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2022
February/March


ICRANet Newsletter
February/March 2022



SUMMARY
1. ICRA - ICRANet - CONICET - UNLP press release "One star could finally reveal the nature of what does lie at the Milky Way center"
2. GCN published by ICRANet, February 25, 2022
3. Important Announcements: 80° anniversary of Prof. Remo Ruffini (Nice, May 16 - 18, 2022) and 6° Bego Rencontre Summer School (Nice, July 4 - 14, 2022)
4. Visit of H.E. Tsovinar Hambardzumyan, Ambassador of Armenia in Italy, to the ICRANet center in Pescara, March 16, 2022
5. New cooperation protocol between ICRANet and the University of Western Cape (UWC), March 1, 2022
6. New cooperation protocol between ICRANet and Sogang University, March 28, 2022
7. Renewal of the cooperation protocol between ICRANet and the Institute of High Energy Physics within the Chinese Academy of Sciences (IHEP CAS), March 7, 2022
8. Podcast of Prof. Remo Ruffini "March 20, 1916: Einstein publish the General Theory of Relativity", Radio Storia La Repubblica, March 20, 2022
9. Recent publications




1. ICRA - ICRANet - CONICET - UNLP press release "One star could finally reveal the nature of what does lie at the Milky Way center"

A new study deepens on the nature of the compact object sitting at our Galaxy center, SgrA*, by analyzing the astrometric data of one of the closest and long-studied stars that orbit around it. The international team of researchers from ICRA-ICRANet and CONICET-UNLP has found that besides the traditional black hole (BH) hypothesis, a dense concentration of dark matter (DM) made of fermions (called darkinos) can explain the detailed data (positions and velocities) of the star S2. The work provides a way to distinguish observationally between these two scenarios using the precession of the S2 orbit, very much in the same way that the theory of general relativity was proven using the precession of Mercury's orbit around the Sun. This new article, published in the Monthly Notices of the Royal Astronomical Society Letters1, holds relevant implications about the nature and mass of the dark matter particles.
For about three decades, two independent observational campaigns have monitored a cluster of young and bright stars orbiting the central parsec of our Galaxy to constrain the mass and nature of the massive object harbored at the center. These precise and accurate measurements have been possible thanks to the most powerful telescopes on earth. This achievement led to the Nobel Prize in Physics in 2020 awarded to Reinhard Genzel and Andrea Ghez: for the discovery of a supermassive compact object at the center of our galaxy.
Traditionally, a classical BH has been the most accepted hypothesis for the nature of SgrA*. The reason for this is that the orbits of the few detected S-stars are nearly perfect ellipses, implying the existence of a very compact object placed at its focus. Einstein's theory of general relativity predicts that the orbits cannot be Keplerian because there is a precession of the periapsis. The new work demonstrates that this effect is also present in the case of the DM core model and that its entity agrees with all publicly available data that shows the existence of this relativistic pattern in the S2 orbit. The article predicts that the two scenarios on the nature of SgrA* could be discriminated by measuring the precession of S2 around the next apocenter passage that will occur in 2026. The reason behind this difference is that while the BH predicts a unique prograde precession, in the DM scenario, it can be either retrograde or prograde, depending on the amount of DM filling the orbit, which depends on the mass of the darkinos.
A remarkable aspect of this novel DM interpretation of SgrA* is that the DM distribution is not constrained to the core of the Galaxy. The DM configuration extends to the outskirts of the Galaxy, forming a dilute halo that explains the circular velocity of far away objects as welll!. This result, together with a related study (see https://twitter.com/RAS_Journals/status/1489539729037008899?ref_src=twsrc%5Etfw) obtained by some of the research team, hints towards a paradigm shift in the field of DM halos and supermassive BH formation. It suggests that non-active galaxies as our own host dense DM concentrations at their centers, while more massive and active-galaxies, host supermassive BHs that has been formed from the gravitational collapse of these DM cores.


FIG. 1. Figure taken from [1] with the kind permission of the authors. Relativistic precession of S2 in the projected orbit on the plane of the sky as predicted in the BH and RAR DM models. While it is prograde for the BH and RAR (m = 58 keV/c2) (in dashed black and green respectively), it is retrograde for the RAR DM model (m = 56 keV/c2) (in dashed red). The solid (theoretical) curves and gray (data) points correspond to the first period (≈ 1994-2010) while the dashed (theoretical) curves and cyan (data) points to the second period (≈ 2010-2026). Right panels: zoom of the region around apocentre (top panel) and pericentre (bottom panel). The astrometric measurements are taken from Do et al.2.



FIG. 2. Relativistic precession of S2 as manifested in the right ascension as a function of time after last pericentre passage, where effects are more prominent. BH model (Left panel) and RAR model for m = 56 keV/c2 (Right panel).

Press release on ICRANet website: http://www.icranet.org/communication/
Press release on Oxford University press: https://oxfordjournals.altmetric.com/details/113891044
Press release on Conicet-Argentina: https://laplata.conicet.gov.ar/un-nuevo-paso-para-desentranar-que-hay-en-el-centro-de-la-via-lactea/
Upcoming S2-star astrometry could potentially establish if SgrA* is governed by a classical BH or by a quantum DM system: read more in a paper just published in MNRAS (Argüelles et al) at https://t.co/Wbx3kSMokD . #SagittariusA* #darkmatter #darkinos #fermions #blackholes pic.twitter.com/lWMz7d5l8D
— RAS Journals (@RAS_Journals) February 4, 2022


------------
1 C. R. Argüelles, M. F. Mestre, E. A. Becerra-Vergara, V. Crespi, A. Krut, J. A. Rueda, and R. Ruffini, Monthly Notices of the Royal Astronomical Society: Letters 511, L35 (2021), arXiv:2109.10729, URL https://doi.org/10.1093/mnrasl/slab126.
2 T. Do, A. Hees, A. Ghez, G. D. Martinez, D. S. Chu, S. Jia, S. Sakai, J. R. Lu, A. K. Gautam, K. K. O'Neil, et al., Science 365, 664 (2019), 1907.10731.



2. GCN published by ICRANet, February 25, 2022

TITLE: GCN CIRCULAR
NUMBER: 31648
SUBJECT: GRB 220101A: The first example of a Petanova
DATE: 22/02/25 11:38:50 GMT
FROM: Remo Ruffini at ICRA ruffini@icra.it

R. Ruffini, Y. Aimuratov, L. Becerra, C.L. Bianco, Y-C. Chen, C. Cherubini, Y.F. Cai, S. Eslamzadeh, S. Filippi, M. Karlica, Liang Li, G.J. Mathews, R. Moradi, M. Muccino, G.B, Pisani, F. Rastegar Nia, J.A. Rueda, N. Sahakyan, Y. Wang, S.S. Xue, Y.F. Yuan, Y.L. Zheng, on behalf of ICRA, ICRANet and USTC team, report:
We confirm the results of our previous GCN (Ruffini et al. 2022, GCN 31465). Following the release of the X-ray afterglow (Tohuvavohu et al. 2022, GCN 31347) and the GeV data (Arimoto et al. 2022, GCN 31350) of this source, we can estimate the total (keV+MeV+GeV) isotropic energy (see e.g. Ruffini et al. 2021, MNRAS 504, 5301) to be ~6E54 erg, making this GRB the most powerful GRB in 26 years (a "Petanova"). The period of the new neutron star (see e.g. Ruffini et al. 2021, MNRAS 504, 5301) generating the X-ray afterglow is ~1 ms, the initial mass of the BH (see e.g. Ruffini et al. 2019 ApJ 886, 82) is 6.15 solar mass, the spin parameter is 0.95, and the irreducible mass is 4.98 solar masses (see Fig. 1). The peak of the bolometric flux of supernova is of the order of 1E-17 erg/s/cm^2 and will appear in 73+/-15 days after the GRB trigger, with emissions lasting ~ one month peaking in different infrared bands. The observational follow up of this source is encouraged.
Fig. 1: http://www.icranet.org/docs/GRB220101A.pdf



3. Important Announcements: 80° anniversary of Prof. Remo Ruffini (Nice, May 16 -18, 2022) and 6° Bego Rencontre Summer School (Nice, July 4 - 14, 2022)

The 80th anniversary of Prof. Remo Ruffini
We are happy to invite you to participate to the celebrations of the 80th anniversary of Prof. Remo Ruffini, occurring on May 17, 2022, which will be held from May 16 to 18 at ICRANet Seat Villa Ratti in Nice (France). An hybrid event, both face-to-face and online, will be adopted.
Congratulations, greetings and scientific presentations will be welcomed.
The link to the Indico platform will be announced soon on ICRANet website (http://www.icranet.org/).

The 6th Bego Rencontre Summer School
We are happy to inform you that from July 4 to 14, 2022 ICRANet is organizing the "6th Bego Rencontre" at ICRANet Seat Villa Ratti in Nice.
Topics of this summer school will cover the distribution of dark matter in the Universe, the physics of our galactic center, the extraction of rotational energy from Kerr black holes in Gamma-Ray Bursts (GRBs) and Active Galactic Nuclei (AGNs), the associated fields of quantum and classical electrodynamics, neutron stars, white dwarfs, precision measurements of General Relativity and gravitational waves.
Your contributions in these topics are welcomed. The list of lecturers as well as more details on the electronic link to the Indico platform will be announced soon on ICRANet website (http://www.icranet.org/).



4. Visit of H.E. Tsovinar Hambardzumyan, Ambassador of Armenia in Italy, to the ICRANet center in Pescara, March 16, 2022

On March 16, 2022, the Ambassador Extraordinary and Plenipotentiary of the Republic of Armenia to Italy, H.E. Tsovinar Hambardzumyan and her assistant, Dr Naira Ghazaryan, visited the ICRANet center in Pescara.
Prof. Remo Ruffini, Director of ICRANet, showed and presented to her the center as well as its library and the precious books, pictures and documents collected there. Prof. Ruffini illustrated as well ICRANet current activities, the main research topics and the obtained results. Also, the current projects implemented with the ICRANet center in Pescara have been presented and discussed. The important role by ICRANet in daily fostering scientific exchanges worldwide and establishing agreements with the major Universities and research Institutes worldwide was also highlighted and discussed.

Fig. 3, 4 and 5: Prof. Ruffini, Director of ICRANet, presenting the ICRANet center to H.E. Tsovinar Hambardzumyan, Ambassador of the Republic of Armenia to Italy, March 16, 2022.

Prof. Narek Sahakyan, Director of the ICRANet Seat in Armenia joined the visit by GoToMeeting connection and stressed once again the importance of the ICRANet Armenia center to expand the activities of ICRANet in the regional countries. Both parties strongly highlighted the importance of the Armenian-Italian scientific cooperation in the field of astrophysics and discussed the possibilities of further develop and expand the Armenian-Italian scientific cooperation.

Fig. 6: Prof. Ruffini during his bilateral meeting with H.E. Tsovinar Hambardzumyan, Ambassador of the Republic of Armenia to Italy, March 16, 2022. Fig. 7: Prof. Narek Sahakyan, Director of the ICRANet Seat in Armenia, joining the meeting with Ambassador Hambardzumyan via GoToMeeting, March 16, 2022.

The news has been also published on the official Facebook webpage of the Armenian Embassy in Italy, available at the following link: https://www.facebook.com/HayastaniDespanutyun/



5. New cooperation protocol between ICRANet and the University of Western Cape (UWC), March 1, 2022

On March 1, 2022 ICRANet has signed a new Cooperation protocol with the University of Western Cape (UWC) in South Africa. The Cooperation Protocol has been signed by Prof. Tyrone Brian Pretorius (Rector of UWC), by Prof. Roy Marteens (Prof. in Astronomy & Astrohysics at UWC), by Prof. Remo Ruffini (Director of ICRANet) and by Prof. Narek Sahakyan (Director of ICRANet Seat in Armenia).


The agreement will be valid for 5 years and the main joint activities to be developed under their framework include: the promotion of theoretical and observational activities within the field of Relativistic Astrophysics; the institutional exchange of faculty members, researchers, post-doctorate fellows and students; the promotion of technological developments; the development of Data Centers for Astrophysical data in all wavebands; the organization of training and teaching courses, seminars, conferences, workshops or short courses, the development of inter-institutional research areas associated to local graduate programs and joint publications.
For the text of the agreement: http://www.icranet.org/index.php?option=com_content&task=view&id=1411



6. New cooperation protocol between ICRANet and Sogang University, March 28, 2022


On March 28, 2022 ICRANet has signed a new Cooperation protocol with the Sogang University in South Korea. The Cooperation Protocol has been signed by Prof. Luke Sim Jong-Hyeok SJ (President of Sogang University), by Prof. Stefano Scopel (Director of CQUeST, Sogang University), by Prof. Remo Ruffini (Director of ICRANet) and by Prof. Carlo Luciano Bianco (ICRANet Faculty Professor).
The agreement will be valid for 5 years and the main joint activities to be developed under their framework include: the promotion of theoretical and observational activities within the field of Relativistic Astrophysics; the institutional exchange of faculty members, researchers, post-doctorate fellows and students; the promotion of technological developments; the development of Data Centers for Astrophysical data in all wavebands; the organization of training and teaching courses, seminars, conferences, workshops or short courses, the development of inter-institutional research areas associated to local graduate programs and joint publications.
For the text of the agreement: http://www.icranet.org/index.php?option=com_content&task=view&id=1414



7. Renewal of the cooperation protocol between ICRANet and the Institute of High Energy Physics within the Chinese Academy of Sciences (IHEP CAS), March 7, 2022


On March 7, 2022, the Cooperation Protocol between ICRANet and the Institute of High Energy Physics within the Chinese Academy of Sciences (IHEP CAS) has been renewed. The renewal was signed by Prof. Shuang-Nan Zhang (Director of the Key Laboratory of Particle Astrophysics at IHEP CAS) and by Prof. Remo Ruffini (Director of ICRANet). This agreement will be valid for further 5 years and the main joint activities to be developed under its framework include: the promotion of theoretical and observational activities within the field of Relativistic Astrophysics; the institutional exchange of faculty members, researchers, post-doctorate fellows and students; the promotion of technological developments; the development of Data Centers for Astrophysical data in all wavebands; the organization of training and teaching courses, seminars, conferences, workshops or short courses, the development of inter-institutional research areas associated to local graduate programs and joint publications.
For the text of the agreement: http://www.icranet.org/ihep



8. Podcast of Prof. Remo Ruffini "March 20, 1916: Einstein publish the General Theory of Relativity", Radio Storia La Repubblica, March 20, 2022

On March 20, 2022 the web channel Radio Storia of La Repubblica, one of the most important daily newspaper in Italy, released a podcast registered by Prof. Remo Ruffini, Director of ICRANet.
The podcast, titled "March 20, 1916: Einstein publish the General Theory of Relativity" has been directed by the italian journalist Francesco De Leo and addressed important historical events, as if they are just happened. This podcast has been realized as if we were living on March 20, 1916, when Einstein just published his General Theory of Relativity in the Annals of Physics n° 7. In this article, Einstein illustrated the equation which indicates the gravitational force as the space-time curvature and this represented one of the most impressive combinations of philosophy, physical intuition and mathematical skill.
Prof. Ruffini has been invited to comment this article, in order to better understand its importance and influence on general relativity with Einstein theory of gravitation. Prof. Ruffini pointed out that this was a very important text, since in his work, Einstein resumes and generalize the theory of relativity and he starts to define it as special theory of relativity. He recalls us that one of the most important contribution in this field has been the work of Hermann Minkowski, who recognized the formal equivalence between the spatial and temporal co-ordinates and make them usable for the building of this theory. Einstein explained the mathematical formalism of Tullio Levi Civita and Matteo Ricci and finally obtained the equation of the field and of General Relativity. He showed that, if a ray of light passes close to the Sun, there could be the deflection of the ray of light due to the gravitational field of the Sun and this happen also for a signal of light passing close to a planet. This vision totally changes the traditional Newtonian physics, which claimed that a ray of light propagates itself in a straight line. Einstein also expected that the light originated from a star should change the frequency of its motion in departing from the star, indicating the shift towards longer wavelengths: this is also another concept totally different from the one envisaged by Newton. Moreover, at the times of Newton and Kepler, the classical astronomy conceived the motion as a motion in ellipse; Einstein in 1916 affirmed that there was a small quantity which modified this motion and predicted a motion "a rosetta" of 43 seconds of arc per century: this is a small quantity, but it's conceptually revolutionary.
In commenting the article of Einstein, Prof. Ruffini went on explaining that, as affirmed also by Einstein, it does not exist "the time" but there are 3 spatial components and 1 temporal one which work together, as also expressed by Minkowski. Therefore, since then, Physics has been no more intended as a theory with 1 or 3 components, but as a theory made up by the interaction of 4 dimensions. Einstein said that there is not "the time" but it exists the space - time, described by the metrics introduced by Tullio Levi Civita and Matteo Ricci: all the above represented a big conceptual revolution and gave origin to a new physics, new observations and new knowledge.
To hear the podcast (in Italian): https://www.repubblica.it/podcast/storie/radio-storia/stagione1/



9. Recent publications

Rueda, J. A.; Ruffini, R.; Kerr, R. P., Gravitomagnetic interaction of a Kerr black hole with a magnetic field as the source of the jetted GeV radiation of gamma-ray bursts, The Astrophysical Journal; in press.
We show that the gravitomagnetic interaction of a Kerr black hole (BH) with a surrounding magnetic field induces an electric field that accelerates charged particles to ultra-relativistic energies in the vicinity of the BH. Along the BH rotation axis, these electrons/protons can reach energies of even thousands of PeV, so stellar-mass BHs in long gamma-ray bursts (GRBs) and supermassive BHs in active galactic nuclei (AGN) can contribute to the ultrahigh-energy cosmic rays (UHECRs) thorough this mechanism. At off-axis latitudes, the particles accelerate to energies of hundreds of GeV and emit synchrotron radiation at GeV energies. This process occurs within 60° around the BH rotation axis, and due to the equatorial-symmetry, it forms a double-cone emission. We outline the theoretical framework describing these acceleration and radiation processes, how they extract the rotational energy of the Kerr BH and the consequences for the astrophysics of GRBs.
Link preprint: https://arxiv.org/abs/2203.03471


C. R. Argüelles, E. A. Becerra-Vergara, A. Krut, R. Yunis, J. A. Rueda and R. Ruffini, Reshaping our understanding on structure formation with the quantum nature of the dark matter, published on International Journal of Modern Physics D Vol. 31, No. 02, 2230002 (2022).
We study the nonlinear structure formation in cosmology accounting for the quantum nature of the dark matter (DM) particles in the initial conditions at decoupling, as well as in the relaxation and stability of the DM halos. Different from cosmological N-body simulations, we use a thermodynamic approach for collisionless systems of self-gravitating fermions in general relativity, in which the halos reach the steady state by maximizing a coarse-grained entropy. We show the ability of this approach to provide answers to crucial open problems in cosmology, among others: the mass and nature of the DM particle, the formation and nature of supermassive black holes in the early Universe, the nature of the intermediate mass black holes in small halos, and the core-cusp problem.
DOI: https://doi.org/10.1142/S0218271822300026


Gregory Vereshchagin, Liang Li, Damien Bégué, Is magnetically dominated outflow required to explain GRBs?, published on Monthly Notices of the Royal Astronomical Society, stac757, on March 22, 2022.
The composition of relativistic outflows producing gamma-ray bursts is a long standing open question. One of the main arguments in favour of magnetically dominated outflows is the absence of photospheric component in their broadband time resolved spectra, with such notable example as GRB 080916C. Here, we perform a time-resolved analysis of this burst and confirm the previous detection of an additional spectral component. We show that this subdominant component is consistent with the photosphere of ultrarelativistic baryonic outflow, deep in the coasting regime. We argue that, contrary to previous statements, the magnetic dominance of the outflow is not required for the interpretation of this GRB. Moreover, simultaneous detection of high energy emission in its prompt phase requires departure from a one-zone emission model.
DOI: https://doi.org/10.1093/mnras/stac757


MAGIC collaboration, Combined searches for dark matter in dwarf spheroidal galaxies observed with the MAGIC telescopes, including new data from Coma Berenices and Draco, published in Physics of the Dark Universe, Volume 35, March 2022, 100912.
Milky Way dwarf spheroidal galaxies (dSphs) are among the best candidates to search for signals of dark matter annihilation with Imaging Atmospheric Cherenkov Telescopes, given their high mass-to-light ratios and the fact that they are free of astrophysical gamma-ray emitting sources. Since 2011, MAGIC has performed a multi-year observation program in search for Weakly Interacting Massive Particles (WIMPs) in dSphs. Results on the observations of Segue 1 and Ursa Major II dSphs have already been published and include some of the most stringent upper limits (ULs) on the velocity-averaged cross-section σann v of WIMP annihilation from observations of dSphs. In this work, we report on the analyses of 52.1 h of data of Draco dSph and 49.5 h of Coma Berenices dSph observed with the MAGIC telescopes in 2018 and in 2019 respectively. No hint of a signal has been detected from either of these targets and new constraints on the σann v of WIMP candidates have been derived. In order to improve the sensitivity of the search and reduce the effect of the systematic uncertainties due to the -factor estimates, we have combined the data of all dSphs observed with the MAGIC telescopes. Using 354.3 h of dSphs good quality data, 95% CL ULs on σann v have been obtained for 9 annihilation channels. For most of the channels, these results reach values of the order of 10-24 cm3/s at ∼ 1 TeV and are the most stringent limits obtained with the MAGIC telescopes so far.
DOI: https://doi.org/10.1016/j.dark.2021.100912


MAGIC collaboration, Investigating the Blazar TXS 0506+056 through Sharp Multiwavelength Eyes During 2017-2019, published on The Astrophysical Journal, Volume 927, Issue 2, id.197.
The blazar TXS 0506+056 got into the spotlight of the astrophysical community in 2017 September, when a high-energy neutrino detected by IceCube (IceCube-170922A) was associated at the 3σ level with a γ-ray flare from this source. This multi-messenger photon-neutrino association remains, as per today, the most significant association ever observed. TXS 0506+056 was a poorly studied object before the IceCube-170922A event. To better characterize its broadband emission, we organized a multiwavelength campaign lasting 16 months (2017 November to 2019 February), covering the radio band (Metsähovi, OVRO), the optical/UV (ASAS-SN, KVA, REM, Swift/UVOT), the X-rays (Swift/XRT, NuSTAR), the high-energy γ rays (Fermi/LAT), and the very high-energy (VHE) γ rays (MAGIC). In γ rays, the behavior of the source was significantly different from the behavior in 2017: MAGIC observations show the presence of flaring activity during 2018 December, while the source only shows an excess at the 4σ level during the rest of the campaign (74 hr of accumulated exposure); Fermi/LAT observations show several short (on a timescale of days to a week) flares, different from the long-term brightening of 2017. No significant flares are detected at lower energies. The radio light curve shows an increasing flux trend that is not seen in other wavelengths. We model the multiwavelength spectral energy distributions in a lepto-hadronic scenario, in which the hadronic emission emerges as Bethe-Heitler and pion-decay cascade in the X-rays and VHE γ rays. According to the model presented here, the 2018 December γ-ray flare was connected to a neutrino emission that was too brief and not bright enough to be detected by current neutrino instruments.
DOI: https://doi.org/10.3847/1538-4357/ac531d


MAGIC collaboration, Multiwavelength study of the gravitationally lensed blazar QSO B0218+357 between 2016 and 2020, published on Monthly Notices of the Royal Astronomical Society, Volume 510, Issue 2.
We report multiwavelength observations of the gravitationally lensed blazar QSO B0218+357 in 2016-2020. Optical, X-ray, and GeV flares were detected. The contemporaneous MAGIC observations do not show significant very high energy (VHE; ≳100 GeV) gamma-ray emission. The lack of enhancement in radio emission measured by The Owens Valley Radio Observatory indicates the multizone nature of the emission from this object. We constrain the VHE duty cycle of the source to be <16 2014-like flares per year (95 per cent confidence). For the first time for this source, a broad-band low-state spectral energy distribution is constructed with a deep exposure up to the VHE range. A flux upper limit on the low-state VHE gamma-ray emission of an order of magnitude below that of the 2014 flare is determined. The X-ray data are used to fit the column density of (8.10 ± 0.93stat) × 1021 cm-2 of the dust in the lensing galaxy. VLBI observations show a clear radio core and jet components in both lensed images, yet no significant movement of the components is seen. The radio measurements are used to model the source-lens-observer geometry and determine the magnifications and time delays for both components. The quiescent emission is modelled with the high-energy bump explained as a combination of synchrotron-self-Compton and external Compton emission from a region located outside of the broad-line region. The bulk of the low-energy emission is explained as originating from a tens-of-parsecs scale jet.
DOI: https://doi.org/10.1093/mnras/stab3454


Behzad Eslam Panah, and Khadijie Jafarzade, Thermal stability, P−V criticality and heat engine of charged rotating accelerating black holes, General Relativity and Gravitation. 54 (2022) 19
In this paper, we study thermodynamic features of the charged rotating accelerating black holes in anti-de Sitter spacetime. First, we consider these black holes as the thermodynamic systems and analyze thermal stability/instability through the use of heat capacity in the canonical ensemble. We also investigate the effects of angular momentum, electric charge and string tension on the thermodynamic quantities and stability of the system. Considering the known relation between pressure and the cosmological constant, we extract the critical quantities and discuss how the mentioned parameters affect them. Then, we construct a heat engine by taking into account this black hole as the working substance, and obtain the heat engine efficiency by considering a rectangle heat cycle in the P−V plane. We examine the effects of black hole parameters on the efficiency and analyze their effective roles. Finally, by comparing the engine efficiency with Carnot efficiency, we investigate conditions in order to have a consistent thermodynamic second law.
DOI: https://doi.org/10.1007/s10714-022-02904-9


Tayyebeh Yazdizadeh, Gholam Hossein Bordbar, and Behzad Eslam Panah, The structure of hybrid neutron star in Einstein-Λ gravity, Physics of the Dark Universe 35 (2022) 100982.
In this paper, we investigate the structure of neutron stars by considering both the effects of the cosmological constant and the existence of quark matter for neutron stars in Einstein's gravity. For this purpose, we use a suitable equation of state (EoS) which includes a layer of hadronic matter, a mixed phase of quarks and hadrons, and a quark matter in the core. To investigate the effect of the cosmological constant on the structure of hybrid neutron stars, we utilize the modified TOV equation in Einstein -Λ gravity. Then we derive the mass-radius relation for different values of the cosmological constant. Our results show that for small values of the cosmological constant (Λ), especially for the cosmological constant from the cosmological perspective (Λ=10−52m−2),Λ has no significant effect on the structure of hybrid neutron stars. But for higher values, for example, by considering Λ>10−14 m−2, this quantity affects the maximum mass and radius of these stars. We find an upper limit for the cosmological constant as Λ<9×10−13m−2, based on the fact that the gravitational redshift cannot be more than 1 for stars. The maximum mass and radius of these stars decrease by increasing the cosmological constant Λ. Also, by determining and analyzing radius, the compactness, Kretschmann scalar, and gravitational red shift of the hybrid neutron stars with M=1.4M⊙ in the presence of the cosmological constant, we find that by increasing Λ, they are contracted. Also, our results for dynamical stability show that these stars satisfy this condition.
DOI: https://doi.org/10.1016/j.dark.2022.100982
 
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