4A1 The Universe and Its Stars Flashcards
Explore the life cycle and characteristics of stars and galaxies, and describe the evidence for the origins of the universe. (75 cards)
What is a star?
A massive ball of hot gas undergoing nuclear fusion.
Stars are primarily composed of hydrogen and helium and emit light and heat due to nuclear fusion occurring in their cores.
What is the difference between a star and a planet?
- A star emits light.
- A planet reflects light.
Stars generate energy through nuclear fusion, while planets do not produce their own light but reflect the light of nearby stars.
What are the stages of a star life cycle?
- Nebula
- Protostar
- Main sequence
- Red giant
- Planetary Nebula or Supernova
- White Drawf, Neutron Star, or Black Hole
Average size stars will become red giants, who then become planetary nebulas, and eventually white dwarf stars. Large or massive stars will become red supergiants, who become supernova, who then become either a neutron star or black hole.
What determines a star’s apparent brightness?
Distance and luminosity.
Apparent brightness depends on how far a star is from Earth and how much light it emits.
Fill in the blank:
The ________ of a star measures its total energy output per second.
luminosity
Luminosity depends on both the star’s size and temperature and is a key measure of its brightness.
What is the primary element in a star’s composition?
Hydrogen
Hydrogen fuels nuclear fusion, producing energy and forming helium in a star’s core.
What happens when hydrogen runs out in a main sequence star?
The core contracts and the outer layers expand.
This marks the transition into the next phase, such as becoming a red giant or supergiant, depending on the star’s mass.
What happens to the brightness of a star if its size increases?
It increases.
Larger stars have greater surface areas, emitting more light and increasing their luminosity.
True or False:
A star’s color depends on its temperature.
True
Cooler stars appear red, while hotter stars appear blue. The color corresponds to the surface temperature of the star.
True or False:
A red giant is cooler than a blue star.
True
Red giants are cooler, appearing red, but they are much larger and more luminous than blue stars.
How is temperature of a star related to its spectral type?
Spectral types rank stars by temperature, from O (hottest) to M (coolest).
The sequence O, B, A, F, G, K, M corresponds to decreasing temperature and specific color ranges.
What is the Hertzsprung-Russell (H-R) diagram?
A graph linking a star’s luminosity and temperature.
The H-R diagram organizes stars by their properties, such as main sequence, giants, and white dwarfs.
Which stars are in the upper right of the Hertzsprung-Russell diagram?
Red giants and supergiants.
These stars are large and cool but very luminous due to their size.
What is the first stage in the life cycle of a star?
Nebula
A nebula is a massive cloud of gas and dust in space, primarily hydrogen and helium, where stars begin to form due to gravitational collapse.
What do white dwarfs represent in stellar evolution?
The end stage of low to medium-mass stars.
White dwarfs are the remnants of stars that have shed their outer layers and no longer undergo fusion.
What role does mass play in a star’s life cycle?
It determines the star’s path and end state.
High-mass stars may end as black holes, while low-mass stars become white dwarfs.
At what stage of a star’s life is iron primarily produced?
During silicon burning in massive stars’ cores before supernova.
Iron is formed in the cores of massive stars just before they explode in a supernova, where it cannot undergo fusion to release energy.
What is a protostar?
An early stage of a forming star.
A protostar is a hot, dense core that forms as a nebula collapses, though nuclear fusion has not yet begun.
What triggers a nebula to collapse and form a protostar?
Gravitational forces
Gravitational forces cause regions of higher density within a nebula to collapse, forming a protostar as pressure and temperature increase.
Fill in the blank:
A star spends the majority of its life in the _____ ________ phase.
main sequence
The main sequence phase is the longest in a star’s life, where hydrogen nuclei fuse into helium in the core, producing energy.
What determines the mass of a star?
The amount of matter in the star during its formation.
A star’s mass is determined by the gas and dust available in the region where it forms.
What determines the lifespan of a star?
Its mass.
High-mass stars burn fuel quickly and have shorter lifespans, while low-mass stars burn fuel slowly and live longer.
Fill in the blank:
The faintest stars are typically ______ dwarfs.
red
Red dwarfs are small, cool, and emit low levels of light, making them the faintest main-sequence stars.
True or False:
Nuclear fusion begins in a protostar.
False
Nuclear fusion starts only after the protostar evolves into a main sequence star, when core temperatures reach sufficient levels.