T3: Lec 21-22 Flashcards
(27 cards)
What is the Cosmic Web?
Cosmic Web - the large interconnected entire structure of the universe composed of filaments and voids. Largely made of dark matter, which forms the structure of the universe today. It forms the large-scale backbone of the universe
Galaxies are arranged around the interconnected sections of the cosmic web (where the bubble lines cross)
Desribe the Large Scale Structure of the Universe:
Large Scale-Structure (LSS) - the observable patterns and distributions of galaxies and clusters across the vast cosmic distances spanning hundreds of millions of light years. Structures of filaments, voids, superclusters, and clusters are organized in web-like patterns.
First image was a Cfa known as “stickman” taken in the 1980s - quite small, detailed image showing redshift of galaxies using telescopes to look at each object individually.
Galaxy surveys can help describe the large scale structure of the universe through photographing redshift of galaxies.
Describe SDSS, Fiber Optics, and “bubble size” at 0.002
SDSS - “Sloan Digital Sky Survey” - shows the percentage of speed of light of galaxies in 2D slices of the 3D web. The redshift of galaxies gives positions in the 3D universe.
Uses Fiber optics - telescopes take 1000s of spectra at a single “point” to measure the redshift as a measure of distance.
Bubble size corresponds to redshift of 0.002.
0.002 x (speed of light) = 6,000 km/sec ( galaxy is 80 mpc away, if HC = 75 km/sec/Mpc)
whcih telescope does the SDSS method use?
SDSS Telescope = Apache Telescope - in New Mexico, USA
Explain LSST , and it helps astonomers with, and which telescope it uses:
LSST “Legacy Survey of Space Time” - images the southern sky every 4 days, images halfway to the edge of the universe in 15 secs, but doesn’t use detailed redshift. Tried to find new objects (e.g. stellar mass black holes, dwarf novae, and gravitational microlensing events)
Can imagine anything from Earth-crossing space rocks to distant supernovae.
Helps astronomers understand the evolution of galaxies and distribution of matter in early universe by observing distant, faint objects.
Helps investigate dark energy and matter, and the formation and evolution of our universe.
LSST telescope = Vera Rubin Observatory - gasses luminosity of redshift to find distance.
An 8m wide telescope that can image up to 5* arcsec across (about 19.6* in area in the night sky).
Define a Spiral Galaxy and how it relates to star formation:
Spiral Galaxies - a flat, routine disk that contains stars, gas and dust with a central concentration of stars known as the bulge. Spiral Galaxies have spiral arms, which are reginos of young star creation.
Define elliptical galaxies and how they relate to star formation:
Elliptical Galaxies - no arms, used up all their hot gas in star formation, typically older galaxies with older stars, and no current star formation. Made of more older and fainter stars.
Define Dwarf Galaxies and how they realte to star formation:
Dwarf Galaxies - relatively small, low-luminosity galaxy containing a few billion stars. Typically found orbiting larger galaxies as natural satellites. Can be irregularly shaped, elliptical, spheroidal, and even ultra-diffuse.
Define Active Galaxies (AGN)
Active Galaxies - galaxies that exhibit unusually high energy outputs from their center (also known as AGN - Active Galactic Nucleus). Known for having large amounts of energy in their center due to massive black holes that feed (accreted) on the material surrounding it and generate huge amounts of energy.
Accretion - the process where a supermassive black hole draws in surrounding gas and dust, which heats up and emits radiation, fueling AGN’s activity.
Known to be intrinsically bright (much brighter than normal galaxies) and produce lots of radio waves from their centers.
The first objects known to emit huge amounts of energy from a single point.
Define Quasars and how they relate to AGN:
Quasars (Quasi-Stellar Radio Source) - specific types of active galactic nuclei (AGN), but are the most luminous examples of these galaxies. They are characterized by their extreme brightness/luminosity, their ability to emit light across the entire electromagnetic spectrum, and their vast distance from earth.
First found in the 1950s from imaging when the moon passes in front of that area. When the radio waves stop being picked up, and then start back up again. Astronomers then pointed their telescopes at this area and found the first Quasar.
Briefly explain Beatrice Tinsley’s Scientific Career:
(1941-1981) - was a NZ scientist with a PhD at UT Austin in 1966.
Studied cosmology and galaxy evolution.
Wrote key papers on this field.
Died from Melanoma
Describe the likely long term fate of the Milky Way Galaxy and Other Galaxies:
Andromeda is blue-shifted meaning it is coming towards us and is likely to “crash” into the Milky Way, then merging into one galaxy.
Lovingly named the “Milkdromeda” Galaxy
Galaxies evolve with time - the older the stellar population, with only old stars left and no stars formed.
Old stars return gas so the chemical composition of the universe changes over time.
Galaxies can pass through a phase as AGN (far more quasars at high redshifts)
It’s likely the dark energy acceleration will not “turn off” and the universe will continue expanding forever.
What is the Cosmological Horizon?
Cosmological Horizon - the boundary of the observable universe, making the furthest distance from which light or other information can potentially reach us. It’s defined by the finite speed of light and the speed of the expanding universe.
Explain how the cosmological horizon connects to the expanding universe?
As the universe expands, this means very distant objects recede faster than light, and distant objects speed up. - this means the horizon is more limited as less light is able to reach us as objects are being moved further away as dark energy accelerates the universe’s expansion.
In a Decelerating universe distant objects slow down over time, new galaxies and thus a larger volume of space is visible - this means the horizon “grows” as there is more reachable light.
Who is Fritz Zwicky? What did he predict?
a Swiss-american astonomer (1933) proposed the existence of unseen mass in the Coma Cluster of Galaxies, to explain why the galaxies were moving too fast to remain gravittionally bound together.
He created the backbone of the idea of dark matter
Predicted the existence of neutron stars, and proposed supernova launch particles into space to account for cosmic rays.
He also predicted the existence of low-mass, faint galaxies (dwarf galaxies).
What is dark matter?
Dark matter - hypothetical form of invisible matter that exerts gravitational effects on light and ordinary matter.
only interacts through gravity
25% of the universe
Astronomers noticed that the universe seemed to be missing mass, so dark matter was suggested.
Contrast dark matter idea with modified gravity:
Dark matter as hidden particles - suggests invisible particles swim around galaxies and clusters, far out weighting visible matter.
Every galaxy has a halow of particles that engulfs visible stars and gas, contributing to bulk mass of galaxy
Explains why galaxies on edge of universe move as fast as galaxies towards the center
No Dark Matter, just Modified Gravity - scientists tweak the laws of gravity and Einstein’s general relativity equations to explain the spread of stars at the edge of the universe.
This doesn’t have a lot of evidence, there would have to be lots of tweaks made while dark matter doesn’t need as many tweaks made (it eliminates the problems)
Why can Newton’s laws of gravity not explain solar system scales?
Newtonian gravity cannot deal with the complexity of interactions between multiple bodies (the calculations would be very difficult to solve precisely) and the limitations of the theory itself.
N-body problem - too many objects, too complex, unable to make precise predictions for subtle changes nor long-term
Newton’s model is incomplete, unable to explain Mercury’s perihelion precession
Light bending Problem - too much bend than observed, einstein’s prediction was better
What is the Christmas Tree analogy?
Christmas Tree analogy:
The lights on the christmas tree are the light from galaxies and stars. The tree itself is dark matter, holding the lights up inside the galaxies.
The visible parts of the universe are held by the invisible dark matter.
What is the evidence for Dark matter (do NOT explain them yet)
Rotational curve
Galaxy clusters
Light bending
Bullet Cluster
Big Bang Beginning
Microwave backgrounds
Ultra Faint Galaxies
Explain Microwave Backgrounds and Ultra Faint Galaxies, and how they are evidence for dark matter:
Microwave backgrounds:
The Indicate universe used to be too hot and cold in some places. These places are predicted to be where dark matter resides in the universe.
Ultra Faint Galaxies:
Some galaxies only have a few hundred stars, but exhibit gravitational forces equivalent to what we would expect from hundreds of thousands of galaxies - meaning there’s missing matter we are not seeing that exhibits gravitational forces.
Explain how the Big bang Beginning is evidence of dark matter existing:
We have evidence that the beginning of the big bang produced a smooth universe with only slight bumps. These slight bumps “collapsed” and came together through gravity.
Dark matter can’t interact with itself; it’s only through gravity that we know its there.
Dark matter allowed the creation of these collapsing areas of the universe to form faster. This was simulated, and the images created in this simulation are very similar to the 3D evidence we have of what the universe looks like today - the Cosmic Web.
How did the bullet cluster give evidence for dark matter?
Two galaxy clusters that collided with the smaller one shooting through the other. (taken through Cfa - LSS)
We saw the hot gas from these galaxies get pulled towards each other as they interacted with one another and were pulled together. This is not the case for dark matter.
The dark matter surrounding these galaxies in its little bubble didn’t really change. It stayed surrounding the galaxies, so this shows its not just a “normal” particle that can interact very easily - it only interacts through gravity.
Explain how Light Bending gave evidence for dark matter:
Galaxies can bend the light of further galaxies through their gravitational force creating a lensing or squashing effect.
The pattern of bending of light can give the galaxy’s mass and where it is.
We can use lensing maps to find mass distribution in a 3D topographical map. However, the peaks formed in these maps suggest the presence of more mass than what is found - thus it’s another evidence of dark matter.
