us is 390 light years away.

So what is a pulsar? This is a very small but very dense neutron star. Such stars are formed after the explosion of a giant star, much larger than our Sun, a dwarf. As a result of the cessation of the thermonuclear reaction, the matter of the star is compressed into a very dense object - this is called collapse, and during this, electrons - negative particles, are pressed into the nuclei and combine with protons - positive particles. In the end, all the matter of the star turns out to consist of only neutrons, which gives a huge density - neutrons have no charge and can be located very closely, almost on top of each other.

So, all the matter of a huge star fits into one neutron star, which is only a few kilometers in size. Its density is such that a teaspoon of this star's substance weighs a billion tons.

The first pulsar, discovered by Jocelyn Bell, sent electromagnetic bursts into space with a frequency of 1.33733 seconds. Other pulsars have different periods, but the frequency of their radiation remains constant, although it can lie in different ranges - from radio waves to X-rays. Why is this happening?

The fact is that a neutron star the size of a city rotates very quickly. It can make a thousand revolutions around its axis in one second. Moreover, it has a very powerful magnetic field. Protons and electrons move along the force fields of this field, and near the poles, where the magnetic field is especially strong and where these particles reach very high speeds, they release energy quanta in various ranges. It turns out like a natural synchrophasotron - a particle accelerator, only in nature. This is how two regions are formed on the surface of the star, from which very powerful radiation comes.

Place a flashlight on the table and start rotating it. The beam of light rotates with it, illuminating everything in a circle. Likewise, a pulsar, when rotating, sends out its radiation with the period of its rotation, and it is very fast. When the Earth is in the path of the beam, we see a burst of radio emission. Moreover, this ray comes from a spot on a star, the size of which is only 250 meters! What power is this if we can detect a signal hundreds and thousands of light years away! The magnetic poles and rotation axis of the pulsar do not coincide, so the emitting spots rotate and do not stand still.

You can't even see a pulsar through a telescope.. You can detect the nebula surrounding it - the remains of gas from the exploding star that gave birth to the pulsar. This nebula is illuminated by the pulsar itself, but not by ordinary light. The glow occurs due to moving protons and electrons at near-light speeds. The pulsar itself is visible only in the radio range. Only by pointing a radio telescope at it can you detect it. Although the youngest pulsars have the ability to emit in the optical range, and this was proven using very sensitive equipment, over time this ability disappears.

Many unusual objects with unique, amazing properties have already been discovered in space. These include black holes, pulsating stars, and black holes... Pulsars, and in particular neutron stars, are among the most unusual. The phenomena that occur on them cannot be reproduced in the laboratory, so all the most interesting discoveries related to them are yet to come.