Chapter 19 - Stars Flashcards
What are the requirements for something to be described as a planet?
-Orbits a star.
-Large enough mass to give it a round shape.
-No fusion reactions.
-Orbit cleared of most other objects.
Define planetary satellite.
A body in orbit around a planet.
Define comet.
A small irregular body made up of ice, dust & small pieces of rock, with an eccentric elliptical orbit.
Define solar system.
A system made of a star and the satellites that orbit it.
Define galaxy.
A collection of stars and interstellar dust & gas.
Define universe.
Everything that exists within space and time.
Outline the formation of a star.
-Dust & gas particles gravitate together into a protostar.
-Gravity becomes strong enough for nuclear fusion.
-Main sequence star, where gravity = radiation pressure.
How does a low-mass main sequence star form a red giant?
-Hydrogen in core runs low.
-Star begins to collapse as gravity > radiation pressure.
-Pressure becomes high enough for fusion in the shell around the core, causing expansion.
-Electron degeneracy pressure stops the core getting any smaller.
How does a red giant form into a white dwarf?
-The outer layers drift into space, forming a planetary nebula.
-The core is left behind.
What is electron degeneracy pressure?
A pressure created by the electrons in the core of a collapsing star.
What is the Chandrasekhar limit?
The maximum mass a star can have at which electron degeneracy pressure prevents it from collapsing.
Define planetary nebula.
The outer layers of a red giant that have drifted off into space.
What are the characteristics of a white dwarf?
-No fusion occurs.
-Leaks photons made earlier in its lifecycle.
-Hot & dense.
How does a high-mass main sequence star form a red supergiant?
-Hydrogen is used up quicker.
-Helium in the core fuses into heavier elements, causing expansion.
How does a red supergiant go supernova?
-When fuel runs out, the core contracts.
-Outer layers fall in and rebound, causing a supernova.
-Either a neutron star or a black hole is left.
What are the characteristics of a neutron star?
-Made up of neutrons & neutrinos.
-Very dense, small & fast-rotating.
-Emits radio waves in 2 beams as it rotates.
What are the characteristics of a black hole?
-Core has collapsed into an infinitely dense point (singularity)
-Gravity is so strong that past the event horizon, nothing can escape its pull.
Why do all energy levels have negative values?
‘Zero energy’ is defined as the amount of energy required to free an electron from the atom.
Why do hot gases only emit certain wavelengths of light?
Electrons can only emit certain wavelengths, as this releases enough energy to drop down to their unique energy levels.
Why do different atoms have different sets of spectral lines?
Different elements have their own unique sets of energy levels that require different amounts of energy from the absorption/emission of different wavelengths.
Describe continuous spectra.
All visible wavelengths are present. A heated solid metal will release this type of spectrum.
Describe emission line spectra.
A spectra showing only the wavelengths that are emitted by the element.
Describe absorption line spectra.
A series of dark lines across the background of a continuous spectrum.
