Astronomy Quiz: Milky Way and Star Evolution

The Milky Way’s edge-on view shows a thin rotating disk containing stars and gas, a bright central bulge, and a surrounding stellar halo filled with globular clusters. These structural components define the true geometry of the galaxy. The Sun sits about 28,000 light-years from the center, while the entire galactic disk spans close to 100,000 light-years, making Option B the accurate structural description.

Star masses are constrained by physical forces. At low masses, electron degeneracy pressure prevents sufficient gravitational compression, stopping nuclear fusion in bodies below about 0.08 solar masses. At high masses, intense radiation pressure pushes matter outward, preventing stars above around 100 solar masses from sustaining further growth. These paired mechanisms define the natural mass limits of stars, making degeneracy pressure and radiation pressure the correct explanation.

A 1-solar-mass HR diagram illustrates the evolutionary path of a Sun-like star across different phases. It shows movement from the main sequence to the red giant branch, then to the horizontal branch during helium burning, followed by the asymptotic giant branch and its decline to a planetary nebula before settling as a white dwarf. This full life-cycle trajectory corresponds to how a solar-mass star evolves over billions of years.

An HR diagram plots stellar luminosity versus temperature, revealing how stars group into the main sequence, red giants, white dwarfs, and other evolutionary classes. By understanding this relationship, astronomers can interpret both intrinsic brightness and thermal characteristics. This makes it a key tool for classifying stars and studying stellar evolution, unlike the unrelated options that involve animals, weather, or historical events.

Telescopes surpass the human eye due to their large apertures, which collect far more light, and their superior angular resolution, which separates objects only arcseconds apart. The eye cannot resolve such fine detail or gather enough light to detect faint celestial targets. These combined advantages allow telescopes to reveal dim stars, galaxies, and planetary features with clarity impossible for biological vision.

A star’s spectrum contains absorption lines that reveal temperature through blackbody comparison, composition through elemental fingerprints, line-of-sight velocity through Doppler shifts, and rotation through line broadening. These measurable features allow astronomers to determine the fundamental physics of stars. Distance, color, and age cannot be directly extracted from spectral data alone, making temperature, composition, and motion the correct derived properties.

As an object approaches a black hole, relativistic effects dominate. To an outside observer, the friend's time slows dramatically, and emitted light becomes increasingly redshifted. Before crossing the event horizon, the friend fades from visibility as light wavelengths stretch beyond detection. Near stellar-mass black holes, tidal forces stretch and tear the body. These phenomena match general relativity predictions, making Option D the only scientifically accurate description.

Traveling near light speed results in extreme time dilation and length contraction, allowing astronauts to reach the galactic center in a few subjective years. However, tens of thousands of years pass on Earth during the same interval. Even a return trip would bring travelers back 50,000 years later, long after their contemporaries died. Signals sent from the center would also take 25,000 years to arrive, making communication impossible.

Quasars emit tremendous energy because matter in an accretion disk spirals toward a supermassive black hole. Frictional heating within the disk raises temperatures to millions of degrees, generating intense electromagnetic radiation. The more mass consumed, the more energy released. Accreting roughly one solar mass per year can outshine entire galaxies. This mechanism aligns with astrophysical evidence and explains quasar luminosity accurately.

The shape of galaxies originates from protogalactic cloud properties. High angular momentum causes the cloud to spin rapidly, forming a flattened disk that becomes a spiral galaxy. Low angular momentum prevents this disk formation, producing an elliptical galaxy. Additionally, dense protogalactic clouds cool quickly, forming stars before gas settles into a disk, again resulting in elliptical structures. These combined factors explain morphological differences.