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ICRANet Newsletter
April/May 2023



 


1. Scientific highlights: ICRA – ICRANet Press release - Supermassive black holes formation from fermionic dark matter core collapse

Fundamental questions about the origin and growth of supermassive black holes in the earliest stages of the Universe's life, up to about 800 million years after the Big Bang, challenge the scientific community. An international team of ICRANet, in collaboration with researchers from the University of La Plata (Argentina), Universidad Santiago de Cali (Colombia), and Al-Farabi Kazakh University (Kazakhstan), has made a crucial contribution by proposing a new mechanism that explains how these supermassive giants arise and grow so much, so quickly. The novelty was published on May 31, 2023, by the prestigious journal Monthly Notices of the Royal Astronomical Society: https://doi.org/10.1093/mnras/stad1380.

The observations from the central regions of active galaxies, those that are larger and more massive than the Milky Way and have very intense radiation, suggest supermassive black holes are responsible for generating the emission of energy through jets of matter shooting out from the center of these galaxies. However, contrary to the case of black holes of stellar origin that are formed from the death of a star with a mass similar to that of the Sun, there is still a strong debate about what are the origin and main channel of formation of the progenitors (or seeds) of these supermassive giants formed in the early universe.

In the article, the team proposes a new formation mechanism to form supermassive black holes in the early universe, completely different from existing models associated with the gravitational collapse of primordial gas or hypothetical massive stars. The new model shows supermassive black holes originate from the gravitational collapse of dense nuclei of dark matter that arise in the center of the galactic halos at the time of their formation, according to the model of fermionic dark matter halos proposed by the same experts in previous researches.

The relevance of this new result is both observational and theoretical. With respect to observations, it is shown that these seeds or progenitors of black holes formed from dark matter would be born with masses of millions to hundreds of millions of times the mass of the Sun and then, once formed, grow by accretion (or incorporation) of conventional matter up to the values inferred by the observations made by large telescopes. In Fig. 1 it is shown the evolution of black hole mass for different seeds (right pannel) in the novel formation channel, and for a range of fermionic dark matter particles or darkino masses. As clearly shown in the figure, the black hole seeds formed from the gravitational collapse of the dense dark matter cores, can grow up to 109-1010 M in a fraction of the first Gyr of life of the Universe. In the left panel of Fig. 1 we show the evolution of normalized black hole spin for different efficiencies β.

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Fig. 1: Black hole mass evolution in time for different black hole seeds with maximum efficiency β=1 (right panel), and normalized black hole spin α evolution for different efficiencies (left panel). Initial conditions are αi=0 and darkino masses 56keV, 100keV, 200keV, and 350keV. The spin parameter does not depend on the black hole mass. The initial redshift is z0=5.5 with t0=1022 Myr for a halo mass Mvir=5x1011M.

From the theoretical viewpoint, a new solution to Einstein's General Relativity equations was found for the first time, leading to a distribution of dark matter whose nucleus is on the verge of gravitational collapse towards a massive black hole. This solution implies that the same dark matter that forms the dense nucleus is surrounded by a more diluted halo that explains the galactic rotation curves, all in a realistic and unified picture.

For more details:
On the growth of supermassive black holes formed from the gravitational collapse of fermionic dark matter cores, C. R. Argüelles, K. Boshkayev, A. Krut, G. Nurbakhyt, J. A. Rueda, R. Ruffini, R., J. D. Uribe-Suarez, R. Yunis, Monthly Notices of the Royal Astronomical Society, Volume 523, Issue 2, August 2023, Pages 2209–2218.
 
Link to the journal’s site: https://doi.org/10.1093/mnras/stad1380

Link to the ArXiv: https://arxiv.org/abs/2305.02430

Link to ICRA-ICRANet press release: http://icranet.org/communication/31052023/eng.pdf

Link to the press release on CONICET-Argentina website: https://laplata.conicet.gov.ar/proponen-una-posible-explicacion-a-como-se-formaron-los-agujeros-negros-supermasivos-en-el-universo-temprano/

Other press releases and contact information: Tweets by Royal Astronomical Society (RAS) Journals in https://twitter.com/RAS_Journals/status/1664678764356435969

Contact: Prof. Carlos R. Argüelles (UNLP, CONICET and ICRANet)
E-mail: carguelles@fcaglp.unlp.edu.ar
Prof. Remo Ruffini (Director, ICRANet)
Phone: (+39) 085 2305 4201, mobile: (+39) 339 475 2566
E-mail: ruffini@icra.it
 


2. Visit of Prof. Ruffini to the USA, May 18-23, 2023

From May 18 to 23, 2023 Prof. Remo Ruffini, Director of ICRANet, visited the USA. In particular, until Saturday May 20, he visited Princeton University as well as the Institute for Advanced Study (IAS) in Princeton, since he was invited to take part in the“IAS Founders Day 2023”.

Since its foundation, the IAS has always been an incubator and accelerator for groundbreaking ideas and scholarship. Every year, the Institute organizes an annual event in honor of Louis Bamberger and Caroline Bamberger Fuld, the sibling philanthropists who founded and endowed IAS on May 20, 1930, providing for its lasting and essential independence. The annual event, organized this year on May 19, wanted to celebrate their vision as well as that of Faculty, Board, Members, and Staff, who together ensure that the work of the Institute is as vital today as it ever has been. During this festivity, attendees were invited to explore displays focused on Institute history, followed by the IAS Libraries and Archives. The archivists also provided scholars with the opportunity to view and sign their name in the IAS Registry, an autographed record of Faculty and Members that has been kept since the Institute's inception. Original signatories include Einstein and many other famous names, such as John von Neumann, Kurt Gödel, and Anna Stafford. Also the name of Prof. Ruffini was present in this IAS Registry.
   
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Fig. 2: Prof. Ruffini looking at his signature in the IAS Registry, while attending the IAS Founders Day 2023 in Princeton on May 19, 2023.
 
For more information about the program of the meeting: https://www.ias.edu/founders-day-2023 .

For a recorded summary of the event (Prof. Ruffini is visible at Minute 1:00): https://www.youtube.com/watch?v=focxomx7t3w&t=1s .

Soon after this meeting in Princeton, Prof. Ruffini flew to San Francisco in order to visit Stanford University and, in particular, the Hansen Experimental Physics Laboratory (HEPL). During this visit, he met Prof. Kent Irwin (Director of HEPL), Prof. Giorgio Gratta, Risa Wechsler (Director of theKavli Institute for Particle Astrophysics and Cosmology - KIPAC) and Prof. Francis Everitt (Emeritus Professor at Stanford University, representative of Stanford University in ICRA Assembly as well as Chairman of the ICRANet Steering Committee). On this occasion, Prof. Yu Wang, ICRA President and ICRANet Faculty Professor, joined all the others via GoToMeeting on Monday May 22, in order to make a presentation on the recent scientific results and the ongoing researches of ICRA and ICRANet. This meeting served also as a good opportunity to reinforce the ongoing joint research on the mission Gravity Probe B as well as the recent astrophysical developments and the collaborations with Prof. Peter Michelson, responsible of the FERMI program.

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Fig. 3: From the left to the right: Prof. Kent Irwin (Director of the Hansen Experimental Physics Laboratory HEPL), Prof. Peter Michaelson, Prof. Francis Everitt and Prof. Remo Ruffini at Stanford University. Fig. 4: From the left to the right: Prof. Risa Wechsler (Director, Kavli Institute for Particle Astrophysics and Cosmology KIPAC at Stanford University, Prof. Francis Everitt and Prof. Remo Ruffini in front of the Gravity Probe B in the Hansen Experimental Physics Laboratory (HEPL).
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Fig. 5: Prof. Remo Ruffini with Prof. Francis Everitt in his apartment.
 


3. ICRANet GCN 33723, May 4, 2023

TITLE:   GCN CIRCULAR
NUMBER:  33723
SUBJECT: GRB 230430A: A short GRB from a neutron star merger
DATE:    23/05/04 08:30:05 GMT
FROM:    Remo Ruffini at ICRA <ruffini@icra.it>

R. Ruffini, Y. Aimuratov, L. Becerra, C.L. Bianco, C. Cherubini, S. Filippi, M. Karlica, Liang Li, R. Moradi, F. Rastegar Nia, J.A. Rueda, N. Sahakyan, Y. Wang, S.S. Xue, on behalf of the ICRANet team, report:

GRB 230430A appears to have strong similarities with GRB 090510 originating from merging binary neutron stars (Ruffini et al., 2016). Also in this case no supernova is expected. Attention should be given to the determination of the temporal slope of the late X-ray luminosity which for long GRBs coincide with the common value of the power-law index -1.48+/-0.32 of the afterglow, and for short GRBs appears to have a different power law, to be confirmed (see Fig. 7 in Ruffini et al., 2016). The GeV luminosity for long GRBs has a temporal power-law index -1.19+/-0.04 and for short GRBs it has a temporal power-law index -1.29+/-0.06 (Ruffini et al., 2021). Confirmation of the values of both slopes in GRB 230430A is highly recommended to differentiate short GRBs from long GRBs. We encourage monitoring for the possible appearance of a kilonova signal.

References:
Ruffini, R.; Muccino, M.;  Aimuratov, Y.; et al.; ApJ, 831 (2016) 178.
Ruffini, R.; Moradi, R.; Rueda, J.A; et al.; MNRAS, 504 (2021) 5301.



4. ICRANet participation at the International Conference Abdildin Readings. Actual problems of modern physics, April 12 – 15, 2023 Almaty (Kazakhstan)

From April 12 to 15, 2023, Prof. Remo Ruffini (Director of ICRANet) and Shurui Zhang (ICRANet visiting scientist from USTC – China) have been invited to present a lecture on the occasion of the International Conference Abdildin Readings. Actual problems of modern physics, held both at Al Farabi Kazakh National University in Almaty (Kazakhstan) and online.
 
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The first meeting of this series has been organized in 2013 on the occasion of the 75th anniversary of the Academician Meirkhan Abdildin, and this year, of course, the conference has been organized on the occasion of his 85th anniversary. The main topics of the conference coveredthe main fields of modern physics, including theoretical physics, nuclear and particle physics, astrophysics and cosmology, cosmic rays physics, plasma physics, condensed matter physics, thermal physics, biophysics, medical physics, methodical and philosophic problems of physics. The main goal of the conference was to promote cooperation among Central Asia and key partner countries of the region, as well as to coordinate high-level studies on hot topics in physics at international level and to encourage fruitful collaboration among active researchers and gifted representatives of younger generation.

On Wednesday April 12, Prof. Ruffini presented a lecture titled “New Physics and Astrophysicsfrom GRBs”; here below the abstract:

The observations of Ic supernovae (Ic/SNe) occurring after the prompt emission of long gamma ray bursts (GRBs) are addressed within the binary-driven hypernova (BdHN) model. Here, the GRBs originate from a binary composed of a ∼ 10 M carbon-oxygen (CO) star and a companion neutron star (NS). We assume these same progenitors originate the Ic/SN. The binary evolution depends strongly on the binary period, Pbin. The trigger, given by the CO core collapse, for Pbin of up to a few hours leads to an Ic/SN with a fast-spinning NS (νNS) at its center. For Pbin∼ 4–5 min, BdHN I occur with energies 1052 – 1054 erg, a contribution by the black hole (BH) created by the NS companion collapse, originates the Mev/GeV radiations. The ∼ 1 millisecond νNS originates, by synchrotron radiation, the X-ray afterglow. For Pbin∼ 10 min, BdHN II occurs with energies of 1050–1052erg. For Pbin∼ hours, BdHN III occurs with energies below 1050 erg. The 1–1000 ms νNS, in all BdHNe, originates the X-ray afterglow by synchrotron emission. The SN Ic follows an independent evolution, becoming observable by the nickel decay after the GRB prompt emission. We report 24 Ic/SNe associated with BdHNe, their optical peak luminosity and their time of occurrence are similar and independent of the associated GRBs. We give four examples of BdHNe and their associated hypernovae. We approach, for the first time, new physical processes in BdHNe; we identify seven episodes and their signatures in their spectra.

On the same day, Shurui Zhang presented a talk titled “The transformation of the rotational energy of a Kerr BH”.

For the website of the meeting: http://kazps.kz/index.php?page=conferences/AR



5. ICRANet participation at the Second international conference of the National Institute of Physics (NIP), April 28-29, 2023, Tirana (Albania)
  
From April 28 to 29, 2023, Prof. Remo Ruffini (Director of ICRANet) and Shurui Zhang (ICRANet visiting scientist from USTC – China) have been invited to present a lecture on the occasion of the second International Conference of the National Institute of Physics (NIP), which has been held at the Academy of Sciences of Albania in Tirana.

The NIP aims to promote modern knowledge and excellence in physics within Albania and internationally. The key goals of the conference included the dissemination of research accomplishments in the context of the latest developments in physics (including teaching), the consolidation of a cooperation network between Albanian and foreign physicists, as well as the expansion of NIP through new memberships.


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Fig. 6: Prof. Ruffini presenting his talk on the occasion of the Second international conference of the National Institute of Physics (NIP), April 28, 2023. Fig. 7: Shurui Zhang presenting his talk on the occasion of the Second international conference of the National Institute of Physics (NIP), April 28, 2023.

On Friday April 28, Prof. Ruffini presented a lecture titled “New Physics and Astrophysics from GRBs”; here below the abstract:

The observations of Ic supernovae (Ic/SNe) occurring after the prompt emission of long gamma ray bursts (GRBs) are addressed within the binary-driven hypernova (BdHN) model. Here, the GRBs originate from a binary composed of a ∼ 10 M carbon-oxygen (CO) star and a companion neutron star (NS). We assume these same progenitors originate the Ic/SN. The binary evolution depends strongly on the binary period, Pbin. The trigger, given by the CO core collapse, for Pbin of up to a few hours leads to an Ic/SN with a fast-spinning NS (νNS) at its center. For Pbin∼ 4–5 min, BdHN I occur with energies 1052 – 1054 erg, a contribution by the black hole (BH) created by the NS companion collapse, originates the Mev/GeV radiations. The ∼ 1 millisecond νNS originates, by synchrotron radiation, the X-ray afterglow. For Pbin∼ 10 min, BdHN II occurs with energies of 1050–1052erg. For Pbin∼ hours, BdHN III occurs with energies below 1050 erg. The 1–1000 ms νNS, in all BdHNe, originates the X-ray afterglow by synchrotron emission. The SN Ic follows an independent evolution, becoming observable by the nickel decay after the GRB prompt emission. We report 24 Ic/SNe associated with BdHNe, their optical peak luminosity and their time of occurrence are similar and independent of the associated GRBs. We give four examples of BdHNe and their associated hypernovae. We approach, for the first time, new physical processes in BdHNe; we identify seven episodes and their signatures in their spectra.

On the same day, Shurui Zhang presented a talk titled “The transformation of the rotational energy of a Kerr BH”.


For the website of the meeting: https://ikf-akad.al/english/



6. Measuring the Sun with the Moon: the annular total solar eclipse from 1567 until today. Gerbertian days from  April 20 to May 17, 2023, online meetings

The annual congress in honor of Gerbert of Aurillac, scientist, scholastic astronomer and Pope, took place from April 20 to May 17, 2023 and has been coordinated, as the previous ones, by Prof. Costantino Sigismondi, ICRANet collaborator, at international level. This year, it has been organized as a series of 4 online lessons, held respectively on April 20, on May 4, on May 11 and on May 17, 2023; this is why it has been renamed “Gerbertian days”.

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Fig. 8: Busto-Mira of Angelo Secchi on the Pincio; solar eclipse on April 20, 2023 in Com (Timor Leste, courtesy of InstitutTeknologi Sumatra; sunspot at the flap AR 3262, photo of April 23, 2023 refractor 80 mm f/7.5 in Rome @540±10 nm. Pope Silvester II (Turin, Lit. Giordana, GranDidier and Salussolia, 1854).

The Moon and the Sun: one has a diameter of 1 million and a half km, the other one of 3480 km, one is at 150 millions of km far from the Earth, the other one at 384.000 km far. On Thursday, April 20 at 3 AM in Timor Est, in the South Indian Ocean as well as at the North West of Australia, there has been a rare solar and hybrid eclipse, namely annular towards the extremes and total in the middle of the range. We use the Moon, which never changed its diameter since when is has solidified, in order to measure the Sun, well knowing the distances between us, the Moon and the Sun as well as the profile of the Moon with accuracy.

In order to obtain data, this time Prof. Sigismondi proposed, instead of the telescopes, the mobile phone in Telegramma of the astronomers to all the international scientific committee. ATel #15991: https://www.astronomerstelegram.org/?read=15991 . In this ATel, Prof. Sigismondi summarized the many lessons held together with the students in order to discover the ghost image of the Sun.

Already in 2012, we had in ICRANet Pescara the international congress in honor of the 400 years from the Clavio’s death. On April 20, 2023 the meeting has been devoted to the eclipse with an online event in the footsteps of Cristoforo Clavio, which observed and described it first, in Rome in 1567. On May 4, 2023 the meeting has been devoted to the preparation of the Moon eclipse of penumbra observation  of May 5, twinned with the solar one of April 20,. On May 11, the meeting has been devoted to the inauguration of Volume 20 of Gerbertus with “The Sun” of Angelo Secchi (Italian edition of 1884, now digitalized) as well as with a biography of GerbertusD’Aurillac – Pope Sylvester II, in the 1020th anniversary of his death.

Video of the total annular solar eclipse from West Australia: https://www.youtube.com/watch?t=8455&v=ifILl7GeZpE

The Archimedes experiment to measure the Sun diameter.
In Syracuse, Archimedes thought to observe the rise and the set on the sea, putting a cylinders on a ruler. From one side of the ruler he put the eye, and he put the cylinders at the distance he wanted to measure, in order to darken a bit the sun.  Prof. Sigismondirepente the experiment with the view camera in the laboratory, in view of the annular eclipse of April 20, in order to better feel the spirit of these event as well as of the science.

The name of Archimedes’s text is Arenario and it’s one of the firsts classical texts to study the solar diameter.

For all the videos concerning the experiment: https://www.youtube.com/playlist?list=PLJaer2KV4929jBTdkwxA1P6rGOYfgpues.
For the original text of Archimedes: http://www.icranet.org/scuola_lavoro/2023-2024/20042023/Archimede_Libro_Alfa_Diametro_del_Sole.pdf.

Inauguration of Gerbertus 20.
This journal, devoted to the history and the didactic of science, has reached volume 20 (see it from 2010 on www.icra.it/gerbertus). All the subjects covered until now are available here: https://ui.adsabs.harvard.edu/search/p_=0&q=bibstem%3AGerb&sort=date%20desc%2C%20bibcode%20desc.

For the 1020th Gerbertian anniversary on May 12, 2023 (he died on May 12, 1003), Prof. Sigismondi prepared the monographic n° 20, digital edition of The Sun of Angelo Secchi. It is not as well known as its French edition published in 1877.

The Sun was published in 1884 posthumous, in Italian, and is still now a valid text to understand what can be sees observing the Sun with an instruments such the Merz telescope of 25 cm diameter and 2.5 meters of focal length. This telescope burnt down in July 1958 when it was on the central dome of Monte Mario.

Questo telescopio bruciò nel luglio del 1958 quando si trovava nella cupola centrale di Monte Mario. Giuseppe Armellini, che era il direttore, morì di crepacuore qualche giorno dopo...

The special guests of these Gerbertian days have been Prof. Remo Ruffini, Director of ICRANet, Prof.  Paolo Ochner, Astrophysical Observatory of Asiago and University of Padua, Prof. VirginioOldani,  SAS – Astronomical Station of Sozzago and Prof. Francesco Berrilli, University of Rome Tor Vergata and Accademia dei Lincei.

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Fig. 9: Archimedes, hybrid eclipse of 1996, J.A. Eddy and Clavio: characters of the history of astronomy linked to this type of eclipse for the study of the solar diameter.

For the website of the meeting: http://www.icranet.org/index.php?option=com_content&task=view&id=1491
For the video of the lesson on April 20, 2023: https://www.youtube.com/watch?v=A1iuNAjO4GA
For the video of the lesson on May 4, 2023: https://www.youtube.com/watch?v=R6I2TCdVjW4
For the video of the lesson on May 11, 2023: https://www.youtube.com/watch?v=8AHFy8rc27s
For the video of the lesson on May 17, 2023: https://www.youtube.com/watch?v=17-PYE3KVw0
 


7. Scientific visits to ICRANet

• Prof. Sergio Torres (Centro Internacional de Fisica, Bogotà, Colombia), April 3-28, 2023
• Prof. Narek Sahakyan (Director of ICRANet Armenia), May 11-17, 2023
• Prof. ArbanUka (Epoka University, Albania), May 11-14, 2023
• Prof. Mohamed Gadri (University of Tripoli, Libya), May 11-16, 2023
• Prof. Massimo Della Valle (Osservatorio di Capodimonte - Italy), May 24-25, 2023

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Prof. Sergio Torres Prof. Narek Sahakyan Prof. Arban Uka Prof. Mohamed Gadri Prof. Massimo Della Valle

During their visit, those scientists had an opportunity to discuss their scientific research and to have fruitful exchange of ideas with other researchers from ICRANet and from different parts of the world.



8. Recent publications

S. O. Komarov, A. K. Gorbatsievich, A. S. Garkun, and G. V. Vereshchagin, Electromagnetic Radiation and Electromagnetic Self-Force of a Point Charge in the Vicinity of the Schwarzschild Black Hole, accepted for publication in Nonlinear Phenomena in Complex Systems, vol. 26, no. 1 (2023), pp. 77 – 82.

A point charge, radially moving in the vicinity of a black hole is considered. Electromagnetic field in a wave zone and in the small neighborhood of the charge is calculated. Numerical results of the calculation of the spectrum of electromagnetic radiation of the point charge are presented. Covariant approach for the calculation of the electromagnetic self-force is used for the case of the slowly moving charge. Numerical results for the self-force in the case of the slow motion of a particle are obtained and compared to the results in literature.

Link: https://doi.org/10.33581/1561-4085-2023-26-1-77-82

Argüelles, C. R.; Becerra-Vergara, E. A.; Rueda, J. A.; Ruffini, R., Fermionic Dark Matter: Physics, Astrophysics, and Cosmology, published in Universe, vol. 9, issue 4 on April 20, 2023.

The nature of dark matter (DM) is one of the most relevant questions in modern astrophysics. We present a brief overview of recent results that inquire into the possible fermionic quantum nature of the DM particles, focusing mainly on the interconnection between the microphysics of the neutral fermions and the macrophysical structure of galactic halos, including their formation both in the linear and non-linear cosmological regimes. We discuss the general relativistic Ruffini–Argüelles–Rueda (RAR) model of fermionic DM in galaxies, its applications to the Milky Way, the possibility that the Galactic center harbors a DM core instead of a supermassive black hole (SMBH), the S-cluster stellar orbits with an in-depth analysis of the S2's orbit including precession, the application of the RAR model to other galaxy types (dwarf, elliptic, big elliptic, and galaxy clusters), and universal galaxy relations. All the above focus on the model parameters' constraints most relevant to the fermion mass. We also connect the RAR model fermions with particle physics DM candidates, self-interactions, and galactic observable constraints. The formation and stability of core–halo galactic structures predicted by the RAR model and their relations to warm DM cosmologies are also addressed. Finally, we provide a brief discussion of how gravitational lensing, dynamical friction, and the formation of SMBHs can also probe the DM's nature.
 

Argüelles, C. R.; Boshkayev, K.; Krut, A.; Nurbakhyt, G.; Rueda, J. A.; Ruffini, R.; Uribe-Suárez, J. D.; Yunis, R., On the growth of supermassive black holes formed from the gravitational collapse of fermionic dark matter cores, accepted for publication in MNRAS on May 2023.

Observations support the idea that supermassive black holes (SMBHs) power the emission at the center of active galaxies. However, contrary to stellar-mass BHs, there is a poor understanding of their origin and physical formation channel. In this article, we propose a new process of SMBH formation in the early Universe that is not associated with baryonic matter (massive stars) or primordial cosmology. In this novel approach, SMBH seeds originate from the gravitational collapse of fermionic dense dark matter (DM) cores that arise at the center of DM halos as they form. We show that such a DM formation channel can occur before star formation, leading to heavier BH seeds than standard baryonic channels. The SMBH seeds subsequently grow by accretion. We compute the evolution of the mass and angular momentum of the BH using a geodesic general relativistic disk accretion model. We show that these SMBH seeds grow to  ∼109 - 1010 Min the first Gyr of the lifetime of the Universe without invoking unrealistic (or fine-tuned) accretion rates.
 
 
Helena X. Ren, Matteo Cerruti, Narek Sahakyan, Quasi-periodic oscillations in the γ-ray light curves of bright active galactic nuclei, published in Astronomy & Astrophysics, Volume 672 in April 2023.
 
Context. The detection of quasi-periodic oscillations (QPOs) in the light curves of active galactic nuclei (AGNs) can provide insights into the physics of the super-massive black holes (SMBHs) powering these systems and could represent a signature of the existence of SMBH binaries, setting fundamental constraints on SMBH evolution in the Universe.
Aims. The identification of long-term QPOs, characterized by periods on the order of several months to years, is particularly challenging and can only be achieved via all-sky monitoring instruments that provide unbiased, continuous light curves of astrophysical objects. The Fermi-LAT satellite, thanks to its monitoring observing strategy, is an ideal instrument for such a goal. Here, we aim to identify QPOs in the γ-ray light curves of the brightest AGNs within the Fermi-LAT catalog.
Methods. We analyzed the light curves of the 35 brightest Fermi-LAT AGNs, including data from the beginning of the Fermi mission (August 2008) to April 2021, with energies from 100 MeV to 300 GeV. Two time binnings were investigated: 7 and 30 days. The search for quasi-periodic features was then performed using the continuous wavelet transform. The significance of the result was tested via Monte Carlo simulations of artificial light curves with the same power spectral density and probability distribution function as the original light curves. The significances were then corrected for the look-elsewhere effect and provided as post-trials.
Results. We identified 24 quasars with candidate QPOs. Several of our candidates coincide with previous claims in the literature, namely: PKS 0537−441, S5 0716+714, Mrk 421, B2 1520+31, and PKS 2247−131. All our candidates are transient. The most significant multi-year QPO, with a period of about 1100 days, was observed in the quasar S5 1044+71. It is reported here for the first time.
 
 
 
Sahakyan, N.; Harutyunyan, G. ; Israyelyan, D., Origin of multiwavelength emission from flaring high redshift blazar PKS 0537-286, published in Monthly Notices of the Royal Astronomical Society, Volume 521, Issue 1 on May 2023.

The high redshift blazars powered by supermassive black holes with masses exceeding 109 M have the highest jet power and luminosity and are important probes to test the physics of relativistic jets at the early epochs of the Universe. We present a multifrequency spectral and temporal study of high redshift blazar PKS 0537-286 by analysing data from Fermi-LAT, NuSTAR Swift XRT, and UVOT. Although the time averaged γ-ray spectrum of the source is relatively soft (indicating the high-energy emission peak is below the GeV range), several prominent flares were observed when the spectrum hardened and the luminosity increased above 1049 erg s-1. The X-ray emission of the source varies in different observations and is characterized by a hard spectrum ≤1.38 with a luminosity of >1047 erg s-1. The broad-band spectral energy distribution in the quiescent and flaring periods was modelled within a one-zone leptonic scenario assuming different locations of the emission region and considering both internal (synchrotron radiation) and external (from the disc, broad-line region, and dusty torus) photon fields for the inverse Compton scattering. The modelling shows that the most optimistic scenario, from the energy requirement point of view, is when the jet energy dissipation occurs within the broad-line region. The comparison of the model parameters obtained for the quiescent and flaring periods suggests that the flaring activities are most likely caused by the hardening of the emitting electron spectral index and shifting of the cut-off energy to higher values.

Link: https://doi.org/10.1093/mnras/stad517


B. EslamPanah, Charged Accelerating BTZ Black Holes, accepted for publication in Fortschritte der Physik (Progress of Physics).

In this paper, we first extract general uncharged accelerating BTZ black hole solutions and study some of their properties. Our analysis shows that spacetime's asymptotical behavior depends on four parameters: the cosmological constant, mass, acceleration, and topological constant. Then, we study the temperature of these black holes and find that the temperature is always positive for AdSspacetime. Next, we extend our study for extracting charged accelerating BTZ black hole solutions in the presence of a nonlinear electrodynamics field known as conformally invariant Maxwell. Our findings indicate a coupling between the electrical charge and other quantities of the accelerating BTZ black holes. The asymptotical behavior of charged accelerating BTZ black holes depends on five parameters: the cosmological constant, the electrical charge, mass, the acceleration parameter, and the topological constant. Then, we studied the effects of charge, acceleration parameters, and the topological constant on the root of these black holes. Finally, we investigate the temperature of these black holes in AdSspacetime. For these black holes, the temperature depends on the electrical charge, accelerating parameter, and cosmological constant. Our analysis indicates that the temperature of charged accelerating BTZ AdS black holes is always positive.

Link: https://arxiv.org/abs/2203.12619


Antonio Enea Romano, MairiSakellariadou, The mirage of luminal modified gravitational-wave propagation, accepted for publication in Physical Review Letter.

Using conformal invariance of gravitational waves, we show that for a luminal modified gravity theory, the gravitational-wave propagation and luminosity distance are the same as in general relativity. The relation between the gravitational-wave and electromagnetic-wave luminosity distance gets however modified for electromagnetism minimally coupled to the Jordan frame metric. Using effective field theory we show that the modified relation obtained for luminal theories is also valid for non-luminal theories with Jordan frame matter-gravity coupling. We generalise our analysis to a time-dependent speed of gravitational waves with matter minimally coupled to either the Jordan or Einstein frame metrics.
 
 
Shakeri, Soroush; Hajkarim, Fazlollah, Probing axions via light circular polarization and event horizon telescope, published in Journal of Cosmology and Astroparticle Physics, Volume 2023, Issue 04 on April 11, 2023.

The impact of axion-like particles on the light polarization around the horizon of supermassive black hole (SMBH) is discussed in the light of the latest polarization measurement of the Event Horizon Telescope (EHT). We investigate different sources of the polarization due to axion interaction with photons and the magnetic field of SMBH. These can modify the linear and circular polarization parameters of the emitted light. We have shown that a significant circular polarization can be produced via the photon scattering from the background magnetic field with axions as off-shell particles. This can further constrain the parameter space of ultralight axion-like particles and their couplings with photons. The future precise measurements of circular polarization can probe the features of ultralight axions in the near vicinity of SMBH.
 
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