06 The Lives of Stars Free Online FlashCards

Where do stars form?

Stars form in cold, dense regions of interstellar clouds made mostly of gas and dust.

What marks a protostar's arrival on the main sequence?

It becomes a main-sequence star when its core becomes hot enough to sustain hydrogen fusion.

Which two properties are plotted on an H–R diagram?

An H–R diagram plots a star's luminosity against its surface temperature.

How does high mass generally affect a main-sequence star's temperature and luminosity?

High-mass main-sequence stars are generally hotter and much more luminous than low-mass ones.

What happens to a star's core and outer layers as core hydrogen runs low?

When core hydrogen runs low, the core contracts and heats while the star's outer layers expand.

What can low- and intermediate-mass giants make by fusing helium?

They expand into giants and can fuse helium into carbon and oxygen, but generally cannot fuse those products into much heavier elements.

Why can an iron-rich core collapse in a massive star?

Iron fusion does not provide energy to support the core, so the iron-rich core collapses and can trigger a core-collapse supernova.

What starts the contraction of a star-forming cloud region?

When gravity overcomes the pressure supporting part of a cloud, that region contracts and fragments into denser cores.

What is the main energy source of a protostar?

A protostar gains energy mainly from gravitational contraction as it gathers surrounding material and heats up.

What balances gravity during a star's main-sequence stage?

Fusion creates outward pressure that balances gravity's inward pull, keeping the star stable.

Why do high-mass stars have shorter main-sequence lifetimes?

High-mass stars use their fuel much faster, so their main-sequence lifetimes are shorter.

What is a planetary nebula?

A planetary nebula is an expanding cloud of gas formed from a star's shed outer layers; despite its name, it is not a planet.