Lec 23 Revision and questions Flashcards
(19 cards)
Why isn’t the universe more akin to a black hole, if it was condensed into a singularity?
Black holes are more empty space with a vacuum solution. All the mass of the black hole is at the singularity center
Our expanding universe has matter everywhere and is mathematically different from black holes. Time is dependent on universes while it’s not in a black hole. While our universe does have a cosmological horizon from expanding, it changes as the universe expands (unlike in a black hole with an event horizon).
How does so much matter fit in a singualrity?
Initial singularity - the “zero size” of the universe when time = 0
Since the 1980s, models of cosmology o ther very early universe (within the first 10 ^-36 seconds) show the universe undergoing early period of accelerated expansion (inflation).
All the energy and matter at the singular point with an initial volume less than a single proton. Inflation expands it enough to account all mass in the universe
What is inflation? What does it seem to explain?
Inflation - explains the oddities involving the initial state o the universe (e.g. similar critical and actual densities, why the universe is smooth on a large scale, and the seeds that grow into galaxies come from)
How bright and hot was the Big Bang/ early universe? Explain the 3 pieces evidence?
Evidence from CMB, Planck astonomy, and photons:
Microwave backgrounds show that the universe had intense heat and light. CMB discovered in 1965 by Robert Wilson and Arno Penzias using the Bell Telephone Lab.
More evidence of the intense heat from Planck astronomy - the study of CMB (the relic radiation formed early in the universe) and other astrophysical phenomena through planck satellites.
Used to help understand the origin, evolution, and structure of the universe.
Billions of photons from each proton that stretch by expansion (redshift). Show that the early universe was hotter than todays (enough to naturally have nuclear reactions).
Anything before the BB? how does this realte to the singularity?
Not definitive, but something like the “initial singularity” was the origin of infinite density and temperature followed by the Planck epoch (the time immediately following the singularity).
Some models think the Big Bang might have been a consequence of quantum fluctuations, so the quantum field would have had to precede it.
Why ddi the BB happen? What other theories are there?
Why? - No one really knows why as its just a theory and not an event.
Alternate theories think the Big Bounce occurred, which suggests a cyclical universe with periods of expansion and contraction with “rebirth” rather than a true beginning.
When did the BB happen? What evidence is there?
When - theorised about 13.8 billion years ago. Evidence from:
Redshift light of the furthest distance of galaxies
CMB - the faint radiation of the big Bang afterglow that can estimate the age of the universe
The high ratio of Hydrogen and Helium
Ages of old stars and other celestial objects that can be carbon dated up to 13.8 billion years.
how did initial galaxies form?
Initially tiny density fluctuations amplified by cosmic inflation created pockets of denser areas. Overdensity pulled more matter leading to formation of small dense objects taht merged and grew into initial galaxies.
Inside these proto-galaxies, gas cooled and collapsed into suns, planets, etc.
What evidence is there that we are living in a strange SS?
Rarest structure - Ordered STructure, where the mass of planets seems to sequentially increase with distance to sun
Unusually large number of planets and complex Moons
Larger distance of inner planets, and the existence of an asteroid belt
Presence of liquid water
Gas giant size, composition, and distribution is not super common
Life and Intelligence
Unusually high elements creating our planets (likely from merging neutron stars)
Give 4 reasons why scientists believe the universe contains substantial amounts of dark matter.
- Galaxy rotation curves - galaxies rotate much faster than they should based on visible matter along.
- Gravitational lensing - massive objects like galaxy clusters warp space time and bend light from distant objects bhind the. The degree of light bent is relative to the mass of the lensig object. However, gravitaitonal lensing shows clusters with much more mass than is visible.
- Bullet cluster - two galaxy clusters that collided. we could visibly see an interation in the hot gas of each cluster creating a shockwave. However, gravitaitonal lnesing revealed most of the mass in the merged cluster was not affected.
- CMB - afterglow of BB. the patterns and fluctuations revela the early universe and regions of slightly higher density eventually collapsed for form galaxies and clusters. The structure we see today can only be explain if there was more mass present that what we observe as visible matte.r
Describe 3 ways scientists test specific theories of dark matter:
- Direct Detection - large sensitive detectors deep undergrowth to try and catch dark matter particles taht collide with atoms in the detector and casue faint signals. (example: LUX-Zeplin)
- Indirect Detection - If dark matter particles are their own antiparticles they can annihilate or decay into detectable particles like gamma rays, neutrinos, or positrons. Use Fermi Gamma-ray telescope and neutrino detectors to search for these signals.
- particle Acceleration - collide particles at extremely high energies to maybe create dark matter particles. analyse the debris from collisions for any evidence of missing energy or unusual particles (e.g. LHC)
If Dark matter didn’t exist, what alternative explanation would scientists be likely to invoke to explain observations currently attributed to dark matter?
the alternative explanation would be modified gravity theory. modified gravity is that instead of dark matter existing, that instead we simply dont understand gravity well enough, and have to change around a couple laws and theories as to how to works.
Between Brown dwarfs, white dwards, neutron stars, and black holes. Sort these objects from lowest to highest mass.
- brown dwarfs
- white dwarfs
- neutron stars
- black holes
Between Brown dwarfs, white dwarfs, neutron stars, and black holes. list an approximate size for each type of object (can be qualitative)
- Brown Dwarfs - slightly larger than jupiter.
- White Dwarfs - about the size of earth
- Neutron Stars - about the size of a large city
- Black Holes - their radius is calculated by their mass being roughly city sized (althought supermassive black holes can be millinos of times larger).
Between Brown dwarfs, white dwarfs, neutron stars, and black holes. what type of astronomical object would each of these have been before their current state?
- Brown Dwarfs - would have simply come from dust and gas in nebula nurseries.
- White dwarfs - are the left over remnants of low-mass stars. This is one of the last stages of their life have formed after red giant turns into planetary nebula and the remnant (white dwarf) is left over from the low mass star’s core.
- Neutron stars - the left over remnant of high-mass stars between 8-20 solar masses after their supernova explosion.
- Black holes - formed from the supernova explosion of high mass stars above 20 solar masses.
Between Brown dwarfs, white dwarfs, neutron stars, and black holes. Imagine a hypothetical universe where only brown dwafs exist. Would you expect to find life in such a universe. Why or Why not?
No I would not expect to find life. Life is dependent on chemistry, radiation (energy), and water.
* Brown Dwarfs are unable to perform nuclear fusion in their cores for produce heat and light (so there would be no energy to support life). *Stars are essential to create habitable zones for planets to ahve the potential for life. Without stars, brown dwarfs cannot give of their own light and heat, the habitatbale zone would not exist
* Brown dwarfs are also “sinks” in the universe. thus any resources that go into making Brown dwarfs are not recycled back into theu niverse, so the unvierse would not be enriched at all!
compare Mercury, Moon, and Pluto: State the classification of each object and define what that classification means.
Mercury - a terrestrial planet; a planet made in our solars system. Plants cna only be defined as planets if they have; enough gravity to naturally be shaped spherically, have cleared their orbit around a sun, and have cleared out the other objects iwthin it’s trajectory.
Moon - a moon; this is a celestial object that is orbiting another celestrial object (typically a planet), that is not orbiting a sun. The moon is typically smaller than the planet it orbits.
Pluto - dwarf planet; a planet that is technically able to have enough mass and gravity to naturally be spherical, but it has NOT claered its neighborhood around its orbit.
compare Mercury, Moon, and Pluto: Name at least 1 challenge that you would need to overcome for a mission (crewed or uncrewed) to mercury taht is NOT (or far less) relevant to a mission to the moon or pluto.
At least 1 challenge that you would need to overcome for a crewed mission on mercury that woudl be far less important than on the moon or pluto is the higher intensity of the sun’s radiation and heat (and also the intense change in temperature between night and day). The moon is far enough taht while the radiation fro mthe sun is still highly dangerous, a crewed mission on the moon wouldn’t have to deal with horribly high heat. On the other hand, Pluto is so far from the sun that a crewed mission (if we can figure out how to even get a crewed mission on pluto) would have to be more worried about the intense cold of the planet.
compare Mercury, Moon, and Pluto: Name at least 1 challenge you woudl need to overcome for a mission (crewed or uncrewed) to pluto that is not (or at least far less) relevant to a mission to the Moon or Mercury.
At least one challenge to overcome for a crewed mission to Pluto would be the massive amount of time it would take to reach pluto. For a crewed mission in particular, a mission to the Moon or Mercury is far mroe doable food-wise and time-wise. However, due to the large distance away from Pluto, it becomes a large issue of will ther ebe enough food? Wil the time it takes be too long? Will the crew end up dying before they can come back on time?
