Chapter 33 - Astrophysics and Cosmology

H0

Where ________ is the hubble parameter, defined as ________= 21km /s /Mly • Another way redshift occurs is through gravitational redshift Expansion and the Cosmological Principle • It has been established that the universe looks the same from different points • Every galaxy in the universe is racing away from each other at the Hubble Parameter • Cosmological Principle- The assumption that the universe is isotropic (looks the same from all directions) and homogeneous (looks the same from different locations) • Steady State Model- Assumes the universe is infinitely old and, on average, looks the same now as it always has • The steady state model suggests no large scale changes have occurred in the universe and that uniformity requires mass to be created at a very slow rate 33.6 The Big Bang and the Cosmic Microwave Background • Cosmic Microwave Background- Evidence towards the big bang, this is radiation that comes from the universe as a whole, measured at λ= 7.35cm • Anisotrophy- Having different properties in different directions, this is a property of the universe that has been confirmed • Once the universe cooled to about 3000K, particles could form atoms and free electrons became rare, which allowed photons to travel freely, leading to the CMB Looking Back toward the Big Bang • Lookback Time- The amount of time it takes light from an event to reach an observer • Surface of last scattering- The edge of the observable universe, we can not see past this The Observable Universe • Many theories suggest that the entire universe is larger than the observable universe 33.7 The Standard Cosmological Model: Early History of the Universe • The Standard Cosmological Model- The current most popular theory for the history and current state of the universe • It is believed that after an imbalance of matter and antimatter annihilated most of the antimatter, the universe entered the lepton era where electrons and positrons were formed and destroyed each other, releasing photons • Later, the radiation era began, there were mainly photons and neutrinos but the neutrinos only interacted via the weak force and thus the primary interaction was radiation • The universe then became matter dominated with eh formation of the first atoms and molecules 33.8 Inflation: Explaining Flatness, Uniformity, and Structure Flatness • One theory that explains the flatness of the universe is that the universe has a curvature of 0 and as the observable universe expands, we see more of the flatness CMB Uniformity • The CMB is almost entirely uniform, which can be attributed to the fact that in the beginning, the universe was in thermal equilibrium Galaxy Seeds, Fluctuations • Forces can undergo quantum fluctuations that are so small they are not detectable unless magnified • It is believed that inflation magnified the tiny fluctuations of the early universe and created the density irregularities we see today 33.9 Dark Matter and Dark Energy • Big Crunch- The end of the universe if it has a positive curvature, it would be finite and gravity will eventually overtake to bring everything back together Critical Density • Critical Density- The average mass per volume density threshold that, if surpassed, would give the universe positive curvature, defined as roughly 10−26kg /m3 • We currently believe the universe is expanding at an accelerating rate Dark Matter • Current experiments have many convinced that the universe is flat and that the critical density is exactly the true density, but normal matter only accounts for about 5 % of the critical densitys requirements • Dark matter is believed to be the other 95 %, and observations of stars or galaxies in motion suggest they have considerably more mass than previously thought • Dark matter, if it exists, is likely made of weakly interacting massive particles, which makes it very difficult to detect Dark Energy- Cosmic Acceleration • The expansion of the universe is accelerating • Dark Energy- An unknown force that has been suggested to be responsible for this acceleration • Current estimations on the composition of the universe put the planets and the stars to be about 0.5 % of all the mass- energy available 33.10 Large- Scale Structure of the Universe • Simulations with cold dark energy and dark matter have fit current observations of the universe quite well • Observations of the CMB have been increasing in precision and soon may be able to detect the effects of gravity waves and provide info for both cosmic inflation and particle physics 33.11 Finally, • Anthropic Principle- States that if the universe were even a little different than it is, we would not be here.

Cosmology

________ is the study of the universe as a whole.

Nebula

A large cloud of dust or gas in space

Active Galactic Nuclei

The very bright points in the center of galaxies, thought to come from the matter falling into the center of the black hole

Luminosity

Total power radiated in watts

Apparent Brightness

The power crossing unit area at the Earth perpendicular to the path of the light

Stellar Evolution

The life-cycle that stars go through

Parallax

The apparent motion of a star against the background of more distance stars

Principle of Equivalence

No experiment can be performed that could distinguish between a uniform gravitational field and an equivalent uniform acceleration

Gravitational Lensing

Nearby galaxies acting as a magnifying glass that bends light from distant objects towards us

Cosmological Principle

The assumption that the universe is isotropic (looks the same from all directions) and homogeneous (looks the same from different locations)

Steady State Model

Assumes the universe is infinitely old and, on average, looks the same now as it always has

Cosmic Microwave Background

Evidence towards the big bang, this is radiation that comes from the universe as a whole, measured at λ = 7.35cm

Anisotrophy

Having different properties in different directions, this is a property of the universe that has been confirmed

Lookback Time

The amount of time it takes light from an event to reach an observer

Surface of last scattering

The edge of the observable universe, we cannot see past this

The Standard Cosmological Model

The current most popular theory for the history and current state of the universe

Big Crunch

The end of the universe if it has a positive curvature, it would be finite and gravity will eventually overtake to bring everything back together

Critical Density

The average mass per volume density threshold that, if surpassed, would give the universe positive curvature, defined as roughly 10^−26 kg/m^3

Dark Energy

An unknown force that has been suggested to be responsible for this acceleration

Anthropic Principle

States that if the universe were even a little different than it is, we would not be here