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Register a new userHigh-energy cosmic ray production by a neutron star falling into a black hole
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Added by
Andrei Galiautdinov
Publication date
2017
fields
Physics
and research's language is
English
Authors
Andrei Galiautdinov
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We propose a one-shot mechanism for high-energy cosmic ray generation by a neutron star falling into a black hole surrounded by low density plasma. The function of the black hole in this scenario is to accelerate the star to a speed arbitrarily close to that of light. When the star - essentially, a magnetized sphere - approaches the horizon it imparts energy to the ambient plasma charges via the induced electric field. Disregarding radiation losses, for iron nucleus, a simple estimate gives energies on the order of 10^19 eV for stars with magnetic fields as weak as 10^6 teslas. The proposed mechanism should also work in chance encounters between rapidly moving neutron stars and molecular clouds. The rarity of such encounters may explain the apparent randomness and rarity of the high-energy cosmic ray events.
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The LIGO/Virgo Consortium (LVC) released a preliminary announcement of a candidate gravitational wave signal, S190426c, that could have arisen from a black hole-neutron star merger. As the first such candidate system, its properties such as masses and spin are of great interest. Although LVC policy prohibits disclosure of these properties in preliminary announcements, LVC does release the estimated probabilities that this system is in specific categories, such as binary neutron star, binary black hole and black hole-neutron star. LVC also releases information concerning relative signal strength, distance, and the probability that ejected mass or a remnant disc survived the merger. In the case of events with a finite probability of being in more than one category, such as is likely to occur with a black hole-neutron star merger, it is shown how to estimate the masses of the components and the spin of the black hole. This technique is applied to the source S190426c.
The detections of gravitational waves (GWs) from binary neutron star (BNS) systems and neutron star--black hole (NSBH) systems provide new insights into dense matter properties in extreme conditions and associated high-energy astrophysical processes. However, currently information about NS equation of state (EoS) is extracted with very limited precision. Meanwhile, the fruitful results from the serendipitous discovery of the $gamma$-ray burst alongside GW170817 show the necessity of early warning alerts. Accurate measurements of the matter effects and sky location could be achieved by joint GW detection from space and ground. In our work, based on two example cases, GW170817 and GW200105, we use the Fisher information matrix analysis to investigate the multiband synergy between the space-borne decihertz GW detectors and the ground-based Einstein Telescope (ET). We specially focus on the parameters pertaining to spin-induced quadrupole moment, tidal deformability, and sky localization. We demonstrate that, (i) only with the help of multiband observations can we constrain the quadrupole parameter; and (ii) with the inclusion of decihertz GW detectors, the errors of tidal deformability would be a few times smaller, indicating that many more EoSs could be excluded; (iii) with the inclusion of ET, the sky localization improves by about an order of magnitude. Furthermore, we have systematically compared the different limits from four planned decihertz detectors and adopting two widely used waveform models.
The origin of the heavy elements in the Universe is not fully determined. Neutron star-black hole (NSBH) and neutron star-neutron star mergers may both produce heavy elements via rapid neutron-capture process (r-process). We use the recent detection of gravitational waves from NSBHs, improved measurements of neutron star equation-of-state, and the most modern numerical simulations of the ejected materials from binary collisions to investigate the production of heavy elements from binary mergers. As the amount of ejecta depends on the mass and spin distribution of compact objects, as well as on the equation-of-state of neutron stars, we consider various models for these quantities, informed by gravitational-wave and pulsar data. We find that even in the most favorable model, neutron star-black hole mergers are unlikely to account for more than 77% of the r-process elements in the local Universe. If black holes have preferentially small spins, this bound decreases to 35%. Finally, if black hole spins are small and there is a dearth of low mass ($<5M_{odot}$) black holes in NSBH binaries, the NSBH contribution to r-process elements is negligible.
Detection of electromagnetic counterparts of gravitational wave (GW) sources is important to unveil the nature of compact binary coalescences. We perform three-dimensional, time-dependent, multi-frequency radiative transfer simulations for radioactively powered emission from the ejecta of black hole (BH) - neutron star (NS) mergers. Depending on the BH to NS mass ratio, spin of the BH, and equations of state of dense matter, BH-NS mergers can eject more material than NS-NS mergers. In such cases, radioactively powered emission from the BH-NS merger ejecta can be more luminous than that from NS-NS mergers. We show that, in spite of the expected larger distances to BH-NS merger events, observed brightness of BH-NS mergers can be comparable to or even higher than that of NS-NS mergers. We find that, when the tidally disrupted BH-NS merger ejecta are confined to a small solid angle, the emission from BH-NS merger ejecta tends to be bluer than that from NS-NS merger ejecta for a given total luminosity. Thanks to this property, we might be able to distinguish BH-NS merger events from NS-NS merger events by multi-band observations of the radioactively powered emission. In addition to the GW observations, such electromagnetic observations can potentially provide independent information on the nature of compact binary coalescences.
We propose an analogy between the quantum physics of a black hole in its late stages of the evaporation process and a superfluid Bose Einstein Condensate (BEC), based on the Horowitz and Maldacena quantum final state projection model [JHEP 2004(02), 008]. The superfluid region is considered to be analogous to the interior of a black hole, and the normal fluid/superfluid interface is compared to the event horizon of a black hole. We theoretically investigate the possibility of recovering the wavefunction of particles incident on a superfluid BEC from the normal fluid, facilitated by the mode conversion processes occurring at the normal fluid/superfluid BEC interface. We also study how the correlations of an infalling mode with an external memory system can be preserved in the process, similar to Hayden and Preskills information mirror model for a black hole [JHEP 2007(09), 120]. Based on these analogies, we conjecture that the quantum state of bosons entering a black hole in its final state is the superfluid quantum ground state of interacting bosons. Our analogy suggests that the wavefunction of bosons falling into a black hole can be recovered from the outgoing Hawking modes. In the particular case when a hole-like quasiparticle (a density dip) is incident on the superfluid BEC causing the superfluid to shrink in size, our model indicates that the evaporation is unitary.
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