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Register a new userContinuous gravitational wave from magnetized white dwarfs and neutron stars: possible missions for LISA, DECIGO, BBO, ET detectors
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Recent detection of gravitational wave from nine black hole merger events and one neutron star merger event by LIGO and VIRGO shed a new light in the field of astrophysics. On the other hand, in the past decade, a few super-Chandrasekhar white dwarf candidates have been inferred through the peak luminosity of the light-curves of a few peculiar type Ia supernovae, though there is no direct detection of these objects so far. Similarly, a number of neutron stars with mass $>2M_odot$ have also been observed. Continuous gravitational wave can be one of the alternate ways to detect these compact objects directly. It was already argued that magnetic field is one of the prominent physics to form super-Chandrasekhar white dwarfs and massive neutron stars. If such compact objects are rotating with certain angular frequency, then they can efficiently emit gravitational radiation, provided their magnetic field and rotation axes are not aligned, and these gravitational waves can be detected by some of the upcoming detectors, e.g. LISA, BBO, DECIGO, Einstein Telescope etc. This will certainly be a direct detection of rotating magnetized white dwarfs as well as massive neutron stars.
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Recent evidence of super-Chandrasekhar white dwarfs (WDs), from the observations of over-luminous type Ia supernovae (SNeIa), has been a great astrophysical discovery. However, no such massive WDs have so far been observed directly as their luminosities are generally quite low. Hence it immediately raises the question of whether there is any possibility of detecting them directly. The search for super-Chandrasekhar WDs is very important as SNeIa are used as standard candles in cosmology. In this article, we show that continuous gravitational wave can allow us to detect such super-Chandrasekhar WDs directly.
After the prediction of many sub- and super-Chandrasekhar (at least a dozen for the latter) limiting mass white dwarfs, hence apparently peculiar class of white dwarfs, from the observations of luminosity of type Ia supernovae, researchers have proposed various models to explain these two classes of white dwarfs separately. We earlier showed that these two peculiar classes of white dwarfs, along with the regular white dwarfs, can be explained by a single form of the f(R) gravity, whose effect is significant only in the high-density regime, and it almost vanishes in the low-density regime. However, since there is no direct detection of such white dwarfs, it is difficult to single out one specific theory from the zoo of modified theories of gravity. We discuss the possibility of direct detection of such white dwarfs in gravitational wave astronomy. It is well-known that in f(R) gravity, more than two polarization modes are present. We estimate the amplitudes of all the relevant modes for the peculiar as well as the regular white dwarfs. We further discuss the possibility of their detections through future-based gravitational wave detectors, such as LISA, ALIA, DECIGO, BBO, or Einstein Telescope, and thereby put constraints or rule out various modified theories of gravity. This exploration links the theory with possible observations through gravitational wave in f(R) gravity.
In about last couple of decades, the inference of the violation of the Chandrasekhar mass-limit of white dwarfs from indirect observation is probably a revolutionary discovery in astronomy. Various researchers have already proposed different theories to explain this interesting phenomenon. However, such massive white dwarfs usually possess very little luminosity, and hence they, so far, cannot be detected directly by any observations. We have already proposed that the continuous gravitational wave may be one of the probes to detect them directly, and in the future, various space-based detectors such as LISA, DECIGO, and BBO, should be able to detect many of those white dwarfs (provided they behave like pulsars). In this paper, we address various timescales related to the emission of gravitational as well as dipole radiations. This exploration sets a timescale for the detectors to observe the massive white dwarfs.
We perform population synthesis simulations for Population III (Pop III) coalescing binary neutron stars (NS-NSs), neutron star - black hole binaries (NS-BHs), and binary black holes (BH-BHs) which merge within the age of the universe. We found that the typical mass of Pop III BH-BHs is $sim 30 rm{M}_{odot}$ so that the inspiral chirp signal of gravitational waves can be detected up to z=0.28 by KAGRA, Adv. LIGO, Adv. Virgo and GEO network. Our simulations suggest that the detection rate of the coalescing Pop III BH-BHs is $140 (68) cdot ({rm SFR}_{rm p}/10^{-2.5} rm{M}_{odot} {rm yr}^{-1} {rm Mpc}^{-3}) cdot {rm Err}_{rm sys} ~{rm events} ~{rm yr}^{-1}$ for the flat (Salpeter) initial mass function (IMF), respectively, where $rm SFR_p$ and $rm Err_{sys}$ are the peak value of the Pop III star formation rate and the possible systematic errors due to the assumptions in Pop III population synthesis, respectively. $rm Err_{sys}=1$ correspond to conventional parameters for Pop I stars. From the observation of the chirp signal of the coalescing Pop III BH-BHs, we can determine both the mass and the redshift of the binary for the cosmological parameters determined by Planck satellite. Our simulations suggest that the cumulative redshift distribution of the coalescing Pop III BH-BHs depends almost only on the cosmological parameters. We might be able to confirm the existence of Pop III massive stars of mass $sim 30~rm M_{odot}$ by the detections of gravitational waves if the merger rate of the Pop III massive BH-BHs dominates that of Pop I BH-BHs.
Over the past couple of decades, researchers have predicted more than a dozen super-Chandrasekhar white dwarfs from the detections of over-luminous type Ia supernovae. It turns out that magnetic fields and rotation can explain such massive white dwarfs. If these rotating magnetized white dwarfs follow specific conditions, they can efficiently emit continuous gravitational waves and various futuristic detectors, viz. LISA, BBO, DECIGO, and ALIA can detect such gravitational waves with a significant signal-to-noise ratio. Moreover, we discuss various timescales over which these white dwarfs can emit dipole and quadrupole radiations and show that in the future, the gravitational wave detectors can directly detect the super-Chandrasekhar white dwarfs depending on the magnetic field geometry and its strength.
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