extra astro - from past papers

Measurements of type 1a supernovae in 1999 led to a controversy concerning the behaviour of the universe - describe this controversy and how the measurements led to it.

• the use of type 1a supernovae to measure distances, showed data which suggested that the expanding universe is accelerating, not slowing down

• implicates some not-yet detected energy permeating the universe which acts in opposition to gravity (dark energy)

• because observations of typically constant type 1a supernovae in distant galaxies are less bright than expected, showing they’re further from us than predicted by Hubble’s law

problems with the transit method (exoplanet detection)

• alignment must be correct for planets to eclipse, so many possible exoplanets may not be observed

• earth-like planets may be observed, only if not too far away

describe the links between galaxies, black holes and quasars

• quasars produced by supermassive black holes

• black holes are at the center of active galaxies

brightness of quasars vs galaxies

should have the same brightness

explain how the relative abundance of hydrogen and helium supports the Big Bang theory

• big bang theory predicts that through primordial nucleosynthesis/ nuclear fusion, hydrogen and helium were formed 100s after the big bang in a ratio of 3:1, due to the high temperatures and pressures

• temperatures dropped and the process stopped, leaving the 3:1 ratio, reflected in the abundance of hydrogen (73%) and helium (25%) in the atmosphere today

A star is much more massive than the Sun and may become a supernova and then a black hole. Discuss whether supernovae and black holes can be placed on the HR diagram.

• a black hole’s absolute magnitude is too dim to fit on the scale

• temperature of supernova is too great to fit on the scale

• absolute magnitude of supernova is too bright to fit on the scale (~-20)

quasars are the most distant measurable objects. discuss (one) problem associated with the determination of the distance from the Earth to a quasar

• appear optically very faint due to them being so distant

• must use inverse square law to measure the distance

CCD vs naked eye (when using telescope to observe binary stars)

• the quantum efficiency of the CCD is greater than that of the naked eye, meaning more photons which hit the surface are detected, so the image from the CCD will be more intense

• CCDs have a much greater spatial resolution than the naked eye, so binary stars can be resolved more easily if they are very distant and close together

A different eclipsing binary star system is thought to consist of a white dwarf and a neutron star. Discuss how astronomers could confirm this.

• white dwarf has low absolute magnitude, v. high temp, neutral/ionised helium as predominant spectral line

• neutron stars emit regular pulses of radio waves

• when white dwarf eclipses neutron star, drop in intensity of radio waves from neutron star

• spectral lines of white dwarf shift when moving away/towards us

calculation for intensity ratio

2.51^(m-m)

volume of event horizon of black hole

model as sphere

what is meant by normal adjustment in an astronomical refracting telescope

image seen/formed at infinity

why do CCDs improve ability to observe dim stars

• high quantum efficiency

• can be operated remotely, so telescope can be positioned where light pollution is minimised

conversion from t=1/H to seconds

• x(3.08 × 10²²)

• divide by 1000