Astrophysics and Cosmology 5.5 Flashcards
Define a Planet?
Objects with sufficient mass to clear its orbit and have enough gravity to force it into a spherical shape, no nuclear fusion occurs
Define a Dwarf Planet?
Planets where the orbit has not been cleared of other objects
Define an Asteroid?
Objects which are too small and uneven in shape to be planets with a near circular orbit around the sun
Define a comet?
Small, irregular sized balls of rock, dust and ice, they orbit the sun in eccentric elliptical orbits
What is a galaxy and a solar system?
Solar Systems-The systems containing stars and orbiting objects like planets
Galaxies-collection of stars, dust and gas, each galaxies contain around 100 billion stars
Describe the formation of a star up to the protostar?
- Initially it stars as Nebulae (cloud of gas and dust)
- Gravitational attraction causes dust and gas particles to come together
- As gravitational collapse accelerates, some regions become denser and this causes gravitational energy of gas particles to turn into thermal
- This results in a sphere of hot dense dust and gas called a protostar
Describe the formation of a star from protostar to main phase?
- For a star to form the temperature and pressure must be high enough for the hydrogen gas nuclei to overcome electrostatic forces of attraction and undergo nuclear fusion
- Fusion produces helium nuclei and therefore a star
- The star then remains in a constant equilibrium with the gravitational forces of particles compressing the star and emitted photons and gas pressure counteracting this, this is known as the main stage of the star
Why does the length of a main phase of a star change?
-Length of main phase depends on size e.g. Larger stars are hotter so undergo fusion quicker and therefore have a shorter main phase
What is the value of solar mass and what is it?(M)
1.99*10^30 kg
-It is the mass of the sun
Describe the evolution of a low mass star?
1.Low mass stars remain in main phase for longer until they run lower on hydrogen nuclei then the gravitational forces inwards overcome the radiation and gas pressure and the star begins to collapse inwards
2. A red giant evolves with the inner core being too cool for helium fusion but the outer core has so much pressure and therefore heat for fusion to occur here
3. As helium nuclei runs low the red giant evolves into a white dwarf and the outer shell drifts off into space as a planetary nebula
4. The core remains very dense and has a temperature of about 300k no fusion occurs
5. Photons produced earlier in the evolution leak out and electron degeneracy pressure prevents the core from collapsing, the white dwarf is now stable
What is electron degeneracy pressure?
When two electrons can’t exist in the same state
Describe the evolution of a massive star?
- As the hydrogen supply depletes, the temperature increases to a high enough level for helium fusion to occur this causes a red supergiant to form
- The red supergiant has a core of increasingly heavy elements with an inert iron core (as iron fusion doesn’t release energy)
3.Once the core is produced the star becomes unstable and a type 2 supernova occurs
4.The core collapses and a shockwave ejects the materials in the outer shells out into space - If the remaining mass is greater than 1.4M protons and electrons left combine into neutrons and a neutron star is formed
- If the remaining core has a mass greater than 3M the gravitational forces are so strong that a black hole is formed
What makes a star a low mass star and a large mass star?
Low mass star: between 0.5M and 10M
Large mass star: In excess of 10M
Describe the process of electrons exiting?
-Electrons exist in certain discrete energy levels
-Electrons can move from a lower energy state to a higher one when they absorb a source of external energy(excited)
-When an electron deexcites it releases energy in the form of a photon in a specific wavelength depending on the energy absorbed
What are the different types of spectra?
Emission line spectra, continuous line spectra and absorption line spectra
