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Issue 11, 2025
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Extracts from the Internet


The gravitational-wave burst GW231123

Among the black hole (BH) merger events, registered until recently by gravitational-wave detectors LIGO/Virgo/KAGRA, the record high mass of a BH formed by merger has been ≈ 140M☉. Paper [10] presented the results of observations by two LIGO detectors of the event GW231123, in which the final BH mass is already (190-265)M☉, the merged BH masses are estimated as 137+22−17M☉ and 103+20−52M☉, and their dimensionless spins are ≈ 0.9 and ≈ 0.8. An unusual property of GW231123 is that one or both of the merged BHs had masses falling within the so-called mass gap (60-130)M☉. Within this interval, BHs cannot be formed because of the formation of e+e− pairs in the star core and its mass loss. However, the gap boundaries are not known exactly because of theoretical uncertainties. The presence of BHs within the forbidden gap can be explained by star merger before a gravitational collapse or merging of already formed BHs in a dense cluster. The previous BH mergers can explain the large value of their angular momenta, but the problem of this mechanism is the ejection of BHs from the cluster after the merger due to the recoil rate. Also considered was the model with primordial BHs having masses inside the mass gap and increased spin in the course of accretion [11]. The hypothesis concerning the existence of primordial BHs was proposed in 1966 by Ya B Zel’dovich and I D Novikov [12]. [10] Abac A G et al. arXiv:2507.08219 [astro-ph.HE] [11] De Luca V, Franciolini G, Riotto A arXiv:2508.09965 [astro-ph.CO] [12] Zel’dovich Ya B, Novikov I D Sov. Astron. 10 602 (1967); Astronomich. zh. 43 758 (1966)

Search for dark matter (DM) particles

Dark-matter particle scattering by scintillation NaI(Tl) crystals with a total mass of ≈ 250 kg are being searched for in the DAMA/LIBRA experiment (Gran Sasso National Laboratory, Italy) reporting for 20 years the observation of season signal variations corresponding to the variation of DM flux through the detector in the course of Earth’s orbiting [1, 2]. However, such season variations have not been confirmed in other experiments with lower statistics and using other detection methods. The same NaI(Tl) crystals with a total mass of ≈ 112.5 kg are being used in the ANAIS-112 experiment (Canfranc Underground Laboratory, Spain), and for six years, the amount of statistical data has been obtained sufficient to verify the DAMA/LIBRA results on season variations [3]. However, at a 4 σ confidence level, season variations were not detected either. Thus, it is highly probable that the DAMA/LIBRA experiment data also contain an unaccounted error simulating season variations in the DM flux. The nature of DM constituting about 27 % of the Universe mass remains unclear to date. DM, if it consists, for example, of axions [4] may be undetectable in this type of experiments. [1] Ryabov V A, Tsarev V A, Tskhovrebov A M Phys. Usp. 51 1091 (2008); UFN 178 1129 (2008) [2] Aleksandrov A B et al. Phys. Usp. 64 861 (2021); UFN 191 905 (2021) [3] Amare J et al. Phys. Rev. Lett. 135 051001 (2025) [4] Matveev V A Phys. Usp. 67 1180 (2024); UFN 194 1250 (2024)

Spin-triplet exciton insulator

An exciton insulator is a condensate of excitons, which are bound states of electrons and holes [5]. The exciton insulator phase has previously been observed in some materials, but only in the singlet state with identically directed electron and hole spins. J Liu (University of California, Irvine, USA) and their co-authors were the first to obtain evidence for a spin-triplet state in an experiment with HfTe5 compound in a magnetic field [6]. With increasing magnetic field B, a topological Lifshitz transition [7] to a one-dimensional Weyl phase and a transition of the semimetal to an insulator occurred. The preservation of the insulator state up to B = 72 T suggests the formation of a correlated phase corresponding to the spin-triplet state of an exciton insulator, and a numerical simulation confirms this interpretation. The spin-triplet phase is interesting, in particular, because it can exhibit unusual magnetic properties, such as spin superfluidity. [5] Keldysh L V Phys. Usp. 60 1180 (2017); UFN 187 1273 (2017) [6] Liu J et al. Phys. Rev. Lett. 135 046601 (2025) [7] Volovik G E Phys. Usp. 61 89 (2018); UFN 188 95 (2018)

Transverse Thomson effect

A Takahagi (Nagoya University, Japan) and their co-authors were the first to observe experimentally a transverse version of the well-known thermoelectric Thomson effect [8]. In the usual Thomson effect, discovered as far back as the 19th century, the rate of heat release per unit volume dq/dt is proportional to the vector of the electric current density and the temperature T gradient in the same direction. It is shown in [8] that in the transverse Thomson effect, dq/dt depends on mutually perpendicular current density, gradient T, and the magnetic field direction. The experiment was carried out with Bi88Sb12 polycrystals synthesized by the spark plasma sintering. The applied electric field was modulated to reveal the thermoelectric effect. Thermography using an IR camera in a magnetic field confirmed the variable heat release corresponding to the transverse Thomson effect. [8] Takahagi A et al. Nature Physics 21 1283 (2025)

The imaginary part of time delay

In many physical processes, the transition from the initial to final state proceeds with time delay. Its mathematical expression in terms of the scattering matrix has a complex form in the general case. The real part is interpreted directly as the time the signal spends inside the scattering system, but the meaning of the imaginary additive remained unclear. In 2016, M Asano et al. theoretically showed that the complex part should describe the shift of the central frequency of the wave packet in the Fourier expansion of the signal. I L Giovannelli and S M Anlage (University of Maryland, College Park, USA) confirmed this interpretation in their experiment [9]. Using an oscillograph and a network analyzer, they observed the passage of Gaussian microwave pulses through a loop consisting of two unequally long coaxial cables. Registered was a shift by 0.48 MHz of the central frequency of packets in the Fourier expansion, expressed in terms of the imaginary part of the time delay in accordance with the theory of M Asano et al. [9] Giovannelli I L, Anlage S M Phys. Rev. Lett. 135 043801 (2025)

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The Extracts from the Internet is a section of Uspekhi Fizicheskih Nauk (Physics Uspekhi) — the monthly rewiew journal of the current state of the most topical problems in physics and in associated fields. The presented News is devoted to the fundamental discoveries of physics and astrophysics.

Permanent editor is Yu.N. Eroshenko.

It is compiled from a multitude of Internet sources.
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