Stars Flashcards
Describe the process of star birth, starting from the initial conditions with a cloud of molecular dust and gas.
Star birth begins with a molecular cloud of dust and gas. As it cools, the cloud contracts and becomes more dense. This contraction excites molecules, leading to radiation emission and further expansion and collapse. Once the cloud reaches a critical point, known as Jean’s Mass, it becomes so hot and dense that it forms a protostar and initiates the hydrogen fusion cycle.
How can we measure the distance to stars, and what is the significance of the 10 parsec distance?
Parallax and trigonometry are used to measure the distance to stars. Apparent brightness is converted to true brightness (luminosity) at 10 parsecs, a standard distance for reference.
What information can be obtained through spectral analysis of stars, and how is chemical composition determined?
Spectral analysis provides information on the chemical composition of stars, giving them a spectral type. The width of individual lines in the spectrum is used to determine the size, which in turn helps find the luminosity class.
Describe the life cycle of low-mass stars (less than 2 solar masses), including the fusion processes and the stages they go through.
Low-mass stars initiate fusion through the p-p chain, leading to lifetimes of billions of years as they slowly burn hydrogen. Once the hydrogen is depleted, the star evolves into a red giant where it begins to fuse helium. After the helium is exhausted, the star leaves behind an inert carbon core, and the outer layers are expelled in a nova, leaving a white dwarf as the remnant.
What fusion processes do high-mass stars (greater than 2 solar masses) undergo, and how do their lifetimes compare to low-mass stars?
High-mass stars use the CNO chain to fuse hydrogen and have lifetimes of only millions of years. Once hydrogen is used up, the next fusion depends on the temperature. If the temperature is greater than 100 million K, the star burns helium; temperatures greater than 600 million K allow it to fuse carbon into heavier elements. The final stage depends on the star’s mass: 0.08 to 0.25 solar masses results in a He white dwarf; 0.25 to 4 solar masses leads to a C/O white dwarf; 4 to 8 solar masses results in an O/Ne/Mg White Dwarf; and more than 8 solar masses allows burning of iron before ending in a supernova.
What is the ultimate fate of low-mass stars, and how can white dwarfs continue to be an energy source?
Low-mass stars eventually form white dwarfs, which can siphon material from nearby stars to create accretion discs, serving as an energy source for the star. Throughout its life, the star ejects mass through novas, and eventually supernovas, leaving no mass behind. The consistent brightness of these supernovas allows astronomers to use them to find interstellar distances.
What is the ultimate fate of high-mass stars, and what phenomena can occur as a result of their evolution?
High-mass stars ultimately form neutron stars. Fast-spinning neutron stars are known as pulsars, and their accretion discs can create X-ray bursts. Occasionally, high-intensity X-ray bursts or supermassive star collapses can result in Gamma-ray bursts.
What is the ultimate fate of very high-mass stars, and what evidence supports the existence of black holes?
Very high-mass stars ultimately form black holes. Evidence for their existence includes observations of gamma-ray bursts, X-ray binary systems, direct observation of accretion discs, dynamics of stars at the centre of the Milky Way, and the detection of gravitational waves.
What is the central region of the Milky Way galaxy, and what are the characteristics of the stars in the bulge/peanut?
The central region is the bulge/peanut, accounting for 15% of the total light. Stars in the bulge have random eccentric orbits and medium metallicity.
Describe the structure of the disc in the Milky Way galaxy, including its composition and characteristics of stars.
The disc accounts for 80% of the light in the Milky Way. Stars in the disc have circular orbits of the same speed, high metallicity, and are the youngest in the galaxy. It includes spiral arms, and our Sun is thought to orbit between two of them.
What is the outermost region of the Milky Way galaxy, and what are the characteristics of the stars in the halo?
The outermost region is the halo, contributing 5% of the light. Stars in the halo have random eccentric orbits and very low metallicity.
What other components contribute to the composition of the Milky Way, specifically in terms of star clusters?
The Milky Way is also composed of various star clusters, which are groups of stars that are gravitationally bound and often share a common origin. These clusters can be classified as globular clusters found in the halo or open clusters located in the disc.
Describe the characteristics of globular clusters in the Milky Way.
Globular clusters are spherical in shape and have low metallicity. They are thought to be the remains of ancient stellar systems within the Milky Way.
What distinguishes open clusters in the Milky Way, and what is their likely origin?
Open clusters have irregular shapes, high metallicity, and are thought to be the fossil relics of early stars within the Milky Way.
What happens when stars eject solar wind and later undergo a supernova, and how does it affect the surrounding gas?
As stars eject solar wind and undergo supernova events, the shockwave from the explosion compresses the surrounding gas into stellar bubbles.
