Download The Very Small Array (VSA) - Department of Physics

The Very Small Array (VSA)
by Dr. Keith Grainge, Astrophysics Group, Cavendish Laboratory.
I work as a post-doctoral researcher in the Astrophysics
Group of the Department of Physics at the University of
Cambridge, based at the Cavendish Laboratory. I did an
undergraduate degree in Natural Sciences at Gonville and
Caius College, Cambridge, during which I became interested
in astrophysics. As a result, I decided to stay on at the
Cavendish to do a Ph.D., measuring the rate of expansion of
the Universe (the Hubble constant).
My research is based around studying the cosmic microwave background (CMB) radiation.
This radiation is the relic of the Big Bang, and contains the tiny fluctuations that are the
imprints of the very start of the formation of structures, such as galaxies, in the Universe.
These fluctuations in the CMB are tiny, only one 10,000th of a degree centigrade at most.
I am now the Project Manager of the Very Small Array (VSA). The VSA is a custom-built
radio telescope (operating between 26-36 GHz), designed expressly to make highsensitivity observations of the CMB on angular scales around and below one degree. This
means that we are able to use these observations to:
•
answer some of the fundamental questions about the origin of structures;
•
find some of the key cosmological parameters that describe our Universe, such as its
matter density and age;
•
investigate the mysterious dark matter and dark energy content of the Universe.
The VSA project is a collaboration between astronomers here at the Cavendish, Jodrell
Bank in Manchester and the Instituto de Astrofisica de Canarias in Tenerife.
The Very Small Array (VSA)
© University of Cambridge, Cavendish Laboratory, 2004.
An image of the
Background (CMB)
using the VSA.
Cosmic Microwave
radiation, obtained
Submillimetre-wave Astrophysics
by Dr. Kate Isaak, Astrophysics Group, Cavendish Laboratory.
Sunning yourself on tropical islands, that’s what astronomers do when
they aren’t looking through telescopes, isn’t it? In fact, there is much more
to the job of an astrophysicist! I study astrophysical objects by looking at
the radiation they emit. I am particularly interested in star formation in the
distant Universe. I would like to know:
•
How many stars are being formed in very distant galaxies today?
•
How has the number of stars being formed changed over the
billions of years since the first stars formed in the first galaxies?
•
Why has the number of stars being formed changed over time?
By comparing the star-forming properties of the very distant galaxies with
more local galaxies I hope to make a small step towards answering some
of these questions.
Studies of objects outside our own Galaxy are difficult. The signal from very distant
objects is often very faint. In a similar way, if a light bulb is placed 50m away it looks much
fainter than it does if it is placed only 5m away. There are two added complications –
water and sensitivity. Water in the Earth’s atmosphere emits a lot of radiation at
submillimetre wavelengths, making it harder to collect the much weaker signals at the
same wavelengths arriving at the Earth’s surface from very distant galaxies. For this
reason, telescopes operating at submillimetre wavelengths are built at very high and very
dry locations (such as tropical islands!). The second problem is that it is technically very
challenging to make sensitive detectors that operate at submillimetre wavelengths. In
recent years, incredible advances have been made using the phenomenon of
superconductivity. With this new generation of sensitive detectors, it has been possible to
study traces of star formation in galaxies that are at the edge of the known Universe. The
radiation that we detect now was emitted by these objects many billions of years ago.
I work with people and telescopes in 8 different countries around the world. My job is
very cosmopolitan, with lots of opportunity to travel and to work with people from a very
wide range of different cultures.
The James Clerk Maxwell Telescope (JCMT) on Mauna
Kea, Hawaii. The JCMT is the largest radio telescope
designed to work at submillimetre wavelengths. It can
be used at wavelengths between 0.3 mm and 2 mm.
© University of Cambridge, Cavendish Laboratory, 2004.
Astrophysics at Cambridge
by Rachel Berry, Ph.D. student in Astrophysics at the Cavendish
Laboratory
I come from Birmingham and went to an all girls’ grammar
school. I did three sciences at GCSE, and A levels in
Maths, Further Maths, Physics and Chemistry. Dr. Tony
Gardiner, from Birmingham University, convinced me to
study sciences instead of the humanities at university. He
involves local schoolchildren in Maths workshops that are
much more like university than school, and much more fun
than normal Maths lessons.
After A-levels I took a Gap year at IBM working as a programmer, despite having done no
computing at school. IBM were more interested in my Maths A-level than previous
experience. I came up to Cambridge in 1996 and followed the four-year Natural Sciences
Tripos, specialising in Physics. During the summers I worked again at IBM, at BT research
labs and in the Department of Materials Science and Metallurgy here at the University.
Having interesting and challenging summer jobs where I could apply some of the skills from
my degree course was very useful for focusing my own ideas. At BT, the software I
developed was patented. It was fascinating to see the process of prototype to commercial
development. At the end of my degree I was offered a job with BT's research division.
Now I'm doing my Ph.D. in the Astrophysics group at the Cavendish Laboratory. I am
working on a computational project, modelling electromagnetic fields. I run computer
programs that show how radiation passes through instruments attached to telescopes. We
then use the results to work out the best way to design and build the instruments in the
future. We use the telescopes to detect radiation from astronomical objects such as dust
clouds, black holes and stars. Detecting radiation from space may sound quite abstract
from real life, but there are lots of commercial applications that use this kind of modelling.
For example, deciding where to place mobile phone masts involves the same modelling
techniques that astronomers have to use.
As a Ph.D. student I'm expected to work on my own and decide what I am going to do next.
Most of my time is spent programming, debugging and running the computer program I am
developing. I also attend weekly group seminars on all aspects of Astronomy. All the Ph.D.
students have to give seminars to the group as practice for presenting work at conferences.
Last summer I attended a conference in Barcelona and this year I'll be presenting a paper
in Arizona. The astronomers who actually use the telescopes also spend a lot of time at
exotic telescope locations in Chile, Australia, and America. Most Ph.D. students in physics
also do some sort of teaching of undergraduates. I really enjoy doing the teaching, but it
can be quite tiring. It's strange to be both being taught and teaching, but I do enjoy it.
© University of Cambridge, Cavendish Laboratory, 2004.
The Arcminute MicroKelvin Imager (AMI)
by Dr. Will Grainger, Astrophysics Group, Cavendish Laboratory.
It would be really nice to say that I've always been interested in astronomy and
astrophysics, but it isn't true. However, I am now doing science and technical work that I
find incredibly interesting and fun: I am part of the team that is building a new telescope
called the Arcminute MicroKelvin Imager (AMI), which will make images of features in the
cosmic microwave background radiation (CMB).
The Arcminute MicroKelvin Imager
(AMI) at Lord’s Bridge, near
Cambridge. AMI is made up of ten
dishes that work together using a
technique called aperture synthesis.
Each of the dishes is 3.7 m in
diameter, and will operate at a
wavelength of about 2 cm.
So, how did this happen? How did I end up working on AMI? I did A levels in Chemistry,
Physics and Maths, but couldn't decide which science to do at University. The flexibility of
the Natural Sciences Tripos here at Cambridge appealed to me, so I put in an application,
and I got an offer. In the first year I realised that I was better at physics, and really enjoyed
doing experiments. As the experiments got longer through the four-year course, they went
into more depth, and were more interesting. I decided that I wanted to carry on doing
academic research or commercial research and development (R&D). A spell in the R&D
department of a small laser company convinced me that doing a Ph.D. would be useful.
So, I looked around for interesting Ph.D. studentships, and got offered two: one in
geophysics and one in astrophysics. The former looked like it could lead to a good career,
developing techniques for oil exploration, but would involve some time on a boat just off the
coast of Iceland. The latter was studying a Big Question: how fast is the universe
expanding? Oh, and going to Hawaii. The idea of getting a tan won.
I spent my Ph.D. taking data from telescopes around the world (but not always travelling to
them), and doing lots of data analysing and numerical modelling, mainly using computers. I
was interested in the technology I was using, and after I completed my Ph.D. I got a job as
a post-doctoral researcher with a strong emphasis on hardware. Here I've designed, built,
tested (and fixed!) many of the vital systems for AMI. This has involved many things,
including shovelling concrete, surveying work with theodolites, designing and building
circuit boards, writing the software that controls where the telescope points and where it
displays data. The variety means I'm never bored and always interested. I cannot
recommend it highly enough!
© University of Cambridge, Cavendish Laboratory, 2004.