PHYSICS

entropy

entropy

a measure of the disorder of a system

when matter and anti-matter interact

they annihilate each other, resulting in the conservation of energy

electrons

negatively charged subatomic particles that have 3 quarks

temperature and matter density of the Universe change with time because

they both decrease with time

the Big Bang

the rapid expansion of matter from a state of extremely high density and temperature that marked the universe's origin

evidence of the Big Bang

expansion of the Universe - the measured abundance of hydrogen and helium - presence of the Cosmic Microwave Background

Cosmic Microwave Background

thermal radiation left over from the Big Bang

Planck time

the time required for light to travel a distance of 1 Planck length in vacuum

Planck Era

the era of the universe prior to the Planck time

electromagnetic force

physical interaction that occurs between electrically charged particles

strong nuclear force

keeps atomic nuclei from falling apart

the curvature of the Universe is

flat - zero curvature

deuterium

formed by the combination of 1 proton and 1 neutron

Big Bang Nucleosynthesis

formation of new nuclei in the first few minutes of time

dark matter

matter that does not give off electromagnetic radiation but is quite abundant in the universe

anti-matter

matter with the same mass but opposite charge

fundamental forces

gravity, electromagnetic force, strong nuclear force, weak nuclear force

what event took place 0.001 seconds after the Big Bang?

the first fusion of protons with neutrons

Hubble's Tuning Fork Diagram

organizes galaxies by their morphology

disks of galaxies contain

gas, young stars, and pop I stars

what causes galaxies to acquire different shapes and forms?

difference in the initial proto-galactic cloud and interactions with other galaxies

gravity and pressure

must be in balance to keep a star in equilibrium

degeneracy pressure does not allow the formation of stars with mass less than

0.08 solar masses

why can we use the universe as a time machine to study galaxies at different stages of their lives?

because the speed of light is finite

neutron star

the final form of a core-collapse supernova (type II supernova)

what is the event horizon in the black hole?

the radius around the center of a black hole beyond which no information can escape

neutron capture

the absorption of a neutron by a nucleus

atomic number

the number of protons in the nucleus of an atom

mass number

the sum of the number of neutrons and protons in an atomic nucleus

How old is the universe and how do we know?

14 billion years old; the expansion of the universe appears to have started about this long ago

the universe is said to be closed if

gravity is strong enough to stop the expansion in a finite time

protons

positively charged subatomic particles that have 3 quarks

Higgs Field

gives mass to other fundamental particles such as electrons and quarks

Higgs bosons

a fundamental particle associated with the Higgs field

Theory of Inflation

space underwent a rapid expansion in a very brief period in the early Universe

Electrons and positrons collide and produce

photons

positron

a particle with the mass of an electron but a positive charge

dark energy

a theoretical repulsive force that counteracts gravity and causes the universe to expand at an accelerating rate

carbon

the heaviest element formed as a result of the evolution of low-mass stars

alpha process

process occurring at high temperatures, in which high-energy photons split heavy nuclei to form helium nuclei.

If the universe is open

material will get further and further apart, and eventually no new stars will form

Based on current evidence, how does the actual average density of matter in the universe compare to the critical density?

the actual density of matter, even with dark matter included, is less than about a third of the critical density

Based on current evidence, a supercluster is most likely to have formed in regions of space where

the density of dark matter was slightly higher than average when the Universe was very young

is space expanding within clusters of galaxies?

No, because their gravity is strong enough to hold them together even while the universe as a whole expands.

If WIMPs really exist and make up most of the dark matter in galaxies, which of the following is not one of their characteristics?

they travel at speeds close to the speed of light

How does gravitational lensing tell us about the mass of a galaxy cluster?

Using Einstein's general theory of relativity, we can calculate the cluster's mass from the precise way it distorts the light of galaxies behind it.

How are rotation curves of spiral galaxies determined beyond radii where starlight can be detected?

Through observations of the 21 cm line of atomic hydrogen

I observe a galaxy that is 100 million light-years away. What do I see?

The light from the galaxy as it was 100 million years ago and it is redshifted