Consequence of Hubble's law. Hubble constant

At one time, Hubble's law made a revolution in professional astronomy. At the beginning of the 20th century, the American astronomer Edwin Hubble proved that our Universe is not static, as it seemed before, but is constantly expanding.

Hubble constant: data from various spacecraft

Hubble's law is a physical and mathematical formula that proves that our Universe is constant. Moreover, the expansion of outer space, in which our Milky Way galaxy is also located, is characterized by uniformity and isotropy. That is, our universe is expanding equally in all directions. The formulation of Hubble's law proves and describes not only the theory of the expansion of the Universe, but also the main idea of its origin - the theory.

Most often in the scientific literature, the Hubble law is found under the following formulation: v=H0*r. In this formula, v means the speed of the galaxy, H0 is the proportionality factor that relates the distance from the Earth to the space object with the speed of its removal (this coefficient is also called the "Hubble Constant"), r is the distance to the galaxy.

In some sources there is another formulation of Hubble's law: cz=H0*r. Here c acts as the speed of light, and z symbolizes the redshift - the shift of the spectral lines of chemical elements to the long-wavelength red side of the spectrum as they move away. Other formulations of this law can be found in the physico-theoretical literature. However, the difference in formulations does not change the essence of Hubble's law, and its essence lies in the description of the fact that ours is continuously expanding in all directions.

Law discovery

The age and future of the universe can be determined by measuring the Hubble constant

A prerequisite for the discovery of Hubble's law was a series of astronomical observations. So, in 1913, the American astrophysicist Weil Slider discovered that several other huge space objects are moving at high speed relative to the solar system. This gave the scientist reason to assume that the nebula is not planetary systems forming in our galaxy, but nascent stars that are outside our galaxy. Further observation of the nebulae showed that they are not only other galactic worlds, but are constantly moving away from us. This fact has given the astronomical community the opportunity to assume that the universe is constantly expanding.

In 1927, the Belgian astronomer Georges Lemaitre experimentally established that galaxies in the universe are moving away from each other in outer space. In 1929, the American scientist Edwin Hubble, using a 254-cm telescope, found that the universe is expanding and galaxies in outer space are moving away from each other. Using his observations, Edwin Hubble formulated a mathematical formula that accurately describes the principle of the expansion of the Universe to this day, and is of great importance for both theoretical and practical astronomy.

Hubble's law: application and implications for astronomy

Hubble's law is of great importance for astronomy. It is widely used by modern scientists as part of the creation of various scientific theories, as well as in the observation of space objects.

The main significance of Hubble's law for astronomy is that it confirms the postulate: the Universe is constantly expanding. At the same time, Hubble's law serves as an additional confirmation of the Big Bang theory, because, according to modern scientists, it was the Big Bang that served as the impetus for the expansion of the "matter" of the Universe.

Hubble's law also made it clear that the universe is expanding in all directions equally. At whatever point in outer space the observer would not be, if he looks around him, he will notice that all objects around him are equally moving away from him. This fact can be most successfully expressed by a quote from the philosopher Nicholas of Cusa, who, back in the 15th century, said: "Any point is the center of the Infinite Universe."

With the help of Hubble's law, modern astronomers can, with a high degree of probability, calculate the position of galaxies and clusters of galaxies in the future. In the same way, it can be used to calculate the estimated location of any object in outer space after a certain amount of time.

The reciprocal of the Hubble constant is about 13.78 billion years. This value indicates how much time has passed since the beginning of the expansion of the Universe, and therefore, quite likely indicates its age.
Most often, the Hubble law is used to determine the exact distances to objects in outer space.

3. Hubble's law determines the distance from us to distant galaxies. As for the galaxies closest to us, here its effect is not so pronounced. This is due to the fact that these galaxies, in addition to the speed associated with the expansion of the Universe, also have their own speed. In this regard, they can both move away from us and approach us. But, in general, Hubble's law is relevant for all space objects in the Universe.

The great physicists of the past I. Newton and A. Einstein saw the Universe as static. The Soviet physicist A. Fridman in 1924 came up with the theory of "receding" galaxies. Friedman predicted the expansion of the universe. This was a revolutionary upheaval in the physical representation of our world.

American astronomer Edwin Hubble explored the Andromeda nebula. By 1923, he was able to consider that its outskirts are clusters of individual stars. Hubble calculated the distance to the nebula. It turned out to be 900,000 light years (a more accurately calculated distance today is 2.3 million light years). That is, the nebula is located far beyond the Milky Way - Our Galaxy. After observing this and other nebulae, Hubble came to a conclusion about the structure of the Universe.

The universe is made up of a collection of huge star clusters - galaxies.

It is they who appear to us in the sky as distant foggy "clouds", since we simply cannot consider individual stars at such a great distance.

E. Hubble noticed an important aspect in the data obtained, which astronomers had observed before, but found it difficult to interpret. Namely, the observed length of the spectral light waves emitted by the atoms of distant galaxies is somewhat longer than the length of the spectral waves emitted by the same atoms under the conditions of terrestrial laboratories. That is, in the emission spectrum of neighboring galaxies, a light quantum emitted by an atom during an electron jump from orbit to orbit is shifted in frequency in the direction of the red part of the spectrum compared to a similar quantum emitted by the same atom on Earth. Hubble took it upon himself to interpret this observation as a manifestation of the Doppler effect.

All observed neighboring galaxies are moving away from the Earth, since almost all galactic objects outside the Milky Way have a red spectral shift proportional to the speed of their removal.

Most importantly, Hubble was able to compare the results of his measurements of the distances to neighboring galaxies with the measurements of their removal rates (by redshift).

Mathematically, the law is formulated very simply:

where v is the speed of the galaxy moving away from us,

r is the distance to it,

H is the Hubble constant.

And, although initially Hubble came to this law as a result of observing only a few galaxies closest to us, not one of the many new galaxies of the visible Universe discovered since then, more and more distant from the Milky Way, does not fall out of this law.

So, the main consequence of Hubble's law:

The universe is expanding.

The very fabric of world space is expanding. All observers (and we are no exception) consider themselves to be at the center of the Universe.

4. The Big Bang Theory

From the experimental fact of the recession of galaxies, the age of the Universe was estimated. It turned out to be equal - about 15 billion years! Thus began the era of modern cosmology.

Naturally, the question arises: what happened in the beginning? In total, it took scientists about 20 years to completely turn over the ideas about the Universe again.

The answer was proposed by the outstanding physicist G. Gamow (1904 - 1968) in the 40s. The history of our world began with the Big Bang. This is exactly what most astrophysicists think today.

The Big Bang is a rapid drop in the initially huge density, temperature and pressure of matter concentrated in a very small volume of the Universe. All the matter of the universe was compressed into a dense lump of protomatter, enclosed in a very small volume compared to the current scale of the Universe.

The idea of the Universe, which was born from a superdense clot of superhot matter and has been expanding and cooling since then, is called the Big Bang theory.

There is no more successful cosmological model of the origin and evolution of the Universe today.

According to the Big Bang theory, the early universe consisted of photons, electrons, and other particles. Photons constantly interacted with other particles. As the universe expanded, it cooled, and at a certain stage, electrons began to combine with the nuclei of hydrogen and helium and form atoms. This happened at a temperature of about 3000 K and the approximate age of the universe is 400,000 years. From that moment on, photons were able to move freely in space, practically without interacting with matter. But we are left with "witnesses" of that era - these are relic photons. It is believed that the relic radiation has been preserved from the initial stages of the existence of the Universe and evenly fills it. As a result of further cooling of the radiation, its temperature decreased and now is about 3 K.

The existence of the CMB was predicted theoretically within the framework of the Big Bang theory. It is regarded as one of the main confirmations of the Big Bang theory.

The apparent speed of a galaxy moving away from us is directly proportional to its distance.

Returning from the First World War, Edwin Hubble got a job at Mount Wilson, a high-altitude astronomical observatory in Southern California, which in those years was the best equipped in the world. Using her latest reflecting telescope with a primary mirror diameter of 2.5 m, he made a series of curious measurements that forever changed our understanding of the universe.

In fact, Hubble set out to investigate one long-standing astronomical problem - the nature of nebulae. These mysterious objects, starting from the 18th century, worried scientists with the mystery of their origin. By the 20th century, some of these nebulae had given birth to stars and dispersed, but most of the clouds remained nebulous - and in particular by nature. Here, scientists asked the question: where, in fact, are these nebulous formations located - in our Galaxy? Or do some of them represent other “islands of the Universe”, to use the sophisticated language of that era? Until the commissioning of the Mount Wilson telescope in 1917, this question was purely theoretical, since there were no technical means to measure the distances to these nebulae.

Hubble began his research with the Andromeda Nebula, perhaps the most popular since time immemorial. By 1923, he was able to see that the outskirts of this nebula are clusters of individual stars, some of which belong to the class Cepheid variables(according to astronomical classification). Observing a variable Cepheid for a sufficiently long time, astronomers measure the period of change in its luminosity, and then, from the period-luminosity dependence, they determine the amount of light emitted by it.

To better understand what the next step is, let's use an analogy. Imagine that you are standing in a pitch black night, and then in the distance someone turns on an electric lamp. Since you can’t see anything around you except this distant light bulb, it’s almost impossible for you to determine the distance to it. Maybe it is very bright and glows far away, or maybe it is dim and glows nearby. How to define it? Now imagine that you somehow managed to find out the power of the lamp - say, 60, 100 or 150 watts. The task is immediately simplified, since by the apparent luminosity you can already roughly estimate the geometric distance to it. So: when measuring the period of change in the luminosity of a Cepheid, the astronomer is in approximately the same situation as you, calculating the distance to a distant lamp, knowing its luminosity (radiation power).

The first thing Hubble did was to calculate the distance to the Cepheids on the outskirts of the Andromeda Nebula, and thus to the nebula itself: 900,000 light-years (a more accurately calculated distance to the Andromeda Galaxy, as it is now called, is 2.3 million light years. Note. author) - that is, the nebula is located far beyond the Milky Way - our galaxy. After observing this and other nebulae, Hubble came to a basic conclusion about the structure of the universe: it consists of a set of huge star clusters - galaxies. It is they who appear to us in the sky as distant foggy "clouds", since we simply cannot consider individual stars at such a great distance. This discovery alone, in fact, would have been enough for Hubble for worldwide recognition of his merits to science.

The scientist, however, did not limit himself to this and noticed another important aspect in the data obtained, which astronomers had observed before, but found it difficult to interpret. Namely: the observed length of the spectral light waves emitted by the atoms of distant galaxies is somewhat lower than the length of the spectral waves emitted by the same atoms under the conditions of terrestrial laboratories. That is, in the emission spectrum of neighboring galaxies, a light quantum emitted by an atom during an electron jump from orbit to orbit is shifted in frequency in the direction of the red part of the spectrum compared to a similar quantum emitted by the same atom on Earth. Hubble took it upon himself to interpret this observation as a manifestation of the Doppler effect, meaning that all observed neighboring galaxies are removed from the Earth, since almost all galactic objects outside the Milky Way have precisely red spectral shift proportional to their removal rate.

Most importantly, Hubble was able to compare the results of his measurements of distances to neighboring galaxies (from observations of Cepheid variables) with measurements of their removal rates (from redshifts). And Hubble found that the further away a galaxy is from us, the faster it moves away. This very phenomenon of centripetal "retreat" of the visible Universe with increasing speed as it moves away from the local point of observation is called Hubble's law. Mathematically, it is formulated very simply:

where v is the speed at which the galaxy is moving away from us, r is the distance to it, and H- so-called Hubble constant. The latter is determined experimentally and is currently estimated to be about 70 km/(s·Mpc) (kilometers per second per megaparsec; 1 Mpc is approximately equal to 3.3 million light years). This means that a galaxy at a distance of 10 megaparsecs from us runs away from us at a speed of 700 km/s, a galaxy at a distance of 100 Mpc at a speed of 7000 km/s, etc. And, although initially Hubble came to this law as a result of observing only a few galaxies closest to us, not one of the many new galaxies of the visible Universe discovered since then, more and more distant from the Milky Way, does not fall out of this law.

So, the main and - it would seem - an incredible consequence of the Hubble law: the Universe is expanding! This image seems to me most clearly like this: galaxies are raisins in a rapidly rising yeast dough. Imagine yourself as a microscopic creature on one of the raisins, the dough for which seems transparent: and what will you see? As the dough rises, all other raisins move away from you, and the farther the raisin is, the faster it moves away from you (because there is more expanding dough between you and the distant raisins than between you and the nearest raisins). At the same time, it will appear to you that it is you who are in the very center of the expanding universal test, and there is nothing strange in this - if you were on another raisin, everything would appear to you in exactly the same way. So galaxies scatter for one simple reason: the very fabric of world space is expanding. All observers (and we are no exception) consider themselves to be at the center of the Universe. This was best formulated by the 15th-century thinker Nicholas of Cusa: "Any point is the center of an infinite universe."

However, Hubble's law also tells us something else about the nature of the universe - and this "something" is a thing that is simply extraordinary. The universe had a beginning in time. And this is a very simple conclusion: it is enough to take and mentally “scroll back” the conditional motion picture of the expansion of the Universe that we observe - and we will reach the point when all the matter of the universe was compressed into a dense lump of protomatter, enclosed in a very small volume compared to the current scale of the Universe. The idea of the Universe, which was born from a superdense clot of superhot matter and has been expanding and cooling since then, was called the Big Bang theory, and there is no more successful cosmological model of the origin and evolution of the Universe today. Hubble's law, by the way, also helps to estimate the age of the Universe (of course, very simplified and approximate). Let's assume that all galaxies from the very beginning moved away from us at the same speed v that we are seeing today. Let be t- the time elapsed since the start of their expansion. This will be the age of the Universe, and it is determined by the relations:

v x t = r, or t=r/V

But it follows from Hubble's law that

r/v = 1/H

where H is the Hubble constant. This means that by measuring the receding velocities of the outer galaxies and experimentally determining H, we thereby also obtain an estimate of the time during which the galaxies diverge. This is the estimated time of existence of the universe. Try to remember: the most recent estimate is that our universe is about 15 billion years old, give or take a few billion years. (For comparison: the age of the Earth is estimated at 4.5 billion years, and life on it originated about 4 billion years ago.)

See also:

Edwin Powell Hubble, 1889-1953

American astronomer. Born in Marshfield (Missouri, USA), grew up in Wheaton (Illinois) - then it was not a university, but an industrial suburb of Chicago. He graduated with honors from the University of Chicago (where he also distinguished himself in sports achievements). While still in college, he worked as an assistant in the laboratory of Nobel laureate Robert Milliken (see Millikan's Experience), and during the summer holidays as a surveyor at railway construction. Subsequently, Hubble liked to remember how, together with another worker, they fell behind the last train that took their surveying team back to the benefits of civilization. For three days they wandered in the forests before they reached the populated area. They didn’t have any provisions with them, but, according to Hubble himself, “You could, of course, kill a hedgehog or a bird, but why? The main thing is that there was enough water around.

After receiving a bachelor's degree in 1910, Hubble went to Oxford thanks to a Rhodes scholarship. There he began to study Roman and British law, but, in his own words, "traded law for astronomy" and returned to Chicago, where he began preparing for the defense of his thesis. The scientist conducted most of the observations at the base of the Yerkes Observatory, located north of Chicago. There he was noticed by George Ellery Hale (George Ellery Hale, 1868-1938) and in 1917 invited the young man to the new Mount Wilson Observatory.

Here, however, historical events intervened. The United States entered World War I, and Hubble completed his Ph.D. thesis overnight. D., defended her the next morning - and immediately volunteered for the army. His supervisor, Hale, received a telegram from Hubble that read: “I regret having to decline the invitation to mark the defense. Went to war." The volunteer unit arrived in France at the very end of the war and did not even take part in the hostilities, but Hubble managed to get a shrapnel wound from a stray projectile. Demobilized in the summer of 1919, the scientist immediately returned to the Mount Wilson Observatory in California, where he soon discovered that the Universe consists of expanding galaxies, which was called Hubble's law.

In the 1930s, Hubble continued to actively study the world beyond the Milky Way, for which he soon won recognition not only in scientific circles, but also among the general public. He liked the glory, and in the photographs of those years, the scientist can often be seen posing in the company of famous movie stars of that era.

Hubble's popular science book "The Realm of the Nebulae" (The Realm of Nebulae), which was released in 1936, added to the popularity of the scientist. In fairness, it should be noted that during the Second World War, the scientist left his astrophysical research and honestly engaged in applied ballistics as the chief executive officer of the test site with a supersonic wind tunnel in Aberdeen (Maryland), after which he returned to astrophysics until the end of his days served as chairman of the joint scientific council of the Mount Wilson Observatory and the Palomar Observatory. In particular, he owns the driving idea and technical development of the basic design of the famous two-hundred-inch (five-meter) Hale telescope, commissioned in 1949 on the basis of the Palomar Observatory. This telescope to this day remains the pinnacle of astrometry embodied in the material. And, probably, it is fair that it was Hubble who managed - the first of modern astrophysicists - to look into the depths of the Universe through the eyepiece of this wonderful instrument.

Aside from astronomy, Edwin Hubble was generally a man of uniquely broad interests. So, in 1938 he was elected to the Board of Trustees of the Southern California Huntington Library and the Art Gallery attached to it (Los Angeles, USA). The scientist donated his unique collection of ancient books on the history of science to this library. Hubble's favorite type of recreation was spinning fishing - he achieved heights in this too, and his record catches in the mountain streams of the Rocky Mountains (USA) and on the Test River (England) are still considered unsurpassed ... Edwin Hubble died suddenly on 28 September 1953 as a result of a cerebral hemorrhage.

“In 1744, the Swiss astronomer de Shezo and, independently of him, in 1826 Olbers formulated the following paradox,” writes T. Regge in his book, “which led to the crisis of the then naive cosmological models. Imagine that the space around the Earth is infinite, eternal and unchanging, and that it is evenly filled with stars, and their density is on average constant. Using simple calculations, Szezo and Olbers showed that the total amount of light sent to Earth by stars must be infinite, which is why the night sky will not be black, but, to put it mildly, flooded with light. To get rid of their paradox, they suggested the existence of vast wandering opaque nebulae in space, obscuring the most distant stars. In fact, it is impossible to get out of the situation this way: by absorbing the light from the stars, the nebulae would involuntarily heat up and themselves emit light in the same way as the stars.

So, if the cosmological principle is true, then we cannot accept Aristotle's idea of an eternal and unchanging universe. Here, as in the case of relativity, nature seems to prefer symmetry in its development, rather than the imaginary Aristotelian perfection.

However, the most serious blow to the inviolability of the Universe was dealt not by the theory of stellar evolution, but by the results of measurements of the receding velocities of galaxies obtained by the great American astronomer Edwin Hubble.

Hubble (1889–1953) was born in the small town of Marshfield, Missouri, to John Powell Hubble, an insurance agent, and his wife, Virginia Lee James. Edwin became interested in astronomy early, probably under the influence of his maternal grandfather, who built himself a small telescope.

Edwin graduated from high school in 1906. At the age of sixteen, Hubble entered the University of Chicago, which was then one of the top ten best educational institutions in the United States. The astronomer F.R. Multon, author of the well-known theory of the origin of the solar system. He had a great influence on the further choice of Hubble.

After graduating from university, Hubble managed to get a Rhodes scholarship and go to England for three years to continue his education. However, instead of the natural sciences, he had to study law at Cambridge.

In the summer of 1913, Edwin returned to his homeland, but he never became a lawyer. Hubble strove for science and returned to the University of Chicago, where at the Yerkes Observatory, under the guidance of Professor Frost, he prepared a dissertation for a Ph.D. His work was a statistical study of faint spiral nebulae in several parts of the sky and was not particularly original. But even then, Hubble shared the opinion that "spirals are star systems at distances often measured in millions of light years."

At that time, a great event was approaching in astronomy - the Mount Wilson Observatory, which was headed by the remarkable organizer of science D.E. Hale, was preparing to commission the largest telescope - a hundred-inch reflector (250 cm - Approx. Aut.). Among others, Hubble received an invitation to work at the observatory. However, in the spring of 1917, when he was completing his dissertation, the United States entered the First World War. The young scientist declined the invitation and volunteered for the army. As part of the American Expeditionary Force, Major Hubble ended up in Europe in the fall of 1918, shortly before the end of the war, and did not have time to take part in the hostilities. In the summer of 1919, Hubble demobilized and hurried to Pasadena to accept Hale's invitation.

At the observatory, Hubble began to study nebulae, focusing first on objects visible in the Milky Way band.

In the anthology "Book of Primary Sources on Astronomy and Astrophysics, 1900-1975" by K. Lang and O. Gingerich (USA), which reproduced the most outstanding research for three quarters of the twentieth century, three Hubble works are placed, and the first of them is a work on the classification of extragalactic nebulae. The other two relate to the establishment of the nature of these nebulae and the discovery of the law of redshift.

In 1923, Hubble began observing the nebula in the constellation Andromeda with 60 and 100 inch reflectors. The scientist concluded that the large Andromeda Nebula is indeed another star system. Hubble obtained the same results for the MOS 6822 nebula and the Triangulum nebula.

Although a number of astronomers soon became aware of Hubble's discovery, the official announcement was made only on January 1, 1925, when G. Ressel read Hubble's report at the congress of the American Astronomical Society. The famous astronomer D. Stebbins wrote that the Hubble report "expanded the volume of the material world a hundredfold and definitely resolved the long dispute about the nature of spirals, proving that these are gigantic collections of stars, almost comparable in size to our own Galaxy." Now the Universe appeared before astronomers as a space filled with star islands - galaxies.

Already one establishment of the true nature of the nebulae determined the place of Hubble in the history of astronomy. But an even more outstanding achievement fell to his lot - the discovery of the law of redshift.

Spectral studies of spiral and elliptical "nebulae" were begun in 1912 on the basis of such considerations,1 if they are really located outside our Galaxy, then they do not participate in its rotation and therefore their radial velocities will indicate the motion of the Sun. It was expected that these speeds would be on the order of 200–300 kilometers per second, i.e., they would correspond to the speed of the Sun around the center of the Galaxy.

Meanwhile, with a few exceptions, the radial velocities of galaxies turned out to be much higher: they were measured in thousands and tens of thousands of kilometers per second.

In mid-January 1929, in the Proceedings of the US National Academy of Sciences, Hubble presented a short note entitled "On the Relationship between Distance and Radial Velocity of Extragalactic Nebulae." At that time, Hubble already had the ability to match the speed of a galaxy with its distance for 36 objects. It turned out that these two quantities are related by the condition of direct proportionality: the speed is equal to the distance multiplied by the Hubble constant.

This expression is called the Hubble law. The scientist in 1929 determined the numerical value of the Hubble constant at 500 km / (s x Mpc). However, he made a mistake in establishing the distances to galaxies. After repeated corrections and refinements of these distances, the numerical value of the Hubble constant is now taken to be 50 km/(s x Mpc).

Mount Wilson Observatory began to determine the radial velocities of ever more distant galaxies. By 1936, M. Humason published data for one hundred nebulae. A record speed of 42,000 kilometers per second was recorded from a member of a distant cluster of galaxies in Ursa Major. But this was already the limit of the 100-inch telescope. More powerful tools were needed.

“It is possible to approach the question of the Hubble expansion of the cosmos using more familiar, intuitive images,” says T. Regge. - For example, let's imagine soldiers lined up on some square with an interval of 1 meter. Let the command then be given to move the rows apart in one minute so that this interval increases to 2 meters. No matter how the command is executed, the relative speed of two soldiers standing next to each other will be 1 m / min, and the relative speed of two soldiers standing at a distance of 100 meters from each other will be 100 m / min, if we take into account that the distance between them will increase from 100 to 200 meters. Thus, the speed of mutual removal is proportional to the distance. Note that after the expansion of the series, the cosmological principle remains valid: the “galaxies-soldiers” are still uniformly distributed, and the same proportions between different mutual distances are preserved.

The only drawback of our comparison is that in practice one of the soldiers always stands motionless in the center of the square, while the rest scatter at speeds that are greater, the greater the distance from them to the center. In space, however, there are no milestones against which absolute measurements of velocity could be made; We are deprived of such an opportunity by the theory of relativity: everyone can compare his movement only with the movement of those walking next to him, and at the same time it will seem to him that they are running away from him.

We see, therefore, that Hubble's law ensures that the cosmological principle remains unchanged at all times, and this confirms us in the opinion that both the law and the principle itself are indeed valid.

Another example of an intuitive image is the explosion of a bomb; in this case, the faster the fragment flies, the farther it will fly. A moment after the explosion itself, we see that the fragments are distributed in accordance with Hubble's law, that is, their speeds are proportional to their distances. Here, however, the cosmological principle is violated, because if we move far enough from the explosion site, we will not see any fragments. In this way, the most famous term in modern cosmology "big bang" is suggested. According to these ideas, about 20 billion years ago, all the matter of the Universe was collected at one point, from which the rapid expansion of the Universe to modern sizes began.

Hubble's law was almost immediately recognized in science. The importance of Hubble's discovery was highly appreciated by Einstein. In January 1931, he wrote: "The new observations of Hubble and Humason about redshift ... make it plausible that the general structure of the universe is not stationary."

Hubble's discovery finally destroyed the idea that had existed since the time of Aristotle about a static, unshakable Universe. Currently, Hubble's law is used to determine the distances to distant galaxies and quasars.

CLASSIFICATION OF GALAXIES

The history of the "discovery" of the world of galaxies is very instructive. More than two hundred years ago, Herschel built the first model of the Galaxy, underestimating its size by fifteen times. Studying numerous nebulae, the variety of forms of which he first discovered, Herschel came to the conclusion that some of them are distant star systems "of the type of our star system." He wrote: "I do not find it necessary to repeat that the heavens consist of areas in which the suns are collected in systems." And one more thing: "... these nebulae can also be called the Milky Ways - with a small letter, in contrast to our system."

However, in the end, Herschel himself took a different position regarding the nature of nebulae. And it was no accident. After all, he managed to prove that most of the nebulae discovered and observed by him do not consist of stars, but of gas. He came to a very pessimistic conclusion: "Everything outside our own system is shrouded in the darkness of the unknown."

The English astronomer Agnes Clarke wrote in The System of the Stars in 1890: “It is safe to say that no competent scientist, having all the available evidence, will be of the opinion that even one nebula is a star system comparable in size to Milky way. It has been practically established that all objects observed in the sky (both stars and nebulae) belong to one huge aggregate "...

The reason for this point of view was that for a long time astronomers were not able to determine the distances to these star systems. So, from the measurements carried out in 1907, it allegedly followed that the distance to the Andromeda Nebula does not exceed 19 light years. Four years later, astronomers came to the conclusion that this distance is about 1600 light years. In both cases, the impression was created that the mentioned nebula is indeed located in our Galaxy.

In the twenties of the last century between the astronomers Shapley and Curtis broke out a fierce dispute about the nature of the Galaxy and other objects visible with telescopes. Among these objects is the famous Andromeda Nebula (M31), which is only visible to the naked eye as a star of the fourth magnitude, but unfolds into a majestic spiral when viewed through a large telescope. By this time, outbursts of new stars had been registered in some of these nebulae. Curtis suggested that, at maximum brightness, these stars radiate the same amount of energy as new stars in our Galaxy. So, he found that the distance to the Andromeda Nebula is 500,000 light years. This gave Curtis reason to argue that spiral nebulae are distant stellar universes like the Milky Way. Shapley did not agree with this conclusion, and his reasoning was also quite logical.

According to Shapley, the entire Universe consists of one of our Galaxy, and spiral nebulae like M31 are smaller objects scattered inside this Galaxy, like raisins in a cake.

Suppose, he said, that the Andromeda Nebula has the same dimensions as our Galaxy (300,000 light-years, according to him). Then, knowing its angular dimensions, we find that the distance to this nebula is 10 million light years! But then it is not clear why the new stars observed in the Andromeda Nebula have a greater brightness than in our Galaxy. If the brightness of the new ones in this "nebula" and in our Galaxy is the same, then it follows that the Andromeda Nebula is 20 times smaller than our Galaxy.

Curtis, on the contrary, believed that M31 is an independent island galaxy, not inferior in dignity to our Galaxy and distant from it by several hundred thousand light-years. The creation of large telescopes and the progress of astrophysics led to the recognition of the correctness of Curtis. Shapley's measurements turned out to be wrong. He greatly underestimated the distance to the M31. Curtis, however, was also wrong: it is now known that the distance to M31 is more than two million light years.

The nature of spiral nebulae was finally established by Edwin Hubble, who at the end of 1923 discovered the first Cepheid in the Andromeda Nebula, and soon several more Cepheids. Estimating their apparent magnitudes and periods, Hubble found that the distance to this "nebula" is 900,000 light years. Thus, the belonging of spiral "nebulae" to the world of stellar systems such as our Galaxy was finally established.

If we talk about the distances to these objects, then they still had to be clarified and revised. So, in fact, the distance to the galaxy M 31 in Andromeda is 2.3 million light years.

The world of galaxies turned out to be surprisingly huge. But even more surprising is the diversity of its forms.

The first and rather successful classification of galaxies according to their appearance was already undertaken by Hubble in 1925. He proposed to attribute galaxies to one of the following three types: 1) elliptical (denoted by the letter E), 2) spiral (S) and 3) irregular (1 g).

Those galaxies were classified as elliptical, which have the form of regular circles or ellipses and whose brightness gradually decreases from the center to the periphery. This group is subdivided into eight subtypes from EO to E7 as the apparent contraction of the galaxy increases. SO lenticular galaxies are similar to highly oblate elliptical systems, but have a well-defined central stellar core.

Spiral galaxies, depending on the degree of development of spirals, are divided into subclasses Sa, Sb and Sc. In Sa-type galaxies, the main component is the core, while the spirals are still weakly expressed. The transition to the next subclass is a statement of the fact of the increasing development of spirals and a decrease in the apparent size of the nucleus.

Parallel to normal spiral galaxies, there are also so-called criss-crossed spiral systems (SB). In galaxies of this type, a very bright central core is crossed in diameter by a transverse band. From the ends of this bridge, the spiral branches begin, and, depending on the degree of development of the spirals, these galaxies are divided into subtypes SBa, SBb, and SBc.

Irregular galaxies (Ir) are objects that do not have a clearly defined nucleus and do not have rotational symmetry. Their typical representatives are the Magellanic Clouds.

“I used it for 30 years,” the famous astronomer Walter Baade later wrote, “and although I stubbornly searched for objects that could not really fit into the Hubble system, their number turned out to be so insignificant that I can count them on the fingers.” The Hubble classification continues to serve science, and all subsequent modifications of the creature did not affect it.

For some time it was believed that this classification has an evolutionary meaning, i.e., that galaxies "move" along Hubble's "tuning fork diagram", successively changing their shape. This view is now considered erroneous.

Among the several thousand brightest galaxies, there are 17 percent elliptical, 80 percent spiral, and about 3 percent irregular.

In 1957, the Soviet astronomer B.A. Vorontsov-Velyaminov discovered the existence of "interacting galaxies" - galaxies connected by "bars", "tails", as well as "gamma-forms", i.e. galaxies in which one spiral "twists", while the other "unwinds". Later, compact galaxies were discovered, the size of which is only about 3000 light-years, and star systems isolated in space with a diameter of only 200 light-years. In their appearance, they practically do not differ from the stars of our Galaxy.

The new general catalog (NOC) contains a list of about ten thousand galaxies, along with their most important characteristics (luminosity, shape, distance, etc.) - and this is only a small fraction of the ten billion galaxies that are in principle distinguishable from Earth. A fabulous giant, capable of covering a hundred or two million light-years, looking at the Universe, would see that it is filled with cosmic fog, of which galaxies are droplets. At times there are clusters of thousands of galaxies clustered together. One such giant cluster is in the constellation Virgo.

One of the most important works of Edwin Hubble was the observation of the nebula located in the constellation Andromeda. By studying it with a hundred-inch reflector, the scientist was able to classify the nebula as some kind of star system. The same applies to the nebula in the constellation Triangulum, which also received the status of a galaxy. Hubble's discovery expanded the volume of the material world. Now the Universe began to look like a space filled with galaxies - giant clusters of stars. Consider the law he discovered - Hubble's law, one of the most fundamental laws of modern cosmology.

The Hubble constant is H 0 = (67.80 ± 0.77) (km/s)/Mpc

History and essence of the discovery

The cosmological law that characterizes the expansion of the universe is now known precisely as the Hubble law. This is the most important observational fact in modern cosmology. It helps in estimating the expansion time of the universe. Calculations are made taking into account the coefficient of proportionality, called the Hubble constant. The law itself received its current status at first, as a result of the work of J. Lemaitre, and later E. Hubble, who used the properties for this. These interesting objects have periodic changes in luminosity, which makes it possible to determine their distance quite reliably. Using the period-luminosity relationship, he measured the distances to some Cepheids. He also identified their galaxies, which made it possible to calculate the radial velocities. All these experiments were carried out in 1929.

The value of the coefficient of proportionality, which the scientist deduced, was approximately 500 km / s per 1 Mpc. But in our time, the parameters of the coefficient have changed. Now it is 67.8 ± 0.77 km/sec per 1 Mpc. This inconsistency is explained by the fact that Hubble did not take into account the extinction correction, which had not yet been discovered in his time. Plus, the proper velocities of the galaxies, coupled with the speed common to a group of galaxies, were not taken into account. It should also be taken into account that the expansion of the Universe is not a simple expansion of galaxies in space. It is also a dynamic change in the space itself.

Hubble constant

This is a component of the Hubble law, which links the values of the distance to an object located outside our galaxy and the speed of its removal. The positions of this constant determine the average values of the velocities of galaxies. Using the Hubble constant, it can be determined that a galaxy with a distance of 10 Mpc is receding at a speed of 700 km/sec. And a galaxy 100 Mpc away will have a speed of 7000 km/sec. So far, all discovered objects of ultra-deep space fit into the framework of the Hubble law.

In models where the expanding universe is present, the Hubble constant changes its value over time.

The name is justified by its constancy at all points in the universe, but only at a specific point in time. Some astronomers play on this change by calling the constant a variable.

Conclusions from the law

Having determined that the Andromeda Nebula is a galaxy consisting of individual stars, Hubble drew attention to the shift in the spectral lines of radiation from neighboring galaxies. The shift was shifted to the red side, and the scientist described this as a manifestation of the Doppler effect. It turned out that the galaxies, in relation to the Earth, are moving away. Further research helped to understand that galaxies run away the faster they are from us. It was this fact that determined that Hubble's law is the centripetal receding of the Universe with velocities that increase with distance from the observer. In addition to the fact that the universe is expanding, the law determines that it still had its beginning in time. To understand this postulate, you need to try to start the ongoing expansion visually back. In this case, you can reach the starting point. At this point - a small lump of protomatter - the entire volume of the current Universe was concentrated.

Hubble's law is also able to shed light on the age of our world. If the removal of all galaxies initially occurred at the same rate that is observed now, then the time that has elapsed since the beginning of the expansion is the very value of age. At the current value of the Hubble constant (67.8 ± 0.77 km/sec per 1 Mpc), the age of our Universe is estimated at (13.798 ± 0.037) . 10 9 years old.

Significance in astronomy

Einstein appreciated Hubble's work quite highly, and the law was quickly recognized in science. It was Hubble's observations (together with Humason) of redshifts that made it plausible to assume that the universe is not stationary. The law formulated by the great scientist actually became an indication that there is a certain structure in the Universe that affects the recession of galaxies. It has the property of smoothing the inhomogeneities of cosmic matter. Since receding galaxies do not slow down, as they should due to their own gravity, there must be some force pushing them apart. And this force is called dark energy, which has about 70% of the entire mass/energy of the visible universe.

Now distances to distant galaxies and quasars are estimated using Hubble's law. The main thing is that it really turns out to be true for the entire Universe, boundless in space and time. After all, we still do not know the properties of dark matter, which may well correct any ideas and laws.