Astronomy Quiz on Galaxies and Cosmology
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Questions and Answers

What phenomenon allows us to observe the galactic center despite the obscuring gas and dust?

  • Infrared radiation
  • Visible light
  • Ultraviolet light
  • Gamma rays and radio waves (correct)

What is the shape of the rotation curve expected based on Keplerian orbits?

  • It remains constant with distance
  • It decreases with distance (correct)
  • It increases with distance
  • It flattens out with distance

Which classification of galaxies has tightly wound arms according to the Hubble Tuning Fork?

  • Barred Spiral SBb
  • Spiral Sa (correct)
  • Irregular
  • Elliptical EO-E7

What is one proposed solution to the missing mass problem in galaxies?

<p>Small brown dwarf stars in the galactic halo (A)</p> Signup and view all the answers

Who confirmed the existence of external galaxies through the use of Cepheid variables?

<p>Edwin Hubble (B)</p> Signup and view all the answers

Which type of galaxy typically has little to no gas and dust?

<p>Elliptical (A)</p> Signup and view all the answers

What is the primary cause of spiral arms in galaxies?

<p>Gravitational density waves (A)</p> Signup and view all the answers

What is the estimated mass range of spiral galaxies in solar masses?

<p>$10^9$ to $4 imes 10^{11}$ (D)</p> Signup and view all the answers

What method uses the apparent size of a galaxy to estimate its distance?

<p>Apparent Size (C)</p> Signup and view all the answers

What is the approximate value of Hubble's constant?

<p>65 km/sec/Mpc (C)</p> Signup and view all the answers

What are supernovae primarily used for in astronomy?

<p>Determining distances to galaxies (A)</p> Signup and view all the answers

Which shape of the universe suggests it will expand forever but not accelerate?

<p>Flat (D)</p> Signup and view all the answers

During which era did the strong force split off to establish three fundamental forces?

<p>Electro-Weak Era (C)</p> Signup and view all the answers

What event occurs approximately 3 minutes after the Big Bang?

<p>Formation of helium (C)</p> Signup and view all the answers

What does the term 'Inflationary Epoch' refer to?

<p>A rapid expansion of the universe (D)</p> Signup and view all the answers

What kind of universe will accelerate indefinitely into the future?

<p>Hyperbolic (C)</p> Signup and view all the answers

Which notable phenomenon did Penzias and Wilson observe that supports the Big Bang theory?

<p>Cosmic microwave background radiation (B)</p> Signup and view all the answers

What aspect of the universe does Einstein's equations of General Relativity reveal?

<p>Possible shapes of the universe (B)</p> Signup and view all the answers

What characterizes rich clusters of galaxies?

<p>They have thousands of member galaxies. (D)</p> Signup and view all the answers

What does Hubble's Law describe?

<p>The relationship between recessional velocity and distance of galaxies. (C)</p> Signup and view all the answers

What is the current value of Hubble's constant approximately?

<p>65 km/sec/Mpc (C)</p> Signup and view all the answers

Which method is deemed the most accurate for determining distances to galaxies?

<p>Supernovae (B)</p> Signup and view all the answers

What shape does a hyperbolic universe imply?

<p>It will continue to accelerate outward. (C)</p> Signup and view all the answers

Which era occurred immediately after the Big Bang?

<p>Planck Era (A)</p> Signup and view all the answers

What phenomenon did Penzias and Wilson observe that supports the Big Bang theory?

<p>3 Kelvin background radiation (B)</p> Signup and view all the answers

Which of the following descriptions fits a flat universe?

<p>It expands forever without acceleration. (D)</p> Signup and view all the answers

What determines the distances to galaxies using apparent size?

<p>Smaller apparent size indicates greater distance. (A)</p> Signup and view all the answers

At time T=0 in the history of the universe, what was contained in the initial point?

<p>Time and matter (C)</p> Signup and view all the answers

What is the composition of a galaxy?

<p>A collection of stars, gas, and dust (D)</p> Signup and view all the answers

What was William Herschel's incorrect belief about the Solar system's location?

<p>At the center of the Milky Way (C)</p> Signup and view all the answers

What is the relationship used by Harlow Shapley to estimate distances to globular clusters?

<p>$M = m - 5 ext{log}(d) + 5$ (D)</p> Signup and view all the answers

Which component of the galaxy does interstellar gas and dust obscure?

<p>The galactic center (C)</p> Signup and view all the answers

Which type of star is classified under Population I?

<p>O and B stars (B)</p> Signup and view all the answers

How is tangential velocity of a star calculated?

<p>$T = 4.7 rac{m}{d} rac{km}{sec}$ (A)</p> Signup and view all the answers

What does the Local Standard of Rest (LSR) represent?

<p>The average speed of stars in the local vicinity (A)</p> Signup and view all the answers

What is the approximate mass of the galaxy compared to the Sun?

<p>$9.4 imes 10^{10} M_{sun}$ (A)</p> Signup and view all the answers

What allows the measurement of speeds around the galactic center?

<p>Doppler shifts of spectral lines (D)</p> Signup and view all the answers

Flashcards

Clusters of Galaxies

Groups of galaxies bound together by gravity. They can be 'rich' with thousands of galaxies or 'poor' with only a few dozen.

Local Group

The cluster of galaxies that our Milky Way galaxy belongs to.

Redshift

The shift of light toward longer wavelengths (redder) as a galaxy moves away from us.

Hubble's Law

The relationship between a galaxy's distance and its recessional velocity: the farther away a galaxy is, the faster it's moving away.

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Hubble's Constant

The constant of proportionality in Hubble's Law, representing the expansion rate of the universe.

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HII Regions

Regions of ionized hydrogen gas in galaxies, used as distance indicators.

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Supernova

Extremely bright explosions of stars, used as accurate distance indicators in astronomy.

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Big Bang Theory

The prevailing theory of the universe's origin, stating that it started from an infinitely small point and has been expanding ever since.

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Planck Era

The earliest stage of the universe after the Big Bang, lasting about 10^-43 seconds.

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Universe Shape

The universe can be spherical (eventually collapsing), flat (expanding forever without acceleration), or hyperbolic (accelerating outward).

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Hubble's Constant (H₀)

The rate at which the universe is expanding, measured in kilometers per second per megaparsec (km/sec/Mpc).

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Apparent Size

The apparent size of a galaxy in the sky, useful for estimating its distance. Smaller apparent size implies greater distance.

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Apparent Brightness

The perceived brightness of a galaxy from Earth, used to estimate its distance. Brighter galaxies appear closer.

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HII Region Size

The size of regions in galaxies where hydrogen is ionized, indicating star formation. These regions can be used to estimate distance.

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3° Kelvin Background Radiation

A faint cosmic microwave radiation permeating the universe, predicted by the Big Bang Theory and observed by Penzias and Wilson.

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Inflationary Epoch

A period of extremely rapid expansion (faster than the speed of light) in the early universe, occurring around 10⁻³⁵ seconds after the Big Bang.

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Einstein's Equations of General Relativity

Equations describing the behavior of gravity and spacetime. Solutions for a homogeneous and isotropic universe predict three possible shapes: spherical, flat, and hyperbolic.

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Hyperbolic Universe

A universe that expands forever and accelerates outward. Parallel lines diverge, and the sum of angles in a triangle is less than 180°.

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Galactic Rotation Curve

A graph that plots the speed of objects orbiting a galaxy's center against their distance from the center.

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Missing Mass Problem

The discrepancy between the observed rotation of galaxies and the expected rotation based on visible matter. This suggests the presence of unseen, dark matter.

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Galactic Center

The dense, central region of a galaxy, often containing a supermassive black hole. It's obscured by gas and dust in visible light, but observable in radio and gamma rays.

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Island Universes

Kant's theory that faint, diffuse nebulae were independent galaxies outside our own Milky Way.

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Hubble Tuning Fork Diagram

A classification system for galaxies, dividing them into spiral, barred spiral, elliptical, and irregular types, based on their visual appearance.

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Spiral Arms

Regions of concentrated stars, gas, and dust that trace out a spiral pattern in spiral galaxies. They are caused by density waves that trigger star formation.

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Keplerian Orbits

The expected orbital behavior of objects based on Newton's laws of gravity, where speed decreases with increasing distance from the central body.

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Rotational Curves of Galaxies

Plots that show the orbital velocity of objects in galaxies as a function of distance from the galactic center. They often contradict Keplerian expectations, hinting at dark matter.

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Milky Way

A spiral galaxy containing our solar system and all stars visible to the naked eye.

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What did Galileo observe about the Milky Way?

Galileo was the first to observe that the Milky Way is composed of countless stars.

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RR Lyrae variable

Pulsating stars with a well-defined relationship between their pulsation period and luminosity.

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Period-Luminosity relationship

A correlation between a star's pulsation period and its intrinsic brightness (luminosity).

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Interstellar gas and dust

Clouds of gas and dust found between stars, obscuring our view of the galactic center.

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Population I stars

Stars with high metal content, found in the galactic disk, associated with open clusters and type I Cepheid variables.

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Population II stars

Stars with low metal content, found in the galactic halo, associated with globular clusters and type II Cepheids.

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Proper motion

The apparent angular change in a star's position across the sky due to its movement.

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Tangential velocity

The speed of a star moving across the line of sight.

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Local Standard of Rest (LSR)

A reference point in space with a velocity equal to the average velocity of stars close to the Sun.

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Study Notes

Hubble's Constant

  • To determine Hubble's constant (H₀), Hubble needed to measure distances to a large number of galaxies for which he had spectra (thus velocities).
  • He then plotted recessional velocity versus distance, and the slope of a line fit to the data is the value of H₀.
  • Problem: How do you determine distances to distant galaxies?

Methods of Determining Galactic Distances

  • The size galaxies appear: The smaller they look, the further they must be.
  • The brightness of HII regions: The brighter they appear, the closer they are.
  • Supernovae: Most accurate method.

The Big Bang Theory

  • The universe started as an infinitely small point 15 billion years ago.
  • Time expanded outward, carrying galaxies, gas, and dust.
  • Predicts observed 3° Kelvin background radiation by Penzias and Wilson.
  • Solutions of Einstein's equations of General Relativity for a homogeneous, hyperbolic (saddle-shaped), or flat universe.

Shapes of the Universe

  • Spherical: The universe would eventually collapse back on itself. Parallel lines will eventually intersect, the sum of angles in a triangle are greater than 180°.
  • Flat: The universe will expand forever, but not accelerate. Parallel lines remain parallel, angles in a triangle always equal 180°.
  • Hyperbolic: The universe accelerates outward. Parallel lines will eventually diverge, interior angles in a triangle add to less than 180°.

History of the Universe

  • Universe, space, time, matter, and energy all contained in an infinitesimally small point.
  • Planck Era: Need quantized gravity to know what happened here.
  • Grand Unified Field Era: No normal atoms, strong force, weak force and electromagnetic force are all one force here.
  • Electroweak Era: The strong force splits off, so there now 3 fundamental forces: gravity, strong, and electro-weak. Elementary particles form.
  • Electromagnetic and weak forces separate: Particle era
  • Nucleo-synthesis Era: Protons, neutrons form first atoms, and H forms helium.
  • Radiation Era: Atoms now form part of radiation era (photons become free). Radiation cools the universe expands, atoms are free to pick up electrons, form complete atoms, forming stars and galaxies.
  • Inflationary Epoch: There was a time early on (10⁻³⁵ sec) when the universe expanded faster than the speed of light. This is necessary to explain observations of the background radiation.

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Description

Test your knowledge on galaxies and cosmological concepts with this quiz. Explore topics such as galactic centers, galaxy classification, and the expansion of the universe. Perfect for students of astrophysics or anyone interested in the mysteries of the cosmos.

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