Reading EST Practice passage about The Lives Of Stars

The Life Cycle of Stars: A Cosmic Journey

Stars are among the most fascinating and fundamental objects in the universe. They serve as the building blocks of galaxies, the engines of cosmic evolution, and the source of light and energy that sustains life on Earth. Understanding the life cycle of stars provides insight into the workings of the cosmos and our place within it.

Birth of a Star

The journey of a star begins in vast clouds of gas and dust called nebulae. These regions, often spanning hundreds of light-years, are composed primarily of hydrogen—the simplest and most abundant element in the universe. Within these nebulae, gravity pulls particles together, forming dense clumps known as protostars. As more material accumulates, the core temperature rises until nuclear fusion ignites, transforming hydrogen into helium and releasing immense amounts of energy. This marks the birth of a new star.

During this phase, the star enters what is called the “main sequence,” where it spends approximately 90% of its lifetime. Our Sun, for example, is currently in this stable phase, shining steadily for about 4.6 billion years and expected to continue doing so for another 5 billion years.

Middle Age and Stellar Evolution

As stars age, their behavior depends largely on their initial mass. Low- and medium-mass stars, like our Sun, eventually exhaust their hydrogen fuel. When this happens, the core contracts under gravity while the outer layers expand dramatically, turning the star into a red giant. During this stage, heavier elements such as carbon and oxygen form through nuclear reactions deep within the star’s interior.

High-mass stars follow a similar but far more explosive path. Their immense gravitational forces allow them to fuse not only hydrogen but also heavier elements like helium, carbon, and iron. However, once they reach the iron stage, no further fusion can occur because iron does not release energy during nuclear processes. At this point, the star collapses catastrophically, triggering one of the most spectacular events in the universe: a supernova explosion.

Death of a Star

The death of a star varies depending on its mass. For low- and medium-mass stars, the outer layers drift away, creating beautiful planetary nebulae, while the remaining core condenses into a white dwarf—a small, dense remnant that slowly cools over billions of years. High-mass stars, after their supernovae, leave behind either neutron stars or black holes. Neutron stars are incredibly dense, with a teaspoon of their material weighing billions of tons, while black holes possess gravitational fields so strong that even light cannot escape them.

These remnants play crucial roles in shaping their surroundings. Supernova explosions enrich the interstellar medium with heavy elements necessary for planet formation and life itself. Meanwhile, black holes influence galactic dynamics by pulling in nearby matter and emitting powerful jets of radiation.

Why Study Stars?

Studying stars helps scientists answer profound questions about the universe’s origins, structure, and ultimate fate. By analyzing starlight, astronomers determine chemical compositions, temperatures, distances, and motions. Observatories like the Hubble Space Telescope and the James Webb Space Telescope have revolutionized our understanding of stellar phenomena, revealing details previously hidden from view.

Moreover, stars connect us to the broader cosmos. Every atom of carbon, nitrogen, and oxygen in our bodies was forged inside ancient stars. As astronomer Carl Sagan famously said, “We are made of star-stuff.” This poetic notion underscores humanity’s shared heritage with the universe.

Questions

1. Main Idea

What is the primary purpose of the passage?
A) To describe how telescopes observe stars
B) To explain the life cycle of stars and their significance
C) To compare the properties of different types of stars
D) To argue that stars are the most important celestial objects

2. Vocabulary in Context

The term “nebulae” (line 7) refers to:
A) Dense cores of collapsing stars
B) Clouds of gas and dust where stars form
C) Explosive remnants of dying stars
D) Regions of space devoid of matter

3. Inference

Based on the passage, which statement best describes why supernovae are significant?
A) They mark the beginning of a star’s life.
B) They produce heavy elements essential for life.
C) They result in the formation of white dwarfs.
D) They stabilize galaxies by redistributing mass.

4. Detail

According to the passage, what distinguishes high-mass stars from low- and medium-mass stars during their lifetimes?
A) High-mass stars never enter the red giant phase.
B) High-mass stars fuse heavier elements beyond helium.
C) Low- and medium-mass stars explode as supernovae.
D) Low- and medium-mass stars create black holes upon death.

5. Author’s Perspective

The author quotes Carl Sagan (“We are made of star-stuff”) primarily to:
A) Highlight the destructive power of stars
B) Emphasize humanity’s connection to the universe
C) Illustrate the limitations of modern astronomy
D) Criticize theories about stellar evolution

6. Logical Sequence

Which event occurs immediately after a star exhausts its hydrogen fuel?
A) It becomes a white dwarf.
B) Its outer layers expand into a red giant.
C) It undergoes a supernova explosion.
D) It forms a planetary nebula.

7. Comparative Analysis

How do neutron stars differ from black holes?
A) Neutron stars emit light, while black holes do not.
B) Black holes are less massive than neutron stars.
C) Neutron stars lack gravitational pull, unlike black holes.
D) Black holes form from low-mass stars, while neutron stars form from high-mass stars.

8. Evidence-Based Reasoning

Which detail from the passage supports the claim that studying stars reveals information about the universe’s composition?
A) “Every atom of carbon, nitrogen, and oxygen in our bodies was forged inside ancient stars.”
B) “Observatories like the Hubble Space Telescope… have revolutionized our understanding.”
C) “Supernova explosions enrich the interstellar medium with heavy elements.”
D) “Stars are among the most fascinating and fundamental objects in the universe.”

9. Interpretation

What does the author imply about the role of gravity in stellar evolution?
A) Gravity prevents stars from collapsing prematurely.
B) Gravity drives both the formation and destruction of stars.
C) Gravity has little impact on low-mass stars.
D) Gravity stabilizes stars throughout their entire lifecycle.

10. Synthesis

Based on the passage, which conclusion can be drawn about the relationship between stars and planets?
A) Planets form exclusively from the debris of supernovae.
B) Stars provide the raw materials needed for planetary systems.
C) Only high-mass stars contribute to planet formation.
D) Planets prevent stars from collapsing into black holes.