Compact Objects in Exotic Premise and Underlying Gravitational Waves

Einstein's theory of general relativity and quantum mechanics were among the most startling discoveries in the 20th century. Based on these theories, the maximum mass of a non-rotating non-magnetized white dwarf was found to be about 1.4 solar mass, known as the Chandrasekhar mass-limit. However, over the past decades, various researchers have indirectly predicted many sub- and super-Chandrasekhar limiting mass white dwarfs (white dwarfs which violate the Chandrasekhar mass-limit) from the luminosity based observations of peculiar type Ia supernovae. Several research groups worldwide, earlier proposed different models, including magnetic fields, rotation, modified gravity, noncommutative geometry, and many more, to explain these peculiar white dwarfs. However, no such white dwarfs have so far been observed directly in any observations and hence to predict the correct theory for white dwarfs is still unclear. In this book, we show that if such white dwarfs rotate in such a way that their magnetic field and rotation axes are not aligned with each other, they can emit continuous gravitational radiation, which in the future, various detectors, such as LISA, TianQin, BBO, DECIGO, Einstein Telescope, etc., can detect with a significant signal-to-noise ratio. Thereby one can predict the structure of the white dwarfs and single out the correct theory of gravity. In the related context of modified gravity, we show that even in vacuum, asymptotically flat solution of the modified Einstein equation is possible. All these results argue that the premise of modified theory of gravity seems to be an excellent platform to explain unsolved astronomical problems.