What process powers a star like the Sun?

Fission of heavy elements such as uranium

Combustion of hydrogen with oxygen

Friction between layers of rotating gas

Which diagram plots the brightness of stars against their temperature?

The Hertzsprung-Russell diagram

What happens to a Sun-like star once the hydrogen in its core runs out?

It explodes immediately as a supernova

It collapses straight into a black hole

It cools quietly with no change in size

What is a planetary nebula?

The glowing shell of gas thrown off by a dying star

A cloud in which new planets are forming

A ring of debris circling a young planet

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Space & Astronomy Hard ⚡ 10 Questions ⏱️ ~9 Mins +100 XP

How Stars Live and Die

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A star is a long argument between gravity pulling in and fusion pushing out. This quiz follows that argument from ignition to whatever is left at the end.

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~9m

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About this topic

Every star spends its life balancing two forces. Gravity is trying to crush it, and the energy released by fusion in the core is holding the collapse off. The whole life story of a star is the sequence of ways it finds to keep that balance once each fuel runs out, and the ending depends almost entirely on how much mass it started with. The questions here run from the physics of the Sun to white dwarfs, neutron stars and the elements those endings scatter. It is the harder end of astronomy, but none of it needs mathematics — only a feel for what happens when the pushing stops.

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How Stars Live and Die: all 10 questions and answers

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1What process powers a star like the Sun?
- A Friction between layers of rotating gas
- B Fusion of hydrogen into helium Correct
- C Fission of heavy elements such as uranium
- D Combustion of hydrogen with oxygen
Answer: B. Fusion of hydrogen into helium

Why: The Sun converts roughly 600 million tonnes of hydrogen into helium every second, losing a little mass as energy each time. The light produced in the core takes tens of thousands of years to work its way out to the surface.
2In the standard spectral classification of stars, which class does the Sun belong to?
- A G Correct
- B O
- C M
- D B
Answer: A. G

Why: The sequence runs O, B, A, F, G, K, M from hottest to coolest, and the Sun is a G-type star with a surface around 5,500 degrees Celsius. Most stars in the galaxy are cooler M-type red dwarfs.
3Which diagram plots the brightness of stars against their temperature?
- A The Chandrasekhar diagram
- B The Kepler diagram
- C The Messier diagram
- D The Hertzsprung-Russell diagram Correct
Answer: D. The Hertzsprung-Russell diagram

Why: Ejnar Hertzsprung and Henry Norris Russell arrived at the idea independently in the early twentieth century. Around nine in ten stars fall on a single band across it, the main sequence, where hydrogen fusion is still running in the core.
4What happens to a Sun-like star once the hydrogen in its core runs out?
- A It collapses straight into a black hole
- B It cools quietly with no change in size
- C It swells into a red giant Correct
- D It explodes immediately as a supernova
Answer: C. It swells into a red giant

Why: The core contracts and heats while the outer layers expand enormously, turning the star red and vastly larger. When the Sun does this in roughly five billion years it is expected to swallow Mercury and Venus.
5What is left behind after a star like the Sun sheds its outer layers?
- A A brown dwarf
- B A white dwarf Correct
- C A neutron star
- D A black hole
Answer: B. A white dwarf

Why: The exposed core becomes a white dwarf, roughly the size of Earth but holding a large fraction of the star's mass. It generates no new energy and simply cools for billions of years.
6The Chandrasekhar limit sets the maximum possible mass of which object?
- A A white dwarf Correct
- B A neutron star
- C A red giant
- D A brown dwarf
Answer: A. A white dwarf

Why: Above roughly 1.4 times the mass of the Sun, a white dwarf cannot support itself against gravity and collapses. Subrahmanyan Chandrasekhar worked the figure out in 1930, while still a teenager.
7What compact object is left at the centre of many supernova explosions?
- A A white dwarf
- B A brown dwarf
- C A red giant
- D A neutron star Correct
Answer: D. A neutron star

Why: The core is crushed until protons and electrons merge into neutrons, leaving a city-sized object of extraordinary density. A teaspoon of the material would weigh around a billion tonnes on Earth.
8Which colour indicates the hottest stars?
- A Yellow
- B Orange
- C Blue Correct
- D Red
Answer: C. Blue

Why: Surface temperature sets the colour, and blue stars are the hottest while red ones are the coolest. Rigel glows blue-white at around 11,000 degrees Celsius, while red Betelgeuse sits nearer 3,000.
9What is a planetary nebula?
- A A galaxy seen edge-on
- B The glowing shell of gas thrown off by a dying star Correct
- C A cloud in which new planets are forming
- D A ring of debris circling a young planet
Answer: B. The glowing shell of gas thrown off by a dying star

Why: The name is a leftover from early telescopes, in which the round glowing shells looked like the discs of planets. They fade within a few tens of thousands of years, which is why relatively few are visible at any time.
10Where were most of the carbon and oxygen atoms in your body originally made?
- A Inside stars Correct
- B In the Sun's corona
- C In interstellar dust clouds
- D In Earth's molten core
Answer: A. Inside stars

Why: Fusion inside stars builds light elements up into heavier ones, and dying stars scatter the results back into space. The chain stops producing energy at iron, so heavier elements such as gold need supernovae or colliding neutron stars.

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