We provide an updated assessment of the fundamental physics potential of LISA. Given the very bro... more We provide an updated assessment of the fundamental physics potential of LISA. Given the very broad range of topics that might be relevant to LISA, we present here a sample of what we view as particularly promising directions, based in part on the current research interests of the LISA scientific community in the area of fundamental physics. We organize these directions through a ``science-first'' approach that allows us to classify how LISA data can inform theoretical physics in a variety of areas. For each of these theoretical physics classes, we identify the sources that are currently expected to provide the principal contribution to our knowledge, and the areas that need further development. The classification presented here should not be thought of as cast in stone, but rather as a fluid framework that is amenable to change with the flow of new insights in theoretical physics.
Coalescences of binary white dwarfs represent a copious source of information for gravitational w... more Coalescences of binary white dwarfs represent a copious source of information for gravitational wave interferometers operating in the decihertz band. Moreover, according to the double degenerate scenario, they have been suggested as possible progenitors of supernovae (SNe) Type Ia events. In this paper we discuss the detectability of gravitational waves emitted by the inspiral of double white dwarfs. We focus on the constraints that can be derived on the source's luminosity distance, finding that decihertz interferometers can measure this parameter with relative accuracy better than 1% for binaries at 200 Mpc. We explore the possibility of coincident detections of gravitational and electromagnetic signals, the latter coming from the observation of the supernova counterpart. Confirmation of the double degenerate scenario would allow to use distances inferred in the gravitational wave channel to consistently calibrate SNe as standard candles. We show how multi-messenger observatio...
Monthly Notices of the Royal Astronomical Society: Letters, 2020
The existence of massive stellar black hole binaries (MBHBs), with primary black hole masses $\ge... more The existence of massive stellar black hole binaries (MBHBs), with primary black hole masses $\ge 31 \, \mathrm{ M}_\odot$, was proven by the detection of the gravitational wave (GW) event GW150914 during the first LIGO/Virgo observing run (O1), and successively confirmed by seven additional GW signals discovered in the O1 and O2 data. By adopting the galaxy formation model gamesh coupled with binary population synthesis (BPS) calculations, here we investigate the origin of these MBHBs by selecting simulated binaries compatible in mass and coalescence redshifts. We find that their cosmic birth rates peak in the redshift range 6.5 ≤ z ≤ 10, regardless of the adopted BPS. These MBHBs are then old systems forming in low-metallicity ($Z \sim [0.01\!-\!0.1] \, Z_{\odot }$), low-stellar-mass galaxies, before the end of cosmic reionization, i.e. significantly beyond the peak of cosmic star formation. GW signals generated by coalescing MBHBs open up new possibilities to probe the nature of ...
Quark matter imprint on Gravitational Waves from oscillating stars Abstract We discuss the possib... more Quark matter imprint on Gravitational Waves from oscillating stars Abstract We discuss the possibility that the detection of gravitational waves emitted by compact stars may allow to constrain the MIT bag model of quark matter equation of state. Our results show that the combined knowledge of the frequency of the emitted gravitational wave and of the mass, or the radiation radius, of the source allows one to discriminate between strange stars and neutron stars and set stringent bounds on the bag constants. PACS 04.30.Db · 97.60.Jd · 26.60.+c What is the absolute ground state of matter? A definite answer to this fundamental question is still lacking. Following Bodmer’s seminal paper [1], in 1980s Witten [2] suggested that matter consisting of degenerate up, down and strange quarks, called “strange ” quark matter, might be bound and stable at zero temperature and pressure. This hypotesis, while not being directly verifiable in terrestrial laboratories, may be confirmed by the observat...
Publications of the Astronomical Society of Australia, 2018
With the recent discovery of a dozen dusty star-forming galaxies and around 30 quasars at z > ... more With the recent discovery of a dozen dusty star-forming galaxies and around 30 quasars at z > 5 that are hyper-luminous in the infrared (μ LIR > 1013 L⊙, where μ is a lensing magnification factor), the possibility has opened up for SPICA, the proposed ESA M5 mid-/far-infrared mission, to extend its spectroscopic studies toward the epoch of reionisation and beyond. In this paper, we examine the feasibility and scientific potential of such observations with SPICA’s far-infrared spectrometer SAFARI, which will probe a spectral range (35–230 μm) that will be unexplored by ALMA and JWST. Our simulations show that SAFARI is capable of delivering good-quality spectra for hyper-luminous infrared galaxies at z = 5 − 10, allowing us to sample spectral features in the rest-frame mid-infrared and to investigate a host of key scientific issues, such as the relative importance of star formation versus AGN, the hardness of the radiation field, the level of chemical enrichment, and the proper...
Context. Coalescences of binary white dwarfs represent a copious source of information for gravit... more Context. Coalescences of binary white dwarfs represent a copious source of information for gravitational wave interferometers operating in the decihertz band. Moreover, according to the double degenerate scenario, they have been suggested to be possible progenitors of supernovae (SNe) Type Ia events. Aims. In this paper we discuss the detectability of gravitational waves emitted by the inspiral of double white dwarfs. We focus on the constraints that can be derived on the source’s luminosity distance, and on other binary’s parameters, such as the angular momentum orientation. Methods. We explore the possibility of coincident detections of gravitational and electromagnetic signals; the latter comes from the observation of the supernova counterpart. Confirmation of the double degenerate scenario would allow one to use distances inferred in the gravitational wave channel to consistently calibrate SNe as standard candles. Results. We find that decihertz gravitational wave interferometer...
Using the results of a numerical simulation which follows the evolution, metal enrichment and ene... more Using the results of a numerical simulation which follows the evolution, metal enrichment and energy deposition of both Population III and Population II stars, we predict the redshift dependence of the formation rate of black hole remnants of Population III stars with masses 100 −500M ⊙ and of neutron stars (black holes) remnants of Population II stars with masses 8 − 20M ⊙ (20 − 40M⊙). We describe the gravitational wave spectrum produced by Population III and Population II sources adopting the most appropriate signals available in the literature and we compute the stochastic backgrounds resulting from the cumulative emission of these sources throughout the history of the Universe. With the aim of assessing whether these backgrounds might act as foregrounds for signals generated in the Inflationary epoch, we compare their amplitudes with the sensitivity of currently planned and future ground/space-based interferometers. The predicted Population III background lies in the sensitivity...
Carbon-enhanced metal-poor (CEMP) stars are the living fossils holding records of chemical enrich... more Carbon-enhanced metal-poor (CEMP) stars are the living fossils holding records of chemical enrichment from early generations of stars. In this work, we perform a set of numerical simulations of the enrichment from a supernova (SN) of a first generation of metal-free (Pop III) star and the gravitational collapse of the enriched cloud, considering all relevant cooling/heating processes and chemical reactions as well as the growth of dust grains. We adopt faint SN models for the first time with progenitor masses MPopIII = 13–$80 \ {\rm M_{\bigodot }}$, which yield C-enhanced abundance patterns ([C/Fe] = 4.57–4.75) through mixing and fallback of innermost layers of the ejecta. This model also considers the formation and destruction of dust grains. We find that the metals ejected by the SN can be partly re-accreted by the same dark matter minihalo, and carbon abundance of the enriched cloud A(C) = 3.80–5.06 is lower than the abundance range of observed CEMP stars (A(C) ≳ 6) because the m...
We provide an updated assessment of the fundamental physics potential of LISA. Given the very bro... more We provide an updated assessment of the fundamental physics potential of LISA. Given the very broad range of topics that might be relevant to LISA, we present here a sample of what we view as particularly promising directions, based in part on the current research interests of the LISA scientific community in the area of fundamental physics. We organize these directions through a ``science-first'' approach that allows us to classify how LISA data can inform theoretical physics in a variety of areas. For each of these theoretical physics classes, we identify the sources that are currently expected to provide the principal contribution to our knowledge, and the areas that need further development. The classification presented here should not be thought of as cast in stone, but rather as a fluid framework that is amenable to change with the flow of new insights in theoretical physics.
Coalescences of binary white dwarfs represent a copious source of information for gravitational w... more Coalescences of binary white dwarfs represent a copious source of information for gravitational wave interferometers operating in the decihertz band. Moreover, according to the double degenerate scenario, they have been suggested as possible progenitors of supernovae (SNe) Type Ia events. In this paper we discuss the detectability of gravitational waves emitted by the inspiral of double white dwarfs. We focus on the constraints that can be derived on the source's luminosity distance, finding that decihertz interferometers can measure this parameter with relative accuracy better than 1% for binaries at 200 Mpc. We explore the possibility of coincident detections of gravitational and electromagnetic signals, the latter coming from the observation of the supernova counterpart. Confirmation of the double degenerate scenario would allow to use distances inferred in the gravitational wave channel to consistently calibrate SNe as standard candles. We show how multi-messenger observatio...
Monthly Notices of the Royal Astronomical Society: Letters, 2020
The existence of massive stellar black hole binaries (MBHBs), with primary black hole masses $\ge... more The existence of massive stellar black hole binaries (MBHBs), with primary black hole masses $\ge 31 \, \mathrm{ M}_\odot$, was proven by the detection of the gravitational wave (GW) event GW150914 during the first LIGO/Virgo observing run (O1), and successively confirmed by seven additional GW signals discovered in the O1 and O2 data. By adopting the galaxy formation model gamesh coupled with binary population synthesis (BPS) calculations, here we investigate the origin of these MBHBs by selecting simulated binaries compatible in mass and coalescence redshifts. We find that their cosmic birth rates peak in the redshift range 6.5 ≤ z ≤ 10, regardless of the adopted BPS. These MBHBs are then old systems forming in low-metallicity ($Z \sim [0.01\!-\!0.1] \, Z_{\odot }$), low-stellar-mass galaxies, before the end of cosmic reionization, i.e. significantly beyond the peak of cosmic star formation. GW signals generated by coalescing MBHBs open up new possibilities to probe the nature of ...
Quark matter imprint on Gravitational Waves from oscillating stars Abstract We discuss the possib... more Quark matter imprint on Gravitational Waves from oscillating stars Abstract We discuss the possibility that the detection of gravitational waves emitted by compact stars may allow to constrain the MIT bag model of quark matter equation of state. Our results show that the combined knowledge of the frequency of the emitted gravitational wave and of the mass, or the radiation radius, of the source allows one to discriminate between strange stars and neutron stars and set stringent bounds on the bag constants. PACS 04.30.Db · 97.60.Jd · 26.60.+c What is the absolute ground state of matter? A definite answer to this fundamental question is still lacking. Following Bodmer’s seminal paper [1], in 1980s Witten [2] suggested that matter consisting of degenerate up, down and strange quarks, called “strange ” quark matter, might be bound and stable at zero temperature and pressure. This hypotesis, while not being directly verifiable in terrestrial laboratories, may be confirmed by the observat...
Publications of the Astronomical Society of Australia, 2018
With the recent discovery of a dozen dusty star-forming galaxies and around 30 quasars at z > ... more With the recent discovery of a dozen dusty star-forming galaxies and around 30 quasars at z > 5 that are hyper-luminous in the infrared (μ LIR > 1013 L⊙, where μ is a lensing magnification factor), the possibility has opened up for SPICA, the proposed ESA M5 mid-/far-infrared mission, to extend its spectroscopic studies toward the epoch of reionisation and beyond. In this paper, we examine the feasibility and scientific potential of such observations with SPICA’s far-infrared spectrometer SAFARI, which will probe a spectral range (35–230 μm) that will be unexplored by ALMA and JWST. Our simulations show that SAFARI is capable of delivering good-quality spectra for hyper-luminous infrared galaxies at z = 5 − 10, allowing us to sample spectral features in the rest-frame mid-infrared and to investigate a host of key scientific issues, such as the relative importance of star formation versus AGN, the hardness of the radiation field, the level of chemical enrichment, and the proper...
Context. Coalescences of binary white dwarfs represent a copious source of information for gravit... more Context. Coalescences of binary white dwarfs represent a copious source of information for gravitational wave interferometers operating in the decihertz band. Moreover, according to the double degenerate scenario, they have been suggested to be possible progenitors of supernovae (SNe) Type Ia events. Aims. In this paper we discuss the detectability of gravitational waves emitted by the inspiral of double white dwarfs. We focus on the constraints that can be derived on the source’s luminosity distance, and on other binary’s parameters, such as the angular momentum orientation. Methods. We explore the possibility of coincident detections of gravitational and electromagnetic signals; the latter comes from the observation of the supernova counterpart. Confirmation of the double degenerate scenario would allow one to use distances inferred in the gravitational wave channel to consistently calibrate SNe as standard candles. Results. We find that decihertz gravitational wave interferometer...
Using the results of a numerical simulation which follows the evolution, metal enrichment and ene... more Using the results of a numerical simulation which follows the evolution, metal enrichment and energy deposition of both Population III and Population II stars, we predict the redshift dependence of the formation rate of black hole remnants of Population III stars with masses 100 −500M ⊙ and of neutron stars (black holes) remnants of Population II stars with masses 8 − 20M ⊙ (20 − 40M⊙). We describe the gravitational wave spectrum produced by Population III and Population II sources adopting the most appropriate signals available in the literature and we compute the stochastic backgrounds resulting from the cumulative emission of these sources throughout the history of the Universe. With the aim of assessing whether these backgrounds might act as foregrounds for signals generated in the Inflationary epoch, we compare their amplitudes with the sensitivity of currently planned and future ground/space-based interferometers. The predicted Population III background lies in the sensitivity...
Carbon-enhanced metal-poor (CEMP) stars are the living fossils holding records of chemical enrich... more Carbon-enhanced metal-poor (CEMP) stars are the living fossils holding records of chemical enrichment from early generations of stars. In this work, we perform a set of numerical simulations of the enrichment from a supernova (SN) of a first generation of metal-free (Pop III) star and the gravitational collapse of the enriched cloud, considering all relevant cooling/heating processes and chemical reactions as well as the growth of dust grains. We adopt faint SN models for the first time with progenitor masses MPopIII = 13–$80 \ {\rm M_{\bigodot }}$, which yield C-enhanced abundance patterns ([C/Fe] = 4.57–4.75) through mixing and fallback of innermost layers of the ejecta. This model also considers the formation and destruction of dust grains. We find that the metals ejected by the SN can be partly re-accreted by the same dark matter minihalo, and carbon abundance of the enriched cloud A(C) = 3.80–5.06 is lower than the abundance range of observed CEMP stars (A(C) ≳ 6) because the m...
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