Which of the following best defines a star?

A large rocky body that orbits a galaxy and reflects light from nearby sources Any object in space that produces visible light A massive ball of plasma held together by gravity and generating energy through nuclear fusion in its core A cloud of hot gas that has not yet formed into a planet

What is plasma — the state of matter that stars are made of?

A very dense solid formed under extreme gravitational pressure An extremely hot ionized gas in which electrons have been stripped from their atoms, creating a mix of free electrons and positive ions A type of liquid metal found only in very large stars Another word for the hydrogen gas inside a star

What process triggers the birth of a star?

Two planets collide and the explosion creates enough heat to start fusion A cloud of gas and dust collapses under gravity, heating the core until nuclear fusion ignites at about 10 million degrees Celsius The Sun sheds material that forms into smaller stars A large asteroid falls into a gas cloud and sparks nuclear reactions

What is the minimum mass required for an object to become a true hydrogen-burning star?

About 1% of the Sun's mass — even small objects can fuse hydrogen About 50% of the Sun's mass — objects must be at least half the Sun's size About 8% of the Sun's mass (roughly 80 times Jupiter's mass) Exactly the same mass as the Sun — no more, no less

What is a brown dwarf?

A very old star that has cooled to a brown colour An object larger than a planet but smaller than a star — too small to sustain hydrogen fusion, though it may briefly fuse deuterium A neutron star that has been heated by accretion A star that has used up most of its hydrogen and begun fusing helium

How does hydrostatic equilibrium keep a star stable?

The outward pressure from fusion energy exactly balances the inward pull of gravity, keeping the star at a constant size The star spins fast enough that centrifugal force prevents it from collapsing The star's magnetic field acts as a rigid cage keeping its shape stable Electrons in the plasma repel each other, preventing the star from contracting

How does the mass of a star relate to its temperature, brightness, and lifetime?

More massive stars are cooler and dimmer but have longer lifetimes All stars have roughly the same brightness — only their size differs More massive stars are hotter and brighter but burn through their fuel far faster, giving them much shorter lifetimes Mass has no effect on brightness — only a star's chemical composition matters

Our Sun is sometimes described as a fairly average star. In what ways is this accurate?

The Sun is the largest and most massive star in the Milky Way The Sun is the smallest true star — all others are larger The Sun is a middle-mass, middle-age, middle-brightness star on the main sequence — unremarkable compared to the full range of stellar types The Sun is average only in age — it is far hotter and brighter than most stars

What is the most massive a star can be before it becomes unstable?

About 10 times the Sun's mass — larger stars always collapse immediately About 150 times the mass of the Sun — above this limit radiation pressure tears the star apart There is no upper mass limit — stars can be any size About 1,000 solar masses — which is why no star has ever exceeded this

Where in our galaxy are most new stars being formed today?

Near the galactic center, where stars are most densely packed In dense molecular clouds and nebulae along the spiral arms of the Milky Way On the outer edge of the galaxy, where there is no competition for material Near old stars like the Sun, which shed material that forms new stars