Galaxies & Cosmology – B. Cosmology Flashcards
What is the Doppler principle for radial velocities.
Radial velocity is how fast an object is travelling in the direction of the line of sight. When an object moves (Solar System object, star or galaxy) we can measure changes in its spectrum. These changes are known as Doppler shifts and will show redshift (or/and blueshift) and from that scientists can deduce velocity.
Light from distant galaxies is shifted to what?
Some galaxies appear to have more red lines in their spectrum. Red light operates at a longer wavelength and means the object showing the red light is moving away from the observer. These objects are said to show a redshift.
In the Local Group, is blue-shift is possible?
There are some galaxies that have a small blueshift, meaning they are moving towards us. These are galaxies in our Local Group. The Andromeda galaxy is travelling towards us and will eventually collide with ours in billions of years’ time.
What are quasars?
They show large redshifts in their light meaning they are moving away from us at very high speeds and are typically billions of light years away from us. They are the oldest objects that we know about.
How did astronomers discover quasars?
1950s scientists detected them by radio telescope but were unable to detect a visible object associated with them until 1960. Their broad emission lines meant they were not stars. In 1962, scientists measured a source as it occulted the Moon, showing a large redshift in the spectral lines. This redshift was given the name “quasi-stellar radio sources.
What formula is used to find the relationship between distance and redshift of distant galaxies?
v=Hd (v is the speed at which a distant object is receding from us, d is its distance, and H is the Hubble constant).
Describe the existence and significance of cosmic microwave background (CMB) radiation.
The CMB is the furthest (and therefore, oldest) signal detected by a telescope. The temperature is 2.7 K. THE CMB is the heat remnant of the Big Bang, the background temperature of the Universe. To our eyes (and telescopes) space appears black, but to a sensitively calibrated radio telescope, a background glow appears. This is consistent in any direction with very minor variations in density - the apparent ‘ripples’ in the radiation.
As the heat and plasma from the Big Bang expanded, the Universe became transparent and the radiation cooled to its present temperature.
How was CMB discovered?
CMB was theorised before it was discovered. With the formation of the Big Bang theory, the question arose as to what happened to all the heat in the Universe from that time.From the mid 1940s to the mid 1960s, various scientists theorised of the temperature of the Universe and its form. There were estimates to within a fair degree of accuracy.
In 1964, Arno Penzias and Robert Wilson at Bell Labs worked on a sensitive 6 metre ‘horn antenna’ radio telescope. They eliminated all known radio waves but still detected a faint but consistent noise. it was spread throughout the sky and did not change throughout the day. The wavelength they worked on did not come from the Milky Way, but from outside the galaxy.
Princeton University scientists were working on detecting microwaves left over from the Big Bang. When they heard about Penzias and Wilson, the two sets of research produced proof of the CMB.
What is the possible nature and significance of dark matter?
Scientists have measured the mass of galaxies (by studying the light coming from them and their velocity). It has been found that they are moving faster than they ought to for their mass. This should not be possible within other laws of physics. Their mass should be many times higher.
Scientists believe that there is some invisible matter - dark matter - that cannot be directly observed that can make up over 90% of the matter in galaxies.
Candidates could be dark dust, black holes, brown dwarfs, neutrinos or a new type of object or matter, yet to be observed.
What is the significance of dark energy?
It appears to be a force that moves galaxies away from each other. The expansion of the Universe since the Big Bang should have slowed down the rate of movement between galaxies. The opposite is happening, however; the rate of movement is increasing. Scientists believe an invisible force – dark energy – is responsible for this.
What is the observational evidence for an expanding Universe.
Edwin Hubble proved that galaxies are moving away from each other because they show a redshift (see the Doppler page). Evidence of redshift galaxies shows us that it is still expanding.
Demonstrate an understanding of the past evolution of the Universe and the main arguments in favour of the Big Bang.
The Universe is thought to have expanded from a single point called a singularity around 13.7 billion years ago. Within the first second of creation, matter and antimatter were created. hydrogen and helium were created and these are the most abundant elements in the Universe today. Within minutes of the Big Bang the temperature of the Universe exceeded 10,000 million degrees. It gradually cooled enough for stars to form.
Demonstrate an awareness of the different evolutionary models of the Universe (past and future) and why cosmologists are unable to agree on a model.
We have moved from a flat Earth to a round one, and a geocentric model to a heliocentric one in our Solar System, putting the Sun at the centre. Although we give credit to Copernicus, the idea was around a long time before him. In the western world however, we had still clung on to the geocentric model.
The theory was formed from the evidence we had at the time, and most scientists think it is the best fit. Until many crucial questions are answered however, there is some uncertainty.
Some serious scientists propose a multiverse - many Universes, each having different laws, dimensions and time systems.
