Birth of Stars
The cloud of dust and gas that might form into a star is called this.
nebula
A star will spend about _____ % of its life as main sequence star.
90%
Most stars that leave the main sequence will then become this.
a red giant (or red supergiant)
The event that signals that a star is no longer a star.
fusion ends
The final outcome of a star after it blows off its outer layers depends only on this.
the mass of the star
When this happens, the cloud of dust and gas officially becomes a star.
Fusion
During this stage, these two forces must balance each other.
gravity (pulls inward) and heat (causing outward expansion)
Compared to the main sequence, most red giants are (more luminous / less luminous?)
more luminous
Stars that are at least 5x the mass of sun will end their lives as a star when this happens.
supernova explosion
After a sun-sized star blows off its outer layers, the remaining core becomes this.
a white dwarf
In the earliest stages of a star, _____ fuses to make _____ .
hydrogen fuses to make helium
A very large star will spend (more / less) time than a smaller star as a main sequence star.
Less
The main reason for the high luminosity of red giant stars is ___ .
their increase in size (surface area)
By the time the hydrogen in a star's core is used up, this has built up in the core of the star.
helium
The core of a star that is 1.5 to 5 times the mass of our sun will end its life as this.
neutron star
This force causes the cloud of dust and gas to heat up enough for fusion to occur.
gravity
This determines the what happens in the next stage of the star's life.
the mass of the star
The surface of a red giant (or supergiant) is (hotter / cooler) than the main sequence star from which it formed.
cooler
When fusion in the core stops, the core will do this.
contract, or collapse on itself
The core of a star that is greater than 5 times the mass of our sun will become this.
a black hole
If the nebula never gets hot enough to start fusion, it may become a _____ .
a brown dwarf
Scientists believe that the most numerous star in the sky is this type.
a red dwarf
The ejection of the outer layers of a main sequence star.
planetary nebula
The heaviest element that can form in the core of the star is _____ .
iron or oxygen
The radius around a black hole beyond which nothing (not even light) can escape is called this.
the event horizon