18 - Light, Gravity, and the Cosmos Flashcards
This deck expands our focus to the cosmos beyond our solar system. You'll explore the life cycle of stars, from their birth to their eventual demise, and the process of nuclear fusion that powers them. Additionally, you'll learn about the evidence for the expansion of the universe, including concepts like redshift and the cosmic microwave background. By understanding the origin, evolution, and structure of the universe, you'll gain a deeper appreciation for our place in the cosmos. (48 cards)
Define:
star
A luminous sphere of plasma.
Stars primarily consist of hydrogen and helium. Through nuclear fusion, they convert hydrogen into helium, producing the energy that makes them shine.
Explain:
What are the main phases in the life cycle of a star?
- Nebula
- Protostar
- Main Sequence
- Red Giant / Supergiant
- Supernova (for massive stars) / White Dwarf (for smaller stars)
- Black Hole / Neutron Star (for massive stars)
Nebula – A large cloud of gas and dust where stars are born.
Protostar – A young star still gathering mass from its surrounding nebula, not yet undergoing fusion.
Main Sequence – The stable phase where a star fuses hydrogen into helium in its core.
Red Giant / Supergiant – The star expands and cools as it exhausts its hydrogen, beginning fusion of heavier elements.
Supernova (for massive stars) / White Dwarf (for smaller stars) – A massive star explodes, while a smaller star sheds outer layers, leaving a dense core.
Black Hole / Neutron Star (for massive stars) – For massive stars, the core collapses into a black hole or neutron star, depending on the remaining mass.
Identify:
What is the cloud of dust and gas that surrounds a newly formed star?
Nebula
Nebulae are the birthplaces of stars. The gas and dust within them collapse under gravity, forming protostars that eventually become fully formed stars.
Explain:
What happens during the main sequence phase of a star?
The star fuses hydrogen into helium in its core.
The main sequence phase is the longest in a star’s life, during which it maintains a stable size and temperature while generating energy through fusion.
Our Sun is currently in this phase.
Define:
protostar
A young star still gathering mass from its surrounding nebula.
A protostar forms when a cloud of gas and dust contracts, heating up before nuclear fusion begins.
Identify:
What is a dense remnant of a star after it exhausts its nuclear fuel?
White dwarf
White dwarfs are stellar remnants of low- to medium-mass stars that no longer undergo fusion and gradually cool over time.
True or False:
All stars end as white dwarfs.
False
Only low and medium-mass stars end as white dwarfs. More massive stars become neutron stars or black holes after a supernova.
Fill in the blank:
A _____ ____ is a region in space where gravity is strong enough to trap light.
black hole
Black holes form when massive stars collapse under their own gravity after exhausting their nuclear fuel.
Explain:
What are the possible end states of a star, based on its mass?
- White dwarf
- Neutron star
- Black hole
White dwarf - End state of low to medium-mass stars.
Neutron star - End state of more massive stars, but not enough to form a black hole.
Black hole - End state of the most massive stars following a supernova collapse.
True or False:
A neutron star can eventually collapse into a black hole.
True
If a neutron star exceeds a certain mass (the Tolman–Oppenheimer–Volkoff limit), it can collapse into a black hole.
Fill in the blank:
The Sun is currently in the ____ _______ phase.
main sequence
The Sun is still fusing hydrogen into helium in its core and will remain in the main sequence phase for billions more years.
Explain:
What happens to a star when it runs out of hydrogen fuel?
It expands into a red giant or supergiant.
As hydrogen runs out, the core contracts and heats up, while the outer layers expand and cool, initiating fusion of heavier elements.
Identify:
What element is primarily fused in the core of a red giant?
Helium
After a red giant exhausts its hydrogen fuel, it begins fusing helium and other heavier elements in its core.
Explain:
Why do stars with higher mass have shorter lifespans?
They burn through their fuel faster due to higher temperatures.
More massive stars generate more energy, causing them to consume hydrogen more quickly, leading to shorter lifespans.
True or False:
Stars in the main sequence phase are fusing helium into carbon.
False
In the main sequence phase, stars fuse hydrogen into helium. Helium fusion occurs later in the star’s evolution.
Explain:
How does a supernova occur?
A massive star’s core collapses, triggering an explosion.
When a massive star runs out of fuel, its core collapses and sends a shockwave through the outer layers, causing them to explode. The supernova ejects heavy elements into space, contributing to the chemical enrichment of the universe.
Explain:
What is the difference between a supernova and a nova?
- A supernova is a huge explosion from a dying massive star.
- A nova is a smaller explosion from a white dwarf.
Novae are less intense than the large, powerful explosions of supernovae.
identify:
Which diagram plots stars by their luminosity and temperature?
Hertzsprung-Russell (H-R)
The H-R diagram shows how stars are distributed based on their color, size, and brightness, helping astronomers classify them.
Identify:
What are the primary factors that determine a star’s color?
Temperature and age
Hotter stars appear blue, while cooler stars appear red. A star’s age also affects its color as it evolves.
Define:
luminosity
The total amount of energy a star emits per second.
Luminosity is measured relative to the Sun’s output, and it depends on a star’s size and surface temperature.
Explain:
How does a star’s temperature affect its position on the H-R diagram?
Hotter stars are located on the left side of the diagram.
The H-R diagram’s x-axis represents temperature, with cooler stars on the right and hotter ones on the left.
Define:
apparent brightness
The amount of light received from a star as observed from Earth.
Apparent brightness depends not only on the star’s luminosity but also on how far it is from Earth.
True or False:
A star’s apparent brightness depends only on its luminosity.
False
Apparent brightness also depends on distance. A nearby star appears brighter than a more luminous but distant star due to the inverse square law of light.
Define:
nuclear fusion
The process of fusing lighter nuclei to release energy.
In stars, hydrogen nuclei fuse into helium, releasing energy as light and heat. More massive stars fuse heavier elements like carbon and iron.
