Unit 2 Module 5 - Modelling the universe Flashcards
What is a galaxy?
A cluster of many billions of stars slowly rotating around its own centre of gravity
What is the nucleus of a galaxy?
Where the concentration of stars is greatest. There is bulge.
How can you detect stars?
They emit electromagnetic radiation, using their energy supply of fusion.
Why is brightness misleading?
An extremely bright but distant star will look less bright than a much less bright but much closer star.
What is a planet?
A cold object which has a nearly circular orbit around a star
How can we tell a star has a planet orbiting it?
The gravitational force from the planet on the star causes it to wobble slightly, which can be detected.
Why is it difficult to detect planets?
They are not hot enough to emit any visible radiation. They are only visible because they reflect light.
What is a moon?
A satellite of a planet
What are nebulae?
Density of space is not constant. There are some regions where the density is larger and these regions therefore have a greater gravitational force so they gradually become more dense. The density will rise at an ever increasing rate until some of the gases are hot enough to glow. They are the birthplace of stars
How do protostars form?
In the nebulae the atoms move closer together, losing potential energy and gaining kinetic energy so the temperature rises. This results in a large core of material. It continues to attract material so mass increases and surface temperature is large enough to emit light. When the star is dense enough the pressure is very large due to temperature, the fusion of nuclei becomes possible.
What is a main sequence star?
A star which is stable because it has reached thermal equilibrium. It radiates electromagnetic energy into space at the same rate that fusion happens
How is a red giant created?
Rate of hydrogen fusion will decrease so the core will contract. The loss of potential energy causes an increase in temperature and therefore pressure on the core. This causes the entire star to grow. The surface temperature will be much lower than it is now. The fusion of helium will take place at the core.
What is a white dwarf?
Once the fusion of helium finishes in the core of a red giant, the star becomes unstable and most of the mass is radiated outwards in huge ion sprays. The rest of the star will shrink to a white dwarf, causing the surface temperature to rise again.
What is a comet and how is it visible?
It is a body of ice and rock with a cloud of gas. When it comes close to the Sun the solar wind causes the gases to spread out and ionise, and therefore glow.
What are the two orbits of comets?
Elliptical - where they circle back at regular intervals
Hyperbolic - they appear once and are never seen again
What are meteorites?
Tiny fragments of rock that enter the Earths atmosphere and heat up due to the friction with the atmosphere
What are binary stars?
A pair of stars that circle each other
How does a supernovae happen?
If a star is big enough when in the red giant phase further nuclear reactions occur in the core. During the immense pressure protons absorb electrons and form neutrons. When the core collapses there is an intense heating followed by an explosive blowing of the outer shell and compression of the core.
What is a neutron star?
Under certain conditions the nucleus of a neutron star can remain intact. They rotate rapidly and emit electromagnetic waves. The magnetic field is large and the frequency of the pulses is at the rate of the star and magnetic field rotating. They are pulsars.
What are black holes?
If a star is big enough the neutron star will collapse in on itself and density will become infinite. The escape velocity is greater than c so no light can escape.
