Cosmology and extragalactic astronomy

Mat Page

Mullard Space Science Lab, UCL

Revision Lecture

Recap of everything!• Galaxies:

– Classification+Structure– Dark Matter

• Hubble’s law– redshift and distance indicators

• Cosmological Principles, Olbers’s Paradox

• Cosmic microwave background– results and implications

• Inflation

• Nucleosynthesis, baryogenesis

Galaxies and dark matter

• Hubble’s tuning fork diagram

• Spirals + barred spirals– Sa: large bulge, tight arms. – Sc: small bulge, loose arms

• Star formation, gas and dust in arms

• Density wave model

• Rotation, rotation curve -> dark matter

• MACHOs, WIMPs, how they are detected

• 109-1011 Mo

Galaxies and dark matter

• Ellipticals

• E0-E7, En where n=10(1-b/a)

• Classified according to view from Earth

• Old, red stars (no star formation)

• little gas, little dust

• 105-1013 Mo

• Lenticulars (S0)– like spirals but no arms, just disc

• Irregulars– tend to be small, no definite structure

Where are the galaxies and how did they form?

– Galaxies form in dark matter haloes– Most of the galaxies in rich clusters are

ellipticals– bottom up vs. top down– hierarchical model - ellipticals built up by

merging of disc galaxies– spirals created when galaxies accrete gas (with

angular momentum) from the intergalactic medium

• Massive accreting black holes in galactic nuclei.

• 90% are radio quiet, but can be identified by their strong emission lines.

• Most quasars are seen at large redshifts (z>0.3)

Quasars

Hubble’s law

Hubble’s law

Cosmic distance ladder

Cosmic microwave background:

Inflation

• What is it?– A period of rapid expansion in the early

Universe– Caused by a state change as the Universe cools

• Why do we need it?– The horizon problem– large scale structure– flatness– the monopole problem

Olbers’s paradox

• Night sky should be infinitely bright!• Solution:

– The Universe is only 14 billion years old!– Light from stars more distant than 14 billion light

years has not have reached us yet.– There is a limit to the size of the Universe which can

illuminate the night sky.– The sky is allowed to be dark.

Finally:

• Good luck to you all!