Research pursuits

Evolution of massive stars

Massive stars, with masses ranging from 8 to 150 times that of the Sun, are captivating entities in the universe due to their large size and high temperatures. Their evolution is rapid and intense, going through phases like the main sequence, red supergiant, and ending with a supernova. Understanding the intricate evolution of these stars is crucial not only for comprehending their individual behavior, but also for gaining insights into the broader context of the universe. Researchers are utilizing observational data, theoretical modeling, and simulations, as well as advancements in technology such as high-resolution spectroscopy and imaging, to study the physical processes and internal structure of massive stars.

The study of massive stars not only sheds light on the behavior of individual stars, but also has far-reaching implications for the universe as a whole. Supernovae, which mark the final stage of massive stars' life cycle, play a vital role in the formation and distribution of new elements throughout the galaxy, and serve as significant sources of energy that impact their surrounding environment. Therefore, current research in the field of massive stars is focused on gaining new knowledge about these complex objects and their contributions to the formation and evolution of the universe. By delving into the mysteries of massive stars, researchers aim to uncover the secrets of the universe's origin and evolution.

Core-collapse supernovae

Core-collapse supernovae are extraordinary events that release an immense amount of energy, making them among the most energetic and powerful phenomena in the universe. These explosive events occur when the core of a massive star collapses, resulting in a tremendous explosion that can outshine an entire galaxy. The energy released during core-collapse supernovae includes gamma rays and gravitational waves, which can be detected from Earth, providing invaluable data for astrophysical research.

One of the fascinating phenomena associated with core-collapse supernovae is long-duration gamma-ray bursts (GRBs). These bursts are incredibly bright and emit intense gamma-ray radiation for several seconds to minutes. Long-duration GRBs are believed to be caused by the collapse of a massive star's core and the subsequent formation of a rapidly spinning black hole or a neutron star with a powerful magnetic field. They offer a unique opportunity to study the formation of black holes and neutron stars, as well as the physics of extreme astrophysical environments.

The study of core-collapse supernovae and long-duration GRBs has been revolutionized by recent advancements in observational and computational technologies. Observational facilities such as the Laser Interferometer Gravitational-Wave Observatory (LIGO) and the Fermi Gamma-ray Space Telescope have provided crucial data on the properties and behavior of these phenomena, while computational simulations are being used to model and simulate the complex physical processes that occur during core-collapse supernovae and GRBs. This interdisciplinary approach has led to exciting new insights into these extreme astrophysical events and their significance in shaping our understanding of the universe.

Binary stars

Binary stars are a pair of stars that are bound by gravity and orbit around a common center of mass. They are quite common in the universe, and studying them can provide insights into the physical properties of stars, their formation and evolution, and the structure and evolution of galaxies.

The formation of binary stars can occur through several mechanisms. One is the fragmentation theory, where a collapsing cloud of gas and dust breaks into two or more pieces, which eventually evolve into binary systems. Alternatively, the capture theory suggests that a single star can capture another star through gravitational interactions, leading to the formation of a binary system.

Once formed, binary stars can evolve through different channels, which are influenced by the masses and lifetimes of the stars. Isolated binary evolution channels refer to the ways in which binary stars evolve without external interference from other stars. These channels can lead to the creation of various binary systems and compact objects such as white dwarfs, neutron stars, and black holes.

There are three primary isolated binary evolution channels: common envelope evolution, conservative mass transfer, and stable mass transfer. The common envelope evolution involves one star evolving into a giant or supergiant and its outer layers engulfing the companion star. This leads to the formation of a close binary system with a compact remnant. Conservative mass transfer occurs when one star transfers mass to its companion through an accretion disk, resulting in the donor star becoming a white dwarf, while the companion star may become a more massive star or a neutron star or black hole. Finally, stable mass transfer involves two stars exchanging mass over time in a stable orbit and can result in different binary systems, including those with two white dwarfs or a white dwarf and a main sequence star.

Gravitational waves

Gravitational waves are ripples in the fabric of spacetime that are caused by the acceleration of massive objects, such as black holes and neutron stars. They were predicted by Albert Einstein's theory of general relativity, which describes the way gravity works as a curvature of spacetime. Gravitational waves are extremely difficult to detect because they are very weak and interact very weakly with matter. However, the recent development of highly sensitive detectors, such as the Laser Interferometer Gravitational-Wave Observatory (LIGO) and the Virgo interferometer, has allowed scientists to detect gravitational waves for the first time.

The progenitor stars of gravitational waves are typically massive stars that have reached the end of their lives and undergone supernova explosions or collapsed into black holes. When a massive star dies, it can leave behind a neutron star or a black hole, which can then produce gravitational waves as they orbit around each other. The most powerful sources of gravitational waves are binary black holes, which are two black holes that are orbiting around each other and merging into a single black hole. Binary neutron stars and black hole-neutron star systems can also produce gravitational waves, but they are typically weaker.

Studying gravitational waves and their progenitor stars can provide valuable insights into the structure and evolution of the universe. For example, the detection of gravitational waves from binary black holes has confirmed the existence of black holes and provided evidence for the existence of gravitational waves, which were predicted by Einstein's theory but had never been directly detected before. Furthermore, studying the properties of binary neutron stars and black hole-neutron star systems can help scientists understand the behavior of matter at extremely high densities, which can be used to test the predictions of theories of nuclear physics and particle physics.

Extreme mass ratio inspirals (EMRIs)