Stars and Galaxies Practice Questions
20 free Stars and Galaxies practice questions for the General Science. Tap an option to answer — you get instant feedback, the correct answer, and a detailed explanation for every question.
What is the primary nuclear fusion process that powers a main-sequence star like our Sun?
- A Triple-alpha process
- B Proton-proton chain reaction
- C Carbon-nitrogen-oxygen cycle
- D Helium flash
Correct answer: Proton-proton chain reaction
In stars with masses similar to the Sun, the proton-proton chain reaction is the dominant process. It converts four hydrogen nuclei into one helium nucleus, releasing a tremendous amount of energy in the form of gamma rays and neutrinos.
Which type of galaxy is characterized by a smooth, featureless light profile and contains mostly old, red stars with very little gas and dust?
- A Spiral galaxy
- B Barred spiral galaxy
- C Elliptical galaxy
- D Irregular galaxy
Correct answer: Elliptical galaxy
Elliptical galaxies range from nearly spherical to highly elongated shapes. Because they lack the cool gas and dust necessary for new star formation, they are populated primarily by older, evolved stars.
The Hertzsprung-Russell (H-R) diagram plots which two fundamental stellar properties against each other?
- A Mass and Radius
- B Luminosity and Temperature
- C Distance and Apparent Magnitude
- D Age and Chemical Composition
Correct answer: Luminosity and Temperature
The H-R diagram is a crucial tool in astronomy that relates a star's absolute magnitude or luminosity to its spectral type or classification temperature. This visualization allows astronomers to track the evolutionary stages of stars.
What is the name of the boundary around a black hole beyond which nothing, not even light, can escape?
- A Accretion disk
- B Singularity
- C Event horizon
- D Schwarzschild radius
Correct answer: Event horizon
The event horizon marks the 'point of no return' where the escape velocity exceeds the speed of light. Any matter or radiation crossing this boundary is inexorably drawn into the central singularity.
Which of the following describes the 'Chandrasekhar Limit'?
- A The maximum mass of a neutron star
- B The minimum temperature required for hydrogen fusion
- C The maximum mass of a stable white dwarf
- D The distance at which a star's parallax is one arcsecond
Correct answer: The maximum mass of a stable white dwarf
The Chandrasekhar Limit is approximately 1.4 solar masses. If a white dwarf exceeds this mass, electron degeneracy pressure can no longer support it against gravitational collapse, leading to a Type Ia supernova.
What is the most likely end-state for a star with a starting mass of less than 8 times that of the Sun?
- A Neutron star
- B Black hole
- C White dwarf
- D Pulsar
Correct answer: White dwarf
Low-to-medium mass stars shed their outer layers as planetary nebulae after the red giant phase. The remaining carbon-oxygen core contracts to become a white dwarf, supported by electron degeneracy pressure.
Which class of stars is the most numerous in the Milky Way galaxy?
- A Blue giants
- B Red dwarfs
- C Yellow dwarfs
- D White dwarfs
Correct answer: Red dwarfs
Red dwarfs (M-type main-sequence stars) make up about 75% of the stars in our galaxy. Although they are the most common, they are so dim that none are visible to the naked eye from Earth.
The Milky Way is classified as which type of galaxy?
- A Grand design spiral
- B Lenticular
- C Barred spiral
- D Dwarf spheroidal
Correct answer: Barred spiral
Recent observations have confirmed that the Milky Way has a central bar-shaped structure composed of stars. This makes it a barred spiral galaxy, specifically classified as SBbc in the Hubble sequence.
What stellar remnant is formed after a high-mass star undergoes a Type II supernova, leaving behind a core between 1.4 and 3 solar masses?
- A Stellar black hole
- B White dwarf
- C Neutron star
- D Brown dwarf
Correct answer: Neutron star
A neutron star is an extremely dense object composed almost entirely of neutrons. It is held up by neutron degeneracy pressure and is typically only about 20 kilometers in diameter.
In which region of a spiral galaxy does most active star formation occur?
- A The central bulge
- B The galactic halo
- C The spiral arms
- D The galactic nucleus
Correct answer: The spiral arms
The spiral arms contain high concentrations of interstellar gas and dust. These 'density waves' compress the gas, triggering the gravitational collapse that leads to the birth of new, hot blue stars.
What is the name of the nearest major spiral galaxy to the Milky Way?
- A Large Magellanic Cloud
- B Andromeda Galaxy
- C Triangulum Galaxy
- D Sombrero Galaxy
Correct answer: Andromeda Galaxy
The Andromeda Galaxy (M31) is the largest galaxy in the Local Group and is located about 2.5 million light-years from Earth. It is currently on a collision course with the Milky Way and will merge with it in roughly 4 billion years.
Which spectral class represents the hottest stars on the main sequence?
- A Class M
- B Class G
- C Class A
- D Class O
Correct answer: Class O
The spectral sequence (O, B, A, F, G, K, M) is ordered by decreasing surface temperature. O-type stars are blue and extremely hot, with temperatures exceeding 30,000 K.
A 'Pulsar' is a rapidly rotating version of which celestial object?
- A White dwarf
- B Neutron star
- C Quasar
- D Red supergiant
Correct answer: Neutron star
Pulsars are highly magnetized, rotating neutron stars that emit beams of electromagnetic radiation out of their magnetic poles. As they rotate, these beams sweep across Earth like a lighthouse beacon, appearing as regular pulses.
What is the 'Hubble constant' used to measure?
- A The speed of light in a vacuum
- B The expansion rate of the universe
- C The mass of the Milky Way
- D The luminosity of a Cepheid variable
Correct answer: The expansion rate of the universe
The Hubble constant ($H_0$) describes the relationship between a galaxy's distance and its recession velocity. It is a fundamental parameter in cosmology used to estimate the age and size of the universe.
Which of the following is the 'pioneer' stage of a star, before nuclear fusion begins in its core?
- A T Tauri star
- B Protostar
- C Brown dwarf
- D Main sequence
Correct answer: Protostar
A protostar forms from the contraction of a giant molecular cloud. It glows due to the release of gravitational energy as it collapses, but it does not become a true star until temperatures reach the point for hydrogen fusion.
What is the primary evidence for the existence of 'Dark Matter' in galaxies?
- A The presence of supermassive black holes
- B Unexpectedly flat galactic rotation curves
- C The high temperature of the cosmic microwave background
- D The redshifting of distant light
Correct answer: Unexpectedly flat galactic rotation curves
Stars at the edges of galaxies orbit much faster than can be explained by the visible mass. This suggests the presence of a vast 'halo' of invisible matter that provides the extra gravitational pull.
Which element is the heaviest that can be produced by nuclear fusion inside a high-mass star before it goes supernova?
- A Carbon
- B Oxygen
- C Iron
- D Uranium
Correct answer: Iron
Fusion of iron is an endothermic process, meaning it consumes energy rather than releasing it. Once a star develops an iron core, it can no longer support itself against gravity, leading to a core-collapse supernova.
What is a 'Nebula' in the context of astronomy?
- A A failed star
- B A cloud of gas and dust in space
- C A cluster of older galaxies
- D A planet outside our solar system
Correct answer: A cloud of gas and dust in space
Nebulae are vast clouds of interstellar medium. They can be regions where new stars are being born (emission nebulae) or the remains of dying stars (planetary nebulae and supernova remnants).
Which type of star is used as a 'standard candle' to measure distances to other galaxies because of its predictable relationship between luminosity and pulsation period?
- A Red dwarf
- B Neutron star
- C Cepheid variable
- D Blue supergiant star
Correct answer: Cepheid variable
The period-luminosity relationship of Cepheid variables allows astronomers to calculate their intrinsic brightness. By comparing this to their apparent brightness, the distance to the host galaxy can be determined.
What is the term for a group of thousands to millions of old stars tightly bound by gravity, typically found in the halo of a galaxy?
- A Open cluster
- B Globular cluster
- C Stellar association
- D Galaxy cluster
Correct answer: Globular cluster
Globular clusters are spherical collections of stars that are among the oldest objects in the universe. In the Milky Way, they orbit the galactic center in the halo, far from the gas-rich disk.