What do scientists call a neutron star? Neutron star
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 are spherical compact objects whose dimensions do not go beyond the boundary big 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 “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 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 from 100 million to 1 quadrillion times stronger than Earth. 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 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 get 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.
Using 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 pulsation may be disrupted 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 supernova remnants, then it has a huge energy reserve and fast speed rotation. 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 an explosion of more large stars. Let's get to know these formations better.
When a star 4-8 times more massive than the Sun explodes, what remains is a core with high density, which 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 capable of reaching 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 about extreme conditions substances, the composition of neutron stars and methods of 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. Material flows along 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.
Neutron stars, often called “dead” stars, are amazing objects. Their study in recent decades has become one of the most fascinating and discovery-rich areas of astrophysics. Interest in neutron stars is due not only to the mystery of their structure, but also to their colossal density and strong magnetic and gravitational fields. The matter there is in a special state, reminiscent of a huge atomic nucleus, and these conditions cannot be reproduced in earthly laboratories.
Birth at the tip of a pen
The discovery of a new elementary particle, the neutron, in 1932 led astrophysicists to wonder what role it might play in the evolution of stars. Two years later, it was suggested that supernova explosions are associated with the transformation of ordinary stars into neutron stars. Then calculations were made of the structure and parameters of the latter, and it became clear that if small stars (like our Sun) at the end of their evolution turn into white dwarfs, then heavier ones become neutron ones. In August 1967, radio astronomers, while studying the flickering of cosmic radio sources, discovered strange signals: very short, lasting about 50 milliseconds, pulses of radio emission were recorded, repeated at a strictly defined time interval (of the order of one second). This was completely different from the usual chaotic picture of random irregular fluctuations in radio emission. After a thorough check of all the equipment, I was confident that the pulses had extraterrestrial origin. It is difficult for astronomers to be surprised by objects emitting with variable intensity, but in in this case the period was so short, and the signals were so regular, that scientists seriously suggested that they could be news from extraterrestrial civilizations.
Therefore, the first pulsar was named LGM-1 (from English Little Green Men “Little Green Men”), although attempts to find any meaning in the received impulses ended in vain. Soon, 3 more pulsating radio sources were discovered. Their period again turned out to be much less than the characteristic times of vibration and rotation of all known astronomical objects. Due to the pulsed nature of the radiation, new objects began to be called pulsars. This discovery literally shook up astronomy, and reports of pulsar detections began to arrive from many radio observatories. After the discovery of a pulsar in the Crab Nebula, which arose due to a supernova explosion in 1054 (this star was visible during the day, as the Chinese, Arabs and North Americans mention in their annals), it became clear that pulsars are somehow related to supernova explosions .
Most likely, the signals came from an object left after the explosion. It took a long time before astrophysicists realized that pulsars were the rapidly rotating neutron stars they had been looking for for so long.
Crab Nebula
The outbreak of this supernova (photo above), sparkling in the earth's sky brighter than Venus and visible even during the day, occurred in 1054 earth clock. Almost 1,000 years is a very short period of time by cosmic standards, and yet during this time the beautiful Crab Nebula managed to form from the remains of the exploding star. This image is a composition of two pictures: one of them was obtained by the Hubble Space Optical Telescope (shades of red), the other by the Chandra X-ray telescope (blue). It is clearly seen that high-energy electrons emitting in the X-ray range very quickly lose their energy, therefore blue colors prevail only in the central part of the nebula.
Combining two images helps to more accurately understand the mechanism of operation of this amazing cosmic generator, emitting electromagnetic oscillations of the widest frequency range - from gamma rays to radio waves. Although most neutron stars have been detected by radio emission, they emit the bulk of their energy in the gamma-ray and x-ray ranges. Neutron stars are born very hot, but cool quickly enough, and already at a thousand years of age they have a surface temperature of about 1,000,000 K. Therefore, only young neutron stars shine in the X-ray range due to purely thermal radiation.
Pulsar physics
A pulsar is simply a huge magnetized top spinning around an axis that does not coincide with the axis of the magnet. If nothing fell on it and it did not emit anything, then its radio emission would have a rotational frequency and we would never hear it on Earth. But the fact is that this top has a colossal mass and high temperature surface, and the rotating magnetic field creates an electric field of enormous intensity, capable of accelerating protons and electrons almost to the speed of light. Moreover, all these charged particles rushing around the pulsar are trapped in its colossal magnetic field. And only within a small solid angle about the magnetic axis they can break free (neutron stars have the strongest magnetic fields in the Universe, reaching 10 10 10 14 gauss, for comparison: the earth’s field is 1 gauss, the solar one 10 50 gauss) . It is these streams of charged particles that are the source of the radio emission from which pulsars were discovered, which later turned out to be neutron stars. Since the magnetic axis of a neutron star does not necessarily coincide with the axis of its rotation, when the star rotates, a stream of radio waves propagates through space like the beam of a flashing beacon, only momentarily cutting through the surrounding darkness.
X-ray images of the Crab Nebula pulsar in its active (left) and normal (right) states
nearest neighbor
This pulsar is located only 450 light years from Earth and is a binary system of a neutron star and a white dwarf with an orbital period of 5.5 days. The soft X-ray radiation received by the ROSAT satellite is emitted by the polar ice caps PSR J0437-4715, which are heated to two million degrees. During its rapid rotation (the period of this pulsar is 5.75 milliseconds), it turns toward the Earth with one or the other magnetic pole, as a result, the intensity of the gamma ray flux changes by 33%. The bright object next to the small pulsar is a distant galaxy that, for some reason, actively glows in the X-ray region of the spectrum.
Almighty Gravity
According to modern theory evolution, massive stars end their lives with a colossal explosion, turning most of them into an expanding gas nebula. As a result, what remains from a giant many times larger than our Sun in size and mass is a dense hot object about 20 km in size, with a thin atmosphere (of hydrogen and heavier ions) and a gravitational field 100 billion times greater than that of the Earth. It was called a neutron star, believing that it consists mainly of neutrons. Neutron star matter is the densest form of matter (a teaspoon of such a supernucleus weighs about a billion tons). The very short period of signals emitted by pulsars was the first and most important argument in favor of the fact that these are neutron stars, possessing a huge magnetic field and rotating at breakneck speed. Only dense and compact objects (only a few tens of kilometers in size) with a powerful gravitational field can withstand such a rotation speed without falling into pieces due to centrifugal inertial forces.
Neutron star consists of a neutron liquid with an admixture of protons and electrons. "Nuclear liquid", very similar to the substance from atomic nuclei, 1014 times denser than ordinary water. This huge difference is understandable, since atoms consist mostly of empty space, in which light electrons flit around a tiny, heavy nucleus. The nucleus contains almost all the mass, since protons and neutrons are 2,000 times heavier than electrons. The extreme forces generated by the formation of a neutron star compress the atoms so much that the electrons squeezed into the nuclei combine with protons to form neutrons. In this way, a star is born, consisting almost entirely of neutrons. A super-dense nuclear liquid, if brought to Earth, would explode like nuclear bomb, but in a neutron star it is stable due to the enormous gravitational pressure. However, in the outer layers of a neutron star (as, indeed, of all stars), pressure and temperature drop, forming a solid crust about a kilometer thick. It is believed to consist mainly of iron nuclei.
Flash
The colossal X-ray flare of March 5, 1979, it turns out, occurred far beyond our Galaxy, in the Large Magellanic Cloud, a satellite of our Milky Way, located at a distance of 180 thousand light years from Earth. Joint processing of the gamma-ray burst on March 5, recorded by seven spacecraft, made it possible to quite accurately determine the position of this object, and the fact that it is located precisely in the Magellanic Cloud is today practically beyond doubt.
The event that happened on this distant star 180 thousand years ago is difficult to imagine, but it flashed then like 10 supernovae, more than 10 times the luminosity of all the stars in our Galaxy. The bright dot at the top of the figure is a long-known and well-known SGR pulsar, and the irregular outline is the most likely position of the object that flared up on March 5, 1979.
Origin of the neutron star
A supernova explosion is simply the transition of part of the gravitational energy into heat. When an old star runs out of fuel and the thermonuclear reaction can no longer heat its interior to the required temperature, a collapse of the gas cloud occurs at its center of gravity. The energy released in this process scatters the outer layers of the star in all directions, forming an expanding nebula. If the star is small, like our Sun, then an outburst occurs and a white dwarf is formed. If the mass of the star is more than 10 times that of the Sun, then such a collapse leads to a supernova explosion and an ordinary neutron star is formed. If a supernova erupts in the place of a very large star, with a mass of 20 x 40 solar, and a neutron star with a mass of more than three solar is formed, then the process of gravitational compression becomes irreversible and a black hole is formed.
Internal structure
Hard crust outer layers A neutron star consists of heavy atomic nuclei arranged in a cubic lattice, with electrons flying freely between them, which is reminiscent of earthly metals, but only much denser.
Open question
Although neutron stars have been intensively studied for about three decades, their internal structure is not known for certain. Moreover, there is no firm certainty that they really consist mainly of neutrons. As you move deeper into the star, pressure and density increase and matter can be so compressed that it breaks down into quarks - the building blocks of protons and neutrons. According to modern quantum chromodynamics, quarks cannot exist in a free state, but are combined into inseparable “threes” and “twos”. But perhaps, at the boundary of the inner core of a neutron star, the situation changes and the quarks break out of their confinement. To further understand the nature of a neutron star and exotic quark matter, astronomers need to determine the relationship between the star's mass and its radius ( average density). By studying neutron stars with satellites, it is possible to measure their mass quite accurately, but determining their diameter is much more difficult. More recently, scientists using the XMM-Newton X-ray satellite have found a way to estimate the density of neutron stars based on gravitational redshift. Another unusual thing about neutron stars is that as the mass of the star decreases, its radius increases as a result smallest size have the most massive neutron stars.
Black Widow
The explosion of a supernova quite often imparts considerable speed to a newborn pulsar. Such a flying star with a decent magnetic field of its own greatly disturbs the ionized gas filling interstellar space. A kind of shock wave is formed, running in front of the star and diverging into a wide cone after it. The combined optical (blue-green part) and X-ray (shades of red) image shows that here we are dealing not just with a luminous gas cloud, but with a huge flow elementary particles, emitted by this millisecond pulsar. The linear speed of the Black Widow is 1 million km/h, it rotates around its axis in 1.6 ms, it is already about a billion years old, and it has a companion star circling around the Widow with a period of 9.2 hours. The pulsar B1957+20 received its name for the simple reason that its powerful radiation simply burns its neighbor, causing the gas that forms it to “boil” and evaporate. The red cigar-shaped cocoon behind the pulsar is the part of space where the electrons and protons emitted by the neutron star emit soft gamma rays.
Result computer modeling allows you to very clearly, in cross-section, imagine the processes occurring near a fast-flying pulsar. Rays diverging from a bright point this is a conventional image of that flow radiant energy, as well as the stream of particles and antiparticles that comes from the neutron star. The red outline at the boundary of the black space around the neutron star and the red luminous clouds of plasma is the place where the stream of relativistic particles flying almost at the speed of light meets the dense shock wave interstellar gas. By braking sharply, the particles emit X-rays and, having lost most of their energy, no longer heat up the incident gas so much.
Cramp of the Giants
Pulsars are considered one of the early stages life of a neutron star. Thanks to their study, scientists learned about magnetic fields, and about the speed of rotation, and about future fate neutron stars. By constantly monitoring the behavior of a pulsar, one can determine exactly how much energy it loses, how much it slows down, and even when it will cease to exist, having slowed down so much that it cannot emit powerful radio waves. These studies confirmed many theoretical predictions about neutron stars.
Already by 1968, pulsars with a rotation period from 0.033 seconds to 2 seconds were discovered. The periodicity of the radio pulsar pulses is maintained with amazing accuracy, and at first the stability of these signals was higher than the earth's atomic clocks. And yet, with progress in the field of time measurement, it was possible to register regular changes in their periods for many pulsars. Of course, these are extremely small changes, and only over millions of years can we expect the period to double. The ratio of the current rotation speed to the rotation deceleration is one of the ways to estimate the age of the pulsar. Despite the remarkable stability of the radio signal, some pulsars sometimes experience so-called "disturbances." In a very short time interval (less than 2 minutes), the rotation speed of the pulsar increases by a significant amount, and then after some time returns to the value that was before the “disturbance.” It is believed that the “disturbances” may be caused by a rearrangement of mass within the neutron star. But in any case, the exact mechanism is still unknown.
Thus, the Vela pulsar undergoes large “disturbances” approximately once every 3 years, and this makes it very interesting object to study such phenomena.
Magnetars
Some neutron stars, called repeating soft gamma ray burst sources (SGRs), emit powerful bursts of "soft" gamma rays at irregular intervals. The amount of energy emitted by an SGR in a typical flare lasting a few tenths of a second can only be emitted by the Sun in a whole year. Four known SGRs are located within our Galaxy and only one is outside it. These incredible explosions of energy can be caused by starquakes - powerful versions of earthquakes when the solid surface of neutron stars is torn apart and powerful streams of protons burst from their depths, which, stuck in a magnetic field, emit gamma and X-ray radiation. Neutron stars were identified as sources of powerful gamma-ray bursts after the huge gamma-ray burst on March 5, 1979, released as much energy in the first second as the Sun emits in 1,000 years. Recent observations of one of the most active neutron stars currently appear to support the theory that irregular, powerful bursts of gamma-ray and X-ray radiation are caused by starquakes.
In 1998, the famous SGR suddenly woke up from its “slumber,” which had shown no signs of activity for 20 years and splashed out almost as much energy as the gamma-ray flare of March 5, 1979. What struck the researchers most when observing this event was the sharp slowdown in the speed of rotation of the star, indicating its destruction. To explain powerful gamma-ray and X-ray flares, a magnetar-neutron star model with a superstrong magnetic field was proposed. If a neutron star is born, rotating very quickly, then the combined influence of rotation and convection, which plays important role in the first few seconds of a neutron star's existence, can create a huge magnetic field through a complex process known as an "active dynamo" (the same way the field is created inside the Earth and the Sun). Theorists were amazed to discover that such a dynamo, operating in a hot, newborn neutron star, could create a magnetic field 10,000 times stronger than the normal field of pulsars. When the star cools (after 10 or 20 seconds), convection and the action of the dynamo stop, but this time is enough for the necessary field to arise.
The magnetic field of a rotating electrically conducting ball can be unstable, and a sharp restructuring of its structure can be accompanied by the release of colossal amounts of energy (a clear example of such instability is the periodic transfer of the Earth’s magnetic poles). Similar things happen on the Sun, in explosive events called "solar flares." In a magnetar, the available magnetic energy is enormous, and this energy is quite enough to power such giant flares as March 5, 1979 and August 27, 1998. Such events inevitably cause deep disruption and changes in the structure of not only electric currents in the volume of a neutron star, but also in its solid crust. Another mysterious type of object that emits powerful X-ray radiation during periodic explosions is the so-called anomalous X-ray pulsarsAXP. They differ from ordinary X-ray pulsars in that they emit only in the X-ray range. Scientists believe that SGR and AXP are phases of the life of the same class of objects, namely magnetars, or neutron stars, which emit soft gamma rays by drawing energy from a magnetic field. And although magnetars today remain the brainchild of theorists and there is not enough data confirming their existence, astronomers are persistently searching for the necessary evidence.
Magnetar candidates
Astronomers have already studied our home galaxy, the Milky Way, so thoroughly that it costs them nothing to depict its side view, indicating the position of the most remarkable of the neutron stars.
Scientists believe that AXP and SGR are simply two stages in the life of the same giant magnet neutron star. For the first 10,000 years, the magnetar is an SGR pulsar, visible in normal light and producing repeated bursts of soft x-ray radiation, and for the next millions of years it, already like an anomalous pulsar AXP, disappears from the visible range and puffs only in the X-ray range.
The strongest magnet
Analysis of data obtained by the RXTE satellite (Rossi X-ray Timing Explorer, NASA) during observations of the unusual pulsar SGR 1806-20 showed that this source is the most powerful magnet known to date in the Universe. The magnitude of its field was determined not only on the basis of indirect data (from the slowing down of the pulsar), but also almost directly from measuring the rotation frequency of protons in the magnetic field of the neutron star. The magnetic field near the surface of this magnetar reaches 10 15 gauss. If it were, for example, in the orbit of the Moon, all magnetic storage media on our Earth would be demagnetized. True, taking into account the fact that its mass is approximately equal to that of the Sun, this would no longer matter, since even if the Earth had not fallen on this neutron star, it would have been spinning around it like crazy, making full turn in just an hour.
Active dynamo
We all know that energy loves to change from one form to another. Electricity easily turns into heat, and kinetic energy into potential energy. Huge convective flows of electrically conductive magma, plasma or nuclear matter, it turns out, can also convert their kinetic energy into something unusual, for example, into a magnetic field. The movement of large masses on a rotating star in the presence of a small initial magnetic field can lead to electric currents, creating a field in the same direction as the original one. As a result, an avalanche-like increase in the own magnetic field of a rotating current-conducting object begins. The greater the field, the greater the currents, the greater the currents, the greater the field and all this is due to banal convective flows, due to the fact that a hot substance is lighter than a cold one, and therefore floats up
Troubled neighborhood
The famous Chandra space observatory has discovered hundreds of objects (including in other galaxies), indicating that not all neutron stars are destined to lead a solitary life. Such objects are born in dual systems that survived the supernova explosion that created the neutron star. And sometimes it happens that single neutron stars in dense stellar regions such as globular clusters capture a companion. In this case, the neutron star will “steal” matter from its neighbor. And depending on how massive the star is to accompany it, this “theft” will cause different consequences. Gas flowing from a companion with a mass less than that of our Sun onto such a “crumb” as a neutron star cannot immediately fall due to its own angular momentum being too large, so it creates a so-called accretion disk around it from the “stolen » matter. Friction as it wraps around the neutron star and compression in the gravitational field heats the gas to millions of degrees, and it begins to emit X-rays. Other interesting phenomenon, associated with neutron stars that have a low-mass companion, X-ray bursts (bursters). They usually last from several seconds to several minutes and at maximum give the star a luminosity almost 100 thousand times greater than the luminosity of the Sun.
These flares are explained by the fact that when hydrogen and helium are transferred to the neutron star from the companion, they form a dense layer. Gradually, this layer becomes so dense and hot that a thermonuclear fusion reaction begins and releases great amount energy. In terms of power, this is equivalent to the explosion of the entire nuclear arsenal of earthlings on every square centimeter of the surface of a neutron star within a minute. A completely different picture is observed if the neutron star has a massive companion. The giant star loses matter in the form of stellar wind (a stream of ionized gas emanating from its surface), and the enormous gravity of the neutron star captures some of this matter. But here the magnetic field comes into its own, causing the falling matter to flow along the lines of force towards the magnetic poles.
This means that X-ray radiation is primarily generated at hot spots at the poles, and if the magnetic axis and the rotation axis of the star do not coincide, then the brightness of the star turns out to be variable - it is also a pulsar, but only an X-ray one. Neutron stars in X-ray pulsars have bright giant stars as companions. In bursters, the companions of neutron stars are faint, low-mass stars. The age of bright giants does not exceed several tens of millions of years, while the age of faint dwarf stars can be billions of years old, since the former consume their nuclear fuel much faster than the latter. It follows that bursters are old systems in which the magnetic field has weakened over time, while pulsars are relatively young, and therefore the magnetic fields in them are stronger. Perhaps bursters pulsated at some point in the past, but pulsars are yet to burst in the future.
Pulsars are also associated with binary systems with the most short periods(less than 30 milliseconds) so-called millisecond pulsars. Despite their rapid rotation, they turn out to be not the youngest, as one would expect, but the oldest.
They arise from binary systems where an old, slowly rotating neutron star begins to absorb matter from its also aged companion (usually a red giant). Falling onto the surface of a neutron star, matter transfers to it rotational energy, causing it to spin faster and faster. This happens until the neutron star's companion, almost freed of excess mass, becomes a white dwarf, and the pulsar comes to life and begins to rotate at a speed of hundreds of revolutions per second. However, recently astronomers discovered a very unusual system, where the companion of a millisecond pulsar is not a white dwarf, but a giant bloated red star. Scientists believe that they are observing this binary system just at the stage of “liberation” of the red star from excess weight and becoming a white dwarf. If this hypothesis is incorrect, then the companion star could be an ordinary globular cluster star accidentally captured by a pulsar. Almost all neutron stars that are currently known are found either in X-ray binaries or as single pulsars.
And recently, Hubble noticed in visible light a neutron star, which is not a component of a binary system and does not pulsate in the X-ray and radio range. This provides a unique opportunity to accurately determine its size and make adjustments to ideas about the composition and structure of this bizarre class of burnt-out, gravitationally compressed stars. This star was first discovered as an X-ray source and emits in this range not because it collects hydrogen gas as it moves through space, but because it is still young. It may be the remnant of one of the stars in the binary system. As a result of a supernova explosion, this binary system collapsed and the former neighbors began an independent journey through the Universe.
Baby star eater
Just as stones fall to the ground, so big star, releasing its mass piece by piece, gradually moves to a small and distant neighbor, which has a huge gravitational field near its surface. If the stars did not revolve around a common center of gravity, then the gas stream could simply flow, like a stream of water from a mug, onto a small neutron star. But since the stars swirl in a circle, the falling matter must lose most of its angular momentum before it reaches the surface. And here, the mutual friction of particles moving along different trajectories and the interaction of the ionized plasma forming the accretion disk with the magnetic field of the pulsar help the process of matter fall to successfully end with an impact on the surface of the neutron star in the region of its magnetic poles.
Riddle 4U2127 solved
This star has been fooling astronomers for more than 10 years, showing strange slow variability in its parameters and flaring up differently each time. Only latest research The Chandra space observatory was able to unravel the mysterious behavior of this object. It turned out that these were not one, but two neutron stars. Moreover, both of them have companions: one star is similar to our Sun, the other is like a small blue neighbor. Spatially, these pairs of stars are separated by a fairly large distance and live an independent life. But on the stellar sphere they are projected to almost the same point, which is why they were considered one object for so long. These four stars are located in the globular cluster M15 at a distance of 34 thousand light years.
Open question
In total, astronomers have discovered about 1,200 neutron stars to date. Of these, more than 1,000 are radio pulsars, and the rest are simply X-ray sources. Over the years of research, scientists have come to the conclusion that neutron stars are real originals. Some are very bright and calm, others periodically flare up and change with starquakes, and others exist in binary systems. These stars are among the most mysterious and elusive astronomical objects, combining the strongest gravitational and magnetic fields and extreme densities and energies. And each new discovery from their turbulent life gives scientists unique information necessary to understand the nature of Matter and the evolution of the Universe.
Universal standard
It is very difficult to send something outside the solar system, so together with the Pioneer 10 and 11 spacecraft that headed there 30 years ago, earthlings also sent messages to their brothers in mind. To draw something that will be understandable to the Extraterrestrial Mind is not an easy task; moreover, it was also necessary to indicate the return address and the date of sending the letter... How clearly the artists were able to do all this is difficult for a person to understand, but the very idea of using radio pulsars for indicating the place and time of sending the message is brilliant. Intermittent rays of various lengths emanating from a point symbolizing the Sun indicate the direction and distance to the pulsars closest to the Earth, and the intermittency of the line is nothing more than a binary designation of their period of revolution. The longest beam points to the center of our Galaxy Milky Way. The frequency of the radio signal emitted by a hydrogen atom when the mutual orientation of the spins (direction of rotation) of the proton and electron changes is taken as the unit of time in the message.
The famous 21 cm or 1420 MHz should be known to all intelligent beings in the Universe. Using these landmarks, pointing to the “radio beacons” of the Universe, it will be possible to find earthlings even after many millions of years, and by comparing the recorded frequency of pulsars with the current one, it will be possible to estimate when these man and woman blessed the flight of the first spaceship that left the solar system.
Nikolay Andreev
It occurs after a supernova explosion.
This is the twilight of a star's life. Its gravity is so strong that it throws electrons from the orbits of atoms, turning them into neutrons.
When it loses the support of its internal pressure, it collapses and this leads to supernova explosion.
The remains of this body become a Neutron star, the mass of which is 1.4 times the mass of the Sun, and the radius is almost equal to the radius Manhattan in the USA.
The weight of a piece of sugar with the density of a neutron star is...
If, for example, you take a piece of sugar with a volume of 1 cm3 and imagine that it is made of neutron star matter, then its mass would be approximately one billion tons. This is equal to the mass of approximately 8 thousand aircraft carriers. Small object with incredible density!
The newborn neutron star boasts a high rotation speed. When a massive star turns into a neutron star, its rotation speed changes.
A rotating neutron star is a natural electrical generator. Its rotation creates a powerful magnetic field. This enormous force of magnetism captures electrons and other particles of atoms and sends them deep into the Universe at tremendous speed. High-speed particles tend to emit radiation. The flickering that we observe in pulsar stars is the radiation of these particles.But we notice it only when its radiation is directed in our direction.
The spinning neutron star is a Pulsar, an exotic object created after a Supernova explosion. This is the sunset of her life.
The density of neutron stars is distributed differently. They have bark that is incredibly dense. But the forces inside a neutron star can pierce the crust. And when this happens, the star adjusts its position, which leads to a change in its rotation. This is called: the bark is cracked. An explosion occurs on a neutron star.
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Neutron star
Neutron star
Neutron star
- a super-dense star formed as a result of a supernova explosion. The matter of a neutron star consists mainly of neutrons.
A neutron star has a nuclear density (10 14 -10 15 g/cm 3) and a typical radius of 10-20 km. Further gravitational compression of the neutron star is prevented by the pressure of nuclear matter arising due to the interaction of neutrons. This pressure of the degenerate significantly denser neutron gas is able to keep masses up to 3M from gravitational collapse. Thus, the mass of a neutron star varies within the range of (1.4-3)M.
Rice. 1. Cross-section of a neutron star with mass 1.5M and radius R = 16 km. The density ρ is indicated in g/cm 3 in different parts of the star.
Neutrinos produced during a supernova collapse quickly cool the neutron star. Its temperature is estimated to drop from 10 11 to 10 9 K in a time of about 100 s. Then the cooling rate decreases. However, it is high on a cosmic scale. A decrease in temperature from 10 9 to 10 8 K occurs in 100 years and to 10 6 K in a million years.
There are approximately 1200 known objects that are classified as neutron stars. About 1000 of them are located within our galaxy. The structure of a neutron star with a mass of 1.5M and a radius of 16 km is shown in Fig. 1: I – thin outer layer of densely packed atoms. Region II is crystal lattice atomic nuclei and degenerate electrons. Region III is a solid layer of atomic nuclei supersaturated with neutrons. IV – liquid core, consisting mainly of degenerate neutrons. Region V forms the hadronic core of the neutron star. In addition to nucleons, it can contain pions and hyperons. In this part of the neutron star, the transition of neutron liquid into solid is possible crystalline state, the appearance of pion condensate, the formation of quark-gluon and hyperon plasma. Certain details of the structure of a neutron star are currently being clarified.
Detect neutron stars optical methods difficult due to its small size and low luminosity. In 1967 E. Hewish and J. Bell ( Cambridge university) discovered cosmic sources of periodic radio emission - pulsars. The repetition periods of pulsar radio pulses are strictly constant and for most pulsars lie in the range from 10 -2 to several seconds. Pulsars are rotating neutron stars. Only compact objects with the properties of neutron stars can maintain their shape without collapsing at such rotational speeds. Conservation of angular momentum and magnetic field during the collapse of a supernova and the formation of a neutron star leads to the birth of rapidly rotating pulsars with a very strong magnetic field of 10 10 –10 14 G. The magnetic field rotates along with the neutron star, however, the axis of this field does not coincide with the axis of rotation of the star. With this rotation, the radio emission from the star glides across the Earth like a lighthouse beam. Each time the beam crosses the Earth and hits an observer on Earth, the radio telescope detects a short pulse of radio emission. Its repetition frequency corresponds to the rotation period of the neutron star. Radiation from a neutron star occurs when charged particles (electrons) from the surface of the star move outward along magnetic field lines, emitting electromagnetic waves. This is the mechanism of radio emission from a pulsar, first proposed
Neutron stars concept
The concept of neutron stars is not new: the first suggestion about the possibility of their existence was made by talented astronomers Fritz Zwicky and Walter Baarde from California in 1934. (Somewhat earlier, in 1932, the possibility of the existence of neutron stars was predicted by the famous Soviet scientist L.D. Landau.) In the late 30s, it became the subject of research by other American scientists Oppenheimer and Volkov. The interest of these physicists in this problem was caused by the desire to determine the final stage of evolution of a massive contracting star. Since the role and significance of supernovae were discovered around the same time, it was suggested that the neutron star could be the remnant of a supernova explosion. Unfortunately, with the outbreak of World War II, the attention of scientists turned to military needs and detailed study of these new and highly mysterious objects was suspended. Then, in the 50s, the study of neutron stars was resumed purely theoretically in order to determine whether they were related to the problem of the birth of chemical elements in the central regions of stars.remain the only astrophysical object whose existence and properties were predicted long before their discovery.
In the early 60s the discovery cosmic sources X-rays were very encouraging to those who had considered neutron stars as possible sources of celestial X-rays. By the end of 1967 was discovered new class celestial objects - pulsars, which led scientists to confusion. This discovery was the most important event in the study of neutron stars, as it again raised the question of the origin of cosmic X-ray radiation. Speaking about neutron stars, it should be taken into account that they physical characteristics established theoretically and very hypothetical, since physical conditions, existing in these bodies, cannot be reproduced in laboratory experiments.
Properties of neutron stars
The properties of neutron stars are decisively influenced by gravitational forces. According to various estimates, the diameters of neutron stars are 10-200 km. And this volume, insignificant in cosmic terms, is “filled” with such an amount of matter that can make up a celestial body like the Sun, with a diameter of about 1.5 million km, and a mass almost a third of a million times heavier than the Earth! A natural consequence of this concentration of matter is the incredibly high density of the neutron star. In fact, it turns out to be so dense that it can even be solid. The gravity of a neutron star is so great that a person would weigh about a million tons there. Calculations show that neutron stars are highly magnetized. It is estimated that the magnetic field of a neutron star can reach 1 million. million gauss, whereas on Earth it is 1 gauss. Neutron star radius is assumed to be about 15 km, and the mass is about 0.6 - 0.7 solar masses. The outer layer is a magnetosphere, consisting of rarefied electron and nuclear plasma, which is penetrated by the powerful magnetic field of the star. This is where radio signals originate, which are hallmark pulsars. Ultrafast charged particles, moving in spirals along magnetic field lines, give rise to various types of radiation. In some cases, radiation occurs in the radio range of the electromagnetic spectrum, in others - radiation at high frequencies.Neutron star density
Almost immediately under the magnetosphere, the density of the substance reaches 1 t/cm3, which is 100,000 times greater than the density of iron. The next layer after the outer layer has the characteristics of metal. This layer of “superhard” substance is in crystalline form. Crystals consist of atomic nuclei with atomic mass 26 - 39 and 58 - 133. These crystals are extremely small: to cover a distance of 1 cm, about 10 billion crystals need to be lined up in one line. The density in this layer is more than 1 million times higher than in the outer layer, or otherwise, 400 billion times higher than the density of iron.Moving further towards the center of the star, we cross the third layer. It includes the area heavy nuclei type cadmium, but also rich in neutrons and electrons. The density of the third layer is 1,000 times greater than the previous one. Penetrating deeper into the neutron star, we reach the fourth layer, and the density increases slightly - about five times. However, at such a density, the nuclei can no longer maintain their physical integrity: they decay into neutrons, protons and electrons. Most of the matter is in the form of neutrons. There are 8 neutrons for every electron and proton. This layer, in essence, can be considered as a neutron liquid, “contaminated” with electrons and protons. Below this layer is the core of the neutron star. Here the density is approximately 1.5 times greater than in the overlying layer. And yet, even such a small increase in density leads to the fact that particles in the core move much faster than in any other layer. Kinetic energy The motion of neutrons mixed with a small number of protons and electrons is so great that inelastic collisions of particles constantly occur. In collision processes, all particles and resonances known in nuclear physics are born, of which there are more than a thousand. In all likelihood there is big number particles not yet known to us.
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