... When at the sunset, tired,
The flaming sheaf of dusk declines,
The tower lifts its visor like a knight,
A telescope flies up to meet the night.
The planet listens to the even
Procession of the echoing minutes,
Holds its breath, until —
The melody of light conquers the dome!
...Don'tyou hear —
the stars are singing?
V. P. Romanenko
THE SPECIAL Astrophysicai Observatory of the Russian Academy of Sciences, home for the largest Eurasian optical telescope BTA (Large Altazimuth Telescope), a reflector with a 6-meters parabolic mirror, has been existing almost for half a century already— since 1966.
The sixties were a romantic time, when the first space flights were beginning, when the new sciences, like nuclear physics and astrophysics, microelectronics, computer engineering and rocket science were developing. And all of this was related not only to the military tasks of the country's defense, but also to its many other needs. The farther away from us becomes the era of the beginning of the space age, the greater the number of legends and myths appearing around the project of construction of the BTA telescope — no doubt, one of the most successful in the history of Russian science and technology.
First of all, I would like to explain the cause of the creation of this unique instrument, since there is a strong opinion that BTA was constructed solely to surpass the United States with their 5-meter telescope-reflector in California in the area of astronomical equipment. But, to tell about the true reasons for the creation of the 6-meter telescope, one must answer the question of why the new observatory was the named «astrophysicai» instead of «astronomical».
What is astrophysics?
Many people having superficial knowledge on the astronomical science think that the problems of astronomy are mainly associated with the «discovery of new stars». But astrophysics is for the most part, not only detection of certain objects in the Universe (though that happens too!), but a detailed study of the physical processes that occur in them — of the dynamics and evolution of matter, energy release, thermonuclear reactions, and much more. A grand picture of the Cosmos is unveiled before an observer, giving an enormous amount of scientific information, both at the Megaworld scale and at the level of elementary particles. After all, the life of stars and galaxies is ultimately defined by the properties and interactions of these particles. One can get this information, among other ways, with the help of a telescope. One of the greatest physicists of the middle of the XXth century, academician L. A. Artsimovich, said that, having a large telescope, there was no need to build expensive experimental physical installations requiring a very expensive operation. Of course, the telescope is also nota cheap facility, but its costs are much less than the costs of creating and supporting a powerful particle accelerator (e.g., the Large Hadron Collider).
However, the study of the physical picture of the World requires not only building a good telescope, but also equipping it with a sensitive and advanced enough registering equipment for solving the astrophysicai problems. Today the majority of the astrophysicai information is provided by the optoelectronic systems that utilize the methods of spectral analysis. The radiation from an astronomical object is resolved into a spectrum — a band similar to rainbow. This operation is performed by a special device called spectrograph (or spectrometer). Spectrographs of different types and designs can be used in astrophysics, depending on the scientific tasks at hand. With the development of spectral methods of astrophysics it turned out that by applying them, one can determine the chemical composition and temperature of celestial objects, measure distances to the most distant galaxies and study the dynamics of gases in their disks, discover magnetic fields of stars and determine their strength. The spectrograms made it possible to study the mechanisms of thermonuclear reactions in stars, to recognize the so-called «black holes» and gravitational lenses. All of these are astrophysicai effects existing in the Grand Universe. Thus, the spectral analysis became the main and the most powerful method established in modern astrophysics.
However, this method also involves certain difficulties, which are particularly strong in the case of studying weakand distant objects. The spectral decomposition of light (for example, light from a star) does not focus the radiation in a point, but distributes it on a plane, so the brightness of the image is reduced considerably. For the spectrum to be registered on a photographic plate (this was the medium used up until the 70 s), it was necessary to collectas much light as possible from the source of radiation. This was done, and is being done today, by utilizing the concave mirrors of large diameter (and therefore of large area). This was the reason behind the decision to create a telescope with a mirror of the maximum possible diameter. And even now, when the galaxies that are billions of light years away from us are being studied, the problem of the amount of light collected by a telescope remains relevant. Today we are witnessing the creation of super-large telescopes with optical mirrors of 34,42 and even 100 m in diameter! The telescopes with 8 to 10 m mirrors have become common astronomical instruments.
The BTA telescope
In I960 the Crimean astrophysicai Observatory's telescope with a mirror diameter of 2.6 m,— at the time the largest instrument in Europe, was put into operation in USSR.Somewhat later a similar instrument was installed in Armenia. However, these telescopes could not provide the opportunities for studying the very distant and faint objects of outer space with astrophysicai methods. Therefore, almost simultaneously with the completion of their construction, the development of a new project was started.The new instrument's possibilities had to be comparable with those of the world's largest 5-meter reflector, already working at the Palomar observatory. The Chief designer of the telescope,
Bagrat Konstantinovich loannisiani, Laureate of the Lenin prize,answering a question on choosing the mirror's diameter, said in 1979: «the analysis of the capabilities of the USSR's industry showed that we were able to build a telescope with up to 6-meter diameter mirror.This, and not someone's desire to surpass the United States at any cost, became the main reason behind selecting the size of the telescope».
The first requirements specification for the construction of the 6-meter telescope was formulated in 1959 in the Department of astronomical instrumentation of GAO (Main Astronomical Observatory, Pulkovo). And then, on March 25,1960, on the recommendation of the USSR Academy of Sciences, the Council of Ministers adopted a Decree: «On the construction of the Special astrophysicai Observatory of the USSR Academy of Sciences (SAO AS USSR — author) and the construction of its Large optical telescope with the main mirror diameter of 6 meters». The Observatory was built especially for the 6-meter telescope, hence its name — Special.
It should be remembered that an observatory is not only a telescope installed in a domeshaped pavilion (such pavilions are traditionally called towers), but a whole complex of buildings, structures and utilities with appropriate infrastructure. By the scale of the task, building an observatory with a large telescope belongs to the category of megaprojects, and requires the involvement of many organizations, enterprises and research teams.The official name of the 6-meter instrument is specified as BTA — Boishoi Teleskop Ait-azimutalnyi, or, in English, the Large Altazimuth Telescope.
Why altazimuth? A telescope is not just an optical tube. To observe the heavenly bodies, their diurnal motion on the celestial sphere has to be tracked very, very precisely. For that purpose, the tube is placed on a special mechanism, which is called a telescope mount.The mount is the instrument that allows moving the optics, compensating for the Earth's rotation around its axis. Before BTA, all telescopes in the world were built on the so-called equatorial mount, when the optical tube was installed on one, but inclined axis that was parallel to the axis of the Earth and rotated in the direction opposite to that of the Earth's rotation with the diurnal rate (fig. 3). Without going into technical details, we can say that this scheme is extremely disadvantageous for telescopes with large and therefore massive mirrors. The reason is that the mirror undergoes deformations under its own weight, and in the equatorial scheme these deformations are constantly changing not only in amplitude, but also in direction, therefore requiring complex and heavy machinery for their compensation. This leads to the considerable increase in the weight of the entire structure, mechanical loads and to a higher cost of the telescope.
In the altazimuth scheme, the telescope tube is installed on a horizontal axis turning in the «up-down» direction around it, and that whole construction is placed on a vertical «fork» rotating azimuthally in the «left-right» direction relatively to the horizon (fig. 4). Thus, the diurnal rotation of the Earth is compensated by addition of simultaneous movements along two axes. In this case, the mirror is affected by the weight loads only in the vertical plane, the weight compensation mechanisms can be simplified and the weight of the whole structure reduced significantly. The structure becomes graceful, easy and harmonious. The use of an equatorial mount for the 6-meter telescope would have lead to a mass of more than 3.5 thousand tons, while the altazimuth mount allowed to create the instrument, the moving part of which is not more than 700 tons, i.e. almost 5 times less! The altazimuth telescope mount was used for a large telescope for the first time in the world.
But the use of such a mount leads to significant increase in the telescope operation complexity as compared to the equatorial scheme, so for an altazimuth telescope, computers become essential. The specialists at LOMO under the supervision of E.M.Neplohov brilliantly solved this problem too — they developed a specialized computing system, which was the world's first computer operating a large telescope. Few people would be surprised today, when computer control has long since become commonplace in all fields of technology and everyday life. But at that time, in the beginning of the 70 s, it was a bold, almost a revolutionary step.
Choosing the location of the construction of SAO has also proved to be a daunting task. Back in 1959, when the first design studies of the complex were only begun, 16 expeditions to different regions of the USSR were organized in GAO under the supervision of N.N.Kucherov to find a site of the future Observatory. Eastern Siberia, Middle Asia, Crimea and Caucasus were studied. Areas with the best astrociimate were to be determined, taking into account the economic, transport and other factors. Astrociimate means a complex of conditions, including the number of cloudless nights in a year, the transparency of the atmosphere, the level of its dustiness and others.The transport facilities are of significance primarily because the heavy large parts of the telescope need to be delivered to the construction site, and also the primary mirror, which mass, according to preliminary estimates, should be more than 40 tons. It was finally decided in 1962 to install the 6-meter telescope in the North Caucasus, Karachai-Cherkessia, at the height of 2070 m near the mountain of Semirodniki, 25 km from the Zelenchukskaya town.
The construction of the SAO complex began in 1965 with the construction of the road from Zelenchukskaya to the telescope's installation site. The construction required to cut through the wooded slope of a mountain range, to blow up rock ledges, to lay drainage channels for the drainage of small mountain rivers. The clause that the road slope should not exceed 5 degrees was strictly observed. High quality of the pavement was required, its profile was carefully controlled with molds throughout the route, as evidenced by photographs (fig. 6). In addition, several bridges had to be built, one of them across the full-flowing Bolshoy Zelenchuk River, each of them was designed to carry a 150-on weight.
On July 11, 1965 a bulldozer raised the first layer of soil on the construction site of the BTA. During the year the concrete plant, a dining room, the generator room, and a temporary residence for workers and specialists were built. In December 1965, the builders began the digging of the pit for the BTA's foundation. It should be mentioned that the site to install the telescope was chosen so that there was a solid rock under the soil layer. It was expedient both from the point of view of instrument's position stability and seismic stability. But digging the foundation pit in the solid rock had to be done without the use of explosive technologies, using only chisel hammers and crow-bars, to maintain the integrity of the bedrock. However, already in the beginning of March 1966, the first foundation formwork and on March 18 a bronze memorial plate were installed and set in the first concrete at the base of the telescope (fig. 7).
The pre-assembly of the telescope's structure was completed successfully in Leningrad (now St. Petersburg) on May 7,1968. After all the necessary tests the telescope was again disassembled into its individual components and the transportation to the final installation location was begun. The telescope parts were moved from Leningrad to Rostov-on-Don by water on barges, and then by road to the construction site of the observatory. On July 22, 1968 the first train with the biggest part of BTA — its supporting platform — arrived to Nizhny Arkhyz (fig. 9). There it was met by the first Director of the SAO, Dr. Ivan Miheevich Kopylov, a wonderful man and an outstanding scientist, who gave the Observatory more than a quarter of a century of his life.
At the time when the telescope was being created, the installers of the «Yujstalkonstruktsia» trust and the builders of «Sevkavgidrostroy» were building the tower of the telescope. A special feature of this building is that its dome with the weight of 1000 tons should rotate freely, repeating the azimuth motion of the telescope.
Before observations, a many tons visor of the dome raises and opens the way for the light to reach the surface of the main mirror. All the mechanisms responsible for these movements were installed as carefully and accurately as the telescope itself. The construction of the tower 53 meters high with a diameter of 42 meters was completed in the summer of 1970, and the LOMO specialists together with the constructors began the installation and the assembly of the 6-meter telescope (fig. 12).
The most complex task was still the production of the main mirror. A special shop was designed and built within 3 years at the Lytkarino Optical Glass Factory (LOGF, Lytkarino city) for the production of this mirror. The main equipment of the shop was unique and in some cases did not have any analogues in the world. For example, there was a giassmaking furnace designed for 380 tons of glass mass. Liquid glass of a temperature of about 1.5 thousand degrees was moved into the casting form through a pipe of pure platinum more than 5 m in length and with a diameter of 135 mm, which was being warmed in hydrogen flames so that the glass mass doesn't congeal when moving. After the billet's casting it was necessary to, as experts say, «anneal» it, i. e. to cool it down slowly from 1050 to 600 degrees at first, and then very carefully with a speed of 0, 03-0,04 deg/hour from 600 to 400 degrees, and further, increasing the speed of cooling until 20 degrees Celsius.This process was performed in the annealing furnace, also built specifically for manufacturing of the 6-meter mirror.
The first attempt of casting of the mirror billet in November 1964 was a failure — a crack appeared on its surface. For the manufacture of the other two billets it was decided to change their shape and the annealing procedure, and after the annealing the glass was to be treated with diamond powders exclusively.
The most important stage of the 6-meter mirror manufacture is giving it the required geometric form, i.e. grinding and polishing under constant accuracy control. And the accuracy is to be the highest here, too — the deviations from the theoretical shape of the paraboloid should not exceed 0.5 microns. To process the mirror, in 1963 a special carousel machine was created at the Kolomna factory of heavy machine-tool construction.It still exists in working condition. The mirror billet weight was 70 tons; the weight of the finished product was 42 tons. Thus, it was necessary to remove the allowance of 28 tons. It took 7 long years and 12 thousand carats of natural diamond (!) in the form of special pastes and powders to create the BTA mirror. The machine for grinding and polishing of the mirror is shown on the fig. 13. It took 7 years to create the first BTA mirror out of the second billet, however, the lack of experience in production and control of the large-sized optics led to the fact that this instance was still of insufficient quality.
However, after grinding, polishing and quality control the first mirror was packaged in a special container and sent to the Observatory in the same way as the parts of the telescope before: by water to Rostov-on-Don, and then by road. The mirror designed for deep space research was being pulled on 150-wheeled chassis by the same powerful trucks that transport carrier-rockets (fig. 14), pulled gently, with a speed of 3-4 km per hour, with police escort, under the curious and proud looks of compatriots. On August 21,1974 the main mirror was delivered to the Observatory; after that it was to be installed on the telescope, and the operabiiity of the whole complex was to be checked.
The assembling of the Large Altazimuth Telescope (BTA) had been completed by the end of 1974. In winter of 1975, after the final adjustments and system checks, the first images of celestial objects were obtained.
The general view of the 6-meter BTA telescope is shown on fig. 15. Anyone who sees the BTA telescope for the first time is impressed by its seemingly easy and fluid movements, though in fact the total weight of the rotating parts of the telescope is 650 tons. The openwork structure, which is called the tube, is rotating almost noiselessly in the vast dome hall, not at all like the bulky tubes with lenses which were created in the past. However, it is a tube, just is not covered by a solid casing.The casing is simply not necessary, because the dome effectively protects the optics from stray light during the night. In the upper part of the tube there is a primary focus cabin, installed on the extensions ofthe massive ring. Various receivers of light are situated in the cabin, forming images or spectra ofthe observed objects. A 42-on parabolic mirror is located at the bottom of the tube (fig. 17). It should be noted that the telescope's main mirror is a sophisticated optomechanic complex, which involves, in addition to the actual glass part, the temperature control sensors, as well as the precise distortion correction mechanisms that compensate for the changes of the mirror's shape under its own weight. These mechanisms are systems of weights and levers that are activated in different points ofthe mirror with different forces. There are 60 of these mechanisms sum total, and they are mounted in 60 blind holes cut into the rear part ofthe main mirror (fig. 18).
The reflecting surface ofthe mirror is covered with extremely thin aluminum foil, several microns thick. Over time, this coating is getting dim, and it has to be washed periodically; and changed completely approximately every five years. For this purpose, a special camera —VMAP — Vacuum Mirror Aluminizing Plant has been mounted in the BTA tower (fig. 19). The mirror is removed from its frame completely and moved into the camera, where the 10-5 atmosphere vacuum is created. Heated aluminum is evaporated in vacuum conditions, settling on the surface of the mirror and being fixed chemically in a special chamber after that.
...Even today, at the beginning of the XXIth century, many people perceive the observations process as the same as it was in the distant past— an astronomer climbs to the telescope at night, points it at a star or some other object, looks into the ocular for a long time and, noticing something interesting, makes an entry in a notepad. It was probably like that in the XVII-XIX centuries.
Today, the very subjective impressions of the observers are replaced by the strict and precise measurements made with special instruments; the observer is looking at a computer screen instead of an ocular, which can be situated faraway from the telescope (fig. 20). In SAO, the majority of observations with the BTA is controlled remotely, computers and automated devices work at the telescope itself, and people are needed to go up to the telescope only for equipment maintenance or for adjustments ofthe observational instruments. The romance of visual observations is completely gone, but it was replaced by the romance of exciting discoveries, which will be discussed below.
Most of the sky we observe at night is filled with stars, the glowing points of varying brightness and color. Scientists of the distant past considered them to be divine lights attached to a solid and fixed celestial sphere (one can often encounter the expression «the heavenly firmament» in ancient manuscripts). Today we know that the stars are giant spheres of gas, consisting mainly of hydrogen. In their bowels, under the conditions of giant pressures (tens of billions of atmospheres) and extreme temperatures (tens of millions of degrees), 4 hydrogen atoms are connecting to create 1 atom of helium in a thermonuclear synthesis reaction. As a result, considerable energy is released, which is what makes stars bright and hot space objects. The distances from the Earth to the stars, even within our stellar system (the Milky Way galaxy), are very large — from 4 thousand to several hundred thousand light years. Different apparent brightness of stars is caused not only by their own different luminosity, but, first of all, by different distances to them — the greater the distance to a star, the dimmer it seems.
A star is an object maintaining a state of thermodynamic equilibrium over billions of years. This means that gravity is trying to collapse all the matter of a star in its centre, but the force of pressure of the hot gas is working in the opposite direction. If these forces are balanced, the star is stable over a long period of time. The research of physical processes in stars, their chemical composition and evolution are among the main objectives ofthe SAO RAS.
It should be understood, when talking about old or young stars, that their age is not comparable to the duration of human life. Stars like the Sun exist, almost without changing their energy output, for 8 toi 0 billion years. However, the duration of a star's existence depends strongly on their mass. The larger the mass, the more intense are the thermonuclear reactions in the depths ofthe star, the faster the thermonuclear fuel is spent, a nd the shorter the lifespan of a star. The life of supermassive stars is relatively short— millions, or even hundreds of thousands of years instead of billions. Supermassive stars with masses of 40 to 120 solar masses (astronomers call them LBV-Luminous Blue Variable) are rare, truly exotic objects in the Cosmos.Therefore the search for them and their study is a difficult and very interesting task. Only about a dozen ofthe most massive stars in the Galaxy are known, however, the theory predicts that there should be several dozen.
Another difficulty is that all the still undiscovered LBVs are hidden from us by light-absorbing dust shells. As one ofthe results ofthe infrared space telescope «Spitzer» observations, a list of «LBV candidates» was compiled, which was studied later with the BTA using spectral methods. One ofthe spectra of a star with a circular dust nebula showed that a new LBV star in the Galaxy was discovered. This discovery was made with the telescope BTA telescope by the astrophysicists of the Sternberg State Astronomical Institute (SAI) and ofthe SAO RAS — V.V.Gvaramadze, A. M. Cherepashchuk, S. N. Fabrika et al. The star received the name MN112 (fig. 21). According to the results of studying MN112, its evolution will soon end in a giant space firework — an explosion that will lead to the formation of a so-called «black hole», a super-dense small-scale object.
Discovering the LBV-type objects becomes a tradition in SAO RAS.The 6-meter telescope facilities allow one to discover them not only in our Galaxy, but also beyond. Thus, a massive variable blue star of high luminosity was discovered in the closest of the dwarf galaxies, DD068, in 2008, also belonging to the LBV-type stars, according to its properties (fig. 22). The study was conducted by the team of SAO RAS astronomers under the supervision of S.A. Pustilnik with the 6-m BTA telescope. The discovered star is also likely to explode as a supernova and turn into a black hole in a short (by cosmic standards, of course) time.
It should be noted that the LBV stars studied with the 6-meter telescope are at very large distances and have low observed brightness; therefore their spectroscopy with high-reso-lution spectrographs would be ineffective. Another instrument is used for studying these objects — a universal image reducer "SCORPIO". The instrument's name, of course, has nothing to do with predatory insects, it is an abbreviation of Spectral Camera with Optical Reducer for Photometrical and Interferometrical Observations. The designer of this unique device is Dr V. L. Afanasiev. The majority ofthe observatory's most important results of the latest years are associated with the instrument (fig. 23).
The dying LBV stars are not the only sources of giant flares in the Universe. In the last decades of the XXth century, flares with the luminosity comparable to that of an entire galaxy have been registered with the help of satellites equipped with X-ray and gamma telescopes. The X-ray flares are relatively frequent, but the gamma-ray flares (specialists call them gamma-ray bursters, or GRB; they occur in the gamma-ray range) are registered much less frequently. A flare can be identified as a gamma-ray burster from space only, and that is an ongoing task of special satellites, which not only register the signal in the gamma range, but also determine the celestial coordinates ofthe GRB. However, the flash can be easily observed in the visible range of spectrum, too. To obtain a series of spectra of such a cosmic event in the visible range means to get a key to understanding the nature of gamma-ray bursters. This is a big scientific success. On the night of July 26/27, 2009 astronomers at the SAO RAS received a message from the SWIFT space telescope about the GRB090726 gamma-ray burst. In half an hour after the burst, a group of SAO RAS astronomers, headed by DrV.V.Sokolov, obtained the first images (fig. 24) of a fading source. It was also possible to obtain the spectrum of the object with the BTA telescope.
The nature of the GRBs remains uncertain. Their spectra show that these objects are removed to distances of billions of light years. It is possible that the cause of the truly enormous power of the gamma-ray bursts is the collision of two massive neutron stars.
However, in astrophysics not only very distant objects can be of interest. Bright events (literally) in the lives of stars occur in close areas of space, too. Fig. 25 shows the «light echo» of a so-called «nova» star in the Monoceros constellation.This unusual red nova, V838, exploded in January 2002. The flare was so powerful that the 6-meter telescope was not needed to obtain the image — it was taken with the 1-meter telescope of SAO RAS by the staff of the stellar physics laboratory, headed by Dr S. N. Fabrika. The «Light echo» ofthe flare looks like a concentric nebula — the light is reflected by the interstellar molecular clouds. The distance to the nova is only 13 thousand light-years.
The capabilities ofthe 6-m BTA telescope are not limited to the ability to make very far and faint space light sources visible. In accordance with the laws of optics, the larger the mirror's diameter, the bet-terone can determine the structure ofthe objects consisting of several components.The theoretical resolution of a telescope with a 6-meter mirror is 0.02 arcseconds.This should allow to recognize an image of a close group of stars not as a singular object, but as a stellar system consisting of several separate stars (as specialists say, to «resolve it into» components). Long-term observations of such a system can provide an opportunity to determine the orbits of its components and, therefore, their masseslThis is perhaps one ofthe few methods of direct measurement of stellar masses, which is very important for the study of evolution of stellar systems.
However, the resolving power of a telescope, even as large one as the BTA, is substantially limited by the Earth's atmosphere. The observations carried out through an air layer about 100 km thick, in which vortex motions (turbulence) are occurring continuously, distort the images of celestial bodies. However, there is a method that allows one to compensate for these distortions and achieve the theoretical maximum resolution.This method is called speckle interferometry. Its main idea is for the registering device to obtain a series of several thousand highly magnified images of a spot blurred by the atmosphere (hence the name of the method).The images then undergo the mathematical reducing procedures carried out by a computer, which looks for identical parts in the images and adds them up, thus restoring the image ofthe observed object.The system for speckle-interferometry for the BTA was developed in the SAO's Laboratory of high resolution astronomy, under the supervision ofYu. Yu. Balega, Corresponding Member of RAS.
The opportunities of the method are well illustrated by an image of a young triple star system SI 40IRS3 (fig. 26), surrounded by gas shells. The area of space represented is only 7 arcseconds, but the structure of the object is detected in every detail.
Journeys to galaxies
Galaxies are gigantic islands of matter, consisting of hundreds of billions of stars and of gas. The distances between them are truly enormous.Today we know that the closest to us large spiral galaxy in the constellation of Andromeda (the «Andromeda nebula») is 2.3 million light years away. The disputes about where these objects were and what they were began as early as the end of the XlXth century. Insufficient capacities of the telescopes and the lack of reliable methods for determining distances led to very different hypotheses. One of them was that they were conventional gas nebulae, which were abundant in the Milky Way. They became known as galaxies. A telescope built in Ireland by Lord Ross (1845), a giant one for the time, let him see that some ofthe nebulae had spiral structure. The confident resolution of the closest of these «nebulae» into stars became possible only after the 2.5-meter reflecting telescope of Mount Wilson had been built in the USA.Soon afterwards the possibility to measure distances to these objects appeared. The spiral nebulae turned out to be stellar systems, removed to distances from millions to billions (!) light years. The field of science that studies the objects outside the Milky Way is called extragalactic astronomy. The BTA provides a possibility for a detailed study of separate stars in nearby galaxies with the methods of spectral analysis. As for the more distant objects, many of them are observable with the 6-m telescope, even if the distances to them amount to hundreds of millions and billions of light years. Detailed pictures of distant galaxies were obtained already in the first years of observations in SAO. Images of galaxies M51 and M81 ofthat period, recorded on glass photographic plates, are presented on fig. 28.
Today the telescope allows obtaining color images of galaxies from very distant regions of space.
Some ofthe galaxies photographed with BTA are shown in the fig. 29-33. The most distant one of them is located at the distance of about 350 million light years. For the registration of images of these galaxies were used not photographic plates, (they became obsolete at the end oftheXXth century), buta special semiconductor matrix.a kind of electronic photographic plate, similar to those who are used in digital cameras. Its main feature is that it is cooled in liquid nitrogen to the temperature of ~ -190 °C to reduce thermal noises. This matrix is built into a sophisticated electronic device capable to work with a computer, the memory of which is where the image accumulates. Such a device — the CCD photometer — was designed and fabricated by one ofthe SAO RAS laboratories under the supervision Dr S.V. Marke I ov. The CCD photometer (see fig. 34) allowed the astronomers of SAO RAS not only to obtain pictures, but also to study galaxies in detail.
It is interesting that the new opportunities that appear with developing more advanced registering equipment for telescopes, allow for a more detailed study of the previously detected objects. Studying archived astronomical images, a team of Cambridge astronomers discovered an interesting object, the nature of which was unknown — a red galaxy surrounded by a blue ring (fig. 35).
To study it, an optical spectrum was needed, but only a very powerful instrument could handle such a task.Therefore on May 15,2007, observations were conducted with the 6-meter telescope of SAO RAS.Justan hour of exposition, using a multimodal device "SCORPIO", SAO astronomer A.V.Moiseev managed to obtain spectra of the required quality, the analysis of which led to an interesting discovery: the object turned out to be a «gravitational lens». The spectrum of the blue ring corresponded to a younger and very distant galaxy — the spectrum analysis showed that the light from it arrived in about 9 billion (!) years. The central part of the object was an elliptical galaxy (the distance was about 4 billion lightyears),the color of which was determined by old stars ofthe solar type. This massiveand closer galaxy deflected the rays coming from the distant galaxy with its gravitational field, and they were refracted, like in a giant lens. In this case, the lens was not only stretching the image into a ring, but also strengthened its brightness more than 30 times. Because of its characteristic shape the object discovered with the BTA received the name of «Cosmic horseshoe».
Further building of the BTA telescope's capacity is primarily associated with the installation of a new main mirror. For forty years of its operation, the BTA mirror was washed annually
and its aluminum reflective coating was washed away and reapplied every five years. This procedure takes its toll on the mirror's surface, as alkaline solutions used to remove the aluminum layer gradually erode it. Such a process is called surface erosion. Because of it, the reflective properties ofthe mirror deteriorate noticeably, and the telescope's «eyesight» diminishes. We have already mentioned that the quality of the first mirror made for BTA was not good enough. In 1979 it was removed and replaced by one of a better quality, made from the third casting. For all the previous years the replaced mirror has been kept in a special container, and now it has been decided to send it to the Lytkarino Optical Glass Factory (Lytkarino city, Moscow region) for re-polishing, which will be carried out using the newest technology. After re-polishing, it will be installed on the 6-meter telescope, which then will be able to provide images of a 10 times better quality than today. We have no doubt that this will lead to new interesting observational results and new discoveries.
The organization of observations on large telescopes is a rather complicated and troublesome matter. Large instruments are in all respects quite expensive machines, and not only because of their high costs.The observing time, taking into account all costs (materials, energy, transport, staff salaries, etc.) is also quite expencive. Therefore, every minute of these observations should be used very effectively. But to ensure this effectiveness, it is necessary to carefully bring to perfection the new astrophysicai equipment, test it in the conditions of real observations, conduct preliminary study of astronomical objects to exclude those of no interest to the major observational programs. This necessary preparation can take a considerable time.
There is another consideration to be taken into account when planning the work of such telescopes as the BTA.Many celestial objects that are bright enough are very interesting from the astrophysicai point of view, but in order to study them, one does not require the telescopes with mirrors several meters in diameter— it would be wiser to use the instruments of a more modest size. Given these circumstances, every major observatory has the so-called supporting telescopes.The SAO RAS has such instruments too. The largest of them is the 1-meter ZEISS-1000 telescope.
Unlike the BTA, this telescope was manufactured not in Russia (the USSR), but in Germany (GDR). This serial astronomic instrument was bought even before the commissioning of the BTA. It was planned that it would be installed in a short time not far from the 6-meter telescope site, and as the larger telescope would be constructed, the astronomers would conduct observations on the Zeiss-1000 one, using it to define the main directions ofthe future research with the BTA. But it turned out differently. All resources were directed to the launch ofthe observatory's main telescope, and the 1 -meter one was in a warehouse in its package for that entire time. And only in 1989 ZEISS -1000 began operation.
However, the telescope was not suitable for modern astrophysicai observations. It was initially meant mainly for obtaining images on photographic plates, had neither a modern control system, nor modern registering devices capable of creating an image in digital format. Therefore, within three years, the engineers of the Observatory carried out a significant modernization, as a result of which the ZEISS-1000 became a fully automated instrument.
It turned out to be simple in operation and reliable, so that even the inexperienced observers are able to operate it, not resorting to the services of the engineers. One only has to enter the coordinates of the object to observe, and the telescope points precisely to the desired area of the celestial sphere, and the dome turns synchronously with its tube.
The possibilities of the 1-meter telescope became especially apparent in the studies of the Hale-Bopp comet (fig. 38) in 1997. The specificity of the observations of this interesting object required multiple resetting of the telescope to point it in strictly defined points of the object, for a few nights in a row. The telescope carried out this task very well. ZEISS-1000 is still being used for studying bright stars, testing new equipment and trying out various new astrophysicai methods.
A window to the radio-Universe
The radiation coming from space does not consist only of visible light — the space objects emit the electromagnetic waves in all ranges, they can emit infrared radiation, x-rays and even gamma rays. Similarly, almost all cosmic bodies — stars, galaxies, planets, gas nebulae and others — also emit in the range of radio waves. Radiation in the radio range, as well as in the optical, carries important information about processes occurring in space. Therefore, the modern astrophysics cannot exist without radio astronomical observations.
In SAO RAS, the radio astronomical observations are carried out on one ofthe largest radio telescopes in the world, called the RATAN-600 (fig. 40). The name of this radio telescope means Radio astronomical Telescope ofthe Academy of Sciences, 600 meters. The last number is the diameter of the ring antenna — a metallic mirror. Even by the modern standards, the RATAN-600 radio telesco ре is a giant astronomical instrument, which can be seen with the naked eye from the orbit! The construction of this telescope began in 1968. The site for the telescope was chosen on the southern outskirts ofthe Zelenchuk village, 24 km from the 6-meter BTA optical telescope.This was done deliberately, so that the two major instruments could operate in the structure of one observatory, and their observations could complement each other and give as complete a picture ofthe physical processes in the objects observed as possible.The site for RATAN is removed from major industrial enterprises and is surrounded by a ring of mountains at the horizon, which protects it from the remote terrestrial interferences.
What are the characteristics of this giant radio telescope? The antenna — a composite ring-shaped metallic mirror consisting of 895 aluminum panels — has a total area of 15 thousand square meters. The accuracy of the observed object's coordinates is 1 to 10 arcseconds. The maximum angular resolution is 2 arcseconds, which is entirely comparable with the actual (taking into account the influence of the atmosphere) resolution of the BTA optical reflector. The RATAN is capable of receiving radio waves in the wide range ofthe centimeter wavelengths: 1 to 50 centimeters. Notable is the telescope's ability to discern useful information against the background of various interferences and noise. We could give the value characterizing this ability, but a figurative comparison would be more illustrative. Imagine a system able to distinguish a mosquito squeak against the background of an artillery bombardment! This is what the RATAN-600 radio telescope is like.
A lot of organizations, institutes and enterprises of our country took part in the construction of the radio telescope, as well as the construction of the BTA.The construction of this instrument, the employing of the scientific staff and formulating the research programs was supervised from the very beginning by Yuri Nikolaevich Parijsky, a RAS academician today, chief researcher of the Department of Radio astronomy of SAO RAS.
The observations on the radio telescope began in March, 1977.The first object of the observation in the radio range was the closest star — our Sun.
The Sun is the central object of our Solar system. Processes occurring on the Sun have the strongest influence on the Earth's atmosphere. Solar flares eject enormous amounts of charged particles into the surrounding space, which then enter the Earth's ionosphere and deform the magnetic field of our planet («magnetic storms»), interfere with the radio communication, disrupt the work of electrical networks, etc.
Today we know that the harvest, the frequency of epidemics, accidents on the roads, storms — a lot of what happens in our everyday life depends on the solar activity. For this reason, the studies ofthe Sun, by radio methods as well, are an extremely important task, not only scientific, but to some extent practical, too. As it turned out, the flares can not only be observed, but also predicted (fig. 41).
Unlike optical astronomy, methods of radio astronomy do not provide colorful multi-color images. Its results are usually presented in the form of graphs, tables, monochrome radio maps with lines of equal brightness, called radio iso-photes. However, despite this, the importance of these results is doubtless. They can be made easier to understand if one combines the radio image of the observed object with the optical one. Fig. 42 (left) shows the superposition ofthe optical image ofthe brightest radio galaxy in the early Universe, born in the first billion years of its existence (the blue area in the center) and of a radio map made in the form of isophotes — concentric figures in red, green, and blue. It can be seen clearly that the maximum of radio brightness falls on a compact area close to the center ofthe optical image.
In-depth analysis ofthe processes that occur in the radio galaxy allows to reconstruct a picture of what it looks like from the outside. Most likely, there is a massive black hole in the centre of this object, with a rapidly rotating gas-dust disk formed around it. In the disk (astrophysics call them «accretion disks» — from the word «accretion», i. е., fall) the matter falling into the black hole is accelerated to speeds close to the speed of light, and an enormous pressure is created on the inner side ofthe disk. As a result, two jets of matter are ejected into space at sub light speed velocities along the disk's rotation axis (on the right).
The application of radio astronomical methods shows how the optical and radio telescopes complement each other. An optical telescope can determine the exact coordinates of an extended object. It gives the chance to scan it witha radio telescope and geta kind of «radio cut» — a plot of the radio emission intensity variation across its diameter.The green line on the fig. 43 is a plot obtained during the observations with the RATAN-600 radio telescope, it shows a significant increase in radio brightness at the 31 cm wavelength in the center of our galaxy, the Milky Way. It is impossible to study the center of the Milky Way in the optical range of electromagnetic waves, as it is shielded from us by a solid mass of interstellardustand gas. But this environment is not an obstacle for radio waves. Therefore the methods of radio astronomy are the only way to study the objects hidden inside the cosmic gas-dust clouds.
It is impossible to mention all the research and observations conducted on the RATAN by the astronomers of SAO RAS, of astronomical centers of Russia and other countries in a short popular scientific essay. However, I would like to tell you about one other program, which is crucial for science. It is focused on the study of the so-called «cosmic background» which was already mentioned above.
In accordance with the main hypothesis about the formation ofthe Universe, its existence began with the rapid expansion ofthe so-called «singularity», a superdense and ultra-compact particle, i. e. with its «explosion», although the concept of explosion is not quite correct in this case, because neither time nor space existed. In astrophysics the event was originally called the «Big clap». After the «clap», several stages of transformation ofthe Universe have passed, which has resulted in the formation of atoms, and then galaxies, stars, and other forms of matter. The consequences ofthe «Big clap» can be observed even now in the form ofthe expansion ofthe Universe — the recession of galaxies, as well as the so-called «relie» radio emission, or background. An important remark has to be made here.The temperature ofthe intergalactic space is exceptionally low. While the lowest temperature possible in nature is -273 °C (the absolute zero, 0 degrees Kelvin), the temperature of the space in question does not exceed 3 K, i.e., only three degrees above the absolute zero. However, in accordance with the laws of physics, any body or environment having a temperature above 0 emits radio waves.
The radio emission corresponding to 3 К carries very important information on the era of the history of the Universe, when there were no galaxies and stars, i. e. on the first years of its existence. The study of the cosmic background radiation, its properties and inho-mogeneities can give answers to a number of fundamental questions about the origin of our World. Why are the energy proportions of elementary particles and atomic nuclei of our Universe the ones we have, and not different? Why is the chemical composition the one we have? How did galaxies form? Radio telescopes with good spatial resolution and the highest sensitivity possible are necessary for the study of the cosmic background of the Universe. RATAN-600 is, undoubtedly, one of these telescopes. That is why at the end of the XX century a research program called «The Universe Gene» was started there, a study of the relic radio emission ofthe Universe.
RATAN-600 is being continuously upgraded and improved. It is being equipped with the latest radio registering devices, with the sensitivity ten times that ofthe first receivers, used 30 years ago. A special laboratory works to ensure that the antenna surface is close to ideal. The observations with the radio telescope, unlike with the optical one, are carried out round the clock. They probably are being continued right now, when the dear reader is holding this magazine.
In the first half of the last century astronomy and astrophysics were still associated exclusively with optical observations. Radio astronomy was added later. And only with the beginning ofthe space era, which started with the launch of the first Soviet artificial Earth satellite in 1957, the opportunity to watch the Space in all ranges — in radio, optical, infrared, x-ray and gamma-radiation — was created. To do this, orbital telescopes are launched, which do not suffer from the interference of either various man-made disturbances or the planet's atmospheric instability. Such telescopes register phenomena and objects that are simply impossible to observe from the Earth. At the turn of XX-XXI centuries astrophysics became all-wavelength.
It would seem that there is no need to build large telescopes on Earth now? It turns out, they are necessary for the development of science.
The space telescopes are removed from the observers, they are controlled remotely, and to reconfigure such a telescope or to re-equip it with new equipment is usually impossible. Besides, space telescopes have a limited lifetime. The height of their orbits is constantly decreasing due to friction in the upper layers of the atmosphere, and it should be restored equally constantly.This will consume the working mass of the shunting engines, and its replenishing is a very expensive operation that requires additional launches of manned spacecrafts for maintenance. The repairs of equipment in orbit are difficult for the same reason. Many instruments for astrophysicai studies are too heavy and large; their launch into orbit is not possible yet. And finally, in many cases, the success of the observations requires the presence of an astronomer nearthe telescope, but not every astronomer-observer is able to be an astronaut.
On the other hand, in the recent decades a new technology was developed, making it possible to create telescopes with composite mirrors of arbitrarily large diameter— 25, 40 or even 100 m! As it was noted above, there are ways to compensate the effects of the Earth's atmosphere, and these methods are more efficient with the larger mirrors of the ground-based telescopes. In essence, astrophysics is the area of science which has a lot of problems that require different telescopes for their solving — both space and ground-based, very large and quite modest in size. Their harmonious use and combination will allow the successful investigation of any astrophysicai problems in the most rational way. That is why astronomy and astrophysics became the field of cooperation of scientists from the entire world.
Among mountains and forests
The Special Astrophysicai observatory is located in the Lower Arkhyz village. In the valley of the Bolshoy Zelenchuk river, on its right bank, 24 km to the south of the Zelenchukskaya town (Karachay-Cherkessia), at an altitude of 1100 meters above the sea level, the buildings of laboratories, offices, houses of scientists and specialists stand. There also are: a school, a hotel, a palace of culture, a stadium — everything that is needed for comfortable life and fruitful work. The BTA telescope is higher— about 2100 m above sea level. Thick beech forest surrounds the village. According to the estimations of biology experts, beech forests are the most powerful oxygen factories on Earth. No wonder the village of astronomers has another name— Bukovo («buk» means «beech» in Russian). Bukovo is included in the territorial complex of Arkhyz, which lies in the basin of the Bolshoy Zelenchuk river from the village of Lower Ermolovka to the Main Caucasian ridge. Several of its alps can be seen clearly from the Upper scientific platform (USP) of the Observatory. This area is famous not only for its wonderful mountain scenery, but also for dozens of beautiful lakes, the purest water of the mountain rivers originating from glaciers and waterfalls. It is no coincidence that the «Arkhyz» water produced here is considered to be among the ecologically cleanest in the world.
And yet, the most important reason for the existence ofthe Special astrophysicai observatory, of its telescopes and the village of specialists is the scientific research of the outer Space. During many years of the existence of the SAO RAS a strong team of professionals of the highest qualification, of scientists of international reputation has formed here. They are wonderful people, enthusiasts who left big cities and came here so that a world-class astrophysicai research center could be created in the mountains of Karachay-Cherkessia.
Of course, even larger telescopes will be built over time; the methods of observations will change and become more perfect. But we hope that the results of the BTA and RATAN-600 telescopes will always be important and relevant for the domestic and international science.
By Vladimir Romanenko