Ch25 Stars And The Universe Flashcards
Define stable star:
A star that is not collapsing/expanding because the inward force of gravity is balanced by radiation pressure, which pushes outwards
Define plasma:
A completely ionized gas in which the temperature is too high for neutral atoms to exist, so it consists of electrons and positively charged atomic nuclei
Define solar mass:
Equal to the mass of the sun (2 x 10^30kg)
Define light year:
The distance traveled in space by light in one year
9.5 x 10^15m
Define protostar:
A very young star that is still gathering mass from its parent molecular cloud
Define interstellar cloud:
A cloud of gas and dust that occupies the space between stars
Define molecular cloud:
A cloud of interstellar gas that consists mostly of molecular hydrogen and is cold and dense enough to collapse to form stars
Define radiation pressure:
The outward forced due to the high temperature of the star
Define red giant:
A star that began with fewer than eight solar masses and is burning helium in its core;
It’s shell of hydrogen has expanded and cooled
Define main sequence:
Stable star that is burning hydrogen in its core;
Once it has used up 12% of its hydrogen, it goes onto another stage of its life cycle
Define white dwarf:
The final stage of a star that started with fewer than eight solar masses after all its fuel has been used up
Define planetary nebula:
A bubble of gas surrounding a white dwarf star that used to be the outer shell of a red giant from which it collapsed
Define red supergiant:
Similar to red giants, they form when stars with at least eight times the mass of the sun run out of hydrogen fuel in their core, but fusion of hydrogen continues in the outer shells
Define supernova:
An exploding star that began life with more than eight solar masses and has run out of fuel
Define neutron star:
Collapsed star composed almost entirely of neutrons, which forms when a star with more than eight solar masses reaches the end of its life
Define black hole:
The final stage in the life cycle of a star that started with more than eight solar masses; it has enough mass left over after exploding as a supernova to collapse to a point where gravity is so strong that not even light can escape
Define absorption spectrum:
Dark lines in a spectrum that are produced when light passing through cooler gas is absorbed
Define redshift:
An increase in the observed wavelength of electromagnetic radiation (including visible light) from a star/galaxy because it is moving away from us
Define Big Bang theory:
The universe (space, time, matter, energy) was created at a single point13.8 billion years ago and has been expanding and cooling ever since
What is the equation for Hubble constant?
Hubble constant = speed of galaxy moving away from earth/distance of the galaxy from earth
Ho = v/d
What is the equation to estimate the age of the universe?
d/v =1/Ho
Define Hubble’s law:
Distant galaxies are moving away from earth with a speed, v, that is proportional to their distance, d, from earth;
v = Hod where Ho is Hubble constant
Define Hubble’s constant:
The slope of a graph of galaxy speed against distance
Define Hubble time:
The inverse of the Hubble constant, which gives an estimate for the age of the universe
