What are pulsars and quasars? Space, pulsars and neutron stars. A discovery that does not fit into the framework of modern theories

The remnant of the supernova Corma-A, which has a neutron star at its center

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 larger than our Sun. This happens in a supernova explosion.

After such an explosion, the outer layers are thrown 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 contracts catastrophically.

Despite their small diameter - about 20 km, neutron stars can boast 1.5 times more mass than our Sun. Thus, they are incredibly dense.

A small spoonful of star matter on Earth would weigh about one hundred million tons. In it, protons and electrons combine to form neutrons - a process 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 greater than that of the Earth or even the Sun. This gravitational force is especially impressive because it is small in size.
They all rotate around an axis. During compression, the angular momentum of rotation is maintained, and due to the reduction in size, the rotation speed increases.

Due to the enormous 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 staggering pressures that exist in the core may be similar to those that existed at the time of the big bang, but unfortunately they cannot be simulated on Earth. Therefore, these objects are ideal natural laboratories where we can observe energies unavailable on Earth.

Radio pulsars

Radio ulsars 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 pulsars) are rotating neutron stars whose particle jets move almost at the speed of light, like a rotating lighthouse beam.

After spinning continuously 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.

Wind from Pulsar, Chandra telescope 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 around neutron stars

Today we know that four have planets. When it is in a binary system, it is possible to measure its mass. Of these radio or X-ray binaries, the measured masses of neutron stars were about 1.4 times the mass of the Sun.

Dual systems

A completely different type of pulsar is seen in some X-ray binaries. In these cases, the neutron star and the ordinary one form a binary system. A strong gravitational field pulls material from an ordinary star. The material falling onto it during the accretion process is heated so much that it produces X-rays. Pulsed X-rays are visible when hot spots on the 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.

The existence of radio sources in space has been known for quite some time. But such an object emitting fast pulses was detected for the first time. They appeared like clockwork, once a second. At first they thought that the signal came from an orbiting satellite, but this idea was quickly discarded. After several more similar objects were found, they were called pulsars due to their rapidly pulsating nature.

Bright pulsars have been discovered at almost every wavelength of light. Some can actually be seen. Most people tend to confuse pulsars with quasars. But these two objects are completely different. Quasars are objects that produce enormous amounts of energy. Most likely, they arose as a result of a huge black hole at the center of a young galaxy. But a pulsar is something completely different.

Pulsars: The Beacon Factor

A pulsar is essentially a rapidly rotating neutron star. A neutron star is the highly compacted core of a dead star left over from a supernova explosion. This neutron star has a powerful magnetic field. This magnetic field is about one trillion times stronger than the Earth's magnetic field. The magnetic field causes the neutron star to emit strong radio waves and radioactive particles from its north and south poles. These particles can include various radiations, including visible light.

Graphical model of a pulsar

Pulsars that emit powerful gamma rays are known as gamma ray pulsars. If a neutron star has its pole facing the Earth, then we can see radio waves every time one of the poles comes into our view. This effect is very similar to the lighthouse effect. To a stationary observer, it seems that the light of the rotating beacon is constantly blinking, then disappearing, then appearing again. In the same way, a pulsar appears to us to blink as it rotates its poles relative to the Earth. Different pulsars emit pulses at different speeds, depending on the size and mass of the neutron star. Sometimes a pulsar may have a satellite. In some cases, it can attract its companion, which causes it to spin even faster. The fastest pulsars can emit more than a hundred pulses per second.

Neutron stars

The formation of a pulsar occurs when a massive star dies after exhausting its fuel reserves. A large explosion occurs, known as a supernova - the most powerful and brightest event in the Universe. Without the counterbalancing force of nuclear fusion, gravity begins to pull stellar masses inward until they become very compressed. In a pulsar, gravity compacts them until they form an object consisting mostly of neutrons, packed so tightly together that they can no longer exist as ordinary matter.

Diagram of the structure of a neutron star

Physicist Chandrasekhar Subrahmanian proposed that if the mass of the core of a destroyed star is 1.4 times the mass of the star itself, protons and electrons will combine into neutrons in the neutron star. This number is known today as the Chandrasekhar limit. If this limit is not reached as a result of the destruction of the core, then a white dwarf is formed. If this limit is significantly exceeded, a black hole may result.

The collapsing star begins to rotate more quickly, which is known as conservation of momentum during rotation. This process is similar to figure skaters trying to clasp their hands tightly together to spin even faster. The result is a rapidly rotating ball of tightly packed neutrons inside an iron shell. Extreme gravity forces make this shell very smooth and shiny. The resulting neutron star is only about 30-35 km in diameter, while containing most of the mass of the original star with which it was formed. The matter of this neutron star is packed so tightly that a piece of this star the size of a sugar cube would weigh more than 100 million tons on Earth.

Discovery of pulsars and neutron stars

New pulsars are being discovered even today using large radio telescopes. The largest radio telescope in the world is located in Arecibo, Puerto Rico. It was one of the key tools in the search for pulsars. Several new pulsars have been discovered over the past few years. The pulsar is located inside the famous Crab Nebula (M1).

The fastest pulsar, PSR1937 +21, has a pulse period of 1.56 ms, or 640 times per second. The strongest pulsar is PSR 0329 +54, with a very slow pulse of only 0.715 seconds. Recently, pulsars such as PSR 1257 +12 were discovered. Scientists believe that planets revolve around them.

Pulsars were discovered completely by accident in the mid-60s of the twentieth century. This happened during observations using a radio telescope, which was originally designed to study various flickering sources in the uncharted depths of space. What are these space objects?

Discovery of pulsars by British researchers

A group of scientists - Jocelyn Bell, Anthony Huis and others - conducted research at the University of Cambridge. These pulses arrived with a frequency of 0.3 seconds, and their frequency was 81.5 MHz. At that time, astronomers had not yet thought about what a pulsar really was and what its nature was. The first thing they noticed was the amazing frequency of the “messages” they discovered. After all, ordinary flickering occurred in a chaotic mode. Among scientists there was even an assumption that these signals are evidence of an extraterrestrial civilization trying to reach humanity. To designate them, the name LGM was introduced - this English abbreviation meant little green men (“little green men”). Researchers began to make serious attempts to decipher the mysterious "code", and for this they attracted eminent codebreakers from all over the planet. However, their attempts were unsuccessful.

Over the next three years, astronomers discovered 3 more similar sources. And then scientists realized what a pulsar was. It turned out to be another object of the Universe that has nothing to do with alien civilizations. It was then that pulsars got their name. For their discovery, scientist Anthony Hewish was awarded the Nobel Prize in Physics.

What are neutron stars?

But despite the fact that this discovery happened quite a long time ago, many are still interested in the answer to the question “what is a pulsar.” This is not surprising, because not everyone can boast that astronomy was taught at the highest level at their school or university. We answer the question: a pulsar is a neutron star that is formed after a supernova explosion occurs. And so the constancy of the pulsation, which was surprising at one time, can be easily explained - its reason is the stability of the rotation of these neutron stars.

In astronomy, pulsars are designated by a four-digit number. Moreover, the first two digits of the name indicate hours, and the next two - minutes, in which the right ascension of the pulse occurs. And in front of the numbers are two Latin letters, which encode the location of the opening. The very first of all discovered pulsars was called CP 1919 (or "Cambridge Pulsar").

Quasars

What are pulsars and quasars? We have already figured out that pulsars are the most powerful radio sources, the radiation of which is concentrated in individual pulses of a certain frequency. Quasars are also one of the most interesting objects in the entire Universe. They are also extremely bright - exceeding the overall radiation intensity of galaxies that are similar to the Milky Way. Quasars were discovered by astronomers as objects with a high redshift. According to one of the widespread theories, quasars are galaxies at the initial stage of their development, inside which there is

The brightest pulsar in history

One of the most famous such objects in the Universe is the pulsar in the Crab Nebula. This discovery shows that a pulsar is one of the most amazing objects in the entire Universe.

The explosion of a neutron star in the current Crab Nebula was so powerful that it cannot even fit into modern astrophysics theory. In 1054 AD e. A new star shone in the sky, which today is called SN 1054. Its explosion was observed even in the daytime, which was attested in the historical chronicles of China and Arab countries. It is interesting that Europe did not notice this explosion - then society was so absorbed in the proceedings between the Pope and his legate, Cardinal Humbert, that not a single scientist of that time recorded this explosion in his works. And several centuries later, a new nebula was discovered at the site of this explosion, which later became known as the Crab Nebula. For some reason its shape reminded its discoverer, William Parsons, of a crab.

And in 1968, the pulsar PSR B0531+21 was first discovered, and it was this pulsar that was the first of all that scientists identified with supernova remnants. The source of the pulsation, judging more strictly, is not the star itself, but the so-called secondary plasma, which is formed in the magnetic field of a star rotating at a breakneck speed. The rotation frequency of the Crab Nebula pulsar is 30 times per second.

A discovery that does not fit into the framework of modern theories

But this pulsar is surprising not only for its brightness and frequency. PSR B0531+21 was recently discovered to emit radioactive rays in a range that exceeds the 100 billion volt mark. This number is millions of times higher than the radiation used in medical equipment, and it is also ten times higher than the value described in modern theory of gamma rays. Martin Schroeder, an American astronomer, puts it this way: “If just two years ago you had asked any astrophysicist whether this kind of radiation could be detected, you would have received a resounding “no.” There is simply no such theory into which the fact we discovered can fit.”

What are pulsars and how did they form: the mystery of astronomy

Thanks to studies of the Crab Nebula pulsar, scientists have an idea of ​​the nature of these mysterious space objects. Now you can more or less clearly imagine what a pulsar is. Their occurrence is explained by the fact that at the final stage of their evolution, some stars explode and flash with huge fireworks - a supernova is born. They are distinguished from ordinary stars by the power of their flare. In total, about 100 such flares occur per year in our Galaxy. In just a few days, a supernova increases its luminosity several million times.

Without exception, all nebulae, as well as pulsars, appear at the site of supernova explosions. However, pulsars cannot be observed in all remnants of this type of celestial body. This should not confuse astronomy lovers - after all, a pulsar can only be observed if it is located at a certain angle of rotation. In addition, due to their nature, pulsars “live” longer than the nebulae in which they form. Scientists still cannot accurately determine the reasons that cause a cooled and seemingly long-dead star to become a source of powerful radio emission. Despite the abundance of hypotheses, astronomers will have to answer this question in the future.

Pulsars with the shortest rotation period

Probably, those who are wondering what a pulsar is and what the latest news from astrophysicists about these celestial objects will be interested in knowing the total number of stars of this kind discovered to date. Today, scientists know of more than 1,300 pulsars. Moreover, a huge number - about 90% - of these stars pulsate within the range from 0.1 to 1 second. There are even pulsars with even shorter periods - they are called millisecond. One of them was discovered by astronomers in 1982 in the constellation Vulpecula. Its rotation period was only 0.00155 seconds. A schematic representation of a pulsar includes the rotation axis, magnetic field, and radio waves.

Such short periods of rotation of pulsars served as the main argument in favor of the assumption that by their nature they are rotating neutron stars (pulsar is a synonym for the expression “neutron star”). After all, a celestial body with such a rotation period must be very dense. Research on these objects is still ongoing. Having learned what neutron pulsars are, scientists did not stop at previously discovered facts. After all, these stars were truly amazing - their existence could only be possible under the condition that the centrifugal forces that arise as a result of rotation are less than the gravitational forces that bind the pulsar matter.

Different types of neutron stars

Later it turned out that pulsars with millisecond rotation periods are not the youngest, but, on the contrary, one of the oldest. And pulsars in this category had the weakest magnetic fields.

There is also a type of neutron star called X-ray pulsars. These are celestial bodies that emit X-rays. They also fall into the category of neutron stars. However, radio pulsars and X-ray emitting stars act differently and have different properties. The first pulsar of this kind was discovered in 1972 in

The nature of pulsars

When researchers first began to study what pulsars are, they decided that neutron stars have the same nature and density as atomic nuclei. This conclusion was made because all pulsars are characterized by hard radiation - exactly the same as that that accompanies nuclear reactions. However, further calculations allowed astronomers to make a different statement. A type of cosmic object, a pulsar, is a celestial body that is similar to giant planets (otherwise called “infrared stars”).

Astronomers have studied the skies 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 had not even imagined. One of them were quasars and pulsars.

Despite the enormous distances to these objects, scientists were able to study some of their properties. But despite this, they still hide many unsolved secrets.

What are pulsars and quasars

A pulsar, as it turned out, is a neutron star. Its discoverers were E. Hewish and his graduate student D. Bell. They were able to detect pulses, which are narrowly directed streams of radiation that become visible at certain time intervals, since this effect occurs due to the rotation of neutron stars.

A significant densification of the star’s magnetic field and its density itself occurs during its compression. It can shrink to sizes 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 radiated waves come from.

Quasars and pulsars can be called the most unusual and mysterious discoveries in 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 ejection of electrons from the magnetic poles of the star. 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 list of unusual phenomena associated with neutron stars, we should note their outer layer. In this sphere there are spaces in which the core cannot be destroyed due to insufficient density of matter. The consequence of this is the covering of the densest crust due to the formation of a crystalline structure. As a result, tension accumulates and at a certain point this dense surface begins to crack. Scientists nicknamed this phenomenon a “starquake.”

Pulsars and quasars remain completely unexplored. But if amazing research told us about pulsars or the so-called. While neutron stars contain a lot of new things, quasars keep astronomers in suspense of the unknown.

The world first learned about quasars in 1960. The discovery stated that these are objects with small angular dimensions, which are characterized by high luminosity, and according to their class they belong to extragalactic objects. Because they have a fairly small angular size, for many years it was believed that they were just stars.

The exact number of quasars discovered is unknown, but in 2005, studies were carried out in which there were 195 thousand quasars. So far, nothing available for explanation is known about them. There are a lot of assumptions, but none of them have any evidence.

Astronomers have only found out that over a time period of less than 24 hours, their brightness shows sufficient variability. Based on these data, one can note their relatively small size of the radiation region, which is comparable to the size of the Solar System. Found quasars exist at distances of up to 10 billion light years. We were able to see them due to their high level of luminosity.

The closest such object to our planet is located approximately 2 billion light years away. Perhaps future research and the latest technologies used in them will provide humanity with new knowledge about the white spots of outer space.