Ch19&20: Astrophysics and Cosmology Flashcards
Define a planet.
An object with enough mass for their gravity to make them spherical, no nuclear fusion and with an orbit clear of other objects.
What is the difference between a dwarf planet and a planet.
A dwarf planet is typically smaller with an orbit not clear of other objects.
What are planetary satellites?
Bodies that orbit a planet.
Define an asteroid.
An object too small and uneven to be a planet with a near circular orbit.
What is the difference between asteroids and comets?
Comets have elliptical orbits, and are irregularly shaped. Asteroids are more spherical and have circular orbits.
Define a solar system.
Systems containing stars and orbital objects.
Define a galaxy.
A collection of stars, interstellar dust, and gas held together by mutual gravitational force.
Define emission spectra.
A set of specific frequencies of electromagnetic radiation, visible as bright lines on a dark spectrum, created by excited atoms giving off specific photons as they transition between energy levels. Every element has a unique line spectrum.
Define a continuous spectrum.
A spectrum in which all visible frequencies of light are present.
Define absorption line spectra.
A set of specific frequencies of electromagnetic radiation, visible as dark lines on a continuous spectrum, they are absorbed by electrons moving between energy levels in the form of photons.
Every element has a unique line spectrum.
How many arcseconds in 1 degree?
3600
What quantity do arc seconds measure?
Angles.
What is Wein’s law?
The blackbody radiation curve for different temperatures peaks at a wavelength inversely proportional to the temperature of the object.
What is Stefan’s law?
Total radiant heat energy emitted by a blackbody is proportional to the 4th power of its absolute temperature.
What is the equation for Stefan’s law?
L=4πr²T^4σ
Define a light year.
The distance travelled by light in one year. Speed of light x Seconds in a year
What is 1 Au?
The average distance from the Earth to the sun. 1.5 x 10^11m
What is the first stage in the life cycle of a star?
Nebula, Collection of dust, gas and rock.
How is a protostar formed from a nebula?
Gravity clumps the nebula together, the gpe turns into heat at the centre of the protostar.
What is the approximate make up of a nebula?
75% hydrogen, 25% helium.
What is the requirement for a protostar to become a main sequence, and why?
When the temperature is above 15 Million Kelvin. This is the minimum energy needed to overcome electrostatic force for nuclear fusion.
What keeps a main sequence star stable?
The balance of Gravitational forces inwards and radiation pressure outwards.
What happens to main sequence stars below a mass of 10☉as they run out of hydrogen?
They become red giants. The reduction in energy causes the star to begin to collapse, this increase in pressure allows fusion to take place in shells.
What happens to main sequence stars above 10☉?
They become red supergiants, fusing heavy elements up to and including iron.
What happens to a red giant when fusion stops?
Outer layers escape as new nebulae and the hot dense core becomes a white dwarf.
What is the maximum mass of a white dwarf?
1.44M☉
Why is there a limit on mass of White dwarf, what is this limit called?
The chandrasekhar limit. If mass is any higher, electron degeneracy pressure will not be great enough to sustain the star from collapse.
What causes supernova of a red supergiant?
The pressure of fusion in the core no longer withstands the gravitational pressure, and the star collapses.
What happens to a star after supernova?
Either becomes a neutron star, for masses under 3M☉ or a blackhole, for masses over 3M☉.
What is a neutron star?
A star made almost entirely of neutrons, with a mass of around 2M☉ and a diameter of around 10km.
What is a blackhole?
Very massive objects with gravitational fields so strong, light cannot escape them.
What are the two axis of the Hertzsprung-Russell diagram? What is irregular about them?
- Luminosity (y) against Temperature (x)
- Temperature decreases along axis
What is the cosmological principle?
The universe is isotropic and homogenous.
Define Isotropic.
Looks the same in all directions when viewed from any point.
Define homogenous.
Uniformly distributed with the same density over large volumes.
What is the doppler effect?
When wavelengths of moving objects appear to change because they are moving toward/away from us.
Define ‘red shifted’.
Wavelength is appearing to increase, an object is moving away from us.
Define ‘blue shifted’.
Wavelength is appearing to decrease, the object is moving toward us.
How can the age of the universe be determined using Hubble’s law?
T = 1/Ho
What are the two main pieces of evidence for the Big Bang theory?
- Red Shift
- Microwave background radiation.
How can a parsec be derived?
- 1 Parsec = 1 Au/tan(1 arcsecond)
- tan(small angle)=angle
- so, 1 Pc=1 Au/1 Arcsecond
What is the equation used to determine distances using stellar parallax? What units are used?
d = 1/p
d: parsecs
p: arcseconds
Describe the state of the universe at the time of the Big Bang.
Universe is a hot, dense, singularity.
Describe the state of the universe at a time of 10^-35 seconds.
Inflation, no matter yet, only gamma photons and electromagnetic radiation. Temperature is around 10^28 K
Describe the state of the universe at a time of 10^-6s.
First fundamental particles gain mass through a mechanism involving the Higgs Boson.
Describe the state of the universe at a time of 10^-3 seconds.
First hadrons created from quarks, most mass in universe created through pair production.
Describe the state of the universe at a time of 1 second.
Creation of matter stops, temperature of around 10^9K
Describe the state of the universe at a time of 100s
Rapid expansion continues, protons and neutrons form to create helium and deuterium nuclei, no heavier elements than lithium or beryllium. About 25% of all matter is helium nuclei.
Describe the state of the universe at a time of 380,000 years.
Cool enough for atoms to form, nuclei capture electrons. Electromagnetic radiation from this stage is what is detected today as background radiation.
Describe the state of the universe at a time of 30 million years.
First stars appear, through fusion they create the first heavier elements.
Describe the state of the universe at a time of 200 million years.
Our galaxy forms.
Describe the state of the universe at a time of 9 billion years.
Our solar system forms, then our sun forms, then Earth around 2 billion years after.
At what age of the universe do the first particles gain mass?
10^-6 seconds.
At what age of the universe do atoms form?
380,000 years.
Define intensity.
Energy per unit area.
State Hubble’s law.
Recessional speed of a galaxy is proportional to its distance from us.
State two properties of a black hole.
- Very dense and very small
- Traps light, slows time, high escape velocity.
