The law of universal recession of galaxies. Hubble constant

To the great physicists of the past, I. Newton and A. Einstein, the Universe seemed static. Soviet physicist A. Friedman in 1924 came up with the theory of “scattering” galaxies. Friedman predicted the expansion of the Universe. This was a revolutionary revolution in the physical understanding of our world.

American astronomer Edwin Hubble explored the Andromeda nebula. By 1923, he was able to see that its outskirts were clusters of individual stars. Hubble calculated the distance to the nebula. It turned out to be 900,000 light years (the 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 consists of a collection of huge star clusters - galaxies.

It is they who appear to us as distant foggy “clouds” in the sky, since we simply cannot see individual stars at such a huge 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 spectral light waves emitted by atoms of distant galaxies is slightly greater than the length of spectral waves emitted by the same atoms in terrestrial laboratories. That is, in the radiation spectrum of neighboring galaxies, the quantum of light emitted by an atom when an electron jumps from orbit to orbit is shifted in frequency towards the red part of the spectrum compared to a similar quantum emitted by the same atom on Earth. Hubble took the liberty of interpreting 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 exhibit a red spectral shift proportional to the speed of their removal.

Most importantly, Hubble was able to compare the results of its measurements of distances to neighboring galaxies with measurements of their recession rates (based on redshift).

Mathematically, the law is formulated very simply:

where v is the speed at which the galaxy is moving away from us,

r is the distance to it,

H is the Hubble constant.

And, although Hubble initially 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 that have been discovered since then, increasingly distant from the Milky Way, falls outside the scope 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 you and I 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.

The question naturally arises: what happened in the beginning? It took scientists only about 20 years to completely revolutionize their understanding of the Universe.

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 enormous 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 proto-matter, contained in a very small volume compared to the current scale of the Universe.

The idea of the Universe, born from a super-dense clump of super-hot matter and ever since expanding and cooling, 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 an approximate age of the Universe of 400,000 years. From this moment on, photons were able to move freely in space, practically without interacting with matter. But we still have “witnesses” of that era - these are relict photons. It is believed that the cosmic microwave background radiation has been preserved from the initial stages of the existence of the Universe and fills it evenly. As a result of further cooling of the radiation, its temperature decreased and is now about 3 K.

The existence of cosmic microwave background radiation was predicted theoretically within the framework of the Big Bang theory. It is considered as one of the main confirmations of the Big Bang theory.

The universe consists of a collection of huge star clusters - galaxies.

It is they who appear to us as distant foggy “clouds” in the sky, since we simply cannot see individual stars at such a huge distance.

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

Most importantly, Hubble was able to compare the results of its measurements of distances to neighboring galaxies with measurements of their recession rates (based on redshift).

Mathematically, the law is formulated very simply:

where v is the speed at which the galaxy is moving away from us,

r is the distance to it,

H is the Hubble constant.

So, the main consequence of Hubble's law:

The universe is expanding.

The very fabric of world space is expanding. All observers (and you and I 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.

The question naturally arises: what happened in the beginning? It took scientists only about 20 years to completely revolutionize their understanding of the Universe.

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 idea of the Universe, born from a super-dense clump of super-hot matter and ever since expanding and cooling, is called the Big Bang theory.

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

Yu.N. Efremov

The most ambitious phenomenon known to man is the expansion of our Universe, proven in 1929. The distances between clusters of galaxies are continuously increasing, and this is the most important fact for understanding the structure of the Universe. Determinations of the expansion rate - the Hubble constant - and its dependence on time remain the most important subject of ground-based and orbital observations.

1. Faint nebulae

The first signs of the expansion of the Universe were discovered about 80 years ago, when most astronomers believed that our Galaxy was the entire Universe. The faint nebulous specks, tens of thousands of which have been discovered since the advent of astrophotography, were thought to be distant gaseous nebulae on the outskirts of the overarching Milky Way star system.

Weston Slifer at the Flagstaff Observatory in Arizona was for many years the only person in the world to obtain the spectra of these “faint nebulae.” Their most striking representative was the well-known Andromeda nebula. In 1914, Slifer published the first determination of the radial velocity of this nebula from a spectrogram obtained by him with a 24-inch refractor.

It turned out that M31 is approaching us at a speed of about 300 km/s. By 1925, Slifer's collection included spectra of 41 objects. These spectra had a strange feature - the velocities of all of them were very high, and the negative velocity of M31 turned out to be a rare exception; The average speed of the nebulae was +375 km/s, and the highest speed was +1125 km/s. Almost all of them were moving away from us, and their speeds exceeded the speed of any other objects known to astronomers. (Recall that negative velocities are directed towards us, positive ones - away from us.)

The observatory in Flagstaff was built by Percival Lovell specifically for observing the canals of Mars. Some of us came to astronomy, fascinated by his book, which talked about a wave of darkening, about the splitting of channels overflowing with water in the Martian spring... However, no less fantastic, but completely real things were discovered at this observatory. Slipher's work marked the first step towards the discovery of the expansion of the Universe.

Disputes about the nature of “faint nebulae” have been going on since the end of the 18th century. William Herschel suggested that they could be distant star systems similar to the Milky Way system. In 1785, he was sure that it was impossible to resolve nebulae into stars only because their distance was too great. However, in 1795, while observing the planetary nebula NGC 1514, he clearly saw a single star in its center, surrounded by nebulous matter. The existence of genuine nebulae was thus beyond doubt, and there was no need to think that all nebulous spots were distant star systems. And in 1820 Herschel said that beyond the limits of our own system everything is covered in the darkness of the unknown.

In the 19th century, in nebulae that could not be resolved into stars, they preferred to see planetary systems in the process of formation - in the spirit of Laplace’s hypothesis; NGC 1514 seemed to be an example of far-advanced evolution - the central star had already condensed from the primary nebula.

By mid-century, John Herschel had added another 5,000 to the 2,500 nebulae discovered by his father, and the study of their distribution across the sky provided the main argument against the assumption that they were distant star systems (“island universes”) similar to our Milky Way system. A "zone of avoidance" was discovered - the almost complete absence of these faint spots of light near the plane of the Milky Way. This was understood as a clear indication of their connection with the Milky Way system. The absorption of light, which is strongest in the plane of the Galaxy, was still unknown.

In 1865, Heggins first observed the spectrum of nebulae. The emission lines of the Orion Nebula clearly indicated its gas composition, but the spectrum of the Andromeda Nebula (M31) was continuous, like that of stars. It would seem that the dispute has been resolved, but Heggins concluded that this type of spectrum of M31 only indicates the high density and opacity of its constituent gas.

In 1890, Agnia Clerk, in a book about the development of astronomy in the 19th century, wrote: “The question of whether nebulae are external galaxies hardly deserves discussion now. The progress of research has answered it. It is safe to say that not a single competent thinker before "In the face of existing facts, it will not be possible to assert that at least one nebula can be a star system comparable in size to the Milky Way."

I would like to know which of the current equally categorical statements will turn out to be just as incorrect over time... Note that a hundred years before Clerk, a diametrically opposite judgment was made. "The stars... appear to be collected in various groups, some of which contain billions of stars... Our Sun and the brightest stars may be part of one of these groups, which apparently encircles the sky, forming the Milky Way." This cautious but absolutely correct formulation belongs to the great Laplace.

At the beginning of the 20th century, photographs taken by Keeler with a 36-inch reflector showed that there were at least 120,000 faint nebulae. The stellar spectrum of reflection (mostly dust) nebulae around the Pleiades stars seemed to confirm the idea that it was impossible to solve the problem by spectral studies. This allowed V. Slipher to suggest that the spectrum of the Andromeda nebula is also explained by the reflection of the light of the central star (for which he took the core of the galaxy...)

To solve the question of the nature of "faint nebulae" it was necessary to know their distance. Discussion on this issue continued until 1925; it deserves a separate story and here we will only briefly describe how the distance of the key object - the Andromeda "nebula" - was established.

2. Discovery of the Universe

Already by 1910, George Ritchie, using the 60" telescope of the Mount Wilson Observatory, obtained magnificent photographs in which it was clear that the spiral branches of large nebulae were strewn with star-shaped objects, but the images of many of them were blurred and foggy. These could be compact nebulae, star clusters, and several merged images of stars.

Edwin Hubble (1889 - 1953), a young astronomer at the same observatory, was able to prove that we see single stars in large “nebulae” in 1924. Using a 100" telescope, he found 36 Cepheids in the Andromeda nebula. The amplitudes of changes in the brightness of these variable supergiant stars fully corresponded to those known from the Cepheids of our Galaxy and this proved that we are dealing with single stars. And most importantly, the period-luminosity relationship established by Cepheids of the Magellanic Clouds and the Galaxy, made it possible to determine the luminosity of the stars found by Hubble, and comparing it with the brilliance gave the distance. It took the Andromeda nebula far beyond the boundaries of our star system. Faint nebulae turned out to be distant galaxies.

You can only see what you think is possible to see... When in the early 20s. Humason showed Shapley several variable stars - probable Cepheids, which he had marked on a plate depicting the Andromeda nebula. Shapley erased his marks - there could be no stars in this gaseous nebula!

3. The beginning of cosmology

So, the Universe is populated by galaxies, not isolated stars. Only now have it become possible to test the conclusions of the nascent cosmology - the science of the structure and evolution of the Universe as a whole. In 1924, K. Wirtz discovered a weak correlation between the angular diameters and the recession velocities of galaxies and suggested that it could be related to the cosmological model of W. de Sitter, according to which the recession rate of distant objects should increase with their distance. De Sitter's model corresponded to an empty universe, but in 1923 the German mathematician G. Weyl noted that if matter is placed in it, it should expand. The non-static nature of the de Sitter Universe was also discussed in Eddington’s book, published in the same year.

De Sitter, who published his work "On Einstein's Theory of Gravitation and Its Astronomical Consequences" in 1917, immediately after the appearance of the general theory of relativity, knew only three radial velocities; for M31 it was negative, and for two faint galaxies it was positive and large.

Lundmark and then Strömberg, who repeated Wirtz’s work, did not obtain convincing results, and Strömberg even stated in 1925 that “there is no dependence of radial velocities on distance from the Sun.” However, it was only clear that neither the diameter nor the brightness of galaxies could be considered reliable criteria for their distance.

The expansion of a non-empty Universe was also discussed in the first cosmological work of the Belgian theorist J. Lemaitre, published in 1925. His next article, published in 1927, was called “A Homogeneous Universe of Constant Mass and Increasing Radius, Explaining the Radial Velocities of Extragalactic Nebulae.” The coefficient of proportionality between speed and distance, obtained by Lemaitre, was close to that found by Hubble in 1929. In 1931, on the initiative of Eddington Lemaitre's article was reprinted in Monthly Notices and has since been widely quoted; A.A. Friedman's works were published back in 1922-1924, but became widely known among astronomers much later. In any case, Lemaitre was the first to clearly state that the objects inhabiting the expanding Universe, the distribution and speed of which should be the subject of cosmology, are not stars, but giant star systems, galaxies. Lemaitre relied on the results of Hubble, which he became acquainted with while in the USA in 1926 at his report.

The American theorist H. Robertson in 1928, using Hubble data from 1926, also found that the speed of recession of galaxies is proportional to their distance. Apparently, Hubble knew this work. Since 1928, on his instructions, M. Humason (1891-1972) persistently tried to measure the redshift of the most distant galaxies. Soon after 45 hours of exposure, the galaxy NGC 7619 in the Perseus cluster was measured to have a recession speed of 3779 km/s. (Needless to say, the last two digits are redundant). Hubble himself developed criteria for determining distances for distant galaxies, the Cepheids in which remained inaccessible to a 100" telescope. They were based on the assumption that the brightest individual stars within different galaxies were identical in brightness. By 1929, he had confident distances of two dozen galaxies, within including in the Virgo cluster, whose speeds reached approximately 1100 km/s.

4. Hubble's Law

And so on January 17, 1929, the Proceedings of the National Academy of Sciences of the United States received Humason's article on the radial velocity of NGC 7619 and Hubble's article, entitled "Relation between the distance and radial velocity of extragalactic nebulae." A comparison of these distances with radial velocities showed a clear linear dependence of speed on distance, now rightly called Hubble's law.

Hubble understood the significance of his discovery. Reporting about it, he wrote that “the velocity-distance relationship may represent the de Sitter effect and, therefore, it can provide quantitative data for determining the general curvature of space.” Numerous attempts to explain the Hubble dependence not by the expansion of the Universe, but by something else, which can still be found today, invariably fail. Thus, the old assumption that over a long journey time photons “age”, lose energy and the corresponding wavelength increases does not work - in this case, images of distant objects would also be blurred, and the value of the red shift would depend on the wavelength, which is not observed . Direct evidence of the correctness of the conclusion that more distant objects have a greater redshift was recently obtained from studying the light curves and spectra of distant Supernovae.

We emphasize that the methods for determining the distances of galaxies developed by Hubble were of decisive importance, which required direct photographs on a 100-inch reflector.

In the thirties, Hubble and his collaborators occupied more than half of the observing time of the largest - and practically the only telescope then suitable for such work. And this concentration of effort led to the greatest achievements of observational astronomy of the 20th century!

By 1935, Humason had spectrograms of 150 galaxies up to distances 35 times greater than the Virgo galaxy cluster, and by 1940 the highest galaxy recession velocities he discovered were 40,000 km/s. And up to the greatest distances, a direct proportional relationship remained between the red shift of the lines in the spectrum,

and distance, which is generally written as follows:

Where c- speed of light, z- distance and v- radial velocity. Proportionality factor H was later called the Hubble constant.

This new law of nature was explained in models of the universe based on general relativity even before it was firmly established. Priority should be given to A.A. Friedman; the models obtained earlier by Einstein and de Sitter turned out to be limiting cases of Friedmann's models. For a long time, only the results of Lemaitre (unfamiliar with Friedman’s work at that time) remained widely known, who, after the publication of Hubble’s work, reminded Eddington of his work in 1927 - in this work Lemaitre came to the conclusion about expanding the model

Universe with a finite average density of matter in it. However, already in 1931, Einstein, speaking about the expanding Universe, noted that Friedman was the first to take this path.

However, Hubble himself soon lost confidence that the redshift meant the expansion of the Universe, probably under the influence of the inexorable conclusion from this assumption. As G. Russell wrote then, “it is premature to accept de Sitter’s theory without reservations. It is philosophically unacceptable for all galaxies to be together before. We do not find an answer to the question “why.” It was for these reasons that Einstein introduced a cosmological constant into his 1916 equations, which should stabilize the Universe. This deepest problem is the subject of A.D. Chernin’s article “Physical Vacuum and Cosmic Antigravity” on the website www.site and here we only note that the accelerated expansion of the Universe, discovered in 1998 by Type Ia Supernovae, is explained by the negative pressure of the cosmic vacuum, the existence which is reflected by the additional cosmological term of Einstein’s equations.

In the summer of 1929, Hubble attacked de Sitter for daring to publish a detailed work comparing theoretical and observational conclusions about the expansion of the Universe. He wrote to de Sitter that the speed-distance relationship was a "Mount Wilsonian achievement" and that "the first discussion of new data naturally belongs to those who actually did the work." However, in 1931, after the appearance of Zwicky's hypothesis about the possibility of photon aging, Hubble wrote to de Sitter that "the interpretation should be left to you and very few others who are competent to discuss the subject with authority" ... Until the end of his life (1953) Hubble Apparently, he still hasn’t decided for himself whether the red shift indicates the expansion of the Universe, or whether it is due to “some new principle of nature.” One way or another, his name will forever remain on the list of the greatest scientists of all time.

A red shift proportional to distance does not mean that galaxies are moving away from us, but an increase in all distances between all objects of the Universe (more precisely, between objects not connected by gravity - i.e. clusters of galaxies) with a speed proportional to the distance, just as the distances between all points located on the surface of the inflating ball increase. An observer in any galaxy sees that all other galaxies are scattering away from him. The expansion rate of the Universe remains one of the most important problems in astronomy.

Let us first tell you how Hubble himself solved it in 1935.

He had data on the redshift of 29 nearby galaxies, located, however, outside the Local Group: galaxies that are too close obviously cannot be used, since for them the velocities of removal from us, due to the expansion of the Universe, are too small and comparable to their random velocities in space .

In these 29 galaxies, Hubble determined the magnitudes of the brightest stars. Since their luminosities in all galaxies, as Hubble found, are approximately the same, their magnitudes should be a function of distance, and indeed, they show a dependence on the receding velocity v.

This dependence, according to Hubble data, is represented by the formula. On the other hand, , , and , where M- absolute value. From these three formulas follows the expression with which the Hubble constant is determined: . In general terms, it follows from Hubble’s law and formula, i.e. .

The absolute magnitude of the brightest stars found by Hubble was equal to -6.35 m, and the magnitude H(Hubble denoted it) it turned out to be 535 (km/s)/Mpc.

Since the luminosity of the brightest stars was determined by comparing them with Cepheids, a revision of the zero point of the period-luminosity relationship (W. Baade, 1952) meant the need for a revision of the value of the Hubble constant. Humason, Mayall and Sandage in 1955, using new data on the redshift and taking into account Baade's correction to the zero point of the period-luminosity relationship, obtained H=180 (km/s)/Mpc.

In 1958, Allan Sandage, continuing the work of his teacher Hubble, published the results of a new revision of the constant H. Based mainly on Novayas, Sandage concluded that the distance magnitudes of the Magellanic Clouds, M31, M33 and NGC 6822 should be increased by an average of 2.3 m compared with the values accepted by Hubble. Consequently, the absolute magnitudes of the brightest stars must be brightened by the same amount; they were also refined by using new data on the brightest stars of the Local Group galaxies. But, in addition to these clarifications, Sandage also discovered a serious mistake in his teacher - the objects that Hubble took for the brightest stars in galaxies lying outside the Local Group are in fact compact emission nebulae, HII regions.

Hubble, which in the twenties could only work with blue-ray-sensitive plates, had no way of distinguishing images of compact HII regions from stars, especially in distant galaxies. Even in M31, despite careful searches, he did not find a single emission nebula, although 981 of them are now known there. This is probably why the possibility of such confusion did not occur to Hubble. Only Baade, who photographed M31 in different rays and, in particular, used plates sensitive to red rays and filters that cut out the red hydrogen line Hα, was able to find them. Sandage, photographing the galaxy NGC 4321 = M100 in the Virgo cluster in different rays, discovered that the brightest HII regions are 1.8 m brighter than the brightest stars - this is how much Hubble underestimated the distance modulus, determining it from the “brightest stars”. The total error in the distance modules accepted by Hubble is therefore about 4.0 m! As a result, according to Sandage, the Hubble constant should be in the range of 50-100 (km/s)/Mpc. He attributed the reason for the remaining uncertainty mainly to the dispersion of the absolute values of the brightest stars. Sandage's results meant that Hubble underestimated the distances of distant galaxies by a factor of 6-7!

In 1968, Sandage determined the Hubble constant in a different way. Hubble also established that the brightest members of galaxy clusters - giant elliptical galaxies - have almost the same absolute magnitude. It is also possible for them to construct a relationship between visible magnitudes and redshift (below is this diagram for the 65 brightest galaxies in clusters, constructed by Sandage, Christian and Westphal in 1976) and if we determine the luminosity of at least one of them, from this relationship we can determine the Hubble constant, similar to how Hubble himself did it with the brightest stars. It is especially important that we can now go immeasurably further - the brightest galaxies in clusters are 11 m -12 m brighter than the brightest stars! The luminosity of the brightest galaxy in clusters can be determined by knowing the distance of at least one cluster. The closest rich cluster is the Virgo cluster, and Sandage used globular clusters in the elliptical galaxy M87 to determine its distance.

Assuming further, together with Sandage, that the luminosity of the brightest star clusters in galaxies rich in them is the same, knowing the integral absolute magnitude of the brightest cluster of our Galaxy (-9.7 m B, ω Centaur) and M31 (-9.8 m B, B282), and also the brightness of the brightest cluster M87 (21.3 m B), we obtain the distance modulus of M87 and the entire galaxy cluster: m-M=21.3 m +9.8 m = 31.1 m. It follows that the brightest galaxy in the Virgo cluster (the elliptical galaxy NGC 4472, which also has a lot of globular clusters) - and therefore the brightest galaxies in all clusters in general - has an absolute magnitude of -21.7 m.

Knowing the absolute magnitude of galaxies and the dependence of their apparent magnitudes on red shift, it is easy to find the Hubble constant. In this way Sandage received the meaning in 1968 H=75 (km/s)/Mpc, which was considered the most probable for a long time.

However, in a series of papers published in 1974-1975, A. Sandage and Swiss astronomer G. Tammann obtained a value of 55 (km/s)/Mpc for the Hubble constant. Having determined the distances of the Local Group and M81 galaxies using Cepheids, they obtained a relationship between the linear sizes of the HII regions and the luminosity of the galaxy containing them. Using this dependence, they found the distances of many irregular and spiral field galaxies from the angular diameters of the HII regions and determined the luminosity of the giant spiral ScI galaxies, which can be distinguished by their appearance. For 50 faint ScI galaxies, Sandage and Tamman determined the radial velocities (all of them were greater than 4000 km/s). Knowing the apparent and absolute values, it is not difficult to obtain the Hubble constant.

Sandage and Tamman insisted that the Hubble constant, with an error of about 10%, was 50 (km/s)/kpc, while J. de Vaucouleurs obtained the value with the same error H=95. The magic number of 10% is inextricably linked to the definitions of this constant; Let us recall that Hubble determined it to be equal to 535 (km/s)/kpc - and estimated the error at exactly 10%... It must be said that most astronomers obtained the value H between 75 and 100, and Sandage and Tamman were almost the only proponents of a long distance scale. Echoes of this debate can still be heard, although the possible range of values for the Hubble constant has narrowed.

This happened mainly due to a special Cepheid observation program at the Hubble Space Telescope. They were found and studied in two dozen galaxies, mainly in the Virgo cluster, and methods (Tulley-Fisher, Supernova Ia, etc.) were calibrated using the distances of these galaxies, making it possible to determine the distances of even more distant galaxies, for which their randomness can be neglected movements. One group of researchers, led by Cepheid expert V. Friedman, received a value in 2001 H=72+/-7, and A. Sandage’s group received the value in 2000 H=59+/-6. The error was again estimated by both groups to be exactly 10%!

6. Expansion of the Universe

The task of determining the Hubble constant was so acute because the scale of the Universe, its average density, and age depend on its value. Extrapolating backwards from the retreat of galaxies, we come to the conclusion that they were once all gathered at one point. If the expansion of the Universe occurred at the same speed, then the reciprocal of the Hubble constant () allows us to say that this moment t=0 took place 13-19 ( H=50) or 7-10 ( H=100) billion years ago. This “expansion age of the Universe”, with a lower value of the Hubble constant, which Sandage invariably obtains, is confidently greater than the age of the oldest stars, which cannot be said about the value H=100. However, now the problem has lost its urgency, since there is now no doubt that the expansion of the Universe proceeded at an unequal speed. Hubble's "constant" is constant only in space, but not in time.

Recent (2003) satellite measurements of the anisotropy of the cosmic microwave background radiation give the Hubble constant a value of 71 (+4\-3) km\s\Mpc, and for the age of the Universe a value of 13.7+\-0.2 billion years (D. Spergel et al., astro-ph/0302209). Pessimists still believe that it is better to talk about values of 45-90 for the Hubble constant and the age of the Universe at 14+\-1 billion years. The best ground-based data (based on the results of large surveys of galaxy redshifts, their peculiar velocities and supernovae Ia - C. Odman et al., astro-ph/0405118) give a value for the Hubble constant of 57 (+15\-14) km\s\ Mpk.

Studies of type Ia supernovae in distant galaxies, the first results of which appeared in 1998, became the beginning of a new revolution in cosmology, which is described in the above-mentioned article by A.D. Chernin. Let's say just a few words here.

The use of SNIa as a “standard candle” for determining very large distances became possible thanks to the work of Yu.P. Pskovsky, carried out at the SAI back in the 1970s. It is believed that the same luminosity at maximum is explained by the fact that the phenomenon of supernova Ia occurs in a close system, including a white dwarf onto which matter is accreted from the second component.

When the mass of a white dwarf reaches its limit value of 1.4 solar masses, an explosion occurs, turning its remnant into a neutron star.

The position of Type Ia supernovae on the Hubble diagram indicates that the expansion of the Universe is accelerating in the modern era. This is most naturally explained by the fact that the negative pressure of the cosmic vacuum accelerates the expansion of galaxy clusters. The anti-gravity of a vacuum means that the expansion of the Universe will continue forever.

If these theoretical conclusions are correct, in an earlier era the expansion of the Universe, on the contrary, should have been slower, since it was slowed down by the gravity of dark matter. Its density became less than that of the vacuum, according to theory, 6-8 billion years ago, and indeed, the few most distant supernovae Ia indicate a slower expansion. Recently, this conclusion was confirmed by completely independent data from the Chandra satellite on hot gas observed in X-rays in galaxy clusters. The ratio of the mass of this gas to the mass of dark matter should be the same in all clusters, and from here the distances of galaxy clusters can be obtained. They showed that the slow expansion of the Universe gave way to an accelerated one 6 billion years ago.

The dominance of vacuum antigravity, according to A.D. Chernin and his colleagues, also explains the paradox noted by A. Sandage back in 1972 - the expansion of the Universe was discovered by Hubble in galaxies that were seemingly too close, the heterogeneity of their distribution in space and the associated gravitational movements would have washed out the overall expansion. Recent data obtained by I.D. Karachentsev and his collaborators at the 6-m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences confirm that the isotropic expansion of the Universe begins very close to us, just outside the Local Group of galaxies.

So, astronomical data made it possible for the first time to determine the vacuum energy density; they are fraught with a new revolution in physics, because the meaning of this density is inexplicable by modern theory.

7. To the edge of the Universe

In conclusion, we will tell you about the results of the search for objects with the highest possible redshift. This required the largest telescopes and many hours of exposure. For many years, there were fewer enthusiasts and large telescopes than there were fingers on one hand. With the commissioning of the 200-inch telescope (in the picture - Hubble in the main focus cabin of this telescope, photograph from the late 40s), Humason was able to measure z=0.20 for a galaxy from the Hydra cluster with V=17.3 m. For a long time, night sky lines prevented us from obtaining redshifts for fainter and more distant galaxies using absorption lines in their spectrum. Using a single emission line, R. Minkowski found in 1960 z=0.46 for radio galaxy 3C295 ( V=19.9 m), which remained a record for galaxies for a long time. In 1971, this value was confirmed by J. Oak using absorption lines, recording the spectrum of 3C295 using a 32-channel spectrometer and determining its shift relative to the standard zero-redshift spectrum. This work took 8 hours of the 200-inch telescope's time. In 1929, Humason needed 40 hours with a 100-inch telescope to determine the redshift of a galaxy eight magnitudes brighter.

In 1975, X. Spinrad, using a 3-meter reflector, found z=0.637 for radio galaxy 3C123 -- s V=21.7 m. Spinrad was able to measure several lines in the spectrum of 3C123 using an electron-optical scanning spectrometer, accumulating photons over 7 hours of observations over 4 nights.

It is a giant elliptical galaxy, four times more radio-powerful than Centaur A. Sandage and his collaborators then found z=0.53 for radio galaxy 3C330. Finally, in 1981, Spinrad, obtaining spectra of radio galaxies, found z=1.050 for 3C13 and z=1.175 for 3C427; exposures again reached 40 hours, but objects were observed that were tens of thousands of times fainter than in 1929.

Measurements of extremely large redshifts remained the lot of individuals, until the idea that by studying the Universe on extremely large scales, we comprehend the physics that governs the microcosm, took hold of the masses...

Astronomy began to transform, half a century later than physics, into Big Science, in which numerous teams work on giant installations. The development of electronics also played a huge role, leading to the creation of effective light detectors.

For the Anglo-Australian 4-m telescope, a device was developed that, using light guides, allows simultaneous acquisition of spectra in an area measuring four square degrees. Of the 250,000 redshifts of galaxies that were planned to be obtained, by the spring of 2001, 150,000 had already been measured. 20 - 30 people are involved in this collaboration. More ambitious are the tasks of the Sloan Numerical Sky Survey, for which a wide-angle 3.5-m telescope was built at the expense of the millionaire Sloan. The survey's goal is to measure, using multicolor photometry, the redshifts of about a million galaxies in a quarter of the sky. 150 astronomers from 11 institutes are already involved here.

Among the first catches of the Sloan survey was the discovery in 2001 of a redshift quasar z=6.28. However, the very next year this record was broken and the champion turned out to be not a quasar, but a galaxy. As we know, quasars are galaxies with an unusually bright nucleus and are easier to detect at greater distances. It was possible to detect the redshift of such a distant ordinary galaxy because the light flux from it was enhanced by 4.5 times due to the effect of gravitational lensing. This galaxy, designated HCM 6A, lies one minute of arc from the center of the massive galaxy cluster Abell 370, which, being much closer to us, served as a gravitational lens. Thanks to the action of this natural telescope, it was possible to record the spectrum of the galaxy in the infrared using the 10-m Keck-II telescope on Mauna Kea. An emission line was found at a wavelength of 9190 angstroms that is almost certainly a redshifted Lyman alpha line z=6.56 from the ultraviolet region of the spectrum.

This identification was confirmed by observations on the nearby Japanese 8-m Subaru Telescope, which showed that in the farther infrared bands the flux is thousands of times weaker than in this emission line, consistent with its identification as a Lyman-alpha line.

The next record was recently set using one of the 8-m telescopes (VLT) of the Southern European Observatory on Mount Paranal in Chile. The gravitational lensing effect was again used to look for faint galaxies, visible only in the infrared, near the center of the rich compact cluster of galaxies Abell 1835. One of these objects, #1916, had a single strong line in its spectrum, the identification of which with Lyman alpha led to redshift z=10.0. Other possible identifications are rejected because in this case several strong lines would be observed in the spectrum (R. Pello et al., astro-ph/0403025

All publications on the same topic >>

“In 1744, the Swiss astronomer de Chezo and independently in 1826 Olbers formulated the following paradox,” T. Regge writes in his book, “which led to a crisis in the then naive cosmological models. Let us 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, Schezot and Olbers showed that the total amount of light sent to Earth by the stars should 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 proposed the existence of vast wandering opaque nebulae in space, obscuring the most distant stars. In fact, there is no way out of the situation: having absorbed light from the stars, the nebulae would inevitably heat up and emit light themselves 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 removal rates of galaxies obtained by the great American astronomer Edwin Hubble.

Hubble (1889–1953) was born in the small town of Marshfield, Missouri, to insurance agent John Powell Hubble 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.

In 1906, Edwin graduated from school. 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. Astronomer F.R. worked there. Multon, author of the famous theory of the origin of the solar system. He had a great influence on the subsequent choice of Hubble.

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

In the summer of 1913, Edwin returned to his homeland, but did not become a lawyer. Hubble aspired to science and returned to the University of Chicago, where he prepared his dissertation for the degree of Doctor of Philosophy at the Yerke Observatory under the direction of Professor Frost. His work was a statistical study of faint spiral nebulae in several areas 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 this time, a great event was approaching in astronomy - the Mount Wilson Observatory, which was headed by the remarkable science organizer D.E. Hale, was preparing to commission the largest telescope - a hundred-inch reflector (250-centimeter - Author's note). Hubble, among others, received an invitation to work at the observatory. However, in the spring of 1917, as he was finishing his dissertation, the United States entered World War I. The young scientist declined the invitation and volunteered for the army. As part of the American Expeditionary Force, Major Hubble arrived in Europe in the fall of 1918, shortly before the end of the war, and did not have time to take part in hostilities. In the summer of 1919, Hubble was discharged and hurried to Pasadena to accept Hale's invitation.

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

The anthology “The Book of Primary Sources on Astronomy and Astrophysics, 1900–1975” by K. Lang and O. Gingerich (USA), which reproduces the most outstanding research for three quarters of the twentieth century, contains three works by Hubble, 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 red shift.

In 1923, Hubble began observing the nebula in the constellation Andromeda using sixty and one hundred 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 came only on January 1, 1925, when G. Russell read out Hubble's report at the meeting of the American Astronomical Society. The famous astronomer D. Stebbins wrote that Hubble's report “expanded the volume of the material world a hundredfold and definitely resolved the long dispute about the nature of spirals, proving that they are gigantic collections of stars, almost comparable in size to our own Galaxy.” Now the Universe appears to astronomers as a space filled with star islands - galaxies.

The mere establishment of the true nature of nebulae determined Hubble's place in the history of astronomy. But he also had an even more outstanding achievement - the discovery of the law of red shift.

Spectral studies of spiral and elliptical “nebulae” were started in 1912 on the basis of such considerations1 if they are really located outside our Galaxy, then they do not participate in its rotation and therefore their radial velocities will indicate the movement 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 greater: they were measured in thousands and tens of thousands of kilometers per second.

In mid-January 1929, in the Proceedings of the National Academy of Sciences of the United States, Hubble presented a short note entitled “On the relation between the distance and radial velocity of extragalactic nebulae.” At that time, Hubble was already able to compare 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 Hubble's law. The scientist determined the numerical value of the Hubble constant in 1929 to be 500 km/(c x Mpc). However, he made a mistake in establishing the distances to the galaxies. After multiple corrections and refinements of these distances, the numerical value of the Hubble constant is now accepted as equal to 50 km/(c x Mpc).

The Mount Wilson Observatory began determining the radial velocities of increasingly 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 the distant Ursa Major cluster of galaxies. But this was already the limit of the capabilities of a hundred-inch telescope. More powerful tools were needed.

“We can approach the issue of the Hubble expansion of space using more familiar, intuitive images,” says T. Rege. - For example, 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 equal to 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, given that the distance between them increases from 100 to 200 meters. Thus, the speed of mutual removal is proportional to the distance. Note that after expanding the series, the cosmological principle remains valid: the “soldier galaxies” are still distributed evenly, and the same proportions between different mutual distances remain.

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 increase the greater the distance from them to the center. In space, there are no milestones against which absolute measurements of speed could be made; We are deprived of such a possibility 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 the immutability of the cosmological principle at all times, and this confirms our opinion that both the law and the principle itself are truly valid.

Another example of an intuitive image would be a bomb exploding; 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 the distances to them. Here, however, the cosmological principle is violated, since if we move far enough from the explosion site, we will not see any fragments. This image suggests the most famous term in modern cosmology, “big bang.” 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 its present size began.”

Hubble's law was almost immediately recognized in science. The significance of Hubble's discovery was highly appreciated by Einstein. In January 1931 he wrote: "The new observations of Hubble and Humason regarding the red shift... make it probable that the general structure of the Universe is not stationary."

Hubble's discovery finally destroyed the idea of a static, unshakable Universe that had existed since the time of Aristotle. Currently, Hubble's law is used to determine 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, reducing its size by fifteen times. Studying numerous nebulae, the diversity of whose forms he was the first to discover, Herschel came to the conclusion that some of them were distant star systems “like our star system.” He wrote: “I do not consider 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 this was no accident. After all, he managed to prove that most of the nebulae discovered and observed by him consist not of stars, but of gas. He came to a very pessimistic conclusion: “Everything outside our own system is covered in the darkness of the unknown.”

The English astronomer Agnes Clarke wrote in her book The Star System in 1890: “It is safe to say that no competent scientist, in possession of all available evidence, would be of the opinion that even one nebula is a stellar 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 unit”...

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. Thus, from measurements taken in 1907 it seemed to follow that the distance to the Andromeda Nebula did not exceed 19 light years. Four years later, astronomers concluded that the distance was about 1,600 light years. In both cases, the impression was created that the mentioned nebula was actually located in our Galaxy.

In the twenties of the last century, a fierce dispute broke out between astronomers Shapley and Curtis about the nature of the Galaxy and other objects visible with telescopes. Among these objects is the famous Andromeda Nebula (M31), which is visible to the naked eye as only a fourth magnitude star, but unfolds into a majestic spiral when viewed through a large telescope. By this time, outbursts of novae had been detected in some of these nebulae. Curtis suggested that at maximum brightness, the mentioned stars emit the same amount of energy as the new stars of our Galaxy. Thus, he established that the distance to the Andromeda Nebula is 500,000 light years. This gave Curtis the basis 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 is the same size as our Galaxy (300,000 light years by his estimate). 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 are brighter than in our Galaxy. If the brightness of novae 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 that Curtis was right. The measurements made by Shapley turned out to be erroneous. He greatly underestimated the distance to 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 and soon several more Cepheids in the Andromeda Nebula. Having estimated 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 M 31 galaxy in Andromeda is 2.3 million light years.

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

The first and quite successful classification of galaxies by their appearance was undertaken by Hubble in 1925. He proposed that galaxies be classified into one of the following three types: 1) elliptical (denoted by the letter E), 2) spiral (S), and 3) irregular (1 g).

Elliptical galaxies are those that look like regular circles or ellipses and whose brightness gradually decreases from the center to the periphery. This group is divided into eight subtypes from EO to E7 as the apparent compression of the galaxy increases. SO lenticular galaxies resemble highly oblate elliptical systems, but have a clearly defined central star-shaped core.

Spiral galaxies, depending on the degree of development of the 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 an increasing development of spirals and a decrease in the apparent size of the nucleus.

Parallel to normal spiral galaxies, there are also so-called crossed spiral systems (SB). In galaxies of this type, a very bright central core is intersected along the diameter by a transverse stripe. The spiral branches begin from the ends of this bridge, 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 exhibit 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 persistently looked for objects that could not really be included in the Hubble system, their number turned out to be so insignificant that I can count them on my fingers.” The Hubble classification continues to serve science, and all subsequent modifications of the creature have not affected it.

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

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

In 1957, Soviet astronomer B.A. Vorontsov-Velyaminov discovered the existence of “interacting galaxies” - galaxies connected by “bridges”, “tails”, as well as “gamma-forms”, i.e. galaxies in which one spiral “twists”, while the other “unwinds”. Later, compact galaxies with dimensions of only about 3,000 light-years and isolated star systems with a diameter of only 200 light-years were discovered. In appearance, they are practically no different from the stars of our Galaxy.

The new general catalog (NCC) 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 visible from Earth. A fairytale giant, capable of covering a hundred or two million light years with his gaze, looking at the Universe, would see that it is filled with cosmic fog, the droplets of which are galaxies. From time to time there are clusters consisting of thousands of galaxies gathered together. One such giant cluster is located in the constellation Virgo.

At one time, Hubble's law revolutionized professional astronomy. At the beginning of the twentieth century, American astronomer Edwin Hubble proved that our Universe is not static, as it previously seemed, 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 located, is characterized by homogeneity 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, Hubble's law is found under the following formulation: v=H0*r. In this formula, v means the speed of the galaxy, H0 is the proportionality coefficient, which 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.

Some sources contain another formulation of Hubble's law: cz=H0*r. Here c acts as the speed of light, and z symbolizes the red shift - the shift of the spectral lines of chemical elements to the long-wave red side of the spectrum as they move away. In the physical and theoretical literature one can find other formulations of this law. However, the difference in formulations does not change the essence of Hubble’s law, and its essence lies in describing the fact that ours is continuously expanding in all directions.

Discovery of the law

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

The prerequisite for the discovery of Hubble's law was a number of astronomical observations. So, in 1913, the American astrophysicist Weil Slider discovered that several other huge space objects were 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 located outside our galaxy. Further observation of the nebulae showed that they are not only other galactic worlds, but are also constantly moving away from us. This fact has led the astronomical community 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, American scientist Edwin Hubble, using a 254-centimeter telescope, discovered 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 to this day accurately describes the principle of expansion of the Universe, and is of great importance for both theoretical and practical astronomy.

Hubble's Law: Applications and Implications for Astronomy

Hubble's law is of great importance for astronomy. It is widely used by modern scientists in 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 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 possible to find out that the Universe is expanding equally in all directions. No matter what point in outer space the observer finds himself, if he looks around him, he will notice that all the 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 Boundless Universe.”

Using Hubble's law, modern astronomers can, with a high degree of probability, calculate the position of galaxies and galaxy clusters 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 approximately 13.78 billion years. This value indicates how much time has passed since the expansion of the Universe began, and therefore quite likely indicates its age.
Most often, Hubble's law is used to determine the exact distances to objects in outer space.

3. Hubble's law determines the distance of distant galaxies from us. As for the galaxies closest to us, its effect is not so pronounced here. 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.

Total:0
In contact with 0
Google+ 0
OK 0
Facebook 0