Science
Some for everyone...
The Big Bang model for the origin and initial evolution of the Universe is by now a familiar and well studied research field. The subsequent, late time, evolution of stars and other celestial objects over billions of years is perhaps even better understood. Less is known, however, about the time between these periods (from about 0.35 to 1 billion years after the Big Bang). During this time the Universe transitioned from being a vast volume filled with a cooling neutral gas to become the realm of cosmic objects that we can now observe from Earth.
At the beginning the Universe was filled with a hot, dense fog of ionized gas until the continued expansion and cooling allowed electrons and protons to combine and form the first neutral atoms, eg. hydrogen. Eventually, the neutral matter clumped together under the effects of gravity, providing the conditions for nuclear fusion to occur, leading to the birth of the first stars and galaxies (period known as the Cosmic Dawn). Subsequently, these objects heated and re-ionised the surrounding hydrogen in the Universe during the Epoch of Re-ionization.
At the Cavendish Radio Cosmology research group we study these early epochs of the Universe by observing radio signals naturally emitted by hydrogen. Hydrogen was the raw material forming the very first stars but also these same hydrogen clouds filling the Universe at the time stop us from directly observing the light from these first stars. Thus, we aim to look at these stars through their interaction with the hydrogen clouds in the same way one would infer a landscape by looking at the shadows in the fog covering it.
For the keen astronomers...
The first stars and galaxies formed some time after the epoch of cosmic recombination (when the Cosmic Microwave Background formed ~378,000 years after the Big Bang at a redshift (z) of ~1100) and before the current 'realm of the galaxies' that we can see today (~1 to 13.7 billion years after the Big Bang). The radiation from these first luminous sources heated and re-ionized the neutral hydrogen that pervaded the primordial Cosmos. Probing these epochs, the 'Dark Ages' before the first galaxies, through cosmic re-ionization and first new light in the Universe, represents the frontier in studies of cosmic structure formation. Neutral hydrogen has a rest wavelength of 21 cm and by observing at low radio frequencies we can study directly its red-shifted radio emission (and absorption) from the gas clouds that were the raw material that formed the first luminous cosmic structures at these early epochs. This is considered to be one of the prime tools to study these epochs given the difficulty to observe these early objects at shorter wavelengths. While the future SKA telescope will aim to do full tomography of the hydrogen emission from the Cosmic Dawn (CD) and the Epoch of Re-ionization (EoR), an in principle simpler way to attempt the detection and study of this signal aims to observe the monopole emission (averaged from all directions in the sky, i.e. global) through cosmological time, red-shifted from 21-cm to a few meters due to the expansion of the Universe, with a stand alone radiometer system.
REACH is the Radio Experiment for the Analysis of Cosmic Hydrogen. It is an antenna radiometer aiming to detect and analyse the redshifted radio emission (and absorption) from the 21-cm line located in the semi dessert and radio quiet region of the Karoo in South Africa and run by our group in collaboration with our international partners. Our group is also heavily involved in the HERA experiment, aiming at detecting the complementary power spectrum (at smaller spatial scales) of the 21-cm signal. Some relevant publications can be found here.
The Big Bang model for the origin and initial evolution of the Universe is by now a familiar and well studied research field. The subsequent, late time, evolution of stars and other celestial objects over billions of years is perhaps even better understood. Less is known, however, about the time between these periods (from about 0.35 to 1 billion years after the Big Bang). During this time the Universe transitioned from being a vast volume filled with a cooling neutral gas to become the realm of cosmic objects that we can now observe from Earth.
At the beginning the Universe was filled with a hot, dense fog of ionized gas until the continued expansion and cooling allowed electrons and protons to combine and form the first neutral atoms, eg. hydrogen. Eventually, the neutral matter clumped together under the effects of gravity, providing the conditions for nuclear fusion to occur, leading to the birth of the first stars and galaxies (period known as the Cosmic Dawn). Subsequently, these objects heated and re-ionised the surrounding hydrogen in the Universe during the Epoch of Re-ionization.
At the Cavendish Radio Cosmology research group we study these early epochs of the Universe by observing radio signals naturally emitted by hydrogen. Hydrogen was the raw material forming the very first stars but also these same hydrogen clouds filling the Universe at the time stop us from directly observing the light from these first stars. Thus, we aim to look at these stars through their interaction with the hydrogen clouds in the same way one would infer a landscape by looking at the shadows in the fog covering it.
For the keen astronomers...
The first stars and galaxies formed some time after the epoch of cosmic recombination (when the Cosmic Microwave Background formed ~378,000 years after the Big Bang at a redshift (z) of ~1100) and before the current 'realm of the galaxies' that we can see today (~1 to 13.7 billion years after the Big Bang). The radiation from these first luminous sources heated and re-ionized the neutral hydrogen that pervaded the primordial Cosmos. Probing these epochs, the 'Dark Ages' before the first galaxies, through cosmic re-ionization and first new light in the Universe, represents the frontier in studies of cosmic structure formation. Neutral hydrogen has a rest wavelength of 21 cm and by observing at low radio frequencies we can study directly its red-shifted radio emission (and absorption) from the gas clouds that were the raw material that formed the first luminous cosmic structures at these early epochs. This is considered to be one of the prime tools to study these epochs given the difficulty to observe these early objects at shorter wavelengths. While the future SKA telescope will aim to do full tomography of the hydrogen emission from the Cosmic Dawn (CD) and the Epoch of Re-ionization (EoR), an in principle simpler way to attempt the detection and study of this signal aims to observe the monopole emission (averaged from all directions in the sky, i.e. global) through cosmological time, red-shifted from 21-cm to a few meters due to the expansion of the Universe, with a stand alone radiometer system.
REACH is the Radio Experiment for the Analysis of Cosmic Hydrogen. It is an antenna radiometer aiming to detect and analyse the redshifted radio emission (and absorption) from the 21-cm line located in the semi dessert and radio quiet region of the Karoo in South Africa and run by our group in collaboration with our international partners. Our group is also heavily involved in the HERA experiment, aiming at detecting the complementary power spectrum (at smaller spatial scales) of the 21-cm signal. Some relevant publications can be found here.
Methods
We develop methods and techniques with a variety of applications:
- Data analysis in 21-cm cosmology experiments (eg. Bayesian inference techniques based on Nested Sampling and Physics-rooted models, maximally smooth functions, etc).
- Calibration of radiometers.
- Signal extraction from noise with applications in astronomy and EM metrology.
- Fast and accurate calibration of wideband ultra large phased arrays.
- Accurate modelling and compact representation of phase array complex beam models affected by electromagnetic mutual coupling.
Technology
The group's research in technology activities is supported by our state-of-the-art experimental labs at the Cavendish Laboratory and the Mullard Radio Astronomy Observatory and expands from the design and development of wide band antennas for radio astronomy to the design of ultra low noise detectors for EM metrology in collaboration with industrial partners. We have a special interest on developing radio technology for a better society inspired by advancements in astronomy. The list of current research activities include:
- Design and development of the SKALA4 antenna for the SKA1-LOW instrument of the SKA. We also have an interest on the design of antenna systems at higher frequencies (eg. the SKA MFAA phased array system - 0.3-1.4 GHz).
- Design of Wideband, wide field of view, phased array systems (eg. the SKA AAVS1 prototype station in WA).
- Development of measurement techniques for EM metrology of very large structures based on the use of UAV systems.
- Recently we started the development of Surface Wave launchers for ultra fast digital communications over twisted pairs. More broadly, the group is currently carrying on a research activity focus on the understanding of the electromagnetic properties of twisted pairs.
- Development of ultra sensitive EM sensors for metrology with a focus on solving future challenges of the IoT society.