What is the solar system?
The solar system is made up of all the planets orbiting the sun. In addition to planets, the solar system is divided into satellites, comets, asteroids, asteroids, dust and gas.
Everything in the solar system or orbits around the sun. The Sun contains approximately 98% of all matter in the solar system. If it's bigger, it's even more powerful. Because the sun is so big, its strong gravitational pull attracts everything else in the solar system's vicinity. At the same time, these objects, moving very quickly, try to escape into outer space. Because the planets are trying to fly away and, at the same time, the sun is trying to pull them back, they are in a balance between the two forces. Balance flew towards the sun and escaped into space. It took them a long time to reach the home star.
How was the solar system formed?
This is an important question, one that is difficult for scientists to know. After all, the creation of the solar system happened billions of years ago, and there were people around to see it. Our own evolution is closely integrated with the evolution of the solar system. Therefore, to understand where the solar system came from, it is difficult to understand how humans came.
Scientists believe that the solar system evolved from a huge cloud of dust and gas. They believe that this dust and gas began to collapse under the weight of its own gravity. In that case, things might start moving in a giant circle, like the water moving out in a loop around the central drain pipe.
In the center, clouds spin and small stars begin to form. The star becomes larger and larger as it collects more dust and gas and is collapsed.
Far from the center of star formation, small clumps of dust and gas also collapse. The center of the star ignited, eventually forming the sun, while the smaller clumps became planets, asteroids, moons, comets, and asteroids.
The English name of Mercury comes from the Roman god Mercury. The symbol is a circle above, a short intersecting vertical line and a semicircle below (Unicode: ?). It is the shape of the wand held by Mercury. In the 5th century, Mercury was actually considered two different planets because it alternated between appearing on either side of the Sun. When it appeared in the evening it was called Mercury; but when it appeared in the morning it was called Apollo in honor of the sun god Apollo. Pythagoras later pointed out that they were actually the same planet. In ancient China, Mercury was called "Chen Xing".
The ancient Chinese called Venus "Taibai" or "Taibai Venus", also called "Qiming" or "Chang Geng". The ancient Greeks called Aphrodite, the goddess of love and beauty in Greek mythology. In Roman mythology, the goddess of love and beauty is Venus, so Venus is also called "Venus". The astronomical symbol of Venus is represented by Venus' vanity mirror. Phase changes of Venus: Like the moon, Venus also has periodic waxing and waning changes (phase changes), but because Venus is too far away from the earth, it cannot be seen with the naked eye. The phase changes of Venus were once used by Galileo as strong evidence to prove Copernicus' heliocentric theory.
The Earth is one of the planets in the solar system, ranking third in order from nearest to far from the sun. It is the largest terrestrial planet in the solar system and the only planet that modern science has confirmed to have life. The planet's age is estimated to be approximately 4.5 billion years (4.5×109). Shortly after the planet formed, its only natural satellite, the moon, was captured. The only intelligent creatures on earth are humans.
Because it looks blood red in the night sky, it is named in the West after Mars, the god of war in Roman mythology (or Ares in Greek mythology). In ancient China, because it glowed like fire, it was called "Yinghuo". Mars has two small natural satellites: Phobos and Deimos (the names of Ares' sons). Both moons are small and oddly shaped and may be asteroids captured by gravity. The prefix areo- in English refers to Mars.
Jupiter is one of the nine planets in the solar system. It is the fifth planet in order from nearest to far from the sun. It is also the largest planet in the solar system and the fastest rotating planet. In ancient China, it was used to mark the year, so it was called the Sui Xing.
In the West, it is called Jupiter, the king of gods in Roman mythology, equivalent to Zeus in Greek mythology.
Saturn is a giant gas planet and the second largest planet in the solar system after Jupiter.
The English name of Saturn (and the names of Saturn in most other European languages) is named after the Roman god of agriculture, Saturn. In ancient China, it was called Zhenxing or Star-filling.
Uranus is one of the nine planets in the solar system. It is ranked seventh outside Saturn and inside Neptune. It is gray-blue in color and is a gas giant. In terms of diameter, Uranus is the third largest planet in the solar system; but in terms of mass, it is lighter than Neptune and ranks fourth. Uranus is named after the god Uranus in Greek mythology.
Neptune is the eighth of the nine planets in the solar system and is a giant planet. Neptune was the first planet discovered through celestial mechanics calculations. Because the orbit of Uranus was different from what was calculated, in 1845 John Cove Adams and Eban Quinvier calculated the possible location of an unknown planet beyond Uranus. On September 23, 1846, Johann Geffrian Gale, director of the Berlin Observatory, actually discovered a new planet at this location: Neptune.
Neptune is currently the second-farthest planet from the sun in the solar system. Neptune's name is Neptune, the god of the sea in Roman mythology.
Pluto is the farthest and smallest planet from the sun among the nine planets in the solar system. It was discovered in 1930. Because it is the farthest from the sun, it is also very cold. It is very similar to the place where Pluto, the god of the underworld, lived in Roman mythology, so it is called "Pluto".
The Milky Way is the galaxy to which the Earth and Sun belong. It is named after the bright band whose main part is projected on the celestial sphere and is called the Milky Way in my country.
The Milky Way is in the shape of a spiral, with four spiral arms extending evenly and symmetrically from the center of the Milky Way. The center of the Milky Way and the four spiral arms are places where stars are densely packed. Seen from a distance, the Milky Way looks like a large discus used for physical exercise. The diameter of the discus is 100,000 light-years, equivalent to 946,080,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000. The thickest part in the middle is about 3000 to 6500 light years. The Sun is located in a spiral arm called the Orion Arm, about 25,000 light-years from the center of the Milky Way.
The discovery of the Milky Way has gone through a long process. After the invention of the telescope, Galileo first used a telescope to observe the Milky Way and discovered that the Milky Way is composed of stars. Later, T. Wright, I. Kant, J.H. Lambert and others believed that the Milky Way and all stars might be integrated into a huge star system. In the late 18th century, F.W. Herschel used a homemade reflecting telescope to start star counting observations to determine the structure and size of the star system. He asserted that the star system was in the shape of a flat disk, and the sun was not far from the center of the disk. After his death, his son J.F. Herschel inherited his father's business, continued in-depth research, and expanded the work of counting stars to the southern sky. At the beginning of the 20th century, astronomers called the star system with the Milky Way as its apparent phenomenon the Milky Way. J.C. Kaptan applied the method of statistical parallax to determine the average distance of stars, combined with star counting, to derive a model of the Milky Way. In this model, the Sun is at the center and the Milky Way is disk-shaped, 8 kiloparsecs in diameter and 2 kiloparsecs thick. H. Shapley used the period-light relationship of Cepheid variables to determine the distance of globular star clusters, and studied the structure and size of the Milky Way from the distribution of globular star clusters. The model he proposed is that the Milky Way is a lens-shaped star system with the sun not in the center. Shapley concluded that the diameter of the Milky Way is 80 kiloparsecs, and the sun is 20 kiloparsecs from the center of the galaxy. These values ??are too large because Shapley did not account for interstellar extinction when calculating distances. In the 1920s, after the rotation of the Milky Way was discovered, Shapley's Milky Way model became recognized.
The Milky Way is a giant spiral galaxy, Sb type, with 4 spiral arms. Contains one to two hundred billion stars. The Milky Way as a whole rotates poorly. The rotation speed of the sun is about 220 kilometers per second. The sun orbits the center of the galaxy for about 250 million years. The visual absolute magnitude of the Milky Way is -20.5. The total mass of the Milky Way is about 1 trillion times the mass of our sun, which is roughly 10 times the total mass of all stars in the Milky Way. This is strong evidence for the presence of dark matter in our galaxy that extends far beyond the disk of bright stars. Regarding the age of the Milky Way, the current mainstream view is that the Milky Way was born shortly after the Big Bang. Using this method to calculate, the age of our Milky Way is about 14.5 billion years old, with an error of more than 2 billion years. Year.
The scientific community believes that the "Big Bang" when the universe was born occurred approximately...
The Milky Way is the star system where the solar system is located, including one to two hundred billion stars and a large number of star clusters, nebulae, and various types of interstellar gas and interstellar dust. Its total mass is 140 billion times the mass of the sun. Most stars in the Milky Way are concentrated in an oblate spheroid of space, shaped like a discus. The protruding part in the middle of the oblate spheroid is called the "nuclear bulge", with a radius of about 7,000 light-years. The middle part of the nuclear ball is called the "silver core" and the surrounding area is called the "silver plate". There is a larger sphere outside the galactic disk, where there are few stars and low density, called the "galactic halo", with a diameter of 70,000 light-years. The Milky Way is a spiral galaxy with a spiral structure, that is, it has a galactic center and two spiral arms. The spiral arms are 4,500 light years apart. The rotation speed and period of each part vary depending on the distance from the galactic center. The sun is about 23,000 light-years away from the center of the galaxy, orbiting the center of the galaxy at a speed of 250 kilometers per second, with a period of about 250 million years.
About 90% of the matter in the Milky Way is concentrated in stars. There are many types of stars. According to the physical properties, chemical composition, spatial distribution and motion characteristics of stars, stars can be divided into 5 star populations. The youngest Extreme Population I stars are mainly distributed in the spiral arms of the galactic disk; the oldest Extreme Population II stars are mainly distributed in the Galactic halo. Stars often clump together. In addition to a large number of double stars, more than 1,000 star clusters have been discovered in the Milky Way. There is also gas and dust in the Milky Way, and its content accounts for about 10% of the total mass of the Milky Way. The distribution of gas and dust is uneven, some gather into nebulae, and some are scattered in interstellar space. Since the 1960s, a large number of interstellar molecules have been discovered, such as CO, H2O, etc. Molecular clouds are the primary sites of star formation. The core of the Milky Way, the galactic center or core, is a very special place. It emits strong radio, infrared, X-ray and gamma-ray radiation. Its nature is still unclear, but there may be a giant black hole there, which is estimated to have a mass of tens of millions of times the mass of the sun. Little is known about the origin and evolution of the Milky Way.
In 1971, British astronomers Lyndon Bell and Martin Ness analyzed infrared observations and other properties of the central region of the Milky Way, pointed out that the energy source in the center of the Milky Way should be a black hole, and predicted that if their hypothesis was correct , a small-scale source emitting radio radiation should be observable in the center of the Milky Way, and the properties of this radiation should be the same as those observed in ground-based synchrotrons. Three years later, such a source was indeed discovered. This was Sagittarius A.
Sagittarius A has a very small scale, only equivalent to the size of an ordinary star. The radio radiation intensity it emits is 2*10 (34th power) erg/second. It is located at 0.2 light in the dynamic center of the Milky Way. Within the year. It is surrounded by ionized gas moving at speeds up to 300 kilometers per second and strong infrared radiation sources. All the known activities of stellar-level objects cannot explain the strange characteristics of Sagittarius A. Therefore, Sagittarius A seems to be the best candidate for a massive black hole. But since there is currently no conclusive evidence for massive black holes, astronomers are careful to avoid using conclusive language to mention massive black holes. Our Milky Way contains approximately 200 billion stars, of which there are approximately more than 100 billion stars, of which the sun is a typical one. The Milky Way is a rather large spiral galaxy with three main components: the galactic disk containing the spiral arms, the central bulge of the galactic center, and the halo.
Spiral galaxy M83, its size and shape are very similar to our Milky Way
Galactic disk:
Galactic disk: in the spiral galaxy , a flat disk composed of stars, dust and gas.
The galactic disk is the main component of the Milky Way. Ninety percent of the detectable matter in the Milky Way is within the scope of the galactic disk. The shape of the galactic disk is like a thin lens, distributed axially symmetrically around the galactic center. Its center is about 10,000 light-years thick, but this is the thickness of the slightly convex nuclear bulge. The galactic disk itself is only 2,000 light-years thick and nearly 10,000 light-years in diameter. 100,000 light years, it can be seen that the galactic disk is very thin overall.
Except for the galactic core within 1000 parsecs, which rotates rigidly around the galactic center, other parts of the galactic disk rotate poorly around the galactic center, that is, the farther away from the galactic center, the slower it rotates. The material in the galactic disk mainly exists in the form of stars. Most of the interstellar matter, which accounts for less than 10% of the total mass of the Milky Way, is also scattered in the galactic disk.
In addition to ionized hydrogen, molecular hydrogen and a variety of interstellar molecules, interstellar matter also contains 10% of interstellar dust. These solid particles with a diameter of about 1 micron are the main cause of interstellar extinction. Most of them are concentrated in the galactic plane. nearby.
Because the sun is located in the galactic disk, it is not easy for us to recognize the original appearance of the galactic disk. In order to ascertain the structure of the galactic disk, based on the study of the spiral arms of the spiral galaxy M31 (Andromeda Nebula) by Bader and Mayall in the 1940s, the main types of spiral arm objects were obtained, and then a census of these types was carried out in the Milky Way. Celestial body, three parallel arms near the sun were discovered. Due to interstellar extinction, optical observations cannot determine the overall appearance of the galactic disk. There is evidence that spiral arms are where interstellar gas accumulates, so detection of interstellar gas can reveal the spiral arm structure. The 21-centimeter radio spectrum line of interstellar gas is not blocked by interstellar dust and can reach almost the entire Milky Way. Both optical and radio observations indicate that the galactic disk does have a vortex structure.
Galaxy Center:
The central bulge of the galaxy is a very bright sphere with a diameter of about 20,000 light-years and a thickness of 10,000 light-years. This area is composed of high-density The stars are mainly composed of red stars that are about 10 billion years old or more. There is a lot of evidence that there is a huge black hole in the central region, and the activity of the galaxy core is very intense. The center of the Milky Way is the intersection of the Milky Way's axis of rotation and the galactic plane.
The galactic center is in the direction of Sagittarius. The 1950 epoch coordinates are: right ascension 174229, declination -28°5918. In addition to being a geometric point, the galactic center also means the central area of ??the Milky Way. The Sun is about 10 kiloparsecs from the galactic center and about 8 parsecs north of the galactic plane. There is a large amount of interstellar dust between the galactic center and the solar system, so it is difficult to see the galactic center in the visible light band with optical telescopes in the northern hemisphere. After the rise of radio astronomy and infrared observation technology, people were able to detect information about the galactic center through interstellar dust in the 2 micron to 73 cm waveband. Observation of the 21-centimeter spectral line of neutral hydrogen revealed that there is an expansion arm of hydrogen flow at a distance of 4 kiloparsecs from the galactic center, the so-called "three-kiloparsec arm" (the distance was initially mistakenly determined to be 3 kiloparsecs, but later, although Revised to 4 kiloparsecs, but still uses the old name). There are about 10 million solar masses of neutral hydrogen rushing toward the solar system at a speed of 53 kilometers per second. On the other side of the galactic center, there is an expanding arm of neutral hydrogen of roughly the same mass, moving away from the galactic center at a speed of 135 kilometers per second. They should have been ejected from the galactic center in an asymmetric manner 10 to 15 million years ago. In the sky area 300 parsecs away from the center of the galaxy, there is a disk of hydrogen gas rotating rapidly around the center of the galaxy, expanding outward at a speed of 70 to 140 kilometers per second. Within the disk are hydrogen molecular clouds with an average diameter of 30 parsecs. At a distance of 70 parsecs from the galactic center, there is a violently disturbed ionized hydrogen region that is also expanding outward at a high speed. It is now known that not only is a large amount of gas pouring out of the galactic center, but there is also a strong radio source at the galactic center, namely Sagittarius A, which emits strong synchrotron radiation. Detection by the Very Long Baseline Interferometer shows that the central area of ??the galactic center radio source is very small, even less than 10 astronomical units, that is, no larger than the orbit of Jupiter around the sun. Infrared observation data of 12.8 microns indicate that the mass of a silver core with a diameter of 1 parsec is equivalent to several million solar masses, of which about 1 million solar masses appear in the form of stars. There is a massive dense core in the galactic center, which may be a black hole. Relativistic electrons flowing into the dense core accretion disk are accelerated in a strong magnetic field, thus producing synchrotron radiation. The motion state of the gas in the galactic center, the strong radio source in the galactic center, and the existence of special galaxies with strong core activities (such as Seyfert galaxies) make us believe that in the evolutionary history of galaxies, including the Milky Way, there were core disturbance activities. This kind of activity has not stopped yet.
Galaxy halo:
The Milky Way halo is dispersed in a spherical area around the galactic disk. The diameter of the galactic halo is about 98,000 light-years. The density of stars here is very low. There are some globular star clusters composed of old stars. Some people believe that there is a huge spherical radio radiation area outside the galactic halo, called the galactic corona. The galactic corona extends to at least one hundred thousand parsecs or more from the galactic center. Three hundred and twenty thousand light-years away.
Cosmic Quotes:
The real mystery of the world is not the invisible things, but the visible things. ——Oscar Wilde
In the vast and silent starry sky, we weep for the lost sun.
——John de Laville de Maimon
In the center of the black furnace, where countless suns are sent out, infinite magic is stored. ——Arthur Rimbold
If a person can meditate on heavenly things, then when he faces earthly things, what he says and thinks will be nobler. ——Cicero
The Milky Way
The star system in which our earth and sun are located is an ordinary galaxy, derived from the milky white bright band projected on the celestial sphere. name. The Milky Way is a lens-shaped system with a diameter of about 25 kiloparsecs and a thickness of about 1 to 2 kiloparsecs. Its body is called the Silver Plate. High-luminosity stars, Milky Way star clusters and Milky Way nebulae form a spiral structure superimposed on the galactic disk. The center of the Milky Way is a massive bulge with a long axis 4 to 5 kiloparsecs long and a thickness of 4 kiloparsecs. The Milky Way is enveloped by a halo of about 30 kiloparsecs in diameter. The brightest members of the galactic halo are globular star clusters. The mass of the Milky Way is 1.4×1011 solar masses, of which stars account for about 90% and interstellar matter composed of gas and dust accounts for about 10%. The Milky Way as a whole is rotating poorly. The sun is about 8 parsecs north of the galactic plane and about 10 kiloparsecs from the galactic center. It orbits the galactic center at a speed of 250 kilometers per second and makes one revolution every 250 million years. The total density of matter (stars and interstellar matter) near the sun is approximately 0.13 solar mass/parsec 3 or 8.8×10-24 g/cm3. The Milky Way is an Sb or Sc type spiral galaxy with one to two hundred billion stars. It is the largest giant galaxy in the Local Galaxy Group except Andromeda. Its apparent absolute magnitude is Mv=-20.5. It evolves on a time scale of 1010 years.
A brief history of research In the mid-eighteenth century, people had realized that in addition to the planets, moon and other solar system objects, the stars in the sky were all "suns" in the distance. Wright, Kant and Lambert first thought that it was possible that all stars were assembled into a huge system that was limited in space.
The first person to study the origin of star systems through observation was F.W. Herschel. He used his own reflecting telescope to count the stars in several areas of the sky. In 1785, based on statistical studies of star counts, he drew a flat, uneven outline of the Milky Way structure with the sun at its center. He used 50 cm and 120 cm aperture telescopes to observe, and found that as the telescope's penetrating power increased, the number of faint stars observed also increased, but the edge of the Milky Way was still not visible. F.W. Herschel realized that the Milky Way was much larger than he originally estimated. After F.W. Herschel's death, his son J.F. Herschel inherited his father's business and expanded the scope of star counting work to the southern half of the sky. In the mid-19th century, the distances of stars began to be determined and all-sky star maps were compiled. In 1906, in order to re-study the structure of the stellar world, Kaptan proposed the "Selected Star Sector" plan, which was later called the "Captan Selection". He came up with a model similar to F.W. Herschel's in 1922, which was also a flat system with the sun in the center, dense stars in the center and sparse at the edges. Shapley discussed the size and shape of the Milky Way on an entirely different basis. He used the period-light relationship of Cepheids in the Magellanic Clouds discovered by LeWitt from 1908 to 1912 to determine the distance of globular star clusters that had Cepheids discovered at that time. Under the premise that there is no obvious interstellar extinction, a lens-shaped model of the Milky Way was established in 1918, with the sun not in the center. By the 1920s, Shapley's model had been recognized by the astronomical community. Shapley overestimated the size of the Milky Way by not taking into account interstellar extinction effects. This deviation was not corrected until 1930, when Trumpler confirmed the existence of interstellar matter.
Composition About 90% of the matter in the Milky Way is concentrated in stars. In 1905, Hertzsprung discovered that stars are divided into giant stars and dwarf stars. In 1913, after the advent of the Hertz-Russell diagram, based on the two parameters of spectral type and luminosity, it was known that in addition to main sequence stars, there are five branches: supergiant, giant, subgiant, subdwarf and white dwarf. In 1944, through observations of the Andromeda Galaxy, Bard determined that stars can be divided into two different star populations: Population I and Population II. Population I stars are young and metal-rich objects, distributed in the spiral arms and associated with interstellar matter. Population II stars are old and metal-poor objects that have no tendency to converge towards the galactic plane. In 1957, based on metal content, age, spatial distribution and motion characteristics, the two star populations were further subdivided into intermediate star population I, spiral arm star population (extreme star population I), disk star population, intermediate star population II and halo star population. StarClan (Extreme StarClan II).
Stars in pairs, clusters and clumps are common phenomena. Less than half of the total number of stars exist as single stars within 25 parsecs of the Sun. So far, 132 globular star clusters, more than 1,000 galactic star clusters, and numerous star associations have been observed. According to statistical deduction, there should be 18,000 galactic star clusters and 500 globular star clusters. At the beginning of the twentieth century, Barnard used photographic observations and discovered a large number of bright and dark nebulae. In 1904, the discovery of ionized calcium spectral lines in stellar spectra revealed the existence of interstellar matter. Subsequent spectroscopic and polarization studies identified the gas and dust components in the nebula. In recent years, through detection in the infrared band, stars are being formed in dense areas of dark nebulae. After the birth of radio astronomy, the 21 cm spectral line of neutral hydrogen was used to outline the spiral structure of the Milky Way. According to the description of the ionized hydrogen zone, it was found that there are three spiral arms near the sun: the Sagittarius Arm, the Orion Arm and the Perseus Arm; the sun is located inside the Orion Arm. In addition, a 3-kiloparsec arm was discovered in the direction of the galactic center. The distance between the spiral arms is about 1.6 kiloparsecs. In 1963, the interstellar molecule OH was observed using radio astronomy methods. This was a major breakthrough since the interstellar molecules CH, CN and CH+ were identified in the optical band between 1937 and 1941. By the end of 1979, more than 50 types of interstellar molecules had been discovered.
Structure The overall structure of the Milky Way is: the main part of the Milky Way's matter is composed of a thin disk, called the galactic disk, and the approximately spherical bulge in the center of the galactic disk is called the bulge. Stars are highly dense in the bulge region, and there is a small dense area in the center, called the galactic core. Outside the galactic disk is a larger, nearly spherical distribution system in which the density of matter is much lower than in the galactic disk, called the galactic halo. There is also a silver corona outside the silver halo, and its material distribution is also roughly spherical. See Milky Way Structure for details about the Milky Way.
Origin and Evolution The great subject of the origin of the Milky Way is currently poorly understood. This requires not only studying the origin and evolution of galaxies in general, but also cosmology. According to the Big Bang cosmology hypothesis, all the galaxies we have observed were formed 1010 years ago when high-density primitive matter fluctuated in density, experienced gravitational instability and continued to expand, gradually forming proto-galaxies and evolving into galaxy clusters including the Milky Way. of. The steady-state universe model hypothesis holds that galaxies are continuously formed in the core region of high-density proto-galaxies.
Research on the evolution of the Milky Way has only made some achievements in recent years. Data on the space motion of old stars near the sun show that during the collapse of the original Milky Way nebula, the first group of halo stars was born. Their age is more than 10 billion years, and their chemical composition is about 73% hydrogen and 27% helium. . Most of the gas material gathered into the galactic disk and subsequently formed a population of disk stars. In recent years, the overall evolution of the Milky Way has been explored from the perspectives of star formation and evolution, changes in element abundance, the activity of the galactic core and its role in evolution. The density wave theory developed in the 1960s has well explained the overall structure of the Milky Way spiral structure and its long-term maintenance mechanism.
What is a light year? A light-year is an astronomical unit of distance, indicating the length of distance traveled by light in one year. The speed of light is 300,000 kilometers per second, and it can travel 25.92 billion kilometers in one day. 365 times this length is one light year. This method of using time to express distance is also used daily in daily life. For example, the distance from Chengdu to Chongqing is 450 kilometers, and you can walk 60 kilometers every day. Therefore, we say that the distance from Chengdu to Chongqing is seven and a half days.
It only takes eight minutes and eighteen seconds for sunlight to reach the earth from the sun. It takes twenty-seven years for the light of Vega to reach the earth. After such a comparison, we will exclaim in surprise: "It's amazing! It's so far away!" But astronomers must laugh at how strange we are. They will tell us that there are countless stars tens of thousands of light years away from the sun, but there are only fifteen stars within ten light years. A few years ago, astronomers saw a star explode. After calculation, they found that the star exploded 1,300 years ago. This means that the star was 1,300 light years away from the earth.
Light-year is an astronomical unit used to express "distance". It is the distance obtained by traveling at the speed of light for one year. In astronomy, kilometers are not used to express distance, mainly because in the universe, the distance between celestial bodies is too far.
Just from the earth to the moon, it is about 380,000 (three hundred and eighty thousand) kilometers; if it is from the earth to the sun, it is more than 149,600,000 (one hundred and forty-nine million six hundred thousand) kilometers. Therefore, we must have larger units to calculate astronomical distances.
In the universe, light travels at the fastest speed, traveling at 3 x 105 kilometers per second, which is equivalent to light traveling around the earth seven and a half times (circling the earth) in just one second. One circle is about 40,000 kilometers). If we use the commonly used "kilometer" to express the distance of celestial bodies, the number obtained will be very large. For example: the moon is about 3.8 x 105 kilometers from the earth, the sun is about 1.5 x 108 kilometers from the earth, and Pluto, the farthest planet in the solar system, is about 6 x 109 kilometers from the earth. Light years are commonly used in astronomy (that is, the distance that light travels in one year = approximately 904605 x 1012 kilometers) to express the distance of celestial bodies. For example, the nearest star to the solar system is approximately 4.3 light years away, and the nearest star in the Milky Way, Andromeda, is approximately There are 2 million light years.
"Black hole" can easily be imagined as a "big black hole", but it is not the case. The so-called "black hole" is a celestial body whose gravitational field is so strong that even light cannot escape.
According to the general theory of relativity, the gravitational field will bend space-time. When a star is very large, its gravitational field has little effect on space-time, and light emitted from a certain point on the star's surface can be emitted in a straight line in any direction. The smaller the radius of the star, the greater its effect on the curvature of the surrounding space-time, and the light emitted at certain angles will return to the star's surface along the curved space.
When the radius of the star is as small as a certain value (called the "Schwarzschild radius" in astronomy), even the light emitted by the vertical surface is captured. At this point, the star becomes a black hole. Calling it "black" means that it is like a bottomless pit in the universe. Once any matter falls into it, it "seems" that it can never escape. In fact, black holes are truly "invisible", which we will talk about in a moment.
So, how are black holes formed? In fact, like white dwarfs and neutron stars, black holes are likely to evolve from stars.
We have introduced the formation process of white dwarfs and neutron stars in more detail. When a star ages, its thermonuclear reactions have exhausted the fuel (hydrogen) in the center, and there is not much energy produced by the center. In this way, it no longer has enough strength to bear the huge weight of the shell. Therefore, under the heavy pressure of the outer shell, the core begins to collapse until it finally forms a small and dense star that is able to balance with the pressure again.
Stars with smaller masses mainly evolve into white dwarfs, while stars with larger masses may form neutron stars. According to scientists' calculations, the total mass of a neutron star cannot be greater than three times the mass of the sun. If this value is exceeded, there will be no force left to contend with its own gravity, triggering another Big Crunch.
This time, according to scientists’ conjecture, matter will march inexorably toward the center point until it becomes a “point” where the volume tends to zero and the density tends to infinity. And once its radius shrinks to a certain extent (Schwarzschild radius), as we introduced above, the huge gravity will prevent even light from being emitted outward, thus cutting off all connections between the star and the outside world - " "Black Hole" was born.
Compared with other celestial bodies, black holes are too special. For example, black holes have "invisibility" and people cannot directly observe them. Even scientists can only make various conjectures about its internal structure. So, how do black holes hide themselves? The answer is - curved space. We all know that light travels in straight lines. This is the most basic common sense. However, according to the general theory of relativity, space will bend under the action of the gravitational field. At this time, although light still travels along the shortest distance between any two points, it is no longer a straight line, but a curve. Figuratively speaking, it seems that light was originally going to go in a straight line, but the strong gravity pulled it away from its original direction.
On Earth, because the gravitational field has a small effect, this bending is minimal. Around a black hole, this deformation of space is very large. In this way, even if a part of the light emitted by a star blocked by a black hole will fall into the black hole and disappear, the other part of the light will bypass the black hole in the curved space and reach the earth.
Therefore, we can effortlessly observe the starry sky behind the black hole as if the black hole does not exist. This is the invisibility of the black hole.
What’s more interesting is that not only the light emitted by some stars towards the earth can reach the earth directly, but the light emitted in other directions may also be refracted by the strong gravity of nearby black holes and reach the earth. In this way, we can not only see the "face" of the star, but also its sides and even its back at the same time!
"Black hole" is undoubtedly one of the most challenging and exciting astronomical theories of this century. Many scientists are working hard to unveil its mystery, and new theories are constantly being proposed. However, these latest results of contemporary astrophysics cannot be explained clearly in a few words here
Black hole pictures:/i?tn=baiduimage&ct=201326592&lm=-1&cl=2&word=%BA%DA%B6%B4&t =3
Solar system pictures:/i?tn=baiduimage&ct=201326592&cl=2&lm=-1&pv=&word=%CC%AB%D1%F4%CF%B5&z=0
Galaxy Picture:/i?tn=baiduimage&ct=201326592&cl=2&lm=-1&pv=&word=%D2%F8%BA%D3&z=0