Alumni Take Over: Jiten Dhandha Exploring the Mysteries of the Early Universe with Cutting-Edge Research

Hello, my name is Jiten! I am a soon-to-be 3rd year PhD student at the Institute of Astronomy, University of Cambridge. My work is focused on theoretical simulations of the early Universe.

What does that mean exactly?

“Early” is a very subjective term, but for me, that means 13 billion years ago — an exciting epoch in cosmology — when the first stars and galaxies emerged from cold gas. These first billion years after the Big Bang are mysterious for several reasons: how did the galaxies form? How did the stars look like? How different were they from the ones we see today? All very good questions, but ones that remain unanswered.

Where do we even begin to answer these questions?

Quite simply, space is very empty, and that means light can travel long distances over cosmic time. By pointing our telescopes at the sky, we can peer past our immediate surroundings to the ancient signals that were emitted when the Universe was young. The signals travel vast distances to reach us, and indeed the further the source of the signal, the more into the past we look — it’s like a snapshot of the Universe from back then.

These snapshots look different across different frequencies — X-rays, radio, ultraviolet, optical, infrared — all giving us small pieces of the cosmic puzzle that we must put together into a coherent story. The images you often see on the internet, by Hubble and James Webb space telescopes, are in the optical and infrared regimes. Most of my work falls outside this, in the radio regime — precisely the 21-cm wavelength.

Why 21-cm?

This is a distinct signature of hydrogen atoms, which is the most abundant element in the Universe. Hydrogen has been present in the cosmos since 3 minutes after the Big Bang, and so it’s the perfect tracer for cosmic history. By looking at 21-cm signals from different parts of the sky, and from increasingly long distances, we can trace how the Universe evolved over hundreds of millions of years.

What’s stopping us then?

Although the signals are constantly passing through us, separating them from noise is a monumental task. Interference from man-made devices like radio towers, cosmic sources like nearby galaxies, and instrumental defects combine to create noise that is 10,000 times brighter than the faint signal which we want to see — an issue that has plagued the field of observational 21-cm cosmology for over three decades.

Are we doomed to ignorance?

All hope is not lost however. We can still make progress! By simulating tens of thousands of Universes, all with different properties, we can rule out the extreme possibilities even with poor data. Even better, by combining data from different frequencies — infrared images of galaxies from the JWST, diffuse X-ray background from Chandra X-ray Observatory, and the ever improving 21-cm signal radio experiments — we can get stronger constraints on the early Universe. This technique, of combining data and performing rigorous Bayesian statistical analysis, is one that has been developed and honed over the years in our research group at Cambridge. In my work, I use the same technique to infer how efficiently stars formed from gas over cosmic time. This requires building sensible theoretical models, running thousands of simulations using our complex in-house code called 21cmSPACE, training neural networks to emulate observable predictions, and performing inference on available observational data — all of which take time, lot of supercomputer hours and…

Oh no, my code just crashed again. Be right back.

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Would you like to read more about Jiten? Check out his website here: https://jitendhandha.com/