p7.4 pt 2 Flashcards
- What happens in the formation of a protostar?
-cloud of dust and gas (hydrogen and helium)= contract by gravity= dense= protostars
- What happens when the cloud of gas forming protostars collapses?
-its temperature increases (and pressure) as its volume decreases
- What provided a possible explanation of the Sun’s energy source?
-nuclear processes discovered in the early 20th Century provided a possible explanation of the Sun’s energy source
- What is nuclear fusion?
-when, if brought close enough together, hydrogen nuclei can fuse into helium nuclei releasing energy
- What happens when light nuclei fuse to make heavier nuclei with masses up to that of the iron
nucleus?
-energy is liberated
- What does everything stand for in Einstein’s equation E = mc2?
- E is the energy produced
- m is the mass lost
- c is the speed of light in a vacuum
- What is used to calculate the energy released during nuclear fusion and fission?
-Einstein’s equation E = mc2
- What happens to the more massive stars?
-the more massive the star, the hotter its core and the heavier the nuclei it can create by fusion
- What is the significance of the core of a star?
-it is where the temperature and density are highest and where most nuclear fusion takes place
- How is energy transferred from core to surface in a star?
- by photons of radiation
- by convection
- What is the significance of the photosphere?
-energy is radiated into space from the star’s surface (photosphere)
- What is the stars surface called?
-photosphere
- What is the Hertzsprung-Russell diagram?
-a plot of temperature (highest to lowest) and luminosity (lowest to highest)
- Where are supergiants located on the Hertzsprung-Russell diagram?
-top right
- Where are giants located on the Hertzsprung-Russell diagram?
-top right
- Where are main sequence stars located on the Hertzsprung-Russell diagram?
-diagonal from top left to bottom right
- Where are white dwarfs located on the Hertzsprung-Russell diagram?
-bottom left
- Why are supernovas not on the Hertzsprung-Russell diagram?
-they happen to quickly, and are not a stable part of the stars life cycle
- Where does hydrogen fusion to helium take place in in main sequence stars?
-in the core
- When does a star leave the main sequence? What happens next?
-when its core hydrogen runs out; it swells to become a red giant or supergiant and its photosphere cools
- What happens in a red giant or supergiant star?
-helium nuclei fuse to make carbon, followed by further reactions that produce heavier nuclei such as nitrogen and oxygen
- What is an example of a low mass star?
-the sun
- What happens to a low mass star at the end of its life?
-becomes a red giant, which lacks the mass to compress the core further at the end of helium fusion; it then shrinks to form a white dwarf
- What happens in a white dwarf star?
-there is no nuclear fusion; the star gradually cools and fades
- What is the mess of a high mass star?
-several times the mass of the Sun
- What happens to a high mass star at the end of its life?
-in a high-mass star nuclear fusion can produce heavier nuclei up to and including iron; when the core is mostly iron, it explodes as a supernova creating nuclei with masses greater than iron and leaving a dense neutron star or a black hole
- What have astronomers found convincing evidence of?
-planets around hundreds of nearby stars
- What may scientists think if even a small proportion of stars have planets?
-that it is likely that life exists elsewhere in the Universe
- What evidence of extraterrestrial life has been found?
-no evidence of extraterrestrial life (at present or in the past) has so far been detected.
