A16 - Cosmology Flashcards
What is redshift, and where is it observed?
-light being shifted to longer wavelengths
-observations of galaxies outside Local Group are receding from us, and the light emitted from them exhibit redshift
Redshift is evidence for the expansion of the Universe
Why didn’t early telescopes have the capability of discovering redshift from other galaxies?
-earlier telescopes had much smaller apertures
-this meant that they had an insufficient light grasp
-they couldn’t capture the light from the much fainter galaxies outside the Local Group that showed substantial redshift
What is the formula for the radial/recessional velocity of a galaxy?
wavelength units can be whatever as long as they are the same on the top and bottom, and the 2 velocities must also have the same unit
λ is observed wavelength, and λ₀ is rest wavelength
Angstroms could be used, and are equal to 10⁻¹⁰m, or 0.1nm
What is Hubble’s constant, and Hubble’s Law?
-a constant of proportionality, H₀, that relates the distance of a galaxy, to its recessional velocity (~69.8km/s/Mpc)
v = H₀d
In the equation, the units for the Hubble constant should be converted to s⁻¹
How can you calculate the age of the Universe, given data about the speed and distance of several galaxies?
-plot velocity (km/s) vs distance (Mpc) for all galaxies
-draw line of best fit and calculate its gradient (units will be in km/s/Mpc)
-convert unit to 1/s and then take its reciprocal to get the age of the Universe in seconds
Name 3 main pieces of evidence that support the Big Bang Theory:
-quasi-stellar objects (abbreviated as quasars, or QSOs)
-cosmic microwave background radiation
-Hubble Deep Field image + redshift
What evidence supports the Steady State Theory?
-redshift
-the expanding Universe
What are quasars? How do they support the Big Bang Theory?
-objects that appear like stars, but are actually supermassive black holes at the centre of ancient galaxies that emit large amounts of X-rays + other radiation
-this is due to the large amount of matter falling into them (an AGN)
-they are only seen at very far distances from Earth, implying that they were only formed in the early stages of the Universe
What is the Cosmic Microwave Background Radiation?
-the heat remnants from the Big Bang that cooled down so much that it is now only 2.7K
-it appears to come from everywhere all at once
Just 2.7°C above absolute zero
What were 2 research missions that were used to enhance the knowledge of the CMBR?
-2001 Wilkinson Microwave Anisotropy Probe (WMAP), NASA
-2009 Planck Surveyor mission, ESA
What did NASA’s WMAP do?
-mapped CMBR, producing the first fine-resolution map of it (0.2° resolution)
-determined the age of the Universe to be 13.73 billion years old (with 1% error)
Planck surveyor basically did the same thing
How does the Hubble Deep Field image support the Big Bang theory?
-it showed a lot of galaxies with higher redshifts than predicted
-lots of galaxies with irregular/disturbed shapes, showing how collisions were much more frequent in the younger Universe
Describe why dark matter is thought to exist:
-the stars on the outer edge are orbiting far too fast for their mass based on our knowledge of physics (they should be slower as they go out, but instead their speeds increase)
-to explain this, scientists think that there is matter that can’t be directly observed that makes up 90% of the matter in galaxies
Analyse the graph to explain the differences between the observed and theoretical speeds of stars in the Milky Way:
-the theory suggests that stars near the edge should travel slower but observation shows that they actually travel faster
-this suggests the existence of dark matter, whose gravity attracts stars further from core
-the dark matter provides an additional force to allow outer stars to travel quickly enough to explain the observations
Why is it hard to study dark matter?
-doesn’t emit any EM radiation
-interacts very weakly with other matter (only through gravity)
