We study neutrino production, propagation, and oscillations within an extremely magnetized background of finite-temperature nuclear matter. We focus on three particularly interesting cases and identify the astrophysical scenarios where such a signal may be found. The first case involves nuclear matter with electrons, and it is found during the central-engine stage of, both, short and long gamma-ray bursts (GRBs). Thus, for the short GRB case it will also be associated to gravitational-wave events where there is an electromagnetic counterpart (e.g., GW170817). The second and third scenarios involve the presence of strange-quark matter (SQM). The second scenario occurs if SQM can become negatively charged (SQM$^-$; which may only occur at high pressure) and, thus, it is embedded in a positron plasma. The third case may be found at the interphase where SQM transitions from positive (SQM$^+$) to negative; here, positrons and electrons may constantly annihilate and give a distinctive neutrino signature. Therefore, this may also be a signature of the existence of strange stars. Given the wide range of magnetic fields we find in the literature, we also briefly discuss the maximum limit that a stellar mass compact object may posses.
Neutron star (NS) mergers provide us with information rich in physics using multi-messenger astrophysical observations. One of the probable remnants of such a merger is a differentially rotating hot hypermassive neutron star. The stability of the merger remnant depends crucially on the underlying Equation of State (EoS) and thus provides a method to probe the nature of dense matter in NSs. In this work, we search for possible signatures of strangeness containing matter in the NS interior on the secular stability of the merger remnant. We also use recently proposed methods to make a rough estim…
During the in-spiral stage of a compact binary, a wind bubble could be blown into interstellar medium, if the electromagnetic radiation due to the binary orbital motion is strong enough. Therefore, short gamma-ray bursts (SGRBs) due to double neutron star mergers would in principle happen in a wind bubble environment, which can influence the propagation of the SGRB jet and the consequent afterglow emission. By calculating the dynamics and synchrotron radiation of the jet-driven external shock, we reveal that an abrupt jump could appear in the afterglow light curves of SGRBs and the observation…
Distinct Signatures of the Nature of Phase Transition in Binary Neutron Star Mergers
Indian Institute of Science Education and Research Bhopal（印度科学教育研究所博帕尔分校）；National Institute for Physics and Nuclear Engineering (IFIN-HH)（罗马尼亚核物理与工程国家研究所）；School of Physical Sciences, National Institute of Science Education and Research, An OCC of Homi Bhabha National Institute（科学教育国家研究所物理科学学院（霍米·巴哈国家研究所附属机构））；Department of Physics, Indian Institute of Technology Delhi（印度德里理工学院物理系）
Recent gravitational wave (GW) observations by LIGO/Virgo show evidence for hierarchical mergers, where the merging BHs are the remnants of previous BH merger events. These events may carry important clues about the astrophysical host environments of the GW sources. In this paper, we present the distributions of the effective spin parameter ($χ_\mathrm{eff}$), the precession spin parameter ($χ_\mathrm{p}$), and the chirp mass ($m_\mathrm{chirp}$) expected in hierarchical mergers. Under a wide range of assumptions, hierarchical mergers produce (i) a monotonic increase of the average of the typi…
Black hole - neutron star (BH-NS) mergers are a major target for ground-based gravitational wave (GW) observatories. A merger can also produce an electromagnetic counterpart (a kilonova) if it ejects neutron-rich matter that assembles into heavy elements through r-process nucleosynthesis. We study the kilonova signatures of the unbound dynamical ejecta of a BH-NS merger. We take as our initial state the results from a numerical relativity simulation, and then use a general relativistic hydrodynamics code to study the evolution of the ejecta with parameterized r-process heating models. The unbo…
While no consensus governs our understanding of the origin of low redshift radio galaxies, the possibility that mergers may trigger accretion from hot cluster halo gas has spurred a recent search for such signatures. Evidence for mergers is at best tenuous, however, and even when found, generates more questions than answers. With scant evidence for minor mergers, some connection to major mergers is found in isolated environments but not where one would expect, i.e. in clusters. We provide an explanation for these recent results by Gordon et al (2019) on the relevance of major mergers in low ex…
GRB 080503 late afterglow re-brightening: signature of a magnetar powered merger-nova
GRB 080503是一个由\emph{Swift}探测到的短伽马射线暴（GRB），被归类为致密恒星合并源GRB。在X射线和光学余辉光变曲线中的软扩展发射和同时的后期再增亮引起了关于其物理起源的有趣问题。我们发现，GRB 080503的宽带数据可以很好地解释在双中子星合并模型的框架内，提供的合并残余物是一个快速旋转的大质量中子星具有极高的磁场（即毫秒磁星）。我们表明，后期的光学再增亮是一致的发射从磁星供电的“合并新星”。这为与短伽玛暴相关的并合新星的不断增长的样本又增加了一个案例。软扩展发射和晚期X射线过量发射通过磁星偶极自旋下降光度演化函数很好地联系在一起，表明直接磁耗散是产生这些X射线的机制。X射线辐射最初是从被短伽玛射线暴喷流刺穿的合并喷出物中的一个洞泄漏出来的。在磁星向下旋转并且磁压力下降到冲压压力以下之后，孔随后关闭。然后X射线光子被捕获在合并新星喷出物的后面，直到喷出物在稍后的时间变得光学薄。这解释了光学和X射线光变曲线中基本上同时发生的再增亮。在这个模型中，未来的引力波源可能与一个明亮的X射线对应物以及合并新星相关联，即使短的伽马射线暴喷流远离地球。
The gravitational wave event GW170817 associated with the short gamma-ray burst (GRB) 170817A confirms that binary neutron star (BNS) mergers are one of the origins of short GRBs. The associated kilonova emission, radioactively powered by nucleosynthesized heavy elements, was also detected. Black hole-neutron star (BH-NS) mergers have been argued to be another promising origin candidate of short GRBs and kilonovae. Numerical simulations show that the ejecta in BH-NS mergers is geometrically much more anisotropic than the BNS merger case. In this paper, we investigate observational signatures o…
Pair instability supernovae are thought to restrict the formation of black holes in the mass range ~50 - 135 solar masses. However, black holes with masses within this "high mass gap" are expected to form as the remnants of binary black hole mergers. These remnants can merge again dynamically in densely populated environments such as globular clusters. The hypothesis that the binary black hole merger GW190521 formed dynamically is supported by its high mass. Orbital eccentricity can also be a signature of dynamical formation, since a binary that merges quickly after becoming bound may not circ…
We review theoretical findings, astrophysical modeling, and current gravitational-wave evidence of hierarchical stellar-mass black-hole mergers. While most of the compact binary mergers detected by LIGO and Virgo are expected to consist of first-generation black holes formed from the collapse of stars, others might instead be of second (or higher) generation, containing the remnants of previous black-hole mergers. Such a subpopulation of hierarchically assembled black holes presents distinctive gravitational-wave signatures, namely higher masses, possibly within the pair-instability mass gap, …
With the first detection of gravitational waves from a binary system of neutron stars, GW170817, a new window was opened to study the properties of matter at and above nuclear-saturation density. Reaching densities a few times that of nuclear matter and temperatures up to $100\,\rm{MeV}$, such mergers also represent potential sites for a phase transition (PT) from confined hadronic matter to deconfined quark matter. While the lack of a postmerger signal in GW170817 has prevented us from assessing experimentally this scenario, two theoretical studies have explored the postmerger gravitational-w…
The joint detection of gravitational waves and the gamma-ray counterpart of a binary neutron star merger event, GW170817, unambiguously validates the connection between short gamma-ray bursts and compact binary object (CBO) mergers. We focus on a special scenario where short gamma-ray bursts produced by CBO mergers are embedded in disks of active galactic nuclei (AGN), and we investigate the $γ$-ray emission produced in the internal dissipation region via synchrotron, synchrotron self-Compton and external inverse-Compton (EIC) processes. In this scenario, isotropic thermal photons from the AGN…
(abridged) We investigate the quark deconfinement phase transition in the context of binary neutron star (BNS) mergers. We employ a new finite-temperature composition-dependent equation of state (EOS) with a first order phase transition between hadrons and deconfined quarks to perform numerical relativity simulations of BNS mergers. The softening of the EOS due to the phase transition causes the merger remnants to be more compact and to collapse to a black hole (BH) at earlier times. The phase transition is imprinted on the postmerger gravitational wave (GW) signal duration, amplitude, and pea…
Neutron star mergers (NSMs) are the first verified sites of rapid neutron capture (r-process) nucleosynthesis, and could emit gamma rays from the radioactive isotopes synthesized in the neutron-rich ejecta. These MeV gamma rays may provide a unique and direct probe of the NSM environment as well as insight into the nature of the r process, just as observed gammas from the 56Ni radioactive decay chain provide a window into supernova nucleosynthesis. In this work, we include the photons from fission processes for the first time in estimates of the MeV gamma-ray signal expected from an NSM event.…
Signatures of a subpopulation of hierarchical mergers in the GWTC-4 gravitational-wave dataset
LIGO Laboratory, Massachusetts Institute of Technology（麻省理工学院 LIGO 实验室）；Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology（麻省理工学院卡弗里天体物理与空间研究研究所）；Department of Physics, Massachusetts Institute of Technology（麻省理工学院物理系）；Williams College（威廉姆斯学院）；Adler Planetarium（阿德勒天文馆）；NSF-Simons AI Institute for the Sky (SkAI)（NSF-Simons 天空人工智能研究所）
Merging binaries of neutron stars are not only strong sources of gravitational waves, but also have the potential of revealing states of matter at densities and temperatures not accessible in laboratories. A crucial and long-standing question in this context is whether quarks are deconfined as a result of the dramatic increase in density and temperature following the merger. We present the first fully general-relativistic simulations of merging neutron stars including quarks at finite temperatures that can be switched off consistently in the equation of state. Within our approach, we can deter…
Spinning down neutron-star merger remnants with the Tayler-Spruit dynamo: Global simulations reveal the formation of massive disks and neutron-rich ejecta
California Institute of Technology（加州理工学院）；Walter Burke Institute for Theoretical Physics, California Institute of Technology（加州理工学院沃尔特·伯克理论物理研究所）
Magnetohydrodynamic (MHD) turbulence in neutron star (NS) merger remnants can impact their evolution and multimessenger signatures, complicating the interpretation of present and future observations. Due to the high Reynolds numbers and the large computational costs of numerical relativity simulations, resolving all the relevant scales of the turbulence will be impossible for the foreseeable future. Here, we adopt a method to include subgrid-scale turbulence in moderate resolution simulations by extending the large-eddy simulation (LES) method to general relativity (GR). We calibrate our subgr…
The production of both gravitational waves and short gamma-ray bursts (sGRBs) is widely associated with the merger of compact objects. Several studies have modelled the evolution of the electromagnetic emission using the synchrotron emission produced by the deceleration of both a relativistic top-hat jet seen off-axis, and a wide-angle quasi-spherical outflow (both using numerical studies). In this study we present an analytical model of the synchrotron and synchrotron self-Compton (SSC) emission for an off-axis top-hat jet and a quasi-spherical outflow. We calculate the light curves obtained …
We describe an unambiguous gravitational-wave signature to identify the occurrence of a strong phase transition from hadronic matter to deconfined quark matter in neutron star mergers. Such a phase transition leads to a strong softening of the equation of state and hence to more compact merger remnants compared to purely hadronic models. If a phase transition takes place during merging, this results in a characteristic increase of the dominant postmerger gravitational-wave frequency relative to the tidal deformability characterizing the inspiral phase. By comparing results from different purel…
Type Ia supernovae from violent mergers of carbon-oxygen white dwarfs: polarisation signatures
两颗碳氧白矮星的剧烈合并被认为是某些Ia型超新星的可能祖先。然而，有人认为，这种模型产生的强烈的喷出物不对称性可能与Ia型超新星爆炸中通常观察到的低偏振度不一致。在这里，我们通过对Pakmor等人（2012）提出的模型进行分光偏振分析来验证这一说法，该模型是在1.1 M $_{\odot}$和0.9 M $_{\odot}$碳氧白矮星双星系统合并期间触发的爆炸。由于喷出物的不对称性，偏振信号随视角显著变化。我们发现，在赤道平面的观察员的偏振水平是适度的（$\lesssim$ 1%），并显示出明确的证据，作为一个主导轴，作为一个后果的喷出物对称的轨道平面。相反，平面外的取向与更高程度的偏振和偏离主轴相关联。虽然这里研究的特定模型与SN 2004dt等高度极化事件有很好的匹配，但它很难再现正常Ia型超新星中常见的低极化水平。具体来说，我们发现，元素分布的显着不对称性导致了丰富的强偏振功能，没有观察到在大多数目前可用的光谱偏振数据的Ia型超新星。未来的研究将绘制出合并情景的参数空间，以调查替代模型是否可以提供与观测更好的一致性。
We present fully relativistic predictions for the electromagnetic emission produced by accretion disks surrounding spinning and nonspinning supermassive binary black holes on the verge of merging. We use the code Bothros to post-process data from 3D general relativistic magnetohydrodynamic simulations via ray-tracing calculations. These simulations model the dynamics of a circumbinary disk and the mini-disks that form around two equal-mass black holes orbiting each other at an initial separation of 20 gravitational radii, and evolve the system for more than 10 orbits in the inspiral regime. We…
We study the properties of the galaxies hosting the first 19 tidal disruption events (TDEs) detected with the Zwicky Transient Facility (ZTF) within the context of a carefully constructed, representative host galaxy sample. We find that the ZTF sample of TDE hosts is dominated by compact "green valley" galaxies. After we restrict the comparison sample to galaxies with a similar concentration, as measured by Sersic index, we find this green valley over representation is even larger. That is, concentrated red sequence galaxies are not producing TDEs at elevated levels. We present host galaxy spe…
Fast material ejected dynamically over $<10$ ms during the merger of a binary neutron-star (BNS) system can give rise to distinctive electromagnetic counterparts to the system's gravitational-wave emission that can serve as a "smoking gun" to distinguish between a BNS and a NS-black-hole merger. We present novel ab-initio modeling of the associated kilonova precursor and kilonova afterglow based on three-dimensional general-relativistic magneto-hydrodynamic simulations of BNS mergers with tabulated, composition-dependent, finite-temperature equations of state (EOSs), weak interactions, and app…
The Electromagnetic Counterpart of the Binary Neutron Star Merger LIGO/VIRGO GW170817. IV. Detection of Near-infrared Signatures of r-process Nucleosynthesis with Gemini-South
The recent detection of gravitational waves and electromagnetic counterparts from the double neutron star merger event GW+EM170817, supports the standard paradigm of short gamma-ray bursts (SGRBs) and kilonovae/macronovae. It is important to reveal the nature of the compact remnant left after the merger, either a black hole or neutron star, and their physical link to the origin of the long-lasting emission observed in SGRBs. The diversity of the merger remnants may also lead to different kinds of transients that can be detected in future. Here we study the high-energy emission from the long-la…
We review the prospects for detecting quark matter in neutron star cores. We survey the proposed signatures and emphasize the importance of data from neutron star mergers, which provide access to dynamical properties that operate on short timescales that are not probed by other neutron star observables.
Synergetic observations of multi-band coincidence signals from merging neutron stars have definitively marked the significance of multi-messenger astronomy. We present a new generic signature of neutron star mergers, positron emission and the associated 511 keV radiation, produced from ejected neutron-rich radioactive merger material. Accounting for historical neutron star mergers within the Milky Way allows to readily explain the origin of the long-observed 511 keV emission line from the Galactic Center. Further, we draw a direct link between heavy element production ($r$-process nucleosynthe…
