P.3.9.2 Stars

Which of the following events is responsible for gamma-ray bursts?

• Formation of a planet

• Formation of a white dwarf

• Collapse of supergiant stars

• Explosion of a supernova

What is the minimum escape velocity required for a black hole?

• Equal to the speed of light

• Less than the speed of light

• Greater than the speed of light

• There is no minimum escape velocity for black holes.

What is the composition of neutron stars?

• Composed of only protons

• Composed of only electrons

• Composed of only neutrons

• Composed of all three particles

Answer explanation

Neutron stars aren't made of only electrons; under extreme conditions, electrons merge with protons to form neutrons

Which of the following is a defining property of supernovae?

• Sudden decrease in brightness

• Rapid increase in absolute magnitude

• Emitting only visible light

• Composed of only neutrons

What is the main reason Type 1a supernovae are used as standard candles to determine distances in the Universe?

• They have a consistent peak luminosity

• They are the most common type of supernovae

• They are the result of a massive star's core-collapse

• They have a consistent duration

Answer explanation

• Type 1a supernovae have a consistent peak luminosity, which makes them ideal standard candles for determining cosmological distances.

A star is currently on the main sequence with an absolute magnitude of +3 and a temperature of 10,000 K. If it evolves to become a red giant, what will likely happen to its position on the HR diagram?

• Move up and to the left

• Move down and to the right

• Move up and to the right

• Move down and to the left

Which of the following stars would most likely be located in the upper-left corner of the Hertzsprung-Russell (HR) diagram?

• A red giant with a temperature of 3,000 K

• A main-sequence star with a temperature of 50,000 K

• A white dwarf with a temperature of 30,000 K

• A yellow-white dwarf with a temperature of 6,000 K

A star on the main sequence has an absolute magnitude of -1 and is classified as a spectral class A star. What is the approximate temperature of this star?

• 2,500 K

• 7,500 K

• 11,000 K

• 25,000 K

Answer explanation

• Spectral class A stars have approximate temperatures around 7,500 K. This classification is part of the OBAFGKM system, where 'A' class stars are hotter than 'F' or 'G' class stars (like our Sun) but cooler than 'B' or 'O' class stars.

As a star similar to our Sun evolves and moves on the HR diagram from its main sequence position to become a red giant, what happens to its absolute magnitude and temperature?

• Absolute magnitude increases, temperature increases

• Absolute magnitude decreases, temperature decreases

• Absolute magnitude increases, temperature decreases

• Absolute magnitude decreases, temperature increases

A main-sequence star has an absolute magnitude of -5 and a temperature of 25,000 K. What is its spectral class?

• Class O

• Class B

• Class A

• Class F

Answer explanation

• A main-sequence star with an absolute magnitude of -5 and a high temperature around 25,000 K fits into the spectral class O. Class O stars are the hottest stars with temperatures typically exceeding 25,000 K.