417 research outputs found
Parameter estimation for strong phase transitions in supranuclear matter using gravitational-wave astronomy
At supranuclear densities, explored in the core of neutron stars, a strong
phase transition from hadronic matter to more exotic forms of matter might be
present. To test this hypothesis, binary neutron-star mergers offer a unique
possibility to probe matter at densities that we can not create in any existing
terrestrial experiment. In this work, we show that, if present, strong phase
transitions can have a measurable imprint on the binary neutron-star
coalescence and the emitted gravitational-wave signal. We construct a new
parameterization of the supranuclear equation of state that allows us to test
for the existence of a strong phase transition and extract its characteristic
properties purely from the gravitational-wave signal of the inspiraling neutron
stars. We test our approach using a Bayesian inference study simulating 600
signals with three different equations of state and find that for current
gravitational-wave detector networks already twelve events might be sufficient
to verify the presence of a strong phase transition. Finally, we use our
methodology to analyze GW170817 and GW190425, but do not find any indication
that a strong phase transition is present at densities probed during the
inspiral.Comment: 17 pages, 11 figure
Lensed or not lensed: Determining lensing magnifications for binary neutron star mergers from a single detection
Advanced LIGO and Advanced Virgo could observe the first lensed gravitational
wave sources in the coming years, while the future Einstein Telescope could
observe hundreds of lensed events. It is, therefore, crucial to develop
methodologies to distinguish between lensed from unlensed gravitational-wave
observations. A lensed signal not identified as such will lead to biases during
the interpretation of the source. In particular, sources will appear to have
intrinsically higher masses. No robust method currently exists to distinguish
between the magnification bias caused by lensing and intrinsically high-mass
sources. In this work, we show how to recognize lensed and unlensed binary
neutron star systems through the measurement of their tidal effects for highly
magnified sources as a proof-of-principle. The proposed method could be used to
identify lensed binary neutron stars, which are the chief candidate for lensing
cosmography studies. We apply our method on GW190425, finding no evidence in
favor of lensing, mainly due to the poor measurement of the event's tidal
effects. However, we expect that future detections with better tidal
measurements can yield better constraints.Comment: 12 pages, 7 figure
On the Nature of GW190814 and Its Impact on the Understanding of Supranuclear Matter
The observation of a compact object with a mass of 2.50-2.67Me on 2019 August 14, by the LIGO Scientific and Virgo collaborations (LVC) has the potential to improve our understanding of the supranuclear equation of state. While the gravitational-wave analysis of the LVC suggests that GW190814 likely was a binary black hole system, the secondary component could also have been the heaviest neutron star observed to date. We use our previously derived nuclear-physics-multimessenger astrophysics framework to address the nature of this object. Based on our findings, we determine GW190814 to be a binary black hole merger with a probability of >99.9%. Even if we weaken previously employed constraints on the maximum mass of neutron stars, the probability of a binary black hole origin is still ∼81%. Furthermore, we study the impact that this observation has on our understanding of the nuclear equation of state by analyzing the allowed region in the mass-radius diagram of neutron stars for both a binary black hole or neutron star-black hole scenario. We find that the unlikely scenario in which the secondary object was a neutron star requires rather stiff equations of state with a maximum speed of sound cs ≥0.6 times the speed of light, while the binary black hole scenario does not offer any new insight
Multimessenger constraints on the neutron-star equation of state and the Hubble constant
Observations of neutron-star mergers with distinct messengers, including gravitational waves and electromagnetic signals, can be used to study the behavior of matter denser than an atomic nucleus and to measure the expansion rate of the Universe as quantified by the Hubble constant. We performed a joint analysis of the gravitational-wave event GW170817 with its electromagnetic counterparts AT2017gfo and GRB170817A, and the gravitational-wave event GW190425, both originating from neutron-star mergers. We combined these with previous measurements of pulsars using X-ray and radio observations, and nuclear-theory computations using chiral effective field theory, to constrain the neutron-star equation of state. We found that the radius of a 1:4-solar mass neutron star is 11:75þ0:86_0:81 km at 90% confidence and the Hubble constant is 66:2þ4:4_4:2 at 1s uncertainty
Generic searches for alternative gravitational wave polarizations with networks of interferometric detectors
The detection of gravitational wave signals by Advanced LIGO and Advanced
Virgo enables us to probe the polarization content of gravitational waves. In
general relativity, only tensor modes are present, while in a variety of
alternative theories one can also have vector or scalar modes. Recently test
were performed which compared Bayesian evidences for the hypotheses that either
purely tensor, purely vector, or purely scalar polarizations were present.
Indeed, with only three detectors in a network and allowing for mixtures of
tensor polarizations and alternative polarization states, it is not possible to
identify precisely which non-standard polarizations might be in the signal and
by what amounts. However, we demonstrate that one can still infer whether, in
addition to tensor polarizations, alternative polarizations are present in the
first place, irrespective of the detailed polarization content. We develop two
methods to do this for sources with electromagnetic counterparts, both based on
the so-called null stream. Apart from being able to detect mixtures of tensor
and alternative polarizations, these have the added advantage that no waveform
models are needed, and signals from any kind of transient source with known sky
position can be used. Both formalisms allow us to combine information from
multiple sources so as to arrive at increasingly more stringent bounds. For now
we apply these on the binary neutron star signal GW170817, showing consistency
with the tensor-only hypothesis with p-values of 0.315 and 0.790 for the two
methods.Comment: 8 pages, 3 figure
Generic searches for alternative gravitational wave polarizations with networks of interferometric detectors
The detection of gravitational wave signals by Advanced LIGO and Advanced Virgo enables us to probe the polarization content of gravitational waves. In general relativity, only tensor modes are present, while in a variety of alternative theories one can also have vector or scalar modes. Recently test were performed which compared Bayesian evidences for the hypotheses that either purely tensor, purely vector, or purely scalar polarizations were present. Indeed, with only three detectors in a network and allowing for mixtures of tensor polarizations and alternative polarization states, it is not possible to identify precisely which nonstandard polarizations might be in the signal and by what amounts. However, we demonstrate that one can still infer whether, in addition to tensor polarizations, alternative polarizations are present in the first place, irrespective of the detailed polarization content. We develop two methods to do this for sources with electromagnetic counterparts, both based on the so-called null stream. Apart from being able to detect mixtures of tensor and alternative polarizations, these have the added advantage that no waveform models are needed, and signals from any kind of transient source with known sky position can be used. Both formalisms allow us to combine information from multiple sources so as to arrive at increasingly more stringent bounds. For now we apply these on the binary neutron star signal GW170817, showing consistency with the tensor-only hypothesis with p-values of 0.315 and 0.790 for the two methods
Probing Quarkyonic Matter in Neutron Stars with the Bayesian Nuclear-Physics Multi-Messenger Astrophysics Framework
The interior of neutron stars contains matter at the highest densities
realized in our Universe. Interestingly, theoretical studies of dense matter,
in combination with the existence of two solar mass neutron stars, indicate
that the speed of sound has to increase to values well above the
conformal limit () before decreasing again at higher densities.
The decrease could be explained by either a strong first-order phase transition
or a cross-over transition from hadronic to quark matter. The latter scenario
leads to a pronounced peak in the speed of sound reaching values above the
conformal limit, naturally explaining the inferred behavior. In this work, we
use the Nuclear-Physics Multi-Messenger Astrophysics framework \textsc{NMMA} to
compare predictions of the quarkyonic matter model with astrophysical
observations of neutron stars, with the goal of constraining model parameters.
Assuming quarkyonic matter to be realized within neutron stars, we find that
there can be a significant amount of quarks inside the core of neutron stars
with masses in the two solar mass range, amounting to up to ,
contributing of the total mass. Furthermore, for the quarkyonic
matter model investigated here, the radius of a neutron star would
be km, at credibility,
without (with) the inclusion of AT2017gfo.Comment: 14 pages, 9 figure
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