Abstracts of Interest
Selected by:
Tristan Betterman
Abstract: 2209.06180
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Title:A simulation experiment of a pipeline based on machine learning for neutral hydrogen intensity mapping surveys
Download PDFAbstract: We present a simulation experiment of a pipeline based on machine learning algorithms for neutral hydrogen (HI) intensity mapping (IM) surveys with different telescopes. The simulation is conducted on HI signals, foreground emission, thermal noise from instruments, strong radio frequency interference (sRFI), and mild RFI (mRFI). We apply the Mini-Batch K-Means algorithm to identify sRFI, and Adam algorithm to remove foregrounds and mRFI. Results show that there exists a threshold of the sRFI amplitudes above which the performance of our pipeline enhances greatly. In removing foregrounds and mRFI, the performance of our pipeline is shown to have little dependence on the apertures of telescopes. In addition, the results show that there are thresholds of the signal amplitudes from which the performance of our pipeline begins to change rapidly. We consider all these thresholds as the edges of the signal amplitude ranges in which our pipeline can function well. Our work, for the first time, explores the feasibility of applying machine learning algorithms in the pipeline of IM surveys, especially for large surveys with the next-generation telescopes.
Abstract: 2209.06196
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Title:Simulations of PBH formation at the QCD epoch and comparison with the GWTC-3 catalog
Download PDFAbstract: The probability of primordial black hole (PBH) formation is known to be boosted during the Quantum Chromodynamics (QCD) crossover due to a slight reduction of the equation of state. This induces a high peak and other features in the PBH mass distribution. But the impact of this variation during the PBH formation has been so far neglected. In this work we simulate for the first time the formation of PBHs by taking into account the varying equation of state at the QCD epoch, compute the over-density threshold using different curvature profiles and find that the resulting PBH mass distributions are significantly impacted. The expected merger rate distributions of early and late PBH binaries is comparable to the ones inferred from the GWTC-3 catalog for dark matter fractions in PBHs within $0.1 < f_{\rm PBH} <1 $. The distribution of gravitational-wave events estimated from the volume sensitivity could explain mergers around $30-50 M_\odot$, with asymmetric masses like GW190814, or in the pair-instability mass gap like GW190521. However, none of the considered cases leads to a multi-modal distribution with a secondary peak around $8-15 M_\odot$, as suggested by the GWTC-3 catalog, possibly pointing to a mixed population of astrophysical and primordial black holes.
Abstract: 2209.06115
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Title:Software and techniques for VLBI data processing and analysis
Download PDFAbstract: Very-long-baseline interferometry (VLBI) is a challenging observational technique, which requires in-depth knowledge about radio telescope instrumentation, interferometry, and the handling of noisy data. The reduction of the raw data is mostly left to the scientists and demands the use of complex algorithms implemented in comprehensive software packages. The correct application of these algorithms necessitates a good understanding of the underlying techniques and physics that are at play. The verification of the processed data produced by the algorithms demands a thorough understanding of the underlying interferometric VLBI measurements. This review describes the latest techniques and algorithms that scientists should know about when analyzing VLBI data.
Abstract: 2209.06088
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Full Text: [ PostScript, PDF]
Title:Suitability of magnetic microbolometers based on paramagnetic temperature sensors for CMB polarization measurements
Download PDFAbstract: High resolution polarization maps of the Cosmic Microwave Background (CMB) are on high demand, since the discovery of primordial B-Modes in the polarization patterns would confirm the inflationary phase of the Universe that would have taken place before the emission of the CMB. Transition Edge Sensors (TES) and Microwave Kinetic Inductance Detectors (MKID) are the predominant detector technologies of cryogenic detector array based CMB instruments that search for primordial B-Modes. In this paper we propose another type of cryogenic detector to be used for CMB survey: A magnetic microbolometer (MMB) that is based on a paramagnetic temperature sensor. It is an adaption of state-of-the-art metallic magnetic calorimeters (MMCs) that are meanwhile a key technology for high resolution $\alpha$, $\beta$, $\gamma$ and X-ray spectroscopy as well as the study of neutrino mass. A complete simulation framework was developed that accounts for the electrical and thermal properties of the bolometer and that can be used to obtain its responsivity and bandwidth, as well as estimating noise. A brief proof of concept case study is analyzed, taking into account typical constraints in CMB measurements and reliable microfabrication processes, to assess the suitability of metallic magnetic sensors in CMB experiments. The results show that MMBs provide a promising technology for CMB polarization measurements as their sensitivity can be tuned for background limited detection of the sky while simultaneously maintaining a low time response to avoid degradation of the point-source response of the telescope. As the sensor technology and its fabrication techniques are compatible with TES based bolometric detector arrays, a change of detector technology would even come with very low cost.
Abstract: 2209.06061
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Title:The dust sublimation region of the Type 1 AGN NGC4151 at a hundred micro-arcsecond scale as resolved by the CHARA Array interferometer
Download PDFAbstract: The nuclear region of Type 1 AGNs has only been partially resolved so far in the near-infrared (IR) where we expect to see the dust sublimation region and the nucleus directly without obscuration. Here we present the near-IR interferometric observation of the brightest Type 1 AGN NGC4151 at long baselines of ~250 m using the CHARA Array, reaching structures at hundred micro-arcsecond scales. The squared visibilities decrease down to as low as ~0.25, definitely showing that the structure is resolved. Furthermore, combining with the previous visibility measurements at shorter baselines but at different position angles, we show that the structure is elongated *perpendicular* to the polar axis of the nucleus, as defined by optical polarization and a linear radio jet. A thin-ring fit gives a minor/major axis ratio of ~0.7 at a radius ~0.5 mas (~0.03 pc). This is consistent with the case where the sublimating dust grains are distributed preferentially in an equatorial plane in a ring-like geometry, viewed at an inclination angle of ~40 deg. Recent mid-IR interferometric finding of polar-elongated geometry at a pc scale, together with a larger-scale polar outflow as spectrally resolved by the HST, would generally suggest a dusty, conical and hollow outflow being launched presumably in the dust sublimation region. This might potentially lead to a polar-elongated morphology in the near-IR, as opposed to the results here. We discuss a possible scenario where an episodic, one-off anisotropic acceleration formed a polar-fast and equatorially-slow velocity distribution, having lead to an effectively flaring geometry as we observe.
Abstract: 2209.06060
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Full Text: [ PostScript, PDF]
Title:Stability and Observability of Magnetic Primordial Black Hole-Neutron Star Collisions
Download PDFAbstract: The collision of a primordial black hole with a neutron star results in the black hole eventually consuming the entire neutron star. However, if the black hole is magnetically charged, and therefore stable against decay by Hawking radiation, the consequences can be quite different. Upon colliding with a neutron star, a magnetic black hole very rapidly comes to a stop. For large enough magnetic charge, we show that this collision can be detected as a sudden change in the rotation period of the neutron star, a glitch or anti-glitch.We argue that the magnetic primordial black hole, which then settles to the core of the neutron star, does not necessarily devour the entire neutron star; the system can instead reach a long-lived, quasi-stable equilibrium. Because the black hole is microscopic compared to the neutron star, most stellar properties remain unchanged compared to before the collision. However, the neutron star will heat up and its surface magnetic field could potentially change, both effects potentially observable.
Abstract: 2209.06059
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Full Text: [ PostScript, PDF]
Title:Bird's eye view of molecular clouds in the Milky Way: II. Cloud kinematics from sub-pc to kpc scales
Download PDFAbstract: The kinematics of molecular gas are crucial for setting the stage for star formation. One key question related to the kinematic properties of gas is how they depend on the spatial scale. We aim to describe the CO spectra, velocity dispersions, and especially the linewidth-size relation, of molecular gas from cloud (parsec-) scales to kiloparsec scales in a complete region within the Milky Way disk. We utilise the census of molecular clouds within 2 kpc from our earlier work, together with CO emission data for them from the literature. We study the kinematics and the Larson's relations for the sample of individual clouds. We also mimic a face-on view of the Milky Way and analyse the kinematics of the clouds within apertures of 0.25-2 kpc in size. In this way, we describe the scale-dependency of the CO gas kinematics and Larson's relations. We describe the spectra of CO gas at cloud scales and in apertures between 0.25-2 kpc in our survey area. The spectra within the apertures are relatively symmetric but show non-Gaussian high-velocity wings. At cloud-scales, our sample shows a linewidth-size relation \sigma_v=1.5*R^{0.3\pm0.1} with a large scatter. The mass-size relation in the sample of clouds is M_{CO}= 794*R^{1.5\pm0.5}. The relations are also present for the apertures at kpc-scales. A suggestive dependency on galactic environment is seen, with apertures closer to the Galactic centre and the Sagittarius spiral arm having slightly higher velocity dispersions. We explore the possible effect of a diffuse component in the survey area, and find that such a component would widen the CO spectra and could flatten the linewidth-size relation. Understanding the nature of the possible diffuse CO component and its effects on observations is crucial for connecting Galactic and extragalactic data.
Abstract: 2209.06014
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Title:Latest results from the DAMPE space mission
Download PDFAbstract: The DArk Matter Particle Explorer (DAMPE) is a space-based particle detector launched on December 17th, 2015 from the Jiuquan Satellite Launch Center (China). The main goals of the DAMPE mission are the study of galactic cosmic rays (CR), the electron-positron energy spectrum, gamma-ray astronomy, and indirect dark matter search. Among its sub-detectors, the deep calorimeter makes DAMPE able to measure electrons and gamma-ray spectra up to 10 TeV, and CR nuclei spectra up to hundreds of TeV, with unprecedented energy resolution. This high-energy region is important in order to search for electron-positron sources, for dark matter signatures in space, and to clarify CR acceleration and propagation mechanisms inside our galaxy. A general overview of the DAMPE experiment will be presented in this work, along with its main results and ongoing activities.
Abstract: 2209.05965
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Title:A probabilistic deep learning model to distinguish cusps and cores in dwarf galaxies
Download PDFAbstract: Numerical simulations within a cold dark matter (DM) cosmology form halos whose density profiles have a steep inner slope (`cusp'), yet observations of galaxies often point towards a flat central `core'. We develop a convolutional mixture density neural network model to derive a probability density function (PDF) of the inner density slopes of DM halos. We train the network on simulated dwarf galaxies from the NIHAO and AURIGA projects, which include both DM cusps and cores: line-of-sight velocities and 2D spatial distributions of their stars are used as inputs to obtain a PDF representing the probability of predicting a specific inner slope. The model recovers accurately the expected DM profiles: $\sim$82$\%$ of the galaxies have a derived inner slope within $\pm$0.1 of their true value, while $\sim$98$\%$ within $\pm$0.3. We apply our model to four Local Group dwarf spheroidal galaxies and find results consistent with those obtained with the Jeans modelling based code GravSphere: the Fornax dSph has a strong indication of possessing a central DM core, Carina and Sextans have cusps (although the latter with large uncertainties), while Sculptor shows a double peaked PDF indicating that a cusp is preferred, but a core can not be ruled out. Our results show that simulation-based inference with neural networks provide a innovative and complementary method for the determination of the inner matter density profiles in galaxies, which in turn can help constrain the properties of the elusive DM.
Abstract: 2209.05926
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Title:Search for photons above 10$^{19}$ eV with the surface detector of the Pierre Auger Observatory
Download PDFAbstract: We use the surface detector of the Pierre Auger Observatory to search for air showers initiated by photons with an energy above $10^{19}$ eV. Photons in the zenith angle range from 30$^\circ$ to 60$^\circ$ can be identified in the overwhelming background of showers initiated by charged cosmic rays through the broader time structure of the signals induced in the water-Cherenkov detectors of the array and the steeper lateral distribution of shower particles reaching ground. Applying the search method to data collected between January 2004 and June 2020, upper limits at 95\% CL are set to an $E^{-2}$ diffuse flux of ultra-high energy photons above $10^{19}$ eV, $2{\times}10^{19}$ eV and $4{\times}10^{19}$ eV amounting to $2.11{\times}10^{-3}$, $3.12{\times}10^{-4}$ and $1.72{\times}10^{-4}$ km$^{-2}$ sr$^{-1}$ yr$^{-1}$, respectively. While the sensitivity of the present search around $2 \times 10^{19}$ eV approaches expectations of cosmogenic photon fluxes in the case of a pure-proton composition, it is one order of magnitude above those from more realistic mixed-composition models. The inferred limits have also implications for the search of super-heavy dark matter that are discussed and illustrated.
Abstract: 2209.05904
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Title:Joint optimization of wavefront sensing and reconstruction with automatic differentiation
Download PDFAbstract: High-contrast imaging instruments need extreme wavefront control to directly image exoplanets. This requires highly sensitive wavefront sensors which optimally make use of the available photons to sense the wavefront. Here, we propose to numerically optimize Fourier-filtering wavefront sensors using automatic differentiation. First, we optimize the sensitivity of the wavefront sensor for different apertures and wavefront distributions. We find sensors that are more sensitive than currently used sensors and close to the theoretical limit, under the assumption of monochromatic light. Subsequently, we directly minimize the residual wavefront error by jointly optimizing the sensing and reconstruction. This is done by connecting differentiable models of the wavefront sensor and reconstructor and alternatingly improving them using a gradient-based optimizer. We also allow for nonlinearities in the wavefront reconstruction using Convolutional Neural Networks, which extends the design space of the wavefront sensor. Our results show that optimization can lead to wavefront sensors that have improved performance over currently used wavefront sensors. The proposed approach is flexible, and can in principle be used for any wavefront sensor architecture with free design parameters.
Abstract: 2209.05888
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Full Text: [ PostScript, PDF]
Title:The Transients Handler System for the Cherenkov Telescope Array Observatory
Download PDFAbstract: The Cherenkov Telescope Array Observatory (CTAO) will be the largest and most advanced ground-based facility for gamma-ray astronomy. Several dozens of telescopes will be operated at both the Northern and Southern Hemisphere. With the advent of multi-messenger astronomy, many new large science infrastructures will start science operations and target-of-opportunity observations will play an important role in the operation of the CTAO. The Array Control and Data Acquisition (ACADA) system deployed on each CTAO site will feature a dedicated sub-system to manage external and internal scientific alerts: the Transients Handler. It will receive, validate, and process science alerts in order to determine if target-of-opportunity observations can be triggered or need to be updated. Various tasks defined by proposal-based configurations are processed by the Transients Handler. These tasks include, among others, the evaluation of observability of targets and their correlation with known sources or objects. This contribution will discuss the concepts and design of the Transients Handler and its integration in the ACADA system.
Abstract: 2209.05632
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Title:Search for a Black Hole Binary in Gaia DR3 Astrometric Binary Stars with Spectroscopic Data
Download PDFAbstract: We report the discovery of a candidate binary system consisting of a black hole (BH) and a red giant branch star from the Gaia DR3. This binary system is discovered from 64096 binary solutions for which both astrometric and spectroscopic data are available. For this system, the astrometric and spectroscopic solutions are consistent with each other, making this system a confident candidate of a BH binary. The primary (visible) star in this system, Gaia DR3 5870569352746779008, is a red giant branch whose mass is quite uncertain. Fortunately, albeit the uncertainty of the primary's mass, the secondary (dark) object in this system has a mass of $>5.25$ $M_\odot$ with a probability of $99$ %, based on the orbital parameters. The mass of the secondary object is much larger than the maximum neutron star mass ($\sim 2.0$ $M_\odot$), which indicates that the secondary object is likely a BH. We argue that, if this dark object is not a BH, this system must be a more exotic system, in which the primary red giant branch star orbits around a triple star system (or a higher-order multiple star system) whose total mass is more than $5.25$ $M_\odot$. Future deep photometric observations are awaited to rule out such an exotic possibility and to determine whether or not this system is a genuine BH binary. If this is a genuine BH binary, this has the longest period ($1352.25 \pm 45.50$ days) among discovered so far.
Abstract: 2209.05493
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Title:The progenitor galaxies of stellar haloes as "failed" Milky Ways
Download PDFAbstract: The stellar halo of the Milky Way records the history of its interactions with dwarf galaxies, whose subsequent destruction results in the formation of an extended stellar component. Recent works have suggested that galaxies with masses comparable to the Large Magellanic Cloud (LMC, $M_\star \sim 10^9\,{\rm M}_\odot$) may be the primary building blocks of the stellar halo of our Galaxy. We use cosmological simulations of the $\Lambda$ Cold Dark Matter model to investigate LMC-mass galaxies at $z=1-2$ using a semi-analytic model of galaxy formation. We find that LMC analogues at $z=2$ evolve until the present day along three distinct pathways: (1) those that are destroyed in Milky Way-mass hosts; (2) those that are themselves the main progenitors of Milky Way-mass galaxies; and (3) those that survive until $z=0$, with stellar mass $\sim$1.0 dex lower than typical Milky Ways. Our model predicts that the properties of these galaxies at $z=2$ (stellar metallicities, sizes, gas content etc.) are more or less indistinguishable, irrespective of which of these pathways is eventually taken; a survey targeting such galaxies in this redshift range would struggle to tell apart a 'destroyed' stellar halo progenitor from a 'surviving' LMC analogue. The only factor that determines the eventual fate of these galaxies is their proximity to a neighbouring Milky Way main progenitor at $z=2$: while the typical separation to a 'surviving' galaxy is around 7 Mpc, it is only 670 kpc to a 'destroyed' galaxy. Our results suggest that the old stellar populations in the Milky Way may be essentially indistinguishable from the progenitors of its stellar halo.
Abstract: 2209.05475
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Title:The False Alarms induced by Gaussian Noise in Gravitational Wave Detectors
Download PDFAbstract: Gaussian noise is an irreducible component of the background in gravitational wave (GW) detectors. Although stationary Gaussian noise is uncorrelated in frequencies, we show that there is an important correlation in time when looking at the matched filter signal to noise ratio (SNR) of a template, with a typical autocorrelation time that depends on the template and the shape of the noise power spectral density (PSD). Taking this correlation into account, we compute from first principles the false alarm rate (FAR) of a template in Gaussian noise, defined as the number of occurrences per unit time that the template's matched filter SNR goes over a threshold $\rho$. We find that the Gaussian FAR can be well approximated by the usual expression for uncorrelated noise, if we replace the sampling rate by an effective sampling rate that depends on the parameters of the template, the noise PSD and the threshold $\rho$. This results in a minimum SNR threshold that has to be demanded to a given GW trigger, if we want to keep events generated from Gaussian noise below a certain FAR. We extend the formalism to multiple detectors and to the analysis of GW events. We apply our method to the GW candidates added in the GWTC-3 catalog, and discuss the possibility that GW200308\_173609 and GW200322\_091133 could be generated by Gaussian noise fluctuations.
Abstract: 2209.05204
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Full Text: [ PostScript, PDF]
Title:Supernova 2009ip outbursts in 2012: From scenario to model
Download PDFAbstract: Spherical and aspherical models are presented for two outbursts in 2012 of supernova 2009ip. Models are based on a scenario which suggests that the August 2012 outburst is caused by the explosive shell ejection from LBV-presupernova. The model predicts an emergence of an unobserved outburst in late July 2012 related to a shock breakout and a subsequent diffusive radiative cooling of the ejected envelope. The luminosity of the first observed outburst in August 2012 was presumably powered by the central source, whereas the second, more powerful outburst in late September 2012, was caused by the ejecta interaction with the circumstellar envelope. Models provide estimates of the ejecta energy and mass along with the mass of the circumstellar shell.
Abstract: 2209.05125
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Full Text: [ PostScript, PDF]
Title:X-ray detection of a nova in the fireball phase
Download PDFAbstract: Novae are caused by runaway thermonuclear burning in the hydrogen-rich envelopes of accreting white dwarfs, which results in the envelope to expand rapidly and to eject most of its mass. For more than 30 years, nova theory has predicted the existence of a "fireball" phase following directly the runaway fusion, which should be observable as a short, bright, and soft X-ray flash before the nova becomes visible in the optical. Here we present the unequivocal detection of an extremely bright and very soft X-ray flash of the classical Galactic nova YZ Reticuli 11 hours prior to its 9 mag optical brightening. No X-ray source was detected 4 hours before and after the event, constraining the duration of the flash to shorter than 8 hours. In agreement with theoretical predictions, the source's spectral shape is consistent with a black body of $3.27^{+0.11}_{-0.33}\times 10^5$ K ($28.2^{+0.9}_{-2.8}$ eV), or a white dwarf atmosphere, radiating at the Eddington luminosity, with a photosphere that is only slightly larger than a typical white dwarf. This detection of the expanding white dwarf photosphere before the ejection of the envelope provides the last link of the predicted photospheric lightcurve evolution and opens a new window to measure the total nova energetics.
Abstract: 2209.05008
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Full Text: [ PostScript, PDF]
Title:Constraining the Hubble constant and its lower limit from the proper motion of extragalactic radio jets
Download PDFAbstract: The Hubble constant ($H_{0}$) is a measurement to describe the expansion rate of the Universe in the current era. However, there is a $4.4\sigma$ discrepancy between the measurements from the early Universe and the late Universe. In this research, we propose a model-free and distance-free method to constrain $H_{0}$. Combining Friedman-Lemaître-Robertson-Walker cosmology with geometrical relation of the proper motion of extragalactic jets, the lower limit ($H_{\rm 0,min}$) of $H_{0}$ can be determined using only three cosmology-free observables: the redshifts of the host galaxies, as well as the approaching and receding angular velocities of radio jets. Using these, we propose to use the Kolmogorov-Smirnov test (K-S test) between cumulative distribution functions of $H_{\rm 0,min}$ to differentiate cosmology. We simulate 100, 200, and 500 extragalactic jets with 3 levels of accuracy of the proper motion ($\mu_{a}$ and $\mu_{r}$), at $10\%$, $5\%$, and $1\%$, corresponding to the accuracies of the current and future radio interferometers. We perform K-S tests between the simulated samples as theoretical distributions with different $H_{0}$ and power-law index of velocity distribution of jets and mock observational data. Our result suggests increasing sample sizes leads to tighter constraints on both power-law index and the Hubble constant at moderate accuracy (i.e., $10\%$ and $5\%$) while at $1\%$ accuracy, increasing sample sizes leads to tighter constraints on power-law index more. Improving accuracy results in better constraints in the Hubble constant compared with the power-law index in all cases but it alleviates the degeneracy.
Abstract: 2209.04873
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Full Text: [ PostScript, PDF]
Title:Neutrino Flux Deduced from $γ$-rays Emitted by Novae
Download PDFAbstract: The recently discovered high energy emission from the recurrent nova RS Ophiuchi by Fermi-LAT ($>$ 100 MeV), H.E.S.S. and MAGIC ($>$ 100 GeV), hints towards a possible hadronic origin of this radiation component. From this high energy photon flux we derive the expected number of neutrino events that could be detected by present and future neutrino telescopes in the different energy ranges. We find the number to be well below the detectors' capabilities. Therefore, both hadronic and leptonic processes remain valid interpretations of this $\gamma$-ray emission. Preliminary estimates indicate that in order to detect a plausible number of neutrino events with {IceCube-DeepCore} and KM3NeT the novae distances should not be greater than $\sim 1$ and $\sim 2$ kpc, respectively. Current values of the rates of nova eruptions in the Milky Way will allow present and future neutrino facilities to detect neutrino events from novae on a time scale of the order of once or twice per decade.
Abstract: 2209.04823
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Full Text: [ PostScript, PDF]
Title:How to delay death and look further into the future if you fall into a black hole
Download PDFAbstract: In this note, we present a pedagogical illustration of peculiar properties of motion in the vicinity and inside black holes. We discuss how a momentary impulse can modify the lifetime of an object radially falling into a Schwarzschild black hole down to singularity. The well known upper limit for a proper time spent within a horizon, in fact, requires an infinitely powerful kick. We calculate the proper time interval (perceived as personal lifetime of a falling observer) till the contact with the singularity, as well as the time interval in the Lemaître frame (which reflects how far into the future of the outer world a falling observer can look), for different values of the kick received by the falling body. We discuss the ideal strategy to increase both time intervals by the engine with a finite power.
This example is suitable for university seminars for undergraduate students specializing in General Relativity and related astrophysical subjects.
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