ByYuvraj Singh, CH-25 STARS AND THE UNIVERSE Aradhya Arora, Rudram Pareek, Saksham Aggarwal, Hardik Sachdeva Stars and Galaxies When you look into the nightsky, The stars you see are all on the south of the Orion Nebula and Have all been formed by the first step called Protostar. The Sun • The Sun is the star at the centre of the Solar System. It is a massive, hot ball of plasma, inflated and heated by energy produced by nuclear fusion reactions at its core. Part of this internal energy is emitted from its surface as light, ultraviolet, and infrared radiation, providing most of the energy for life on Earth. Protostar • A protostar is a very young star that is still gathering mass from its parent molecular cloud. This is the earliest phase in the process of star formation. The phase begins when a molecular cloud fragment first collapses under the force of self-gravity and an opaque, pressure supported core forms inside the collapsing fragment. It ends when the infalling gas is depleted, leaving a premain-sequence star, which contracts to later become a main-sequence star at the onset of hydrogen fusion producing helium. The Universe The universe is all of space and time and their contents, including planets, stars, galaxies, and all other forms of matter and energy. The Big Bang theory is the prevailing cosmological description of the development of the universe. According to this theory, space and time emerged together 13.787±0.020 billion years ago, and the universe has been expanding ever since the Big Bang. While the spatial size, if any, of the entire universe is unknown it is possible to measure the size of the observable universe, which is approximately 93 billion light-years in diameter at the present day. Hubble's Law speed fo galaxy moving away from Earth Hubble Constant = distance of the galaxy from Earth 𝐻0 = 𝑣 𝑑 Estimate for the age of the Universe: 𝑑 1 = 𝑣 𝐻0 Spectroscopy • Spectroscopy is learning about stars from their starlight. The dark lights in a spectrum are produced when light is passed through cooler gas and is absorbed - this phenomena is called Absorption spectrum. • Red-shift - An increase in the observed wavelength of electromagnetic radiation from a star or galaxy because it is moving away from us • Blue-shift – A decrease in the observed wavelength of electromagnetic radiation from a star or galaxy. Doppler affect • Doppler affect is a very common effect which you have noticed in your life time, for E.G- when a very fast vehicle passes by you the volume of sound rises and falls, though the pitch also increases and decreases as it recedes. The Big Bang Theory • 13.8 billion years ago, the universe began as a Big Bang from a tiny point called a singularity. The universe was unimaginably hot and dense but it has been expanding and cooling since then, The early universe was so hot that atoms could not form and they would instantly ionise. Discovery of Cosmic microwave background radiation(CMBR) • The cosmic microwave background is a microwave radiation that fills all space in the observable universe. It is a remnant that provides an important source of data on the primordial universe. With a standard optical radiation, the background space between stars and galaxies is almost completely dark. However, a sufficiently sensitive radio telescope detects a faint background glow that is almost uniform and is not associated with any star, galaxy, or other object. This glow is strongest in the microwave region of the radio spectrum. The accidental discovery of the CMBR in 1965 by American radio astronomers Arno Penzias and Robert Wilson was the culmination of work initiated in the 1940s.
