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Ground-based gravitational wave detection and its implications
Kang Gungwon 한국물리학회 2021 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.78 No.10
A bit of historical review is given for the concept of gravitational waves and detection experiments. In the presence of gravitational waves, it is frequently asked whether the laser light gets stretched and shrunk in the same way as the mirror distances in the interferometer so that gravitational waves cannot be measured. To answer this question, we have reviewed the interaction between light and gravitational waves carefully in both the transverse-traceless (TT) gauge and the proper detector or locally Lorentz frame. In the TT frame, the laser light directly interacts with gravitational waves, its frequency gets modified, but mirrors remain at rest to the linear order of a gravitational wave perturbation. In the detector frame, on the other hand, the frequency of light does not change while “distances” between the beam splitter and the mirrors get modified. Recent results for gravitational wave observations up to the first half of the third observation run in the advanced LIGO and the advanced Virgo are briefly summarized. Tests of general relativity based on gravitational wave data observed during O1 and O2 are described. These tests include residual and inspiral–merger–ringdown signal consistency tests, parameterized deviations in the waveform model, and constraint on the speed of gravitational waves by comparisons with the propagation of the electro-magnetic counterpart observed in the binary neutron star merger event. Some interesting events observed during O3a are also discussed.
Equation of State in the Presence of Gravity
Hyeong-Chan Kim,Gungwon Kang 한국물리학회 2016 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.69 No.10
We investigate how an equation of state for matter is affected when a gravity is present. For this purpose, we consider a box of ideal gas in the presence of Newtonian gravity. In addition to the ordinary thermodynamic quantities, a characteristic variable that represents a weight per unit area relative to the average pressure is required in order to describe a macroscopic state of the gas. Although the density and the pressure are not uniform due to the presence of gravity, the ideal gas law itself is satisfied for the thermodynamic quantities when averaged over the system. Assuming that the system follows an adiabatic process further, we obtain a new relation between the averaged pressure and density, which differs from the conventional equation of state for the ideal gas in the absence of gravity. Applying our results to a small volume in a Newtonian star, however, we find that the conventional one is reliable for most astrophysical situations when the characteristic scale is small. On the other hand, gravity effects become significant near the surface of a Newtonian star.