Nuclear physics aspects of the GW170817 neutron star merger event

High-energy astrophysics plays an increasingly important role in the understanding of our universe. On one hand, this is due to ground-breaking observations, like the gravitational-wave detections of the LIGO and Virgo network or the black-hole shadow observations of the EHT collaboration. On the other hand, the field of numerical relativity has reached a level of sophistication that allows for realistic simulations that include all four fundamental forces of nature. A prime example of how observations and theory complement each other can be seen in the studies following GW170817, the first detection of gravitational waves from a binary neutron-star merger. The same detection is also the chronological starting point of this Thesis. The plethora of information and constraints on nuclear physics derived from GW170817 in conjunction with theoretical computations will be presented in the first part of this Thesis. The second part goes beyond this detection and prepares for future observations when also the high-frequency postmerger signal will become detectable. Specifically, signatures of a quark-hadron phase transition are discussed and the specific case of a delayed phase transition is analyzed in detail. Finally, the third part of this Thesis focuses on the inclusion of radiative transport in numerical astrophysics. In the context of binary neutron-star mergers, radiation in the form of neutrinos is crucial for realistic long-term simulations. Two methods are introduced for treating radiation: the approximate state-of-the-art two-moment method (M1) and the recently developed radiative Lattice-Boltzmann method. The latter promises to be more accurate than M1 at a comparable computational cost. Given that most methods for radiative transport or either inaccurate or unfeasible, the derivation of this new method represents a novel and possibly paradigm-changing contribution to an accurate inclusion of radiation in numerical astrophysics.

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Gamma-Ray Bursts and Binary Neutron Star Mergers

Symposium - International Astronomical Union ◽

10.1017/s0074180900055959 ◽

1996 ◽

Vol 165 ◽

pp. 489-502

Author(s):

Tsvi Piran

Keyword(s):

Neutron Star ◽

Gravitational Radiation ◽

Gamma Ray ◽

Indirect Evidence ◽

Gamma Ray Bursts ◽

Binary Neutron Star ◽

Merger Event ◽

Γ Rays ◽

Γ Ray ◽

The One

Neutron star binaries, such as the one observed in the famous binary pulsar PSR 1913+16, end their life in a catastrophic merger event (denoted here NS2M). The merger releases ∼5 1053 ergs, mostly as neutrinos and gravitational radiation. A small fraction of this energy suffices to power γ-ray bursts (GRBs) at cosmological distances. Cosmological GRBs must pass, however, an optically thick fireball phase and the observed γ rays emerge only at the end of this phase. Hence, it is difficult to determine the nature of the source from present observations (the agreement between the rates of GRBs and NS2Ms providing only indirect evidence for this model). In the future a coinciding detection of a GRB and a gravitational-radiation signal could confirm this model.

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LOFAR 144-MHz follow-up observations of GW170817

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa950 ◽

2020 ◽

Vol 494 (4) ◽

pp. 5110-5117

Author(s):

J W Broderick ◽

T W Shimwell ◽

K Gourdji ◽

A Rowlinson ◽

S Nissanke ◽

...

Keyword(s):

Neutron Star ◽

Low Frequency ◽

Radio Spectrum ◽

Central Frequency ◽

Binary Neutron Star ◽

Upper Limit ◽

Upper Limits ◽

Maximum Elevation ◽

Merger Event

ABSTRACT We present low-radio-frequency follow-up observations of AT 2017gfo, the electromagnetic counterpart of GW170817, which was the first binary neutron star merger to be detected by Advanced LIGO–Virgo. These data, with a central frequency of 144 MHz, were obtained with LOFAR, the Low-Frequency Array. The maximum elevation of the target is just 13${_{.}^{\circ}}$7 when observed with LOFAR, making our observations particularly challenging to calibrate and significantly limiting the achievable sensitivity. On time-scales of 130–138 and 371–374 d after the merger event, we obtain 3σ upper limits for the afterglow component of 6.6 and 19.5 mJy beam−1, respectively. Using our best upper limit and previously published, contemporaneous higher frequency radio data, we place a limit on any potential steepening of the radio spectrum between 610 and 144 MHz: the two-point spectral index $\alpha ^{610}_{144} \gtrsim$ −2.5. We also show that LOFAR can detect the afterglows of future binary neutron star merger events occurring at more favourable elevations.

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Identifying Quark Matter in Hybrid Stars through Relativistic Tidal Deformations

Universe ◽

10.3390/universe5090193 ◽

2019 ◽

Vol 5 (9) ◽

pp. 193

Author(s):

Bryen Irving ◽

Thomas Klähn ◽

Prashanth Jaikumar ◽

Marc Salinas ◽

Wei Wei

Keyword(s):

Neutron Star ◽

Parameter Space ◽

Quark Matter ◽

Specific Model ◽

Nuclear Model ◽

Hartree Fock ◽

Binary Neutron Star ◽

Merger Event ◽

Hybrid Stars ◽

Parameter Ranges

We study a specific model of neutron star matter that supports a phase transition to quark matter at high density and examine parameter ranges for consistency with the mass-weighted tidal deformability of Λ ˜ = 300 − 230 + 420 for a mass ratio of q ∈ [ 0.73 , 1.0 ] , as inferred from observations of gravitational waves from the binary neutron star merger event GW170817. By using this observation to restrict the parameter space for the equation of state (EoS) model used throughout this study, we aim to assess the possibility of a potential solution to the masquerade and flavor camouflage problems for hybrid EoS models. Assuming the two stars have the same EoS, in which the Dirac-Brueckner-Hartree Fock (DBHF) nuclear model transitions to the vBag quark model, we see if the parameter space of these hybrid model stars are restricted due to the adherence to the reported Λ 1.4 ∈ 70 , 580 and M m a x ∈ [ 2.01 , 2.16 ] M ⊙ constraints. Upon completion, we find that, while the parameter space for our model does get restricted, it does not ultimately resolve the masquerade and flavor camouflage problems.

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A mildly relativistic wide-angle outflow in the neutron-star merger event GW170817

Nature ◽

10.1038/nature25452 ◽

2017 ◽

Vol 554 (7691) ◽

pp. 207-210 ◽

Cited By ~ 172

Author(s):

K. P. Mooley ◽

E. Nakar ◽

K. Hotokezaka ◽

G. Hallinan ◽

A. Corsi ◽

...

Keyword(s):

Neutron Star ◽

Wide Angle ◽

Merger Event

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AT 2018lqh and the Nature of the Emerging Population of Day-scale Duration Optical Transients

The Astrophysical Journal ◽

10.3847/1538-4357/ac24fc ◽

2021 ◽

Vol 922 (2) ◽

pp. 247

Author(s):

E. O. Ofek ◽

S. M. Adams ◽

E. Waxman ◽

A. Sharon ◽

D. Kushnir ◽

...

Keyword(s):

Neutron Star ◽

Late Time ◽

Half Maximum ◽

Radioactive Elements ◽

Stellar Envelope ◽

Star Forming ◽

Circumstellar Material ◽

Photometric Observations ◽

Merger Event ◽

Low Mass

Abstract We report on the discovery of AT 2018lqh (ZTF 18abfzgpl)—a rapidly evolving extragalactic transient in a star-forming host at 242 Mpc. The transient g-band light curve’s duration above a half-maximum light is about 2.1 days, where 0.4/1.7 days are spent on the rise/decay, respectively. The estimated bolometric light curve of this object peaked at about 7 × 1042erg s−1—roughly 7 times brighter than the neutron star (NS)–NS merger event AT 2017gfo. We show that this event can be explained by an explosion with a fast (v ∼ 0.08 c) low-mass (≈0.07 M ⊙) ejecta, composed mostly of radioactive elements. For example, ejecta dominated by 56Ni with a timescale of t 0 ≅ 1.6 days for the ejecta to become optically thin for γ-rays fits the data well. Such a scenario requires burning at densities that are typically found in the envelopes of neutron stars or the cores of white dwarfs. A combination of circumstellar material (CSM) interaction power at early times and shock cooling at late times is consistent with the photometric observations, but the observed spectrum of the event may pose some challenges for this scenario. We argue that the observations are not consistent with a shock breakout from a stellar envelope, while a model involving a low-mass ejecta ramming into low-mass CSM cannot explain both the early- and late-time observations.

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The Nuclear Physics of the Neutron Star Crust

10.22323/1.053.0192 ◽

2009 ◽

Author(s):

Andrew Steiner

Keyword(s):

Neutron Star ◽

Nuclear Physics ◽

Neutron Star Crust

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Collimated outflows from long-lived binary neutron star merger remnants

Monthly Notices of the Royal Astronomical Society Letters ◽

10.1093/mnrasl/slaa062 ◽

2020 ◽

Vol 495 (1) ◽

pp. L66-L70 ◽

Cited By ~ 7

Author(s):

Riccardo Ciolfi

Keyword(s):

Black Hole ◽

Neutron Star ◽

Gamma Ray ◽

Gamma Ray Bursts ◽

Spin Axis ◽

Binary Neutron Star ◽

Physical Conditions ◽

Massive Neutron Star ◽

Merger Event ◽

First Time

ABSTRACT The connection between short gamma-ray bursts (SGRBs) and binary neutron star (BNS) mergers was recently confirmed by the association of GRB 170817A with the merger event GW170817. However, no conclusive indications were obtained on whether the merger remnant that powered the SGRB jet was an accreting black hole (BH) or a long-lived massive neutron star (NS). Here, we explore the latter case via BNS merger simulations covering up to 250 ms after merger. We report, for the first time in a full merger simulation, the formation of a magnetically driven collimated outflow along the spin axis of the NS remnant. For the system at hand, the properties of such an outflow are found largely incompatible with an SGRB jet. With due consideration of the limitations and caveats of our present investigation, our results favour a BH origin for GRB 170817A and SGRBs in general. Even though this conclusion needs to be confirmed by exploring a larger variety of physical conditions, we briefly discuss possible consequences of all SGRB jets being powered by accreting BHs.

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Detecting the Hadron-Quark Phase Transition with Gravitational Waves

Universe ◽

10.3390/universe5060156 ◽

2019 ◽

Vol 5 (6) ◽

pp. 156 ◽

Cited By ~ 5

Author(s):

Matthias Hanauske ◽

Luke Bovard ◽

Elias Most ◽

Jens Papenfort ◽

Jan Steinheimer ◽

...

Keyword(s):

Phase Transition ◽

Neutron Star ◽

Equation Of State ◽

Gravitational Wave ◽

Compact Star ◽

Binary Neutron Star ◽

Interesting Part ◽

Merger Event ◽

Tidal Deformations ◽

Quark Phase

The long-awaited detection of a gravitational wave from the merger of a binary neutron star in August 2017 (GW170817) marks the beginning of the new field of multi-messenger gravitational wave astronomy. By exploiting the extracted tidal deformations of the two neutron stars from the late inspiral phase of GW170817, it is now possible to constrain several global properties of the equation of state of neutron star matter. However, the most interesting part of the high density and temperature regime of the equation of state is solely imprinted in the post-merger gravitational wave emission from the remnant hypermassive/supramassive neutron star. This regime was not observed in GW170817, but will possibly be detected in forthcoming events within the current observing run of the LIGO/VIRGO collaboration. Numerous numerical-relativity simulations of merging neutron star binaries have been performed during the last decades, and the emitted gravitational wave profiles and the interior structure of the generated remnants have been analysed in detail. The consequences of a potential appearance of a hadron-quark phase transition in the interior region of the produced hypermassive neutron star and the evolution of its underlying matter in the phase diagram of quantum cromo dynamics will be in the focus of this article. It will be shown that the different density/temperature regions of the equation of state can be severely constrained by a measurement of the spectral properties of the emitted post-merger gravitational wave signal from a future binary compact star merger event.

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