Sternberg Astronomical Institute

Moscow, Russia

Sternberg Astronomical Institute

Moscow, Russia
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News Article | April 19, 2017
Site: www.eurekalert.org

Researches from Sternberg Astronomical Institute, Lomonosov Moscow State University have focused their efforts on one of the major theoretical issues of modern astrophysical fluid dynamics, which is the stability of Keplerian shear flow of liquid or gas. The results are available in the Monthly Notices of the Royal Astronomical Society journal. Keplerian flow is ubiquitous in space: it appears in accretion and protoplanetary discs, where fluid rotates differentially so that its angular velocity decreases inversely to the distance from the rotation axis to the three-halves power. Dr. Viacheslav Zhuravlev, a member of the Relativistic Astrophysics group in Sternberg Astronomical Institute (Lomonosov Moscow State University) and the author of the paper comments: "Numerous observations reveal that both accretion and protoplanetary discs are in turbulent state. Nevertheless, no one has managed so far to model or simulate in laboratory conditions turbulent Keplerian flow of non-ionized matter. In other words, unlike the other known shear flows, the Keplerian flow manifests amazing nonlinear dynamical stability. To date, this stability has been checked up to the Reynolds number of several millions. However, in real astrophysical discs the Reynolds number can be as high as tens of billions". In the project the authors suppose that Keplerian flow breaks into a turbulent state at the Reynolds number not yet attained in the research. As turbulence cannot exist in the absence of growing perturbations of velocity and pressure, they consider in detail how large the growth factor of transiently growing perturbations can be. Generally, those perturbations arise in the form of spirals being unwound by the differential rotation of the bulk flow. Viacheslav Zhuravlev says: "We've managed to show for the first time that such perturbations are able to sustain turbulence also at scales, which significantly exceed the disc thickness. Besides, we predict a value of the Reynolds number, corresponding to transition to turbulence both in Keplerian and super-Keplerian flows". The researchers have been solving the linearised Navier-Stokes equations both numerically and analytically. Moreover, for the first time in astrophysical scientific literature they have employed a so called variational approach in order to determine the optimal perturbations, which demonstrate the highest possible growth of amplitude. The scientist sums up: "We are going to carry out a set of special computer simulations, which will help to reveal an exact mechanism of the shear flow stabilization in the model situation, when angular velocity profile evolves from a so called cyclonic type to the Keplerian type. This, in turn, this will contribute to better understanding of the behavior of Keplerian flow and the evolution of finite amplitude perturbations in it . We believe that the discovery of the nonlinear hydrodynamical instability of Keplerian flow is nearly at hand. In fact, it is directly related to the explanation of the very existence of accretion and protoplanetary discs and, consequently, to the emergence of many other objects in the Universe".


News Article | April 28, 2017
Site: www.rdmag.com

An international team of astrophysicists led by a scientist from the Sternberg Astronomical Institute of the Lomonosov Moscow State University reported the discovery of a binary solar-type star inside the supernova remnant RCW 86. Spectroscopic observation of this star revealed that its atmosphere is polluted by heavy elements ejected during the supernova explosion that produced RCW 86. In particular, it was found that the calcium abundance in the stellar atmosphere exceeds the solar one by a factor of six, which hints at the possibility that the supernova might belong to the rare type of calcium-rich supernovae - the enigmatic objects, whose origin is yet not clear. The research results are published in Nature Astronomy on 2017 April, 24. The evolution of a massive star ends with a violent explosion called a supernova. The central part of the exploded star contracts into a neutron star, while the outer layers expand with a huge velocity and form an extended gaseous shell called supernova remnant (SNR). Currently, several hundreds of SNRs are known in the Milky Way, of which several tens were found to be associated with neutron stars. Detection of new examples of neutron stars in SNRs is very important for understanding the physics of supernova explosions. In 2002 Vasilii Gvaramadze, a scientist from the Sternberg Astronomical Institute, proposed that the pyriform appearance of RCW 86 can be due to a supernova explosion near the edge of a bubble blown by the wind of a moving massive star - the supernova progenitor star. This allowed him to detect a candidate neutron star, currently known as [GV2003] N, associated with RCW 86 using the data from the Chandra X-ray Observatory. If [GV2003] N is indeed a neutron star, then it should be a very weak source of optical emission. But in the optical image obtained in 2010, a quite bright star was detected at the position of [GV2003] N. This could mean that [GV2003] N was not a neutron star. Vasilii Gvaramadze, the leading author of the Nature Astronomy publication, explains: "In order to determine the nature of the optical star at the position of [GV2003] N, we obtained its images using seven-channel optical/near-infrared imager GROND at the 2.2-metre telescope of the European Southern Observatory (ESO). Spectral energy distribution has shown that this star is of solar type (so-called G star). But since the X-ray luminosity of the G star should be significantly less than that was measured for [GV2003] N, we have come to a conclusion that we deal with a binary system, composed of a neutron star (visible in X-rays as [GV2003] N) and a G star (visible in optical wavelengths)". The existence of such systems is a natural result of massive binary star evolution. Recently, it was recognized that the majority of massive stars form in binary and multiple systems. When one of the stars explodes in a binary system, the second one could become polluted by heavy elements, ejected by a supernova. To check the hypothesis that [GV2003] N is a binary system, astrophysicists have got four spectra of the G star in 2015 with the Very Large Telescope (VLT) of the ESO. It was found that the radial velocity of this star has significantly changed during one month, which is indicative of an eccentric binary with an orbital period of about a month. The obtained result has proved that [GV2003] N is a neutron stars and that RCW 86 is the result of supernova explosion near the edge of a wind-blown bubble. This is very important for understanding the structure of some peculiar SNRs as well as for detection of their associated neutron stars. Until recently, the most popular explanation of the origin of the calcium-rich supernovae was the helium shell detonation on low-mass white dwarfs. The results obtained by Vasilii Gvaramadze and his colleagues, however, imply that under certain circumstances a large amount of calcium could also be synthesized by explosion of massive stars in binary systems. Vasilii Gvaramadze sums up: "We continue studying [GV2003] N. We are going to determine orbital parameters of the binary system, estimate the initial and final masses of the supernova progenitor, and the kick velocity obtained by the neutron star at birth. Moreover, we are also going to measure abundances of additional elements in the G star atmosphere. The obtained information could be crucially important for understanding the nature of the calcium-rich supernovae".


News Article | April 28, 2017
Site: www.eurekalert.org

An international team of astrophysicists led by a scientist from the Sternberg Astronomical Institute of the Lomonosov Moscow State University reported the discovery of a binary solar-type star inside the supernova remnant RCW 86. Spectroscopic observation of this star revealed that its atmosphere is polluted by heavy elements ejected during the supernova explosion that produced RCW 86. In particular, it was found that the calcium abundance in the stellar atmosphere exceeds the solar one by a factor of six, which hints at the possibility that the supernova might belong to the rare type of calcium-rich supernovae - the enigmatic objects, whose origin is yet not clear. The research results are published in Nature Astronomy on 2017 April, 24. The evolution of a massive star ends with a violent explosion called a supernova. The central part of the exploded star contracts into a neutron star, while the outer layers expand with a huge velocity and form an extended gaseous shell called supernova remnant (SNR). Currently, several hundreds of SNRs are known in the Milky Way, of which several tens were found to be associated with neutron stars. Detection of new examples of neutron stars in SNRs is very important for understanding the physics of supernova explosions. In 2002 Vasilii Gvaramadze, a scientist from the Sternberg Astronomical Institute, proposed that the pyriform appearance of RCW 86 can be due to a supernova explosion near the edge of a bubble blown by the wind of a moving massive star - the supernova progenitor star. This allowed him to detect a candidate neutron star, currently known as [GV2003] N, associated with RCW 86 using the data from the Chandra X-ray Observatory. If [GV2003] N is indeed a neutron star, then it should be a very weak source of optical emission. But in the optical image obtained in 2010, a quite bright star was detected at the position of [GV2003] N. This could mean that [GV2003] N was not a neutron star. Vasilii Gvaramadze, the leading author of the Nature Astronomy publication, explains: "In order to determine the nature of the optical star at the position of [GV2003] N, we obtained its images using seven-channel optical/near-infrared imager GROND at the 2.2-metre telescope of the European Southern Observatory (ESO). Spectral energy distribution has shown that this star is of solar type (so-called G star). But since the X-ray luminosity of the G star should be significantly less than that was measured for [GV2003] N, we have come to a conclusion that we deal with a binary system, composed of a neutron star (visible in X-rays as [GV2003] N) and a G star (visible in optical wavelengths)". The existence of such systems is a natural result of massive binary star evolution. Recently, it was recognized that the majority of massive stars form in binary and multiple systems. When one of the stars explodes in a binary system, the second one could become polluted by heavy elements, ejected by a supernova. To check the hypothesis that [GV2003] N is a binary system, astrophysicists have got four spectra of the G star in 2015 with the Very Large Telescope (VLT) of the ESO. It was found that the radial velocity of this star has significantly changed during one month, which is indicative of an eccentric binary with an orbital period of about a month. The obtained result has proved that [GV2003] N is a neutron stars and that RCW 86 is the result of supernova explosion near the edge of a wind-blown bubble. This is very important for understanding the structure of some peculiar SNRs as well as for detection of their associated neutron stars. Until recently, the most popular explanation of the origin of the calcium-rich supernovae was the helium shell detonation on low-mass white dwarfs. The results obtained by Vasilii Gvaramadze and his colleagues, however, imply that under certain circumstances a large amount of calcium could also be synthesized by explosion of massive stars in binary systems. Vasilii Gvaramadze sums up: "We continue studying [GV2003] N. We are going to determine orbital parameters of the binary system, estimate the initial and final masses of the supernova progenitor, and the kick velocity obtained by the neutron star at birth. Moreover, we are also going to measure abundances of additional elements in the G star atmosphere. The obtained information could be crucially important for understanding the nature of the calcium-rich supernovae".


News Article | April 28, 2017
Site: www.rdmag.com

An international team of astrophysicists led by a scientist from the Sternberg Astronomical Institute of the Lomonosov Moscow State University reported the discovery of a binary solar-type star inside the supernova remnant RCW 86. Spectroscopic observation of this star revealed that its atmosphere is polluted by heavy elements ejected during the supernova explosion that produced RCW 86. In particular, it was found that the calcium abundance in the stellar atmosphere exceeds the solar one by a factor of six, which hints at the possibility that the supernova might belong to the rare type of calcium-rich supernovae - the enigmatic objects, whose origin is yet not clear. The research results are published in Nature Astronomy on 2017 April, 24. The evolution of a massive star ends with a violent explosion called a supernova. The central part of the exploded star contracts into a neutron star, while the outer layers expand with a huge velocity and form an extended gaseous shell called supernova remnant (SNR). Currently, several hundreds of SNRs are known in the Milky Way, of which several tens were found to be associated with neutron stars. Detection of new examples of neutron stars in SNRs is very important for understanding the physics of supernova explosions. In 2002 Vasilii Gvaramadze, a scientist from the Sternberg Astronomical Institute, proposed that the pyriform appearance of RCW 86 can be due to a supernova explosion near the edge of a bubble blown by the wind of a moving massive star - the supernova progenitor star. This allowed him to detect a candidate neutron star, currently known as [GV2003] N, associated with RCW 86 using the data from the Chandra X-ray Observatory. If [GV2003] N is indeed a neutron star, then it should be a very weak source of optical emission. But in the optical image obtained in 2010, a quite bright star was detected at the position of [GV2003] N. This could mean that [GV2003] N was not a neutron star. Vasilii Gvaramadze, the leading author of the Nature Astronomy publication, explains: "In order to determine the nature of the optical star at the position of [GV2003] N, we obtained its images using seven-channel optical/near-infrared imager GROND at the 2.2-metre telescope of the European Southern Observatory (ESO). Spectral energy distribution has shown that this star is of solar type (so-called G star). But since the X-ray luminosity of the G star should be significantly less than that was measured for [GV2003] N, we have come to a conclusion that we deal with a binary system, composed of a neutron star (visible in X-rays as [GV2003] N) and a G star (visible in optical wavelengths)". The existence of such systems is a natural result of massive binary star evolution. Recently, it was recognized that the majority of massive stars form in binary and multiple systems. When one of the stars explodes in a binary system, the second one could become polluted by heavy elements, ejected by a supernova. To check the hypothesis that [GV2003] N is a binary system, astrophysicists have got four spectra of the G star in 2015 with the Very Large Telescope (VLT) of the ESO. It was found that the radial velocity of this star has significantly changed during one month, which is indicative of an eccentric binary with an orbital period of about a month. The obtained result has proved that [GV2003] N is a neutron stars and that RCW 86 is the result of supernova explosion near the edge of a wind-blown bubble. This is very important for understanding the structure of some peculiar SNRs as well as for detection of their associated neutron stars. Until recently, the most popular explanation of the origin of the calcium-rich supernovae was the helium shell detonation on low-mass white dwarfs. The results obtained by Vasilii Gvaramadze and his colleagues, however, imply that under certain circumstances a large amount of calcium could also be synthesized by explosion of massive stars in binary systems. Vasilii Gvaramadze sums up: "We continue studying [GV2003] N. We are going to determine orbital parameters of the binary system, estimate the initial and final masses of the supernova progenitor, and the kick velocity obtained by the neutron star at birth. Moreover, we are also going to measure abundances of additional elements in the G star atmosphere. The obtained information could be crucially important for understanding the nature of the calcium-rich supernovae".


News Article | May 1, 2017
Site: phys.org

From the upper left, clockwise: 843-MHz image of RCW 86; image of an arc-like optical nebula in the southwest corner of RCW 86; optical and x-ray images of two point sources, [GV2003] N and [GV2003] S, in the centre of the optical arc Credit: Vasilii Gvaramadze An international team of astrophysicists led by a scientist from the Sternberg Astronomical Institute of the Lomonosov Moscow State University has reported the discovery of a binary solar-type star inside supernova remnant RCW 86. Spectroscopic observation of this star reveals that its atmosphere is polluted by heavy elements ejected during the supernova explosion that produced RCW 86. In particular, it was found that the calcium abundance in the stellar atmosphere exceeds the solar abundance by a factor of six, which hints at the possibility that the supernova might belong to a rare type of calcium-rich supernova, enigmatic objects whose origin is yet not clear. The research results are published in Nature Astronomy on 2017 April, 24. The evolution of a massive star ends with a violent explosion called a supernova. The central part of the exploded star contracts into a neutron star, while the outer layers expand with great velocity and form an extended gaseous shell called supernova remnant (SNR). Currently, several hundred SNRs are known in the Milky Way, of which dozens were found to be associated with neutron stars. Detection of new examples of neutron stars in SNRs is very important for understanding the physics of supernova explosions. In 2002, Vasilii Gvaramadze, a scientist from the Sternberg Astronomical Institute, proposed that the pyriform appearance of RCW 86 night be due to a supernova explosion near the edge of a bubble blown by the wind of a moving massive star—the supernova progenitor star. This allowed him to detect a candidate neutron star, currently known as [GV2003] N, associated with RCW 86 using the data from the Chandra X-ray Observatory. If [GV2003] N is, indeed, a neutron star, then it should be a very weak source of optical emission. But in the optical image obtained in 2010, a very bright star was detected at the position of [GV2003] N. This could mean that [GV2003] N was not a neutron star. Vasilii Gvaramadze, the leading author of the Nature Astronomy publication, explains: "In order to determine the nature of the optical star at the position of [GV2003] N, we obtained its images using seven-channel optical/near-infrared imager GROND at the 2.2-metre telescope of the European Southern Observatory (ESO). Spectral energy distribution has shown that this star is of solar type (a so-called G star). But since the X-ray luminosity of the G star should be significantly less than that was measured for [GV2003] N, we have come to a conclusion that it is a binary system composed of a neutron star (visible in X-rays as [GV2003] N) and a G star, visible in optical wavelengths." The existence of such systems is a natural result of massive binary star evolution. Recently, it was recognized that the majority of massive stars form in binary and multiple systems. When one of the stars explodes in a binary system, the second one could become polluted by heavy elements, ejected by a supernova. To check the hypothesis that [GV2003] N is a binary system, astrophysicists have got four spectra of the G star in 2015 with the Very Large Telescope (VLT) of the ESO. It was found that the radial velocity of this star has significantly changed over one month, which is indicative of an eccentric binary with an orbital period of about a month. The obtained result has proved that [GV2003] N is a neutron stars and that RCW 86 is the result of supernova explosion near the edge of a wind-blown bubble. This is very important for understanding the structure of some peculiar SNRs as well as for detection of their associated neutron stars. Until recently, the most popular explanation of the origin of the calcium-rich supernovae was the helium shell detonation on low-mass white dwarfs. The results obtained by Vasilii Gvaramadze and his colleagues, however, imply that under certain circumstances, a large amount of calcium could also be synthesized by the explosion of massive stars in binary systems. Vasilii Gvaramadze says, "We continue studying [GV2003] N. We are going to determine orbital parameters of the binary system, estimate the initial and final masses of the supernova progenitor, and the kick velocity obtained by the neutron star at birth. Moreover, we are also going to measure abundances of additional elements in the G star atmosphere. The obtained information could be crucially important for understanding the nature of the calcium-rich supernovae." Explore further: Search for stellar survivor of a supernova explosion More information: Vasilii V. Gvaramadze et al, A solar-type star polluted by calcium-rich supernova ejecta inside the supernova remnant RCW 86, Nature Astronomy (2017). DOI: 10.1038/s41550-017-0116


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

Members of the Sternberg Astronomical Institute of the Lomonosov Moscow State University have been studying changes in the appearance of emission from around the supermassive black hole in the centre of a galaxy known to astronomers as NGC 2617. The centre of this galaxy, underwent dramatic changes in its appearance several years ago: it became much brighter and things that had not been seen before were seen. This sort of dramatic change can give us valuable information for understanding what the surroundings of a giant black hole are like and what is going on near the black hole. The results of these investigations have been published in the Monthly Notices of the Royal Astronomical Society, one of the world's top-rated astronomical journals. Most galaxies such as our own have a giant black hole in their central nuclei. These monstrous holes have masses ranging from a million to a billion times the mass of our sun. The black hole in our galaxy is inactive, but in some galaxies, the black hole is swallowing gas that is spiraling into it and emitting enormous amounts of radiation. These galaxies are called "active galactic nuclei" or AGNs for short. The energy output from around the black holes of these AGNs can exceed that of the hundreds of billions of stars in the rest of the galaxy. Just how these galaxies get their supermassive black holes is a major mystery. The nuclei of galaxies where the supermassive black holes are vigorously swallowing gas are classified into two types: those where we get a direct view of the matter spiraling into the black hole at a speed that is thousands of times faster than the speed of sound, and those where the inner regions are obscured by dust and we only see more slowly moving gas much further from the black hole. For decades astronomers have wondered why we see the innermost regions of some active galactic nuclei but not others. A popular explanation of the two types of active galactic nuclei is that they are really the same but they appear to be different to us because we are viewing them from different angles. If they are face-on we can see the hot gas spiraling into the black hole directly. If the active galactic nucleus is tilted, then dust around the nucleus blocks our view and we can only see the more slowly moving gas a light year or more away. The leader of the international research team involved in the investigation, Viktor Oknyansky, a Senior Researcher at the Sternberg Astronomical Institute of the Lomonosov Moscow State University says: "Cases of object transition from one type to the other turn out to be a definite problem for this orientation model. In 1984 we found a change in the appearance of another active galactic nucleus known as NGC 4151. It was one of few known cases of this kind in the past. We now know of several dozen active galactic nuclei that have changed their type. In our recent study we have focused on one of the best cases -- NGC 2617." Oknyansky continues: "In 2013 a team of researchers in the US found that NGC 2617 had changed being an active galaxy where the inner regions were hidden to one where the inner regions were now exposed. We didn't not know how long it would remain in this new unveiled state. It could last for only a short period of time or, on the other hand, for dozens of years. The title of the paper by the US astronomers was "The man behind the curtain..." When we began our study we didn't know how long the curtain would remain open, but we've titled our paper "The curtain remains open...", because we are continuing to see into the inner regions of NGC 2617. According to the authors there is no accepted explanation so far of what could cause us to start seeing down to the inner regions of an active galactic nucleus when it was previously hidden. Viktor Oknyansky comments: "It's clear that this phenomenon isn't very rare, on the contrary, we think it's quite typical. We consider various possible explanations. One is that perhaps a star has come too close to the black hole and has been torn apart. However, the disruption of a star by a black hole is very rare and we don't think that such events can explain the observed frequency of type changes of active galactic nuclei. Instead we favour a model where the black hole has started swallowing gas more rapidly. As the material spirals in towards the black holes it emits strong radiation. We speculate that this intense radiation destroys some of the dust surrounding the nucleus and permits us to see the inner regions." Oknyansky continues: "Study of these rapid changes of type is very important for understanding what is going on around supermassive black holes that are rapidly swallowing gas. So, what we have concentrated on is getting observations of the various types of radiation emitted by NGC 2617. This has involved a large-scale effort." The observational data for the project were obtained using the MASTER Global Robotic Network operated by Professor Vladimir Lipunov and his team, the new 2.5-m telescope located near Kislovodsk, a 2-m telescope of the observatory in Azerbajan, the Swift X-ray satellite, and some other telescopes. This research has been conducted in cooperation with colleagues from Azerbaijan, the USA, Finland, Chili, Israel and the South Africa.


Sil'Chenko O.K.,Sternberg Astronomical Institute | Moiseev A.V.,Circassia | Shulga A.P.,Sternberg Astronomical Institute
Astronomical Journal | Year: 2010

We have studied unbarred SO galaxies, NGC 3599 and NGC 3626, the members of the X-ray bright group Leo II, by means of three-dimensional spectroscopy, long-slit spectroscopy, and imaging, with the aim of identifying the epoch and mechanisms of their transformation from spirals. Both galaxies have appeared to bear complex features obviously resulting from minor merging: decoupled gas kinematics, nuclear star-forming rings, and multi-tiered oval large-scale stellar disks. The weak emission line nucleus of NGC 3599 bears all signs of Seyfert activity, according to the line-ratio diagnostics of the gas excitation mechanism. We conclude that the transformation of these lenticular galaxies took place about 1-2 Gyr ago, through gravitational mechanisms unrelated to the hot intragroup medium of Leo II. © 2010. The American Astronomical Society. All rights reserved.


Skugoreva M.A.,Peoples' Friendship University of Russia | Sushkov S.V.,Kazan Federal University | Toporensky A.V.,Sternberg Astronomical Institute
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2013

We consider cosmological dynamics in the theory of gravity with the scalar field possessing a nonminimal kinetic coupling to gravity, κG μνφμφν, and the power-law potential V(φ)=V0φN. Using the dynamical system method, we analyze all possible asymptotical regimes of the model under investigation and show that for sloping potentials with 02. Using a numerical analysis, we also construct exact cosmological solutions and find initial conditions leading to the initial kinetic coupling inflation followed either by a "graceful" oscillatory exit or by the secondary inflation. © 2013 American Physical Society.


Baturin V.A.,Sternberg Astronomical Institute
Astrophysics and Space Science | Year: 2010

State-of-the-art perspectives of the equation of state (EOS) are considered in view of applications to stellar and solar modeling. While the present-day OPAL EOS is the best-known version of EOS, here we discuss the SAHA-S EOS as an alternative. We assume that the accuracy of the EOS is determined by an adequate description of the ionization of a number of chemical components. To get an adequate description of the ionization, one needs an extensive amount of ion levels, an appropriately truncated partition function, such as the Planck-Larkin function, and a high-level approximation to the Coulomb correction. The current version of the SAHA-S EOS includes an extended set of elements. It provides an accurate profile of the adiabatic exponent in the solar convection zone, which is then compared to a result of a helioseismic inversion. © 2009 Springer Science+Business Media B.V.


Many supernovae have been discovered in the last decade with peak luminosity one-to-two orders of magnitude higher than for normal supernovae of known types. These stellar explosions are called Superluminous Supernovae (SLSNe). Some of them have hydrogen in their spectra, while some others demonstrate a lack of hydrogen. The latter are called Type I, or hydrogen-poor, SLSNe-I. SLSNe-I challenge the theory of stellar evolution, since even normal supernovae are not yet completely understood from first principles. Led by Sternberg Astronomical Institute researcher Elena Sorokina, who was a guest investigator at Kavli IPMU, and Kavli IPMU Principal Investigator Ken'ichi Nomoto, Scientific Associate Sergei Blinnikov, as well as Project Researcher Alexey Tolstov, the team developed a model that can explain a wide range of observed light curves of SLSNe-I in a scenario which requires much less energy than other proposed models. The models demonstrating the events with the minimum energy budget involve multiple ejections of mass in presupernova stars. Mass loss and buildup of envelopes around massive stars are generic features of stellar evolution. Normally, those envelopes are rather diluted, and they do not change significantly the light produced in the majority of supernovae. In some cases, large amount of mass are expelled just a few years before the final explosion. Then, the "clouds" around supernovae may be quite dense. The shockwaves produced in collisions of supernova ejecta and those dense shells may provide the required power of light to make the supernova much brighter than a "naked" supernova without pre-ejected surrounding material. This class of the models is referred to as "interacting" supernovae. The authors show that the interacting scenario is able to explain both fast and slowly fading SLSNe-I, so the large range of these intriguingly bright objects can in reality be almost ordinary supernovae placed into extraordinary surroundings. Another extraordinarity is the chemical composition expected for the circumstellar "clouds." Normally, stellar wind consists of mostly hydrogen, because all thermonuclear reactions happen in the center of a star, while outer layers are hydrogenous. In the case of SLSNe-I, the situation must be different. The progenitor star must lose its hydrogen and a large part of helium well before the explosion, so that a few months to a few years before the explosion, it ejects mostly carbon and oxygen, and then explode inside that dense CO cloud. Only this composition can explain the spectral and photometric features of observed hydrogen-poor SLSNe in the interacting scenario. It is a challenge for the stellar evolution theory to explain the origin of such hydrogen- and helium-poor progenitors and the very intensive mass loss of CO material just before the final explosion of the star. These results have been published in a paper accepted by The Astrophysical Journal. Explore further: Magnetar could have boosted explosion of extremely bright supernova More information: Elena Sorokina et al. TYPE I SUPERLUMINOUS SUPERNOVAE AS EXPLOSIONS INSIDE NON-HYDROGEN CIRCUMSTELLAR ENVELOPES, The Astrophysical Journal (2016). DOI: 10.3847/0004-637X/829/1/17

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