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News Article | February 15, 2017
Site: www.eurekalert.org

Scientists from MIPT, the University of Oxford, and the Lebedev Physical Institute of the Russian Academy of Sciences estimated the number of stars disrupted by solitary supermassive black holes in galactic centers formed due to mergers of galaxies containing supermassive black holes. The astrophysicists found out whether gravitational effects arising as two black holes draw closer to one another can explain why we observe fewer stars being captured by black holes than basic theoretical models predict. In their study published in The Astrophysical Journal, the researchers looked into the interplay of various dynamic mechanisms affecting the number of stars in a galaxy that are captured per unit time (tidal disruption rate). (Spoiler Alert! An advanced theoretical model yielded results that are even more inconsistent with observations, leading the team to hypothesize that the disruption of stars in galactic nuclei may occur without our knowledge.) Tidal disruption events, or TDEs, are the only available source of information from inactive galactic nuclei. There is at least one supermassive black hole in the center of most galaxies. Surrounded by dense central star clusters, black holes occupy regions known as galactic nuclei. As their name suggests, black holes do not emit any light. However, when matter falls onto the central massive object, it gets heated to extreme temperatures and can be observed with a telescope. Active galaxies have gas clouds that feed the black hole thus making it visible. However, most of the galaxies--approximately 90 percent of them--remain "silent" because there are no gas clouds in them and so there is no matter for the black hole to feed on, except for stars that occasionally stray too close to it. When this happens, the star is pulled apart by tidal forces, experiencing what is known as spaghettification, and astronomers detect a tidal disruption event (TDE). So far, around 50 flares of radiation linked to TDEs have been observed. It is reckoned that the average rate of stellar disruption amounts to one star per 10,000 to 100,000 years per galaxy. Based on this data, the scientists are trying to develop a reliable model of what goes on in inactive galactic nuclei. The simplest theoretical model involves a galaxy whose nucleus is spherical in shape and has a supermassive black hole at its center. The black hole is orbited by stars that change the direction of their motion as they pass by one another, the way billiard balls bounce off one another when they collide on the table. However, whereas a billiard ball needs to be moving straight toward the hole to fall into it, a star has more options: It is enough for its velocity vector to be in the so-called loss cone, to ensure that the star will eventually be captured and disrupted by the black hole's gravity. According to this very simple model, an average of one star per galaxy should be captured every 1,000 to 10,000 years, i.e., more frequently than observed. Although the model can be improved by taking a number of other factors into account (e.g., the difference in the mass of stars), this would only further increase the predicted tidal disruption rates. At present, there is only one mechanism discussed in published sources that could be responsible for the fact that fewer stars are captured than expected. Curiously, it requires that most of the low-angular-momentum stars vanish, so to speak. But let us first examine an analogous case involving gas diffusion. Suppose there are gas molecules in random motion contained inside a vessel whose walls can absorb the molecules. Now imagine the molecules closest to the walls have been removed. The obvious consequence of this would be less molecules absorbed per unit time, since the remaining molecules have yet to travel a certain distance before they can come in contact with a wall. Similarly, if stars are removed from the center of the galaxy, the stellar disruption rate will fall. Naturally, the stars cannot simply vanish into thin air; but if the galaxy hosts a binary black hole, then individual stars can be ejected from the galaxy by means of a so-called gravitational slingshot, a maneuver also known as a gravity assist when man-made spacecraft are involved. The law of conservation of energy implies that when a star is accelerated (i.e., receives additional kinetic energy), the energy of the binary black hole must be reduced. As a result, the two black holes draw closer to one another and begin to merge. Eventually, when the merger is almost complete, some of the energy is radiated outward in the form of gravitational waves, as demonstrated by this recent sensational discovery. Although a galaxy merger can be accompanied by a decrease in the rate of star disruption, the opposite effect has also been observed. It has to do with the fact that any galactic nucleus which is a product of a merger is slightly nonspherical in shape. In a nonspherical nucleus, stars are more thoroughly intermixed; hence, there are more stars whose orbits lie close to the black hole. This means that more stars are available to be captured and the TDE rate goes up, in spite of the slingshot effect. To find out how the interplay of these two opposing factors impacts the rate of stellar disruption, Kirill Lezhnin and Eugene Vasiliev--both MIPT graduates--performed the necessary calculations and investigated the influence that black hole mass, nuclear star cluster geometry, and initial conditions have on disruption rates. It turned out that the effect of the removal of stars from the center of the galaxy by means of the gravitational slingshot was negligible in all cases except for the spherical-galaxy-in-a-vacuum scenario. It should be noted, however, that the shape of a galaxy formed in a merger is never a perfect sphere. As far as the results of calculations are concerned, the bottom line is that an average of one star per 10,000 years per galaxy should be disrupted. And while this number is in good agreement with prior theoretical predictions, it also begs the question: Why is it the case that fewer TDEs are observed than theoretical models would have us expect? Kirill Lezhnin, one of the authors of the study and a researcher at MIPT's Laboratory of Astrophysics and Physics of Nonlinear Processes, explains the significance of the research findings: "We showed that the observed low disruption rates cannot be accounted for by the slingshot effect. Therefore, another mechanism needs to be found which lies outside the realm of stellar dynamics studies. Alternatively, the TDE rates we arrived at could in fact be accurate. We then need to find an explanation as to why they are not observed."


News Article | February 16, 2017
Site: www.rdmag.com

Scientists from MIPT, the University of Oxford, and the Lebedev Physical Institute of the Russian Academy of Sciences estimated the number of stars disrupted by solitary supermassive black holes in galactic centers formed due to mergers of galaxies containing supermassive black holes. The astrophysicists found out whether gravitational effects arising as two black holes draw closer to one another can explain why we observe fewer stars being captured by black holes than basic theoretical models predict. In their study published in The Astrophysical Journal, the researchers looked into the interplay of various dynamic mechanisms affecting the number of stars in a galaxy that are captured per unit time (tidal disruption rate). An advanced theoretical model yielded results that are even more inconsistent with observations, leading the team to hypothesize that the disruption of stars in galactic nuclei may occur without our knowledge. Tidal disruption events, or TDEs, are the only available source of information from inactive galactic nuclei. There is at least one supermassive black hole in the center of most galaxies. Surrounded by dense central star clusters, black holes occupy regions known as galactic nuclei. As their name suggests, black holes do not emit any light. However, when matter falls onto the central massive object, it gets heated to extreme temperatures and can be observed with a telescope. Active galaxies have gas clouds that feed the black hole thus making it visible. However, most of the galaxies--approximately 90 percent of them--remain "silent" because there are no gas clouds in them and so there is no matter for the black hole to feed on, except for stars that occasionally stray too close to it. When this happens, the star is pulled apart by tidal forces, experiencing what is known as spaghettification, and astronomers detect a tidal disruption event (TDE). So far, around 50 flares of radiation linked to TDEs have been observed. It is reckoned that the average rate of stellar disruption amounts to one star per 10,000 to 100,000 years per galaxy. Based on this data, the scientists are trying to develop a reliable model of what goes on in inactive galactic nuclei. The simplest theoretical model involves a galaxy whose nucleus is spherical in shape and has a supermassive black hole at its center. The black hole is orbited by stars that change the direction of their motion as they pass by one another, the way billiard balls bounce off one another when they collide on the table. However, whereas a billiard ball needs to be moving straight toward the hole to fall into it, a star has more options: It is enough for its velocity vector to be in the so-called loss cone, to ensure that the star will eventually be captured and disrupted by the black hole's gravity. According to this very simple model, an average of one star per galaxy should be captured every 1,000 to 10,000 years, i.e., more frequently than observed. Although the model can be improved by taking a number of other factors into account (e.g., the difference in the mass of stars), this would only further increase the predicted tidal disruption rates. At present, there is only one mechanism discussed in published sources that could be responsible for the fact that fewer stars are captured than expected. Curiously, it requires that most of the low-angular-momentum stars vanish, so to speak. But let us first examine an analogous case involving gas diffusion. Suppose there are gas molecules in random motion contained inside a vessel whose walls can absorb the molecules. Now imagine the molecules closest to the walls have been removed. The obvious consequence of this would be less molecules absorbed per unit time, since the remaining molecules have yet to travel a certain distance before they can come in contact with a wall. Similarly, if stars are removed from the center of the galaxy, the stellar disruption rate will fall. Naturally, the stars cannot simply vanish into thin air; but if the galaxy hosts a binary black hole, then individual stars can be ejected from the galaxy by means of a so-called gravitational slingshot, a maneuver also known as a gravity assist when man-made spacecraft are involved. The law of conservation of energy implies that when a star is accelerated (i.e., receives additional kinetic energy), the energy of the binary black hole must be reduced. As a result, the two black holes draw closer to one another and begin to merge. Eventually, when the merger is almost complete, some of the energy is radiated outward in the form of gravitational waves, as demonstrated by this recent sensational discovery. Although a galaxy merger can be accompanied by a decrease in the rate of star disruption, the opposite effect has also been observed. It has to do with the fact that any galactic nucleus which is a product of a merger is slightly nonspherical in shape. In a nonspherical nucleus, stars are more thoroughly intermixed; hence, there are more stars whose orbits lie close to the black hole. This means that more stars are available to be captured and the TDE rate goes up, in spite of the slingshot effect. To find out how the interplay of these two opposing factors impacts the rate of stellar disruption, Kirill Lezhnin and Eugene Vasiliev--both MIPT graduates--performed the necessary calculations and investigated the influence that black hole mass, nuclear star cluster geometry, and initial conditions have on disruption rates. It turned out that the effect of the removal of stars from the center of the galaxy by means of the gravitational slingshot was negligible in all cases except for the spherical-galaxy-in-a-vacuum scenario. It should be noted, however, that the shape of a galaxy formed in a merger is never a perfect sphere. As far as the results of calculations are concerned, the bottom line is that an average of one star per 10,000 years per galaxy should be disrupted. And while this number is in good agreement with prior theoretical predictions, it also begs the question: Why is it the case that fewer TDEs are observed than theoretical models would have us expect? Kirill Lezhnin, one of the authors of the study and a researcher at MIPT's Laboratory of Astrophysics and Physics of Nonlinear Processes, explains the significance of the research findings: "We showed that the observed low disruption rates cannot be accounted for by the slingshot effect. Therefore, another mechanism needs to be found which lies outside the realm of stellar dynamics studies. Alternatively, the TDE rates we arrived at could in fact be accurate. We then need to find an explanation as to why they are not observed."


News Article | November 2, 2016
Site: www.eurekalert.org

Astronomers using the super-sharp radio vision of the National Science Foundation's Very Long Baseline Array (VLBA) have found the shredded remains of a galaxy that passed through a larger galaxy, leaving only the smaller galaxy's nearly-naked supermassive black hole to emerge and speed away at more than 2,000 miles per second. The galaxies are part of a cluster of galaxies more than 2 billion light-years from Earth. The close encounter, millions of years ago, stripped the smaller galaxy of nearly all its stars and gas. What remains is its black hole and a small galactic remnant only about 3,000 light-years across. For comparison, our Milky Way Galaxy is approximately 100,000 light-years across. The discovery was made as part of a program to detect supermassive black holes, millions or billions of times more massive than the Sun, that are not at the centers of galaxies. Supermassive black holes reside at the centers of most galaxies. Large galaxies are thought to grow by devouring smaller companions. In such cases, the black holes of both are expected to orbit each other, eventually merging. "We were looking for orbiting pairs of supermassive black holes, with one offset from the center of a galaxy, as telltale evidence of a previous galaxy merger," said James Condon, of the National Radio Astronomy Observatory. "Instead, we found this black hole fleeing from the larger galaxy and leaving a trail of debris behind it," he added. "We've not seen anything like this before," Condon said. The astronomers began their quest by using the VLBA to make very high resolution images of more than 1,200 galaxies, previously identified by large-scale sky surveys done with infrared and radio telescopes. Their VLBA observations showed that the supermassive black holes of nearly all these galaxies were at the centers of the galaxies. However, one object, in a cluster of galaxies called ZwCl 8193, did not fit that pattern. Further studies showed that this object, called B3 1715+425, is a supermassive black hole surrounded by a galaxy much smaller and fainter than would be expected. In addition, this object is speeding away from the core of a much larger galaxy, leaving a wake of ionized gas behind it. The scientists concluded that B3 1715+425 is what has remained of a galaxy that passed through the larger galaxy and had most of its stars and gas stripped away by the encounter -- a "nearly naked" supermassive black hole. The speeding remnant, the scientists said, probably will lose more mass and cease forming new stars. "In a billion years or so, it probably will be invisible," Condon said. That means, he pointed out, that there could be many more such objects left over from earlier galactic encounters that astronomers can't detect. The scientists will keep looking, however. They're observing more objects, in a long-term project with the VLBA. Since their project is not time-critical, Condon explained, they use "filler time" when the telescope is not in use for other observations. "The data we get from the VLBA is very high quality. We get the positions of the supermassive black holes to extremely good precision. Our limiting factor is the precision of the galaxy positions seen at other wavelengths that we use for comparison," Condon said. With new optical telescopes that will come on line in future years, such as the Large Synoptic Survey Telescope (LSST), he said, they will then have improved images that can be compared with the VLBA images. They hope that this will allow them to discover more objects like B3 1714+425. "And also maybe some of the binary supermassive black holes we originally sought," he said. Condon worked with Jeremy Darling of the University of Colorado, Yuri Kovalev of the Astro Space Center of the Lebedev Physical Institute in Moscow, and Leonid Petrov of the Astrogeo Center in Falls Church, Virginia. The scientists are reporting their findings in the Astrophysical Journal. The VLBA, dedicated in 1993, now is part of the Long Baseline Observatory. It uses ten, 25-meter-diameter dish antennas distributed from Hawaii to St. Croix in the Caribbean. It is operated from the NRAO's Domenici Science Operations Center in Socorro, NM. All ten antennas work together as a single telescope with the greatest resolving power available to astronomy. This unique capability has produced landmark contributions to numerous scientific fields, ranging from Earth tectonics, climate research, and spacecraft navigation, to cosmology. The Long Baseline Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc.


News Article | November 3, 2016
Site: spaceref.com

Astronomers using the super-sharp radio vision of the Very Long Baseline Array (VLBA) have found the shredded remains of a galaxy that passed through a larger galaxy. This left only the smaller galaxy's nearly-naked supermassive black hole to emerge and speed away at more than 2,000 miles per second. The galaxies are part of a cluster of galaxies more than 2 billion light-years from Earth. The close encounter, millions of years ago, stripped the smaller galaxy of nearly all its stars and gas. What remains is its black hole and a small galactic remnant only about 3,000 light-years across. For comparison, our Milky Way Galaxy is approximately 100,000 light-years across. The discovery was made as part of a program to detect supermassive black holes, millions or billions of times more massive than the Sun, that are not at the centers of galaxies. Supermassive black holes reside at the centers of most galaxies. Large galaxies are thought to grow by devouring smaller companions. In such cases, the black holes of both are expected to orbit each other, eventually merging. "We were looking for orbiting pairs of supermassive black holes, with one offset from the center of a galaxy, as telltale evidence of a previous galaxy merger," said James Condon, of the National Radio Astronomy Observatory. "Instead, we found this black hole fleeing from the larger galaxy and leaving a trail of debris behind it," he added. "We've not seen anything like this before," Condon said. The astronomers began their quest by using the VLBA to make very high resolution images of more than 1,200 galaxies, previously identified by large-scale sky surveys done with infrared and radio telescopes. Their VLBA observations showed that the supermassive black holes of nearly all these galaxies were at the centers of the galaxies. However, one object, in a cluster of galaxies called ZwCl 8193, did not fit that pattern. Further studies showed that this object, called B3 1715+425, is a supermassive black hole surrounded by a galaxy much smaller and fainter than would be expected. In addition, this object is speeding away from the core of a much larger galaxy, leaving a wake of ionized gas behind it. The scientists concluded that B3 1715+425 is what has remained of a galaxy that passed through the larger galaxy and had most of its stars and gas stripped away by the encounter -- a "nearly naked" supermassive black hole. The speeding remnant, the scientists said, probably will lose more mass and cease forming new stars. "In a billion years or so, it probably will be invisible," Condon said. That means, he pointed out, that there could be many more such objects left over from earlier galactic encounters that astronomers can't detect. The scientists will keep looking, however. They're observing more objects, in a long-term project with the VLBA. Since their project is not time-critical, Condon explained, they use "filler time" when the telescope is not in use for other observations. "The data we get from the VLBA is very high quality. We get the positions of the supermassive black holes to extremely good precision. Our limiting factor is the precision of the galaxy positions seen at other wavelengths that we use for comparison," Condon said. With new optical telescopes that will come on line in future years, such as the Large Synoptic Survey Telescope (LSST), he said, they will then have improved images that can be compared with the VLBA images. They hope that this will allow them to discover more objects like B3 1714+425. "And also maybe some of the binary supermassive black holes we originally sought," he said. Condon worked with Jeremy Darling of the University of Colorado, Yuri Kovalev of the Astro Space Center of the Lebedev Physical Institute in Moscow, and Leonid Petrov of the Astrogeo Center in Falls Church, Virginia. The scientists are reporting their findings in the Astrophysical Journal. The VLBA, dedicated in 1993, now is part of the Long Baseline Observatory. It uses ten, 25-meter-diameter dish antennas distributed from Hawaii to St. Croix in the Caribbean. It is operated from the NRAO's Domenici Science Operations Center in Socorro, NM. All ten antennas work together as a single telescope with the greatest resolving power available to astronomy. This unique capability has produced landmark contributions to numerous scientific fields, ranging from Earth tectonics, climate research, and spacecraft navigation, to cosmology. Please follow SpaceRef on Twitter and Like us on Facebook.


News Article | March 2, 2017
Site: phys.org

Researchers at the Institute of Bioorganic Chemistry of the Russian Academy of Sciences and colleagues have proposed a new mechanism for the dynamic self-organization of spatial structures in embryogenesis. Using mathematical modeling methods, the researchers have demonstrated that this self-organization may be due to a significant difference in the mutual penetration rates (diffusion) of morphogen proteins, which occurs due to differently binding biologically active substances (morphogens) in the extracellular matrix. The results of this research, which were published in PLOS ONE, create the preconditions for new models describing the variety of forms in the early stages of organism development. In the early stages of development, the embryonic organs are composed of a plurality of identical cells, which then become complex spatial structures, and their sizes are much larger than the cells themselves. How does this happen? It is believed that such structures are formed as a result of dynamic self-organization, a process in which morphogen proteins secreted by cells and propagated over long distances play an important role. One of the conditions necessary for self-organization is finding a system located in a state of acute disequilibrium, that is, under conditions of strong dissipation of energy. Therefore, such structures formed during self-organization are often referred to as "dissipative." "The increasing complexity of the embryo can be simplistically reduced to laws of territorial division, in which differentiated cells, i.e. those that have different functions, play different roles in the body. In many cases, instructions to this orderly spatial differentiation of embryonic tissue cells are obtained due to the formation of dissipative structures. They usually appear as concentration gradients of morphogen proteins. As a result, embryonic cells at different locations along this gradient are exposed to different morphogen concentrations—for example, hormones—and thus receive signals to differentiate," explains Andrey Zaraiskii, head of the Laboratory of Molecular Bases of Embryogenesis of the Institute of Bioorganic Chemistry of the Shemyakin&Ovchinnikov Institute of Bioorganic Chemistry of the Russian Academy of Sciences. It is known that complex structures arise when there are at least two diffusing and nonlinearly interacting morphogens with sharply differing diffusion coefficients, i.e. the rate of penetration of one substance to another. However, real morphogen proteins have similar size and approximately the same mobility in aqueous solutions. "What exactly leads to the achievement of the difference between the diffusion rates of the morphogens, which is necessary for the self-organization of dissipative structures? For a long time, this question remained open ended," says Alexey Nesterenko, a researcher from the Lomonosov Moscow State University. "Previously, we have shown that in the diffusion process in the intercellular space, different morphogens may bind with varying force with proteoglycans, specific proteins of the extracellular matrix (substance)." The researchers assumed that it is this difference in the nonspecific binding of morphogens that may provide a significant difference in their rate of diffusion. "We have applied a mathematical model to demonstrate that a system comprising two uniformly-mobile morphogens with conditions in which one adsorbs on the extracellular matrix makes it possible to obtain the spatial structure of the mechanism of dynamic self-organization," explains Maxim Kuznetsov, one of the researchers from the P.N. Lebedev Physical Institute of the Russian Academy of Sciences. The authors applied the new model to examples in multiple organisms, including the process of cuckoo-catfish coloring. "This fish of the mochokid catfish family has a yellow coloring, with numerous black spots scattered throughout its body. The model that we have developed provides an adequate explanation for the formation and regular decrease in the number of spots of its color in the tail-to-head direction," says Daria Korotkov, one of the researchers, a student at the Lomonosov Moscow State University. The approach creates the preconditions for the development of mathematical models for increasingly diverse morphological forms in embryogenesis. The researchers are already currently working on its further experimental confirmation. Explore further: Russian biologists determine how frog heads are formed More information: Alexey M. Nesterenko et al. Morphogene adsorption as a Turing instability regulator: Theoretical analysis and possible applications in multicellular embryonic systems, PLOS ONE (2017). DOI: 10.1371/journal.pone.0171212


News Article | February 17, 2017
Site: www.24-7pressrelease.com

HINSDALE, IL, February 17, 2017-- Manfred Kaminsky has been included in Marquis Who's Who. As in all Marquis Who's Who biographical volumes, individuals profiled are selected on the basis of current reference value. Factors such as position, noteworthy accomplishments, visibility, and prominence in a field are all taken into account during the selection process.For more than six decades, Dr. Kaminsky has been a highly regarded physicist known for his work in the laboratory and his consulting work at the federal level. Since 1986, he has been the owner and operator of Surface Treatment Sciences International, a laboratory operated out of Hinsdale, IL. Previously, Dr. Kaminsky came to prominence as a lecturer for the Rostock Medical Technical School, a German research society fellow and graduate assistant in physics at the University of Rostock, and senior assistant for the Physical Institute at the University of Marburg. In addition, Dr. Kaminsky has held numerous roles of increasing responsibility with the Argonne National Laboratory over the course of three decades. He has served as a director of its tribology program, director of its surface science center CTR program, senior physicist, associate, assistant physicist, and research associate. In recognition of his professional excellence, Dr. Kaminsky was honored by the Citizen Council of Chicago as its Outstanding New Citizen of the Year in 1968 and he was selected as Japanese Society Promotion of Science Fellow in 1982. In addition, Dr. Kaminsky was selected for inclusion into Who's Who in America, Who's Who in Science and Engineering, Who's Who in the Midwest, Who's Who in the South and Southwest, and Who's Who in the World.Before establishing himself professionally in the field of physics, Dr. Kaminsky prepared for his career by investing in his education. He earned a first diploma in physics from the University of Rostock in Germany in 1951 and a Ph.D. in physics, which he earned magna cum laude from the University of Marburg in 1957. To stay at the top of his field, he is a fellow of the American Physical Society and a member of the American Chemical Society, the Scientific Research Society, the American Association for the Advancement of Science, honorary member of the American Vacuum Society, the European Physical Society, and a member of the German Physical Society. In addition, Dr. Kaminsky has taken on career opportunities outside of his profession to increase his impact on his industry. He has served as a consultant for the Office of Technical Assessment within the U.S. Congress, a member of the National Research Council Committee on Tribology, and guest professor for the Institute of Energy at the University of Quebec. Dr. Kaminsky has also authored such works as "Atomic and Ionic Impact Phenomena on Metal Surfaces," and edited "Radiation Effects on Solid Surfaces." As he looks to the future, he intends to continue excelling in the field of physics while taking on new research projects and opportunities as they arise.About Marquis Who's Who :Since 1899, when A. N. Marquis printed the First Edition of Who's Who in America , Marquis Who's Who has chronicled the lives of the most accomplished individuals and innovators from every significant field of endeavor, including politics, business, medicine, law, education, art, religion and entertainment. Today, Who's Who in America remains an essential biographical source for thousands of researchers, journalists, librarians and executive search firms around the world. Marquis now publishes many Who's Who titles, including Who's Who in America , Who's Who in the World , Who's Who in American Law , Who's Who in Medicine and Healthcare , Who's Who in Science and Engineering , and Who's Who in Asia . Marquis publications may be visited at the official Marquis Who's Who website at www.marquiswhoswho.com


News Article | February 21, 2017
Site: www.eurekalert.org

Our Galaxy's gravitational field limits the accuracy of astrometric observations of distant objects. This is most clearly appeared for objects that are visually located behind the central regions of the Galaxy and the Galactic plane, where the deviation can be up to several dozen microarcseconds. And, more importantly, the effect of this gravitational "noise" cannot be removed. This means that at a certain moment it will no longer be possible to improve the accuracy of determining the position of reference objects, which are used to define the coordinates of all other sources. The results of the study have been published in The Astrophysical Journal. It is widely known that our planet Earth and the Solar System itself are in the depths of the Milky Way, and it is through this galaxy that we look out onto the Universe. As it turns out, this fact is no small matter in astrophysical studies. How strong an effect can our Galaxy's gravitational field and its non-uniformity have on the accuracy of determining the coordinates of distant - extragalactic - objects? A group of Russian astrophysicists from the Astro Space Center (ASC) of P.N. Lebedev Physical Institute, the Space Research Institute of the RAS, MIPT, and the Max-Planck-Institut fuer Astrophysik (Germany) attempted to find an answer to this question. Proper motions, angular sizes, and trigonometric parallaxes (visible displacements) of celestial bodies, including stars, are the basic parameters for solving many astrophysical problems. These parameters are determined by astrometric techniques, and to calculate the position or radial velocity of star, for example, a coordinate system is needed that can be used to measure them against. All of the coordinate systems currently in use, including the International Celestial Reference Frame (ICRF), are based on the coordinates of several hundred "defining" extragalactic sources. Quasars and distant galaxies are ideal reference points for determining the celestial reference frame, as their angular movement is very small - around one-hundredth of a milliarcsecond (compared to the diameter of the Moon for example, which is a little more than 31 arcminutes). An arcsecond is an astronomical unit used to measure small angles, identical to the second of a plane angle. In the same way that an hour is divided as a time interval, the degree of an angle is divided into 60 minutes, and a minute into 60 seconds. Astrophysical instrumentation is developing rapidly and it is expected that the accuracy of radio interferometric observations will soon reach 1 microarcsecond, and the accuracy of optical observations - 10 microarcseconds per year. However, with this level of accuracy there comes a new challenge - the general theory of relativity, and in particular the deflection of a light beam when moving in a gravitational field, interfere with the observations. When a light beam from a distant source passes close to any object, it is slightly deflected by the gravity of the latter. This deviation is typically very small, but if the beam encounters several of these objects on its path, the deviation may be significant. In addition to this, as the objects are moving, the beam deflection angle changes in time and the source coordinates start to "jitter" around their true value. It is important to note that the coordinate "jittering" effect applies to all distant sources, including those that are used as reference points for different coordinate systems. "In attempting to improve the accuracy of implementing the coordinate reference system, we reach a limitation that cannot be bypassed by improving the accuracy of the detecting instruments. In fact, there is a gravitational noise, which makes it impossible to increase the accuracy of implementing a coordinate system above a certain level," says Alexander Lutovinov, a professor of the RAS, the head of laboratory of the Space Research Institute of the RAS, and a lecturer at MIPT. The researchers tried to estimate how much of an effect gravitational noise can have on observations. The calculations were based on modern models of the Galactic matter distribution. The two-dimensional "maps" of the entire sky were built for each model showing the standard deviation of the angular shifts in positions of distant sources with respect to their true positions. "Our calculations show that over a reasonable observational time of around ten years, the value of the standard deviation of shifts in positions of sources will be around 3 microarcseconds at high galactic latitudes, rising to several dozen microarcseconds toward the Galactic center," says Tatiana Larchenkova, a senior researcher at the ASC of P.N. Lebedev Physical Institute. "And this means that when the accuracy of measurements in absolute astrometry reaches microarcseconds, the "jittering" effect of reference source coordinates, which is caused by the Galaxy's non-stationary field, will need to be taken into account." The scientists investigated the properties of this gravitational noise that, in the future, will enable the noise to be excluded from observational data. They also demonstrated that the "jittering" effect of the coordinates can be partially compensated by using mathematical methods. The study was supported by Grant No. 14-22-00271 of the Russian Science Foundation.


News Article | February 23, 2017
Site: www.rdmag.com

Our Galaxy's gravitational field limits the accuracy of astrometric observations of distant objects. This is most clearly appeared for objects that are visually located behind the central regions of the Galaxy and the Galactic plane, where the deviation can be up to several dozen microarcseconds. And, more importantly, the effect of this gravitational "noise" cannot be removed. This means that at a certain moment it will no longer be possible to improve the accuracy of determining the position of reference objects, which are used to define the coordinates of all other sources. The results of the study have been published in The Astrophysical Journal. It is widely known that our planet Earth and the Solar System itself are in the depths of the Milky Way, and it is through this galaxy that we look out onto the Universe. As it turns out, this fact is no small matter in astrophysical studies. How strong an effect can our Galaxy's gravitational field and its non-uniformity have on the accuracy of determining the coordinates of distant - extragalactic - objects? A group of Russian astrophysicists from the Astro Space Center (ASC) of P.N. Lebedev Physical Institute, the Space Research Institute of the RAS, MIPT, and the Max-Planck-Institut fuer Astrophysik (Germany) attempted to find an answer to this question. Proper motions, angular sizes, and trigonometric parallaxes (visible displacements) of celestial bodies, including stars, are the basic parameters for solving many astrophysical problems. These parameters are determined by astrometric techniques, and to calculate the position or radial velocity of star, for example, a coordinate system is needed that can be used to measure them against. All of the coordinate systems currently in use, including the International Celestial Reference Frame (ICRF), are based on the coordinates of several hundred "defining" extragalactic sources. Quasars and distant galaxies are ideal reference points for determining the celestial reference frame, as their angular movement is very small - around one-hundredth of a milliarcsecond (compared to the diameter of the Moon for example, which is a little more than 31 arcminutes). An arcsecond is an astronomical unit used to measure small angles, identical to the second of a plane angle. In the same way that an hour is divided as a time interval, the degree of an angle is divided into 60 minutes, and a minute into 60 seconds. Astrophysical instrumentation is developing rapidly and it is expected that the accuracy of radio interferometric observations will soon reach 1 microarcsecond, and the accuracy of optical observations - 10 microarcseconds per year. However, with this level of accuracy there comes a new challenge - the general theory of relativity, and in particular the deflection of a light beam when moving in a gravitational field, interfere with the observations. When a light beam from a distant source passes close to any object, it is slightly deflected by the gravity of the latter. This deviation is typically very small, but if the beam encounters several of these objects on its path, the deviation may be significant. In addition to this, as the objects are moving, the beam deflection angle changes in time and the source coordinates start to "jitter" around their true value. It is important to note that the coordinate "jittering" effect applies to all distant sources, including those that are used as reference points for different coordinate systems. "In attempting to improve the accuracy of implementing the coordinate reference system, we reach a limitation that cannot be bypassed by improving the accuracy of the detecting instruments. In fact, there is a gravitational noise, which makes it impossible to increase the accuracy of implementing a coordinate system above a certain level," says Alexander Lutovinov, a professor of the RAS, the head of laboratory of the Space Research Institute of the RAS, and a lecturer at MIPT. The researchers tried to estimate how much of an effect gravitational noise can have on observations. The calculations were based on modern models of the Galactic matter distribution. The two-dimensional "maps" of the entire sky were built for each model showing the standard deviation of the angular shifts in positions of distant sources with respect to their true positions. "Our calculations show that over a reasonable observational time of around ten years, the value of the standard deviation of shifts in positions of sources will be around 3 microarcseconds at high galactic latitudes, rising to several dozen microarcseconds toward the Galactic center," says Tatiana Larchenkova, a senior researcher at the ASC of P.N. Lebedev Physical Institute. "And this means that when the accuracy of measurements in absolute astrometry reaches microarcseconds, the "jittering" effect of reference source coordinates, which is caused by the Galaxy's non-stationary field, will need to be taken into account." The scientists investigated the properties of this gravitational noise that, in the future, will enable the noise to be excluded from observational data. They also demonstrated that the "jittering" effect of the coordinates can be partially compensated by using mathematical methods.


Our galaxy's gravitational field limits the accuracy of astrometric observations of distant objects. This is most apparent for objects that are obscured behind the central regions of the galaxy and the galactic plane, where the deviation can be up to several dozen microarcseconds. And more importantly, the effect of this gravitational "noise" cannot be removed. This means that beyond a certain point, it will no longer be possible to improve the accuracy of determining the position of reference objects that are used to define the coordinates of all other sources. The results of the study have been published in the Astrophysical Journal. It is widely known that Earth and the solar system are embedded within the Milky Way, through which we look out to the universe. As it turns out, this fact is no small matter in astrophysical studies. How strong an effect can our galaxy's gravitational field and its non-uniformity have on the accuracy of determining the coordinates of distant extragalactic objects? A group of Russian astrophysicists from the Astro Space Center (ASC) of P.N. Lebedev Physical Institute, the Space Research Institute of the RAS, MIPT, and the Max-Planck-Institut fuer Astrophysik (Germany) attempted to find an answer to this question. Proper motions, angular sizes, and trigonometric parallaxes (visible displacements) of celestial bodies, including stars, are the basic parameters for solving many astrophysical problems. These parameters are determined by astrometric techniques. To calculate the position or radial velocity of star, for example, a coordinate system is needed that can be used to measure them against. All of the coordinate systems currently in use, including the International Celestial Reference Frame (ICRF), are based on the coordinates of several hundred "defining" extragalactic sources. Quasars and distant galaxies are ideal reference points for determining the celestial reference frame, as their angular movement is very small— around one-hundredth of a milliarcsecond (compared to the diameter of the moon, for example, which is a little more than 31 arcminutes). Astrophysical instrumentation is advancing rapidly, and it is expected that the accuracy of radio interferometric observations will soon reach 1 microarcsecond, and the accuracy of optical observations 10 microarcseconds per year. However, with this level of accuracy, there comes a new challenge—the general theory of relativity, and in particular the deflection of a light beam when moving in a gravitational field, interfere with the observations. When a light beam from a distant source passes close to any object, it is slightly deflected by the gravity of the latter. This deviation is typically very small, but if the beam encounters several of these objects on its path, the deviation may be significant. In addition, as the objects are moving, the beam deflection angle changes in time and the source coordinates start to "jitter" around their true value. It is important to note that the coordinate "jittering" effect applies to all distant sources, including those that are used as reference points for different coordinate systems. "In attempting to improve the accuracy of implementing the coordinate reference system, we reach a limitation that cannot be bypassed by improving the accuracy of the detecting instruments. In fact, there is gravitational noise, which makes it impossible to increase the accuracy of implementing a coordinate system above a certain level," says Alexander Lutovinov, a professor of the RAS, the head of laboratory of the Space Research Institute of the RAS, and a lecturer at MIPT. The researchers tried to estimate how much of an effect gravitational noise can have on observations. The calculations were based on modern models of the galactic matter distribution. The two-dimensional "maps" of the entire sky were built for each model showing the standard deviation of the angular shifts in positions of distant sources with respect to their true positions. "Our calculations show that over a reasonable observational time of around ten years, the value of the standard deviation of shifts in positions of sources will be around three microarcseconds at high galactic latitudes, rising to several dozen microarcseconds toward the galactic center," says Tatiana Larchenkova, a senior researcher at the ASC of P.N. Lebedev Physical Institute. "And this means that when the accuracy of measurements in absolute astrometry reaches microarcseconds, the "jittering" effect of reference source coordinates, which is caused by the galaxy's non-stationary field, will need to be taken into account." The scientists investigated the properties of this gravitational noise, which, in the future, will enable the noise to be excluded from observational data. They also demonstrated that the "jittering" effect of the coordinates can be partially compensated by using mathematical methods. Explore further: Missing stars in the solar neighbourhood reveal the sun's speed and distance to the centre of the Milky Way galaxy More information: Tatiana I. Larchenkova et al. INFLUENCE OF THE GALACTIC GRAVITATIONAL FIELD ON THE POSITIONAL ACCURACY OF EXTRAGALACTIC SOURCES, The Astrophysical Journal (2017). DOI: 10.3847/1538-4357/835/1/51


Flash Physics is our daily pick of the latest need-to-know developments from the global physics community selected by Physics World's team of editors and reporters Calcium-iron arsenide, which is usually not a superconductor, has been made to superconduct by Paul Chu and colleagues at the University of Houston in the US. This was done using an idea first proposed in the 1970s – that superconductivity can be enhanced or even created at the interface between two materials. Chu and colleagues heated calcium-iron arsenide so that it coexists in two different structural phases, neither of which is superconducting. Then the sample is cooled carefully to preserve the two phases. When cooled to below 25 K, the material is a superconductor at the interface between the phases. While this superconducting temperature is too low to be of practical use, Chu believes that the work offers a new direction in the search for more efficient, less expensive superconducting materials. The research is described in Proceedings of the National Academy of Sciences. A bibliometric study by researchers at the National Research University Higher School of Economics (HSE) in Russia has measured the scientific impact of 39 physics institutions belonging to the Russian Academy of Sciences (RAS). Carried out by HSE sociologists Yuriy Kachanov and Natalia Shmatko, together with Yulia Markova from the American Association for the Advancement of Science, they found that the Joint Institute for Nuclear Research, the Alikhanov Institute for Theoretical and Experimental Physics, the Lebedev Physical Institute – all based in Moscow – and the Ioffe Institute in St Petersburg are the top physics research institutions in the country. The study looked at the number of researchers based at each institution, together with publication statistics. "We were able to prove that big institutions held authority on the global science scene and produced more scientific data, which was highly received by the physics community," says Shmatko. A new initiative aimed at strengthening ties between tech firms and the UK's National Physical Laboratory (NPL) was officially launched last night at the Institute of Engineering and Technology in London. The project, known as NPL Instruments, will see experts at the Teddington-based national measurement institute work closely with companies to develop bespoke instruments, products and related services. At the event, NPL chief-executive Peter Thompson told Physics World that the new business unit would focus on products at a moderate stage of development (equivalent to Technology Readiness Levels 4 and 5) in the areas of advanced manufacturing, environment, health and life sciences, and the digital sector. NPL's work on instruments tends to be "hidden in plain view", Thompson told an audience of around 100 lab personnel, industry scientists, engineers and academics at the event, adding that the new business unit is intended to help publicize and expand the lab's role as an "instrument development partner". Paul Shore, who leads both the new unit and NPL's engineering measurement division, gave indoor GPS technologies and "smaller, faster, cheaper" atomic clocks as examples of products where the lab's existing strengths in measurement and sensing could help to catalyse technical advances. The initiative comes on the heels of a transition period for NPL, which announced in August that it would make up to 50 staff members redundant as part of what Thompson called a "rebalancing" of the 116 year-old lab.

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