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)

1
Q

What is a star?

A

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.

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2
Q

What is the difference between a star and a planet?

A
  • 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.

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3
Q

What are the stages of a star life cycle?

A
  1. Nebula
  2. Protostar
  3. Main sequence
  4. Red giant
  5. Planetary Nebula or Supernova
  6. 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.

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4
Q

What determines a star’s apparent brightness?

A

Distance and luminosity.

Apparent brightness depends on how far a star is from Earth and how much light it emits.

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5
Q

Fill in the blank:

The ________ of a star measures its total energy output per second.

A

luminosity

Luminosity depends on both the star’s size and temperature and is a key measure of its brightness.

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6
Q

What is the primary element in a star’s composition?

A

Hydrogen

Hydrogen fuels nuclear fusion, producing energy and forming helium in a star’s core.

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7
Q

What happens when hydrogen runs out in a main sequence star?

A

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.

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8
Q

What happens to the brightness of a star if its size increases?

A

It increases.

Larger stars have greater surface areas, emitting more light and increasing their luminosity.

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9
Q

True or False:

A star’s color depends on its temperature.

A

True

Cooler stars appear red, while hotter stars appear blue. The color corresponds to the surface temperature of the star.

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10
Q

True or False:

A red giant is cooler than a blue star.

A

True

Red giants are cooler, appearing red, but they are much larger and more luminous than blue stars.

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11
Q

How is temperature of a star related to its spectral type?

A

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.

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12
Q

What is the Hertzsprung-Russell (H-R) diagram?

A

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.

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13
Q

Which stars are in the upper right of the Hertzsprung-Russell diagram?

A

Red giants and supergiants.

These stars are large and cool but very luminous due to their size.

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14
Q

What is the first stage in the life cycle of a star?

A

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.

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15
Q

What do white dwarfs represent in stellar evolution?

A

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.

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16
Q

What role does mass play in a star’s life cycle?

A

It determines the star’s path and end state.

High-mass stars may end as black holes, while low-mass stars become white dwarfs.

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17
Q

At what stage of a star’s life is iron primarily produced?

A

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.

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18
Q

What is a protostar?

A

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.

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19
Q

What triggers a nebula to collapse and form a protostar?

A

Gravitational forces

Gravitational forces cause regions of higher density within a nebula to collapse, forming a protostar as pressure and temperature increase.

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20
Q

Fill in the blank:

A star spends the majority of its life in the _____ ________ phase.

A

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.

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21
Q

What determines the mass of a star?

A

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.

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22
Q

What determines the lifespan of a star?

A

Its mass.

High-mass stars burn fuel quickly and have shorter lifespans, while low-mass stars burn fuel slowly and live longer.

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23
Q

Fill in the blank:

The faintest stars are typically ______ dwarfs.

A

red

Red dwarfs are small, cool, and emit low levels of light, making them the faintest main-sequence stars.

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24
Q

True or False:

Nuclear fusion begins in a protostar.

A

False

Nuclear fusion starts only after the protostar evolves into a main sequence star, when core temperatures reach sufficient levels.

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25
What role does **gravity** play in nuclear fusion?
It provides the **pressure** necessary to initiate fusion. ## Footnote The immense gravitational pressure at a star’s core forces atoms to collide, triggering nuclear fusion.
26
# True or False: Nuclear fusion **only** occurs in the core of stars.
True ## Footnote Fusion happens in the star's core where temperatures and pressures are high enough to initiate the process.
27
What fusion process **fuses** hydrogen into helium using carbon, nitrogen, and oxygen?
CNO cycle ## Footnote This cycle occurs in massive stars and is responsible for a significant portion of energy generation.
28
# True or False: Nuclear fusion **stops** once iron is formed in a star's core.
True ## Footnote Fusion ceases at *iron* because it requires more energy than it produces, causing core collapse and potentially leading to a supernova or black hole formation.
29
What **element** is primarily formed in stars like the Sun through nuclear fusion?
Helium ## Footnote The Sun primarily fuses hydrogen into helium through the proton-proton chain reaction.
30
What is the significance of **carbon** in the process of nuclear fusion?
It acts as a **catalyst** in the fusion of heavier elements. ## Footnote In stars with masses greater than the Sun, carbon is used in the CNO cycle, a fusion process that generates energy in massive stars.
31
# True or False: All stars eventually **become** black holes.
False ## Footnote Only the most **massive** stars become black holes; smaller stars end as white dwarfs or neutron stars.
32
What is a **neutron star**?
A dense **core of neutrons**. ## Footnote Neutron stars are the **remnants** of supernovae, formed from collapsed stellar cores where protons and electrons combine to form neutrons.
33
# True or False: Neutron stars are **formed** from the collapse of low-mass stars.
False ## Footnote Neutron stars result from the supernova **collapse** of high-mass stars, not low-mass stars.
34
# Fill in the blank: The Sun is **classified** as a \_\_\_\_\_-type star.
G ## Footnote The Sun is a G-type main-sequence star, with a moderate temperature and yellowish color.
35
# Fill in the blank: A star much larger than the Sun **becomes** a/an \_\_\_\_\_\_\_ at the end of its life cycle.
supergiant ## Footnote Massive stars expand into **supergiants** as they burn heavier elements in their cores near the end of their lives.
36
What is a **white dwarf**?
The **remnant** of a low or medium-mass star. ## Footnote A white dwarf forms after a star ejects its outer layers, leaving behind a hot, dense core that slowly cools over time.
37
# True or False: All stars eventually **become** white dwarfs.
False ## Footnote Only low to medium-mass stars end up as white dwarfs. High-mass stars may explode as supernovae or collapse into black holes.
38
# True or False: A supernova **occurs** when a star runs out of helium.
False ## Footnote A **supernova** happens when massive stars run out of nuclear fuel and their cores collapse, releasing enormous energy.
39
What can form from the **core of a supernova**?
A **neutron star** or **black hole**. ## Footnote The outcome depends on the star’s original mass: *neutron stars* form from medium-mass cores, while *black holes* form from very massive cores.
40
What are **binary stars**?
Two stars that orbit a **common center of mass**. ## Footnote Binary stars are common and help astronomers calculate stellar masses through their orbital dynamics.
41
# Define: Galaxy
A **system** of stars, gas, dust, and dark matter. ## Footnote Galaxies are bound by *gravity* and vary in size and shape.
42
What are the **types of galaxies**?
* Spiral * Elliptical * Irregular ## Footnote **Spiral** galaxies have well-defined arms, **elliptical** galaxies are smooth and oval-shaped, while **irregular** galaxies lack a defined structure and often have an uneven appearance.
43
What is the **Local Group**?
A **collection** of over 80 galaxies, including the Milky Way and Andromeda. ## Footnote The Local Group spans ~10 million light-years and includes **numerous** dwarf galaxies alongside three large spirals—Andromeda (largest), Milky Way (second-largest), and Triangulum (third-largest).
44
# Fill in the blank: The **largest** galaxy in the Local Group is the \_\_\_\_\_\_\_\_\_ galaxy.
Andromeda ## Footnote The *Andromeda Galaxy* is the largest in the Local Group and is also the closest large galaxy to the Milky Way, located about 2.5 million light-years away.
45
What is the **difference** between elliptical and spiral galaxies?
**Ellipticals** lack star formation and contain older stars, while **spirals** form stars in their gas-rich arms. ## Footnote Elliptical galaxies are smoother and redder, with older stars and little star formation. Spiral galaxies have blue star-forming regions and a mix of young and old stars.
46
What is the **universe**?
**Everything that exists**, including matter, space, stars, and galaxies. ## Footnote It is constantly *expanding* and contains all physical entities and phenomena.
47
# True or False: The universe is **finite** and has clear boundaries.
False ## Footnote The universe is believed to be **infinite** or at least unbounded, continuously expanding since the Big Bang.
48
# True or False: The Milky Way is the **largest** galaxy.
False ## Footnote While the Milky Way is large, galaxies such as **IC 1101** are much larger, with IC 1101 being one of the largest known galaxies, vastly outscaling the Milky Way in size and mass.
49
# Fill in the blank: The **Milky Way** is a \_\_\_\_\_\_ galaxy.
spiral ## Footnote The Milky Way is a barred **spiral** galaxy with a central bulge surrounded by a flat, rotating disk containing spiral arms that extend outward.
50
# True or False: The Milky Way is **colliding** with the Andromeda galaxy.
True ## Footnote The two galaxies will **merge** in about 4 billion years.
51
What is the **role** of dark energy in the universe's expansion?
It **accelerates** the expansion. ## Footnote Dark energy drives the universe's accelerated expansion by counteracting gravity on large scales, accounting for about 68–72% of its total energy density.
52
What does dark matter **do** in galaxies?
It helps galaxies stay **intact** by providing additional gravity. ## Footnote It cannot be seen, but its presence is inferred through its gravitational effects.
53
# Fill in the blank: Most **galaxies** have a \_\_\_\_\_\_\_\_ black hole at their center.
supermassive ## Footnote **Supermassive** black holes are millions of times heavier than the Sun.
54
# Fill in the blank: A \_\_\_\_\_\_ \_\_\_\_\_ is a **region** of space where gravity is so strong that nothing, not even light, can escape.
black hole ## Footnote *Black holes* are formed from the remnants of massive stars that collapse under their own gravity after a supernova.
55
What is the **difference** between a star cluster and a galaxy?
* A **star cluster** is a group of stars. * A **galaxy** is a system of stars, gas, dust, and dark matter. ## Footnote Galaxies contain billions of stars and often include other celestial objects like nebulae and black holes.
56
What is the **event horizon** of a black hole?
The **boundary** beyond which nothing can escape. ## Footnote The event horizon is the point where the gravitational pull becomes so strong that escape is impossible.
57
Why do stars **appear to move** across the night sky?
Due to **Earth's rotation**. ## Footnote As Earth rotates on its axis, stars seem to move from *east to west* across the sky, completing one apparent revolution every 24 hours.
58
What is the apparent **shift** in a star’s position due to Earth's orbit?
Stellar parallax ## Footnote *Stellar parallax* is the apparent shift in a star’s position due to Earth's changing vantage point, used to measure star distances.
59
# True or False: All galaxies are moving **toward** each other.
False ## Footnote Most galaxies are moving **away** from each other due to the universe’s expansion.
60
What is the **observable** universe?
The **part** of the universe we can observe. ## Footnote It extends about 93 billion light-years across.
61
How **old** is the universe according to the Big Bang theory?
Approximately 13.8 billion years. ## Footnote This estimate comes from *observations* of cosmic background radiation and the rate of expansion.
62
What **event** started the universe, according to the Big Bang theory?
It began from an **extremely hot** and **dense state**. ## Footnote This event marked the start of the universe's expansion, which continues today.
63
# True or False: The Big Bang theory **explains** the creation of all elements in the universe.
False ## Footnote The *Big Bang theory* explains the formation of the lightest elements, such as hydrogen and helium. Heavier elements were formed later in stars through nuclear fusion and supernovae.
64
# Fill in the blank: The Big Bang theory was **proposed** in the early \_\_\_\_\_ century.
20th ## Footnote The theory emerged in the early *20th century*, with Georges Lemaître proposing cosmic expansion in 1927 and Edwin Hubble providing observational confirmation in 1929.
65
What term **describes** galaxies moving away from each other?
The **expansion** of the universe. ## Footnote This phenomenon was first observed by Edwin Hubble and is evidence of the Big Bang.
66
# Fill in the blank: The redshift of distant galaxies **suggests** that the universe is \_\_\_\_\_\_\_.
expanding ## Footnote As light from distant galaxies shifts to longer wavelengths, it shows that they are moving away from us.
67
# Fill in the blank: The expansion of the universe is **observable** through the \_\_\_\_\_\_\_ of distant galaxies.
redshift ## Footnote **Redshift** occurs when light from distant objects stretches, indicating they are moving away from us.
68
# True or False: The universe’s expansion is **slowing** down.
False ## Footnote Observations show that the expansion is **accelerating** due to dark energy.
69
Who first **observed** that galaxies are moving away from Earth?
Edwin Hubble ## Footnote While *Vesto Slipher* initially measured redshifts of galaxies, *Edwin Hubble* confirmed their proportional relationship to distance (Hubble's Law) in 1929, solidifying the concept of an expanding universe.
70
What is **redshift**?
The shifting of light to **longer** wavelengths as objects move away. ## Footnote Redshift occurs when light stretches to longer wavelengths as space itself expands between distant objects—a key observation supporting cosmic expansion (Hubble's Law).
71
What is the **Hubble constant**?
A value that **represents** the rate of expansion of the universe. ## Footnote It helps determine the age of the universe and the distance between galaxies.
72
What is the **Cosmic Microwave Background**? | (CMB)
**Radiation** left over from the Big Bang. ## Footnote The CMB is the faint afterglow of the Big Bang, providing crucial evidence for the early universe's conditions and supporting the Big Bang theory by showing the universe's cooling over time.
73
# True or False The universe was **once** much hotter and denser than it is now.
True ## Footnote According to the Big Bang theory, the universe *began* in a very hot, dense state before expanding and cooling.
74
What key **observation** supports the Big Bang theory about the universe's composition?
The **abundance** of light elements such as hydrogen and helium. ## Footnote These elements were formed during the first few minutes of the universe's existence in a process called Big Bang nucleosynthesis.
75
# True or False: The Big Bang theory is the **only** explanation for the universe's origin.
False ## Footnote While **alternative** theories like the steady-state model or oscillating universe exist, they *lack* the strong observational evidence, such as redshift, CMB radiation, and primordial element abundances, that support the Big Bang theory.