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Ancient light reveals the structure of the universe

Astronomers can detect faint light from the furthest galaxies to figure out when they first formed. Credit: ‘Screenshot from IMAX® 3D movie Hidden Universe showing the Carina Nebula’ by ESO/T. Preibisch is licensed under CC BY 4.0

Light that is almost as old as the universe is being used to develop simulations of how the very first galaxies developed, as computer modellers get to grips with the inner workings of stars.

It can take many millennia for the light of distant galaxies to cross the vastness of space. Astronomers use this natural form of time travel to observe the early days of the universe.

By building highly sensitive satellites, they are able to detect the faint light from the furthest galaxies, observing them as they were when they first formed.

To turn this into a map of the early universe, cosmologists are using an effect that is similar to what you hear when an ambulance speeds away from you.

On a cosmological scale, if an astronomer knows the original frequency of light from a galaxy, then they can determine its location.

‘Because of the expansion of the universe … this frequency is shifted to lower frequencies the further away an emitting galaxy is,’ explained Professor Hans Kristian Eriksen at the University of Oslo, Norway.

A new experiment called COMAP, led by Dr Kieran Cleary at California Institute of Technology, US, uses light from carbon monoxide, which shines at a known original frequency and can be found in relative abundance in galaxies, to track the frequency shift due to the expansion of the universe.

The analysis of these observations will be led by Dr Ingunn Wehus at the University of Oslo.

‘Our work could also have an impact in other, more applied fields.’

Prof. Isabelle Baraffe, University of Exeter, UK

By taking snapshots of the same galaxies at different frequencies of light, the astronomers can track their development.

‘Essentially, the goal is to make a video of teenage galaxies growing up,’ explained Prof. Eriksen.

Each ‘frame’ of the video will cover half a million years, and the whole video will eventually cover 500 million years.

Deep space

The production of these images requires both extremely precise devices to record the weak, ancient light, and powerful mathematical programs to extract it from the background noise, such as light from our own Milky Way galaxy.

However, this is now possible as deep-space telescopes have improved, and researchers have a wealth of previous experience of extracting weak signals from noisy data.

Part of that experience comes from Prof. Eriksen’s EU-funded ANISOTROPIC UNIVERSE project, which finished in 2015.

During that project, they analysed another signal from the early universe, Cosmic Microwave Background (CMB) radiation. The idea was to determine if fluctuations observed in the CMB radiation were cosmological, or produced due to noise introduced by light from our own galaxy, or even instrumentation errors.

In the ANISOTROPIC UNIVERSE project, the light from carbon dioxide was actually seen as a contaminant in the CMB data.

‘It is often said that “one person's noise is another person's signal,”’ said Prof. Eriksen. ‘That is very much the case here.’

Mathematics

Underpinning this work is the powerful mathematics that can strip out different types of light. It’s also complex mathematics that is enabling another project to model the movement of heat within stars.

The interior of stars consists of shells of turbulence, alternating with zones of calm and stability. Understanding the way that heat and matter are transferred between these zones could improve our understanding of star evolution.

Except there’s a problem – models of stars are very difficult to build in one dimension, let alone three. On top of this, the models need to simulate processes over many hundreds or thousands of years in a star’s life, yet even using a supercomputer, current models can only recreate periods of months or years.

However, the EU-funded TOFU project has produced a new tool, known as MUSIC that has made realistic three-dimensional models of stars possible.

MUSIC is able to do this because it uses clever mathematics to describe what’s happening inside a star at points that are far apart in time. Previous models could only describe the current state of a star based on very recent calculations, making them much less efficient when simulating long periods of time.

Today, astronomers have satellites at their disposal that can probe the inner workings of distant stars. The TOFU team compared the outcomes of their models to these observations and found that their models can provide a long-sought explanation for the data.

‘I think this shows the power of our numerical approach with MUSIC, because you can cover long timescales, you can get a lot of data … which was previously not possible,’ said the project’s principal investigator Professor Isabelle Baraffe, at the University of Exeter, UK.

The TOFU team will now apply their tools to other areas where the transfer of heat is important, such as weather systems on earth.

To do this, they are collaborating with the UK Met Office to improve their weather models. As Prof. Baraffe explained, ‘I think this is interesting because now it is really a cross-disciplinary activity, and our work could also have an impact in other, more applied fields.’

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