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Register a new userGravitational Waves from merging binaries
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Added by
Jasjeet Singh Bagla
Publication date
2019
fields
Physics
and research's language is
English
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We discuss gravitational waves from merging binaries using a Newtonian approach with some inputs from the Post-Newtonian formalism. We show that it is possible to understand the key features of the signal using fundamental physics and also demonstrate that an approximate calculation gives us the correct order of magnitude estimate of the parameters describing the merging binary system. We build on this analysis to understand the range for different types of sources for given detector sensitivity. We also consider known binary pulsar systems and discuss the expected gravitational wave signal from these.
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In this review, I give a summary of the history of our understanding of gravitational waves and how compact binaries were used to transform their status from mathematical artefact to physical reality. I also describe the types of compact (stellar) binaries that LISA will observe as soon as it is switched on. Finally, the status and near future of LIGO, Virgo and GEO are discussed, as well as the expected detection rates for the Advanced detectors, and the accuracies with which binary parameters can be determined when BH/NS inspirals are detected.
The Advanced LIGO and Virgo gravitational wave observatories have opened a new window with which to study the inspiral and mergers of binary compact objects. These observations are most powerful when coordinated with multi-messenger observations. This was underlined by the first observation of a binary neutron star merger GW170817, coincident with a short Gamma-ray burst, GRB170817A, and the identification of the host galaxy NGC~4993 from the optical counterpart AT~2017gfo. Finding the fast-fading optical counterpart critically depends on the rapid production of a sky-map based on LIGO/Virgo data. Currently, a rapid initial sky map is produced followed by a more accurate, high-latency, $gtrsimSI{12}{hr}$ sky map. We study optimization choices of the Bayesian prior and signal model which can be used alongside other approaches such as reduced order quadrature. We find these yield up to a $60%$ reduction in the time required to produce the high-latency localisation for binary neutron star mergers.
The transformation of powerful gravitational waves, created by the coalescence of massive black hole binaries, into electromagnetic radiation in external magnetic fields is revisited. In contrast to the previous calculations of the similar effect, we study the realistic case of the gravitational radiation frequency below the plasma frequency of the surrounding medium. The gravitational waves propagating in the plasma constantly create electromagnetic radiation dragging it with them, despite the low frequency. The plasma heating by the unattenuated electromagnetic wave may be significant in a hot rarefied plasma with strong magnetic field and can lead to a noticeable burst of electromagnetic radiation with higher frequency. The graviton-to-photon conversion effect in plasma is discussed in the context of possible electromagnetic counterparts of GW150914 and GW170104.
We summarize the observations of the spin periods of rapidly accreting neutron stars. If gravitational radiation is responsible for balancing the accretion torque at the observed spin frequencies of ~300 Hz, then the brightest of these systems make excellent gravitational wave sources for LIGO-II and beyond. We review the recent theoretical progress on two mechanisms for gravitational wave emission: mass quadrupole radiation from deformed neutron star crusts and current quadrupole radiation from r-mode pulsations in neutron star cores.
Some fraction of compact binaries that merge within a Hubble time may have formed from two massive stars in isolation. For this isolated-binary formation channel, binaries need to survive two supernova (SN) explosions in addition to surviving common-envelope evolution. For the SN explosions, both the mass loss and natal kicks change the orbital characteristics, producing either a bound or unbound binary. We show that gravitational waves (GWs) may be produced not only from the core-collapse SN process, but also from the SN mass loss and SN natal kick during the pre-SN to post-SN binary transition. We model the dynamical evolution of a binary at the time of the second SN explosion with an equation of motion that accounts for the finite timescales of the SN mass loss and the SN natal kick. From the dynamical evolution of the binary, we calculate the GW burst signals associated with the SN natal kicks. We find that such GW bursts may be of interest to future mid-band GW detectors like DECIGO. We also find that the energy radiated away from the GWs emitted due to the SN mass loss and natal kick may be a significant fraction, ${gtrsim}10%$, of the post-SN binarys orbital energy. For unbound post-SN binaries, the energy radiated away in GWs tends to be higher than that of bound binaries.
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