An insight into the life of aCosmologist

Katy Lancaster

About Me (Past)…..

About Me (Present)…..

• ‘Postdoc’ in the Astrophysics group at Bristol working with Professor Mark Birkinshaw, world expert in our field

• Primarily research, some teaching• Plus Outreach• Various projects, OCRA, AMiBA• Previously – PhD in Cambridge, working on

the VSA• MSci in Bristol (many moons ago!)

About Me…..

Talk Structure:

• Some key concepts in astrophysics, and what we spend our time doing!

• The Cosmic Microwave Background (relic radiation from the Big Bang)

• Galaxy clusters and the Sunyaev Zel’dovich effect

• The experiments that I am working on

Before we go any further….

some things you need to know.

STAR / PLANET

You are here!

GALAXY

GALAXY CLUSTER

THESE OBJECTS ARE THE FOCUS OF MY CURRENT WORK

The Cosmic Web

• Astrophysics: ‘That branch of astronomy which treats of the physical or chemical properties of the celestial bodies. Hence astrophysicist, a student of astronomical physics.’

Topics in Astrophysics…..• Solar System: planets, the sun• Stars: stellar composition, stellar evolution, star

formation, supernovae, extra-solar planets• Galaxies: structure, properties, stellar velocities (dark

matter), formation, evolution, clustering…• Active galaxies: mechanisms, power sources (black

holes)• High-energy phenomena: Gamma ray bursts• Galaxy clusters: galaxy properties, gas properties,

lensing (dark matter), super clustering….• Large scale structure, structure formation theories• Cosmology: properties of the Universe as a whole,

formation (the Big Bang), fate??

Stars

CMB

AGN

Planets

GalaxiesGalaxies

ClustersClusters Clusters

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Stars

CMB

AGN

Planets

GalaxiesGalaxies

ClustersClusters ClustersDIS

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• Cosmology: ‘The science or theory of the Universe as an ordered whole, and of the general laws which govern it. Also, a particular account or system of the universe and its laws.’

What do you astronomers actually DO?

•Obtain data•Go to telescope•Download from archive

•Process data•Work out what it tells us!•Publish in journal

• OBSERVATIONAL

• Observe celestial bodies (stars, galaxies etc) at various wavelengths

• Fit theoretical models to data to choose the most appropriate

• THEORETICAL

• Simulate celestial bodies (stellar evolution, galaxy formation etc)

• Create models of possible physical processes

In practice, need 2 approaches

My Work:

• COSMOLOGY from:– The ‘Cosmic Microwave Background Radiation

(CMB)’– The interaction of the CMB with ‘Galaxy Clusters’

via the ‘Sunyaev Zel’dovich Effect’

• OBSERVATIONAL - ie obtaining data, data processing, extracting science

• Tenerife, Poland, Hawaii, Taiwan…..

Very hot topics in Astrophysics

at the moment!

The Universe started with the ‘Big Bang’, a very hot explosion

Hot things glow (candle, light bulb) in the optical or infra-red

We can still see the ‘glow’ today

Universe cooled - glow is in radio waves

The ‘Cosmic Microwave Background Radiation (CMB)’

The sky is BRIGHT at radio frequencies.

If we observe the sky with a radio telescope, inbetween the stars and

galaxies, it is NOT DARK.

Visualising the CMB…..

•Observe ‘blank’ sky with a radio telescope.

•Rather than darkness, see Uniform, high-energy glow

•Turn up the resolution......

• The ‘heat’ from the Big Bang varies across the sky

• The differences can be observed by sensitive telescopes

• The variations are the ‘imprints’ of the beginnings of galaxy formation

• Observations of these features give us a lot of information about the nature of the Universe

Observing the CMB: COBE

• Low resolution - tells us about the amount of ‘stuff’ in the Universe

A plethora of other experiments followed this up….until….

Observing the CMB: WMAP

• High resolution - tells us about the TYPE of ‘stuff’ in the Universe (normal matter, dark matter)

More ‘features’ in the CMB

• Let’s forget those tiny temperature variations for now!

• Astronomical objects may cause ‘shadows’ in the glow from the CMB

• Eg Galaxy Clusters

Galaxy cluster in OPTICAL light

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Galaxy cluster in XRAY light

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Galaxy Clusters:

• Contain lots of galaxies (made from stars)

• Contain Dark Matter

• Contain lots of GAS

• Gas is thought to be made of similar ‘stuff’ the the Universe as a whole

Clusters are ‘Cosmic Laboratories’Study clusters, study the Universe

Sunyaev and Zel’dovich, 1969

• Postulated that the CMB could interact with the gas in galaxy clusters

• The ‘Sunyaev Zel’dovich (SZ) Effect’

SZ Effect: Sounds complicated!

• Cluster gas makes partial ‘shadow’ in the CMB• INDEPENDENT of the distance of the cluster • Depends ONLY on cluster characteristics• Measure strength of shadow, learn about cluster

(and Universe)

What does it look like?

Very SmallArray

To study Cosmology via clusters, we need lots of them

The SZ effect allows us to find ‘all’ clusters in existence

Hot topic - surveying the sky at radio frequencies to find clusters

What will we learn?

• CLUSTER EVOLUTION: Study clusters near and far and see how they differ– Extrapolate (wildly?) between the two to understand how

they are evolving

• EVOLUTION OF THE UNIVERSE: Count the number of clusters at a great distance, compare with the number of clusters close to earth– Extrapolate (even more wildly?) to understand how the

Universe itself is evolving

My Work

• I previously worked with the Very Small Array, looking at both the CMB and the SZ effect

• I am now involved with two new SZ experiments, OCRA and AMiBA

• We are:– Studying known clusters

– Performing surveys to find new ones

Wot no satellite?

• Going to space is EXPENSIVE!

• Choose your frequency wisely, can achieve a lot from the ground (sometimes before NASA / ESA have even launched their satellite!)

OCRA - One Centimetre Receiver Array

• New detector on Torun telescope, Poland

• 32m dish• Suffers from atmospheric

contamination• Most useful observations

are made in the winter• Will be able to IMAGE

clusters in SZ for the first time

AMiBA - Array for Microwave Background Anisotropy

• Taiwanese project, based in Hawaii

• 6m table, currently 7 ‘telescopes’

• Excellent for performing SURVEYS

• Problems with the platform - not strong enough!

Challenges….• The SZ effect is TINY• The radio sky is bright• Galaxy clusters contain galaxies (!), which may

emit radio waves and drown the SZ signal– Require further information, or observations at multiple

frequencies.

• Remember the fluctuations in the CMB itself? They can also contaminate!– Go to higher resolution

Summary• The Big Bang left behind radiation which we can

observe at radio frequencies today– The Cosmic Microwave Background

• The CMB has imprints upon it caused by the formation of the structures we see today (eg galaxies)

• The CMB tells us much about the Universe as a whole• Galaxy clusters may create ‘shadows’ in the CMB

– The Sunyaev Zel’dovich Effect

• The SZ effect is distance-independent so very useful for cluster physics and also Cosmology

ANY QUESTIONS?