Astronomy: Stars & Galaxies

Arrange the stellar spectral types in order of decreasing surface temperature.

The order is O, B, A, F, G, K, M, where O is the hottest and M is the coolest.

What physical properties are plotted on the axes of a Hertzsprung-Russell (H-R) diagram?

The vertical axis represents luminosity (or absolute magnitude) and the horizontal axis represents surface temperature (or spectral type/color index).

What is the Chandrasekhar limit, and what is its numerical value?

The Chandrasekhar limit is the maximum mass of a stable white dwarf, approximately 1.4 solar masses, beyond which it collapses into a neutron star or black hole.

Define a parsec (pc) in terms of astronomical units and parallax.

A parsec is the distance at which an object has a stellar parallax of one arcsecond, equivalent to approximately 3.26 light-years or 206,265 AU.

What are the three main components of the Milky Way galaxy's structure?

The three main components are the disk (containing spiral arms), the central bulge, and the spherical halo.

State Hubble's Law mathematically and explain what it implies about the universe.

v = H0 * d; it states that the recessional velocity (v) of a galaxy is proportional to its distance (d), implying the universe is expanding.

What is the Cosmic Microwave Background (CMB) radiation?

The CMB is the thermal radiation left over from the 'recombination' era of the Big Bang, appearing as a nearly uniform 2.7 K blackbody spectrum in all directions.

How do galactic rotation curves provide evidence for dark matter?

Stars at the edges of spiral galaxies orbit at nearly the same speed as stars near the center, suggesting a large amount of unseen mass providing gravitational pull.

What is the primary difference between Dark Matter and Dark Energy?

Dark matter acts as an attractive gravitational force that holds galaxies together, while dark energy acts as a repulsive force that accelerates the expansion of the universe.

What is the primary nuclear fusion process occurring in the core of a main-sequence star like the Sun?

The proton-proton (p-p) chain, which fuses four hydrogen nuclei into one helium nucleus, releasing energy in the process.