Ch - 25 (Stars and the Universe) Flashcards
What role does the sun play in the solar system?
- medium sized star
- hydrogen and helium
- radiates infrared, UV, and visible light
How are stars classified?
- Colors
- depends on how hot they are
What is a star’s colour related to?
Surface temperature.
What’s the range of star colors from hottest to coldest?
- Blue start is hottest (30 000 K)
- Red star is coolest (3000 K)
What happens at the center of a stable star?
Hydrogen nuclei undergo nuclear fusion to form helium
What happens during nuclear fusion?
- huge amount of energy is released.
- provides pressure for star that prevents it from collapsing under it’s gravity.
What are galaxies made up of?
Made up of billions of stars.
What is the universe made up of?
made up of many different galaxies
What is astronomical distance?
-distance between stars and galaxies
- very large
- light years
Define one light year.
The distance travelled by light through (the vacuum of) space in one year.
What is the speed of light known as?
Universal speed limit
- tracked slowly as compared to astronomical distances .
What is the diameter of the milky way?
100 000 light years
What is one light year equal to?
9.5 x 10 ^12 Km
9.5 x 10^15 m
What are the main stages of star formation?
- Nebula
- Protostar
- Main sequence star
- low mass star
- High mass star
What happens in the stage of nebula in star formation?
Form a giant interstellar cloud of hydrogen gas and dust called a nebula.
What happens in the stage of protostar in star formation?
- Force of gravity pulls nebula closer together forming a hot ball of gas known as protostar
- particles pulled closer, density of protostar increases
-frequent collisions causing temp to increase
What happens in the stage of main sequence star in star formation?
- when protostar is hot, nuclear fusion happens.
- hydrogen nuclei fuse together to form helium nuclei
- fusion reaction releases heat (and light)
- star is in equilibrium, and is stable
- inward force due to gravity is equal to outward pressure force from fusion reaction
What are the stages in low mass life cycle of a star?
- Red giant
- Planetary nebula
- White dwarf
- Black dwarf
What happens in the stage of red giant in star formation?
- fusion reaction in star runs out
- core starts to die down
- core shrinks (inward force of gravity will become greater than the outward force) and heats up
- helium undergo fusion to form beryllium
- cause outer part of star to expand
- 8 times the mass of the sun
- outer surface cools and turns red
What happens in the stage of main planetary nebula in star formation?
- star becomes unstable
- eject outer layer of dust and gas which is called planetary nebula
What happens in the stage of white dwarf in star formation?
- core collapses completely due to pull of gravity
- White dwarf cools
- amount of energy it emits decreases
What happens in the stage of Black dwarf in star formation?
- lost significant amount of energy
- cools until it eventually disappears
What are the stages in High mass life cycle of a star?
- Red super giant
- Supernova
- Neutron star (or Black hole)
What happens in the stage of red super giant in star formation?
- hydrogen causing fusion reaction runs out
- High mass star more than 8 times the mass of sun
- core starts to die down
- shrinks and heats up
- expands and constricts
- fusion reaction will form elements up to iron
What happens in the stage of supernova in star formation?
- core collapses suddenly
- causes gigantic explosion
- centre of explosion is dense body , called neutron star forms
- outer remnants of star are ejected into space forming new clouds of dust and gas (nebula)
- nebula from new stars may form new stars with orbiting planets
What happens in the stage of neutron star or Black hole in star formation?
- biggest star
- center continue to collapse under force of gravity
- very dense and no light escapes
What happens when an object emits waves?
Wavefront spread out symmetrically.
What 2 factors will a moving object cause a change to?
Wavelength and frequency.
What happens to wavelength and frequency in a moving object?
- wavelength of the waves in front decreases, and frequency increases
- wavelength behind the source increases and frequency decreases
- doppler effect
What does the Doppler effect also affect?
- light
- object moves away then wavelength of light decreases
- this is red shift as light moves to end of spectrum
Define redshift.
An increase in the observed wavelength the electromagnet radiation emitted from receding stars and galaxies.
How does the light from distant galaxies appear?
Redshift
How are the lines on the spectrum and what does it indicate?
- shifting towards red
- galaxies are moving away
- universe is expanding
- supports Big Bang Theory
What is another observation we can conclude from the light spectrum produced from different galaxies?
- Greater the distance to the galaxy, greater the redshift
- the further away the galaxy is, the faster it is moving away from us
How and when did the Big Bang Theory begin?
- 14 billion yrs ago universe bagan from a very small region that was extremely hot and dense
- giant explosion
- universe expanded away from every point
What is an evidence for the universe expanding?
redshift of distant galaxies
What happens when balloon is deflated and expanded? And why?
- Expands - all points become further apart by same amount
- Deflated - all points are close together and equal distance apart
Space itself has expanded between galaxies
What are the main pieces of evidence for the Big Bang Theory?
- Galactic red shift
- Cosmic Microwave Background Radiation (CMBR)
What does it prove when light spectrum produced from distant galaxies are red shifted more than nearby galaxies?
- Greater the distance to the galaxies, greater the red shift
- further away galaxy, faster it is moving
What is CMB Radiation?
- Type of electromagnetic radiation which is remnant from early stages of the Universe
- wavelength of 1mm
What did astronomers discover in 1964?
Microwave from all directions at uniform temperature of 2.73K
Unable to do earlier as microwaves were absorbed
How was the early Universe according to Big Bang Theory?
extremely hot and dense
Emits thermal radiation
How is the thermal radiation of microwave in Big Bang Theory?
- Initially it would be High energy
- wavelength of radiation increased
How is CMB radiation?
- Uniform
- exact profile to be expected from a hot body
What do different colors on CMB radiation mean?
- The red/orange/brown regions represent warmer temperature indicating High density regions
- Blue regions represent cooler temperatures indication lower desnity
what is the formula for measuring the universe and velocity of distant objects from redshifts?
difference between actual wavelength and expected wavelength / actual wavelength = speed of galaxy / speed of light
How do we measure distance in space?
Standard candles including supernovae
What are supernovae?
Exploding stars
how do we measure distance using supernovae?
- some types have have same peak level of brightness (absolute magnitude)
Type 1a supernovae are very brught
what happens in 1929 with astronemer Edwin Hubble?
- showed universe is expanding
- observed the abdsorption of light spectra
- light was shifted towards the red end of the spectrum
- observed more distant galaxies are more red shifted than the light
What does Hubble’s law state?
The recessional velocity v of a galaxy is proportional to its distance from the Earth.
How can Hubble’s law be expressed as symbol?
H0 = v /d
H0 = Hubble constant (per sec)
v = recessional velocity of an object moving away from an observer (km/s)
d = distance between object and earth
Define Hubble constant.
The ratio of the speed at which the galaxy is moving away from the earth, to its distance from the earth
What is the value of Hubble constant?
2.2 x 10^-8 per sec
How can the Hubble law equation be rearranged ?ro calculate
1 / H0 = d /v
