Astrophysics

What are some advantges of reflectors and refractors

State meaning standard candle.

It has a known absolute magnitude.

Type 1a supernova curve: describe

Peak at abs magnitude -19 at t=0: Scale 300 days: gradient LHS > RHS

Why could the evolution of a super-regiant in local part of galaxy be dangerous for life on Earth

Star will undergo supernova collapse or Star will form a neutron star/black hole ✓

which produces a gamma ray burst and consequence for life (kills cells, DNA damage) or reference to being highly collimated

Parsec

the distance at which 1 AU subtends an angle of 1 arcsecond, 1/3600th of a degree

Quasar

A supermassive black hole surrounded by a disc of matter, which as it falls into the black hole, causes jets of radtiation to be emitted from its poles.

Rayleigh criterion definition

Minimum subtended angle between two objects whose (images) can be resolved is when the central maximum of the diffraction pattern of light from one object coincides with the first minimum of the second object.

Compare the use of a CCD with the use of the naked eye to observe binary stars with this telescope.

CCD has better resolution due to having smaller pixels ✓a so the stars could be more easily seen as separate (OWTTE) ✓b (candidates may combine these ideas)

CCDs have higher quantum efficiency and/or can be exposed for a long time ✓a so dimmer or more distant binaries can be observed ✓b

CCDs can detect a wider range of wavelengths ✓a enabling the observation of more binary pairs.

CCDs produce and store image on computer, able to be analysed later.

How white dwarf and nuetron star detected

white dwarf: High temperature and low abs magnitude

Nuetron star: radio emisions due to pulsars

What is property of quasar leading to its discovery

Powerful radio emmiter

Describe evidence for big bang.

Aspect 1 - RedShift • Theory predicts that distant galaxies are all moving away from us •

The further away the galaxy the faster it moves

• Reference to Hubble’s Law

Aspect 2 -CMBR • Theory predicts black body radiation at microwave wavelengths (2.7 K)

• from all directions which indicates that the universe was once very small/in a hot dense state

3: H:He ratio

Predicts 3:1 H:He ration

Which is observed in deep space

Measurements of type 1a supernovae led to a controversy, describe this

Type 1a supernovae were observed to be dimmer than expected, meaning more distant that Hubble’s law predicted: So universe expanding at increasing rate, controversial as energy source was unknown: dark energy

Discuss difficulties associated with detection of Earth-like planet orbiting a sun-like planet.

Transit – dips in brightness as planet crosses in front of star from our point of view.

Alignment must be correct for planets to eclipse (planet passes in front star when viewed from Earth) , so many possible candidates not observed. Earth-like planet could be observed provided not too far away and in correct alignment.

Radial velocity (Doppler) – periodic shift in spectra of star due to star’s movement around common centre of mass with planet. Earth-like planet mass much less than mass of Sun-like star so effect slight. Earth-like planet could be detected with highly sensitive spectrometers.

Direct observation – very unlikely as Earth like planet to small and too near star and too cool (so too dim) to be detected against the brightness of the Sun-like star. Unlikely to be detected.

Expalin quasar properties, evidence for these properties and suggest process of quasar formation when 2 galaxies merge.

Properties

P1 Associated with a supermassive black hole

P2 Large power output (for their size) OR power output ~ 1042 W/idea of bright absolute magnitude

P3 Distant

P4 Small (relative to host galaxy)/about size of solar system.

Evidence

E1 (seen) in centre of (active) galaxies (producing jets)

E2 Bright radio source OR far brighter than their host galaxy

E3 Large red-shift

E4 Rapid fluctuations in power output.

How quasar forms

F1 (merging causes) material/stars to move towards the supermassive black hole(s)

F2 Black hole(s) become active ‘consuming’ nearby stars/material and emitting radiation

Explain what is mean by CMBR: existence supports Big Bang theory

it is the radiation coming from all parts of the Universe

 when the Universe cooled sufficiently for matter and radiation to ‘decouple’, with the combination of protons and electrons to form neutral atoms

 this radiation has been red-shifted into the microwave region as the Universe has expanded

 the spectrum has a peak in the microwave region / corresponds to a temperature of 2.7 K

 It can be interpreted as the radiation left over from the Big Bang / the photons having been stretched to longer wavelengths and lower energies.

Normal adjustment

Final image at infinity

Defining property black hole

escape velocity is greater than speed of light

Parallax definition

Parallax is the ​ apparent change of position of a nearer star in comparison to distant stars the background, ​as a result of the orbit of the Earth around the Sun.

HR diagram: scale, position sun

+15 —> -10. sun abs mag 4.83, class G