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K Belczynski - One of the best experts on this subject based on the ideXlab platform.
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the influence of the distribution of cosmic star formation at different metallicities on the properties of merging double Compact Objects
Monthly Notices of the Royal Astronomical Society, 2019Co-Authors: Martyna Chruslinska, G Nelemans, K BelczynskiAbstract:Binaries that merge within the local Universe originate from progenitor systems that formed at different times and in various environments. The efficiency of formation of double Compact Objects is highly sensitive to metallicity of the star formation. Therefore, to confront the theoretical predictions with observational limits resulting from gravitational waves observations one has to account for the formation and evolution of progenitor stars in the chemically evolving Universe. In particular, this requires knowledge of the distribution of cosmic star formation rate at different metallicities and times, probed by redshift (SFR(Z,z)). We investigate the effect of the assumed SFR(Z,z) on the properties of merging double Compact Objects, in particular on their merger rate densities. Using a set of binary evolution models from Chruslinska et al. (2018) we demonstrate that the reported tension between the merger rates of different types of double Compact Objects and current observational limits in some cases can be resolved if a SFR(Z,z) closer to that expected based on observations of local star-forming galaxies is used, without the need for changing the assumptions about the evolution of progenitor stars of different masses. This highlights the importance of finding tighter constraints on SFR(Z,z) and understanding the associated uncertainties.
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double Compact Objects iii gravitational wave detection rates
The Astrophysical Journal, 2015Co-Authors: Michal Dominik, K Belczynski, R Oshaughnessy, T Bulik, Emanuele Berti, I Mandel, Chris L Fryer, D E Holz, F PannaraleAbstract:The unprecedented range of second-generation gravitational-wave (GW) observatories calls for refining the predictions of potential sources and detection rates. The coalescence of double Compact Objects (DCOs)?i.e., neutron star?neutron star (NS?NS), black hole?neutron star (BH?NS), and black hole?black hole (BH?BH) binary systems?is the most promising source of GWs for these detectors. We compute detection rates of coalescing DCOs in second-generation GW detectors using the latest models for their cosmological evolution, and implementing inspiral-merger-ringdown gravitational waveform models in our signal-to-noise ratio calculations. We find that (1) the inclusion of the merger/ringdown portion of the signal does not significantly affect rates for NS?NS and BH?NS systems, but it boosts rates by a factor of ?1.5 for BH?BH systems; (2) in almost all of our models BH?BH systems yield by far the largest rates, followed by NS?NS and BH?NS systems, respectively; and (3) a majority of the detectable BH?BH systems were formed in the early universe in low-metallicity environments. We make predictions for the distributions of detected binaries and discuss what the first GW detections will teach us about the astrophysics underlying binary formation and evolution.
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double Compact Objects ii cosmological merger rates
The Astrophysical Journal, 2013Co-Authors: Michal Dominik, K Belczynski, T Bulik, Emanuele Berti, I Mandel, Chris L Fryer, D E Holz, R OshaughnessyAbstract:The development of advanced gravitational wave (GW) observatories, such as Advanced LIGO and Advanced Virgo, provides impetus to refine theoretical predictions for what these instruments might detect. In particular, with the range increasing by an order of magnitude, the search for GW sources is extending beyond the local universe and out to cosmological distances. Double Compact Objects (neutron star-neutron star (NS-NS), black hole-neutron star (BH-NS), and black hole-black hole (BH-BH) systems) are considered to be the most promising GW sources. In addition, NS-NS and/or BH-NS systems are thought to be the progenitors of gamma-ray bursts and may also be associated with kilonovae. In this paper, we present the merger event rates of these Objects as a function of cosmological redshift. We provide the results for four cases, each one investigating a different important evolution parameter of binary stars. Each case is also presented for two metallicity evolution scenarios. We find that (1) in most cases NS-NS systems dominate the merger rates in the local universe, while BH-BH mergers dominate at high redshift, (2) BH-NS mergers are less frequent than other sources per unit volume, for all time, and (3) natal kicks may alter the observable properties of populations in a significant way, allowing the underlying models of binary evolution and Compact object formation to be easily distinguished. This is the second paper in a series of three. The third paper will focus on calculating the detection rates of mergers by GW telescopes.
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double Compact Objects ii cosmological merger rates
arXiv: High Energy Astrophysical Phenomena, 2013Co-Authors: Michal Dominik, K Belczynski, T Bulik, Emanuele Berti, I Mandel, Chris L Fryer, D E Holz, R OshaughnessyAbstract:The development of advanced gravitational wave (GW) observatories, such as Advanced LIGO and Advanced Virgo, provides impetus to refine theoretical predictions for what these instruments might detect. In particular, with the range increasing by an order of magnitude, the search for GW sources is extending beyond the "local" Universe and out to cosmological distances. Double Compact Objects (neutron star-neutron star (NS-NS), black hole-neutron star (BH-NS) and black hole-black hole (BH-BH) systems) are considered to be the most promising gravitational wave sources. In addition, NS-NS and/or BH-NS systems are thought to be the progenitors of gamma ray bursts (GRBs), and may also be associated with kilonovae. In this paper we present the merger event rates of these Objects as a function of cosmological redshift. We provide the results for four cases, each one investigating a different important evolution parameter of binary stars. Each case is also presented for two metallicity evolution scenarios. We find that (i) in most cases NS-NS systems dominate the merger rates in the local Universe, while BH-BH mergers dominate at high redshift; (ii) BH-NS mergers are less frequent than other sources per unit volume, for all time; and (iii) natal kicks may alter the observable properties of populations in a significant way, allowing the underlying models of binary evolution and Compact object formation to be easily distinguished. This is the second paper in a series of three. The third paper will focus on calculating the detection rates of mergers by gravitational wave telescopes.
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double Compact Objects as low frequency gravitational wave sources
The Astrophysical Journal, 2010Co-Authors: K Belczynski, M Benacquista, T BulikAbstract:We study the Galactic field population of double Compact Objects (DCOs; NS-NS, BH-NS, BH-BH binaries) to investigate the number (if any) of these systems that can potentially be detected with the Laser Interferometer Space Antenna (LISA) at low gravitational wave frequencies. We calculate the Galactic numbers and physical properties of these binaries and show their relative contributions from the disk, bulge, and halo. Although the Galaxy hosts ~105 DCO binaries emitting low-frequency gravitational waves, only a handful of these Objects in the disk will be detectable with LISA, but none from the halo or bulge. This is because the bulk of these binaries are NS-NS systems with high eccentricities and long orbital periods (weeks/months) causing inefficient signal accumulation (a small number of signal bursts at periastron passage in one year of LISA observations) and rendering them undetectable in the majority of these cases. We adopt two evolutionary models that differ in their treatment of the common envelope (CE) phase that is a major (and still mostly unknown) process in the formation of close DCOs. Depending on the evolutionary model adopted, our calculations indicate the likely detection of about four NS-NS binaries and two BH-BH systems (model A; likely survival of progenitors through CE) or only a couple of NS-NS binaries (model B; suppression of the DCO formation due to CE mergers).
E V Gotthelf - One of the best experts on this subject based on the ideXlab platform.
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the spin down of psr j0821 4300 and psr j1210 5226 confirmation of central Compact Objects as anti magnetars
The Astrophysical Journal, 2013Co-Authors: E V Gotthelf, J P Halpern, Jason AlfordAbstract:Using XMM-Newton and Chandra, we measure period derivatives for the second and third known pulsars in the class of central Compact Objects (CCOs) in supernova remnants, proving that these young neutron stars have exceptionally weak dipole magnetic field components. For the 112 ms PSR J0821–4300 in Puppis A, . Its proper motion, μ = 61 ± 9 mas yr–1, was also measured using Chandra. This contributes a kinematic term to the period derivative via the Shklovskii effect, which is subtracted from to derive dipole Bs = 2.9 × 1010 G, a value similar to that of the first measured CCO, PSR J1852+0040 in Kes 79, which has Bs = 3.1 × 1010 G. Antipodal surface hot spots with different temperatures and areas are deduced from the X-ray spectrum and pulse profiles. Paradoxically, such nonuniform surface temperature appears to require strong crustal magnetic fields, probably toroidal or quadrupolar components much stronger than the external dipole. A spectral feature, consisting of either an emission line at ≈0.75 keV or an absorption line at ≈0.46 keV, is modulated in strength with the rotation. It may be due to a cyclotron process in a magnetic field on the surface that is slightly stronger than the dipole deduced from the spin-down. We also timed anew the 424 ms PSR J1210–5226, resolving previous ambiguities about its spin-down rate. Its is (2.22 ± 0.02) × 10–17, corresponding to Bs = 9.8 × 1010 G. This is also compatible with a cyclotron resonance interpretation of its prominent absorption line at 0.7 keV and its harmonics. These results deepen the mystery of the origin and evolution of CCOs: Why are their numerous descendants not evident?
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the spin down of psr j0821 4300 and psr j1210 5226 confirmation of central Compact Objects as anti magnetars
arXiv: High Energy Astrophysical Phenomena, 2013Co-Authors: E V Gotthelf, J P Halpern, Jason AlfordAbstract:Using XMM-Newton and Chandra, we measure period derivatives for the second and third known pulsars in the class of Central Compact Objects (CCOs) in supernova remnants, proving that these young neutron stars have exceptionally weak dipole magnetic field components. For the 112 ms PSR J0821-4300 in Puppis A, Pdot = (9.28 +/- 0.36)E-18. Its proper motion, mu = 61 +/- 9 mas/yr, was also measured using Chandra. This contributes a kinematic term to the period derivative via the Shklovskii effect, which is subtracted from Pdot to derive dipole Bs = 2.9E10 G, a value similar to that of first measured CCO PSR J1852+0040 in Kes 79, which has Bs = 3.1E10 G. Antipodal surface hot spots with different temperatures and areas are deduced from the X-ray spectrum and pulse profiles. Paradoxically, such nonuniform surface temperature appears to require strong crustal magnetic fields, probably toroidal or quadrupolar components much stronger than the external dipole. A spectral feature, consisting of either an emission line at approximately 0.75 keV or absorption at approximately 0.46 keV, is modulated in strength with the rotation. It may be due to a cyclotron process in a magnetic field on the surface that is slightly stronger than the dipole deduced from the spin-down. We also timed anew the 424 ms PSR J12010-5226, resolving previous ambiguities about its spin-down rate. Its Pdot = (2.22 +/- 0.02)E-17, corresponding to Bs = 9.8E10 G. This is compatible with a cyclotron resonance interpretation of its prominent absorption line at 0.7 keV and harmonics. These results deepen the mystery of the origin and evolution of CCOs: why are their numerous descendants not evident?
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spin down measurement of psr j1852 0040 in kesteven 79 central Compact Objects as anti magnetars
The Astrophysical Journal, 2010Co-Authors: J P Halpern, E V GotthelfAbstract:Using XMM-Newton and Chandra, we achieved phase-connected timing of the 105 ms X-ray pulsar PSR J1852+0040 that provides the first measurement of the spin-down rate of a member of the class of central Compact Objects (CCOs) in supernova remnants. We measure P-dot=(8.68+-0.09) x 10{sup -18}, and find no evidence for timing noise or variations in X-ray flux over 4.8 year. In the dipole spin-down formalism, this implies a surface magnetic field strength B{sub s} = 3.1 x 10{sup 10} G, the smallest ever measured for a young neutron star, and consistent with being a fossil field. In combination with upper limits on B{sub s} from other CCO pulsars, this is strong evidence in favor of the 'anti-magnetar' explanation for their low luminosity and lack of magnetospheric activity or synchrotron nebulae. While this dipole field is small, it can prevent accretion of sufficient fall-back material so that the observed X-ray luminosity of L{sub x} = 5.3 x 10{sup 33}(d/7.1 kpc){sup 2} erg s{sup -1} must instead be residual cooling. The spin-down luminosity of PSR J1852+0040, E-dot=3.0 x 10{sup 32} erg s{sup -1}, is an order of magnitude smaller than L{sub x} . Fitting of the X-ray spectrum to two blackbodies findsmore » small emitting radii, R{sub 1} = 1.9 km and R{sub 2} = 0.45 km, for components of kT{sub 1} = 0.30 keV and kT{sub 2} = 0.52 keV, respectively. Such small, hot regions are ubiquitous among CCOs, and are not yet understood in the context of the anti-magnetar picture because anisotropic surface temperature is usually attributed to the effects of strong magnetic fields.« less
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spin down measurement of psr j1852 0040 in kesteven 79 central Compact Objects as anti magnetars
arXiv: High Energy Astrophysical Phenomena, 2009Co-Authors: J P Halpern, E V GotthelfAbstract:Using XMM-Newton and Chandra, we achieved phase-connected timing of the 105 ms X-ray pulsar PSR J1852+0040 that provides the first measurement of the spin-down rate of a member of the class of Central Compact Objects (CCOs) in supernova remnants. We measure P-dot = 8.68(9)E-18, and find no evidence for timing noise or variations in X-ray flux over 4.8 yr. In the dipole spin-down formalism, this implies a surface magnetic field strength B_s = 3.1E10 G, the smallest ever measured for a young neutron star, and consistent with being a fossil field. In combination with upper limits on B_s from other CCO pulsars, this is strong evidence in favor of the "anti-magnetar" explanation for their low luminosity and lack of magnetospheric activity or synchrotron nebulae. While this dipole field is small, it can prevent accretion of sufficient fall-back material so that the observed X-ray luminosity of L_x = 5.3E33(d/7.1 kpc)^2 erg/s must instead be residual cooling. The spin-down luminosity of PSR J1852+0040, E-dot = 3.0E32 erg/s, is an order-of-magnitude smaller than L_x. Fitting of the X-ray spectrum to two blackbodies finds small emitting radii, R_1 = 1.9 km and R_2 = 0.45 km, for components of kT_1 = 0.30 keV and kT_2 = 0.52 keV, respectively. Such small, hot regions are ubiquitous among CCOs, and are not yet understood in the context of the anti-magnetar picture because anisotropic surface temperature is usually attributed to the effects of strong magnetic fields.
T Bulik - One of the best experts on this subject based on the ideXlab platform.
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double Compact Objects iii gravitational wave detection rates
The Astrophysical Journal, 2015Co-Authors: Michal Dominik, K Belczynski, R Oshaughnessy, T Bulik, Emanuele Berti, I Mandel, Chris L Fryer, D E Holz, F PannaraleAbstract:The unprecedented range of second-generation gravitational-wave (GW) observatories calls for refining the predictions of potential sources and detection rates. The coalescence of double Compact Objects (DCOs)?i.e., neutron star?neutron star (NS?NS), black hole?neutron star (BH?NS), and black hole?black hole (BH?BH) binary systems?is the most promising source of GWs for these detectors. We compute detection rates of coalescing DCOs in second-generation GW detectors using the latest models for their cosmological evolution, and implementing inspiral-merger-ringdown gravitational waveform models in our signal-to-noise ratio calculations. We find that (1) the inclusion of the merger/ringdown portion of the signal does not significantly affect rates for NS?NS and BH?NS systems, but it boosts rates by a factor of ?1.5 for BH?BH systems; (2) in almost all of our models BH?BH systems yield by far the largest rates, followed by NS?NS and BH?NS systems, respectively; and (3) a majority of the detectable BH?BH systems were formed in the early universe in low-metallicity environments. We make predictions for the distributions of detected binaries and discuss what the first GW detections will teach us about the astrophysics underlying binary formation and evolution.
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double Compact Objects ii cosmological merger rates
The Astrophysical Journal, 2013Co-Authors: Michal Dominik, K Belczynski, T Bulik, Emanuele Berti, I Mandel, Chris L Fryer, D E Holz, R OshaughnessyAbstract:The development of advanced gravitational wave (GW) observatories, such as Advanced LIGO and Advanced Virgo, provides impetus to refine theoretical predictions for what these instruments might detect. In particular, with the range increasing by an order of magnitude, the search for GW sources is extending beyond the local universe and out to cosmological distances. Double Compact Objects (neutron star-neutron star (NS-NS), black hole-neutron star (BH-NS), and black hole-black hole (BH-BH) systems) are considered to be the most promising GW sources. In addition, NS-NS and/or BH-NS systems are thought to be the progenitors of gamma-ray bursts and may also be associated with kilonovae. In this paper, we present the merger event rates of these Objects as a function of cosmological redshift. We provide the results for four cases, each one investigating a different important evolution parameter of binary stars. Each case is also presented for two metallicity evolution scenarios. We find that (1) in most cases NS-NS systems dominate the merger rates in the local universe, while BH-BH mergers dominate at high redshift, (2) BH-NS mergers are less frequent than other sources per unit volume, for all time, and (3) natal kicks may alter the observable properties of populations in a significant way, allowing the underlying models of binary evolution and Compact object formation to be easily distinguished. This is the second paper in a series of three. The third paper will focus on calculating the detection rates of mergers by GW telescopes.
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double Compact Objects ii cosmological merger rates
arXiv: High Energy Astrophysical Phenomena, 2013Co-Authors: Michal Dominik, K Belczynski, T Bulik, Emanuele Berti, I Mandel, Chris L Fryer, D E Holz, R OshaughnessyAbstract:The development of advanced gravitational wave (GW) observatories, such as Advanced LIGO and Advanced Virgo, provides impetus to refine theoretical predictions for what these instruments might detect. In particular, with the range increasing by an order of magnitude, the search for GW sources is extending beyond the "local" Universe and out to cosmological distances. Double Compact Objects (neutron star-neutron star (NS-NS), black hole-neutron star (BH-NS) and black hole-black hole (BH-BH) systems) are considered to be the most promising gravitational wave sources. In addition, NS-NS and/or BH-NS systems are thought to be the progenitors of gamma ray bursts (GRBs), and may also be associated with kilonovae. In this paper we present the merger event rates of these Objects as a function of cosmological redshift. We provide the results for four cases, each one investigating a different important evolution parameter of binary stars. Each case is also presented for two metallicity evolution scenarios. We find that (i) in most cases NS-NS systems dominate the merger rates in the local Universe, while BH-BH mergers dominate at high redshift; (ii) BH-NS mergers are less frequent than other sources per unit volume, for all time; and (iii) natal kicks may alter the observable properties of populations in a significant way, allowing the underlying models of binary evolution and Compact object formation to be easily distinguished. This is the second paper in a series of three. The third paper will focus on calculating the detection rates of mergers by gravitational wave telescopes.
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double Compact Objects i the significance of the common envelope on merger rates
The Astrophysical Journal, 2012Co-Authors: Michal Dominik, T Bulik, Emanuele Berti, Chris L Fryer, D E Holz, Krzysztof Belczynski, I MandelAbstract:The last decade of observational and theoretical developments in stellar and binary evolution provides an opportunity to incorporate major improvements to the predictions from population synthesis models. We compute the Galactic merger rates for NS-NS, BH-NS, and BH-BH mergers with the StarTrack code. The most important revisions include updated wind mass-loss rates (allowing for stellar-mass black holes up to 80 M {sub Sun }), a realistic treatment of the common envelope phase (a process that can affect merger rates by 2-3 orders of magnitude), and a qualitatively new neutron star/black hole mass distribution (consistent with the observed {sup m}ass gap{sup )}. Our findings include the following. (1) The binding energy of the envelope plays a pivotal role in determining whether a binary merges within a Hubble time. (2) Our description of natal kicks from supernovae plays an important role, especially for the formation of BH-BH systems. (3) The masses of BH-BH systems can be substantially increased in the case of low metallicities or weak winds. (4) Certain combinations of parameters underpredict the Galactic NS-NS merger rate and can be ruled out. (5) Models incorporating delayed supernovae do not agree with the observed NS/BH 'mass gap', in accordance with our previousmore » work. This is the first in a series of three papers. The second paper will study the merger rates of double Compact Objects as a function of redshift, star formation rate, and metallicity. In the third paper, we will present the detection rates for gravitational-wave observatories, using up-to-date signal waveforms and sensitivity curves.« less
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double Compact Objects i the significance of the common envelope on merger rates
arXiv: High Energy Astrophysical Phenomena, 2012Co-Authors: Michal Dominik, T Bulik, Emanuele Berti, Chris L Fryer, D E Holz, Krzysztof Belczynski, I MandelAbstract:The last decade of observational and theoretical developments in stellar and binary evolution provides an opportunity to incorporate major improvements to the predictions from populations synthesis models. We compute the Galactic merger rates for NS-NS, BH-NS, and BH-BH mergers with the StarTrack code. The most important revisions include: updated wind mass loss rates (allowing for stellar mass black holes up to $80 \msun$), a realistic treatment of the common envelope phase (a process that can affect merger rates by 2--3 orders of magnitude), and a qualitatively new neutron star/black hole mass distribution (consistent with the observed "mass gap"). Our findings include: (i) The binding energy of the envelope plays a pivotal role in determining whether a binary merges within a Hubble time. (ii) Our description of natal kicks from supernovae plays an important role, especially for the formation of BH-BH systems. (iii) The masses of BH-BH systems can be substantially increased in the case of low metallicities or weak winds. (iv) Certain combinations of parameters underpredict the Galactic NS-NS merger rate, and can be ruled out. {\em (v)} Models incorporating delayed supernovae do not agree with the observed NS/BH "mass gap", in accordance with our previous work. This is the first in a series of three papers. The second paper will study the merger rates of double Compact Objects as a function of redshift, star formation rate, and metallicity. In the third paper we will present the detection rates for gravitational wave observatories, using up-to-date signal waveforms and sensitivity curves.
Miguel Zumalacarregui - One of the best experts on this subject based on the ideXlab platform.
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limits on stellar mass Compact Objects as dark matter from gravitational lensing of type ia supernovae
Physical Review Letters, 2018Co-Authors: Miguel Zumalacarregui, Uros SeljakAbstract:The nature of dark matter (DM) remains unknown despite very precise knowledge of its abundance in the Universe. An alternative to new elementary particles postulates DM as made of macroscopic Compact halo Objects (MACHO) such as black holes formed in the very early Universe. Stellar-mass primordial black holes (PBHs) are subject to less robust constraints than other mass ranges and might be connected to gravitational-wave signals detected by the Laser Interferometer Gravitational-Wave Observatory (LIGO). New methods are therefore necessary to constrain the viability of Compact Objects as a DM candidate. Here we report bounds on the abundance of Compact Objects from gravitational lensing of type Ia supernovae (SNe). Current SNe data sets constrain Compact Objects to represent less than 35.2% (Joint Lightcurve Analysis) and 37.2% (Union 2.1) of the total matter content in the Universe, at 95% confidence level. The results are valid for masses larger than ∼0.01 M_{⊙} (solar masses), limited by the size SNe relative to the lens Einstein radius. We demonstrate the mass range of the constraints by computing magnification probabilities for realistic SNe sizes and different values of the PBH mass. Our bounds are sensitive to the total abundance of Compact Objects with M≳0.01 M_{⊙} and complementary to other observational tests. These results are robust against cosmological parameters, outlier rejection, correlated noise, and selection bias. PBHs and other MACHOs are therefore ruled out as the dominant form of DM for Objects associated to LIGO gravitational wave detections. These bounds constrain early-Universe models that predict stellar-mass PBH production and strengthen the case for lighter forms of DM, including new elementary particles.
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limits on stellar mass Compact Objects as dark matter from gravitational lensing of type ia supernovae
Physical Review Letters, 2018Co-Authors: Miguel Zumalacarregui, Uros SeljakAbstract:Author(s): Zumalacarregui, Miguel; Seljak, Uros | Abstract: The nature of dark matter (DM) remains unknown despite very precise knowledge of its abundance in the Universe. An alternative to new elementary particles postulates DM as made of macroscopic Compact halo Objects (MACHO) such as black holes formed in the very early Universe. Stellar-mass primordial black holes (PBHs) are subject to less robust constraints than other mass ranges and might be connected to gravitational-wave signals detected by the Laser Interferometer Gravitational-Wave Observatory (LIGO). New methods are therefore necessary to constrain the viability of Compact Objects as a DM candidate. Here we report bounds on the abundance of Compact Objects from gravitational lensing of type Ia supernovae (SNe). Current SNe data sets constrain Compact Objects to represent less than 35.2% (Joint Lightcurve Analysis) and 37.2% (Union 2.1) of the total matter content in the Universe, at 95% confidence level. The results are valid for masses larger than ∼0.01 M_{⊙} (solar masses), limited by the size SNe relative to the lens Einstein radius. We demonstrate the mass range of the constraints by computing magnification probabilities for realistic SNe sizes and different values of the PBH mass. Our bounds are sensitive to the total abundance of Compact Objects with M≳0.01 M_{⊙} and complementary to other observational tests. These results are robust against cosmological parameters, outlier rejection, correlated noise, and selection bias. PBHs and other MACHOs are therefore ruled out as the dominant form of DM for Objects associated to LIGO gravitational wave detections. These bounds constrain early-Universe models that predict stellar-mass PBH production and strengthen the case for lighter forms of DM, including new elementary particles.
Paolo Pani - One of the best experts on this subject based on the ideXlab platform.
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Testing the nature of dark Compact Objects: a status report
Living Reviews in Relativity, 2019Co-Authors: Vitor Cardoso, Paolo PaniAbstract:Very Compact Objects probe extreme gravitational fields and may be the key to understand outstanding puzzles in fundamental physics. These include the nature of dark matter, the fate of spacetime singularities, or the loss of unitarity in Hawking evaporation. The standard astrophysical description of collapsing Objects tells us that massive, dark and Compact Objects are black holes. Any observation suggesting otherwise would be an indication of beyond-the-standard-model physics. Null results strengthen and quantify the Kerr black hole paradigm. The advent of gravitational-wave astronomy and precise measurements with very long baseline interferometry allow one to finally probe into such foundational issues. We overview the physics of exotic dark Compact Objects and their observational status, including the observational evidence for black holes with current and future experiments.
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ergoregion instability of exotic Compact Objects electromagnetic and gravitational perturbations and the role of absorption
Physical Review D, 2019Co-Authors: Vitor Cardoso, Elisa Maggio, Sam R Dolan, Paolo PaniAbstract:Spinning horizonless Compact Objects may be unstable against an “ergoregion instability.” We investigate this mechanism for electromagnetic perturbations of ultraCompact Kerr-like Objects with a reflecting surface, extending previous (numerical and analytical) work limited to the scalar case. We derive an analytical result for the frequency and the instability timescale of unstable modes which is valid at small frequencies. We argue that our analysis can be directly extended to gravitational perturbations of exotic Compact Objects in the black-hole limit. The instability for electromagnetic and gravitational perturbations is generically stronger than in the scalar case, and it requires larger absorption to be quenched. We argue that exotic Compact Objects with spin χ ≲ 0.7 (χ≲0.9) should have an absorption coefficient of at least 0.3% (6%) to remain linearly stable, and that an absorption coefficient of at least ≈60% would quench the instability for any spin. We also show that—in the static limit—the scalar, electromagnetic, and gravitatonal perturbations of the Kerr metric are related to one another through Darboux transformations. Finally, correcting previous results, we give the transformations that bring the Teukolsky equation in a form described by a real potential also in the gravitational case.
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exotic Compact Objects and how to quench their ergoregion instability
Physical Review D, 2017Co-Authors: Elisa Maggio, Paolo Pani, Valeria FerrariAbstract:Gravitational-wave astronomy can give us access to the structure of black holes, potentially probing microscopic or even Planckian corrections at the horizon scale, as those predicted by some quantum-gravity models of exotic Compact Objects. A generic feature of these models is the replacement of the horizon by a reflective surface. Objects with these properties are prone to the so-called ergoregion instability when they spin sufficiently fast. We investigate in detail a simple model consisting of scalar perturbations of a Kerr geometry with a reflective surface near the horizon. The instability depends on the spin, on the Compactness, and on the reflectivity at the surface. The instability time scale increases only logarithmically in the black-hole limit and, for a perfectly reflecting object, this is not enough to prevent the instability from occurring on dynamical time scales. However, we find that an absorption rate at the surface as small as 0.4% (reflectivity coefficient as large as $|\mathcal{R}{|}^{2}=0.996$) is sufficient to quench the instability completely. Our results suggest that exotic Compact Objects are not necessarily ruled out by the ergoregion instability.
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gravitational wave signatures of exotic Compact Objects and of quantum corrections at the horizon scale
Physical Review D, 2016Co-Authors: Vitor Cardoso, Seth Hopper, Caio F B Macedo, Carlos Palenzuela, Paolo PaniAbstract:Gravitational waves from binary coalescences provide one of the cleanest signatures of the nature of Compact Objects. It has been recently argued that the postmerger ringdown waveform of exotic ultraCompact Objects is initially identical to that of a black hole, and that putative corrections at the horizon scale will appear as secondary pulses after the main burst of radiation. Here we extend this analysis in three important directions: (i) we show that this result applies to a large class of exotic Compact Objects with a photon sphere for generic orbits in the test-particle limit; (ii) we investigate the late-time ringdown in more detail, showing that it is universally characterized by a modulated and distorted train of ``echoes''of the modes of vibration associated with the photon sphere; (iii) we study for the first time equal-mass, head-on collisions of two ultraCompact boson stars and compare their gravitational-wave signal to that produced by a pair of black holes. If the initial Objects are Compact enough as to mimic a binary black-hole collision up to the merger, the final object exceeds the maximum mass for boson stars and collapses to a black hole. This suggests that\char22{}in some configurations\char22{}the coalescence of Compact boson stars might be almost indistinguishable from that of black holes. On the other hand, generic configurations display peculiar signatures that can be searched for in gravitational-wave data as smoking guns of exotic Compact Objects.