Level 1 - Absolute Beginner

A big radio telescope in Canada found a very weak signal from space. The telescope is called CHIME. It sits near a town called Penticton in British Columbia.

The signal came from hydrogen gas. Hydrogen is the most common gas in the universe. The light took about nine billion years to reach Earth.

Scientists used old data from 2019. They looked at 94 nights of work. It took them more than a year to be sure the signal was real.

The signal can help scientists study dark energy. Dark energy makes the universe grow bigger and faster. Nobody knows yet what it is.

telescope

A tool that helps us see or listen to things far away in space.

radio

A kind of invisible wave that can travel through space.

signal

A wave or message that carries information.

gas

A substance like air that is not solid or liquid.

hydrogen

The lightest and most common gas in the universe.

universe

Everything that exists, including all the stars and planets.

billion

The number 1,000,000,000.

data

Facts and numbers collected for study.

Level 2 - Elementary

Astronomers working with the Canadian Hydrogen Intensity Mapping Experiment, known as CHIME, have detected faint radio waves from hydrogen gas that left its source when the universe was about five billion years old. Because the light needed roughly nine billion years to reach us, we are seeing a much younger universe.

The telescope stands near Penticton in British Columbia and is hosted by the National Research Council of Canada. The project also involves the University of British Columbia, McGill University, the University of Toronto, the Dominion Radio Astrophysical Observatory and Arizona State University.

Instead of counting galaxies one at a time, CHIME measures the combined radio glow of hydrogen across large areas of sky. The team pulled the weak signal out of 94 nights of observations recorded in 2019 and then spent more than a year checking that what they had found was genuine rather than noise from space, human equipment or the telescope itself.

The result matters because mapping where hydrogen sits lets researchers work out how the universe expanded over time. That gives them a separate way to test ideas about dark energy, the mysterious thing that appears to be speeding up the expansion. Two papers describing the work appeared in The Astrophysical Journal.

astronomer

A scientist who studies stars, planets and space.

detect

To discover or notice something, often something hidden.

faint

Very weak and hard to see or hear.

galaxy

A huge group of stars held together by gravity.

observatory

A building where scientists watch the sky.

noise

Unwanted signals that make it harder to find the real one.

expand

To grow larger in size.

journal

A magazine where scientists publish their research.

Level 3 - Intermediate

A radio telescope in the interior of British Columbia has picked up a signal so faint that its discoverers spent over a year satisfying themselves it existed. The Canadian Hydrogen Intensity Mapping Experiment, universally shortened to CHIME, has detected radio emission from neutral hydrogen gas dating to a time when the universe was roughly five billion years old. The light took about nine billion years to reach the array near Penticton, which is hosted by the National Research Council of Canada and run with the University of British Columbia, McGill University, the University of Toronto, the Dominion Radio Astrophysical Observatory and Arizona State University.

The technique is the real news. Conventional cosmology at these distances depends on galaxy surveys, patiently cataloguing individual objects and their redshifts, which is slow and expensive. Intensity mapping takes the opposite approach: rather than resolving galaxies, it measures the total hydrogen emission from large swathes of sky and treats the resulting pattern as a map of where matter sits. The signal is correspondingly weak, buried under cosmic background radiation, terrestrial interference and the telescope's own quirks, which is why the team had to develop new processing methods to lift it out of 94 nights of data recorded back in 2019.

Dr Arnab Chakraborty of the University of Toronto first proposed the finding, working with Dr Mark Halpern of the University of British Columbia, who is CHIME's principal investigator, and with Dr Shabbir Shaikh and Dr Simon Foreman of Arizona State University. Two papers setting out the detection and the method have been published in The Astrophysical Journal. As a sanity check, the team estimates that about two percent of the universe's hydrogen was in neutral atomic form at that epoch, a figure broadly in line with independent measurements.

The payoff is a new and comparatively cheap handle on dark energy. Reconstructing the distribution of hydrogen over cosmic time reveals how fast the universe expanded at different stages, which is the quantity that competing explanations for dark energy disagree about. The same maps also constrain models of how galaxies form. CHIME has nearly seven years of recorded observations still to work through, and the team intends to push the method back to when the universe was only about three billion years old.

emission

Light, radiation or gas given out by something.

neutral hydrogen

Hydrogen whose atoms still hold their electrons and are not electrically charged.

array

A set of instruments arranged to work together.

redshift

The stretching of light from distant objects, used to measure their distance.

intensity mapping

Measuring the total light from a region of sky instead of individual objects.

interference

Unwanted signals that disturb a measurement.

Level 4 - Advanced

The most consequential result in observational cosmology this month arrived not from a new instrument but from a seven year old hard drive. Working with the Canadian Hydrogen Intensity Mapping Experiment, an unlovely array of cylindrical reflectors outside Penticton in British Columbia, a Canadian and American collaboration has extracted a radio signal from neutral hydrogen that departed its source when the cosmos was some five billion years old, roughly nine billion years before it reached the dish. The telescope is hosted by the National Research Council of Canada and operated with the University of British Columbia, McGill University, the University of Toronto, the Dominion Radio Astrophysical Observatory and Arizona State University.

The scientific significance lies less in the detection than in the method by which it was obtained. Mapping the large scale structure of the universe at these epochs has conventionally required galaxy surveys: the laborious, instrument hungry business of identifying individual objects and determining each one's redshift. Intensity mapping discards that granularity deliberately. It measures the aggregate twenty one centimetre emission of hydrogen across broad regions of sky and treats the resulting fluctuations as a tracer of the underlying matter distribution. The trade is sensitivity for cost, and the sensitivity problem is severe: the cosmological signal sits several orders of magnitude beneath galactic foregrounds, human generated radio interference and the instrument's own systematics. Recovering it from 94 nights of 2019 observations required new analysis pipelines and, by the collaboration's own account, more than a year of adversarial self checking before anyone was willing to publish.

Dr Arnab Chakraborty of the University of Toronto first put forward the result, alongside Dr Mark Halpern of the University of British Columbia, CHIME's principal investigator, and Dr Shabbir Shaikh and Dr Simon Foreman of Arizona State University. Two companion papers in The Astrophysical Journal lay out the detection and the pipeline. The internal consistency check is reassuring rather than spectacular: the inferred neutral hydrogen fraction at that epoch comes out near two percent, broadly concordant with determinations from entirely different techniques, which is the sort of agreement that makes a novel method credible.

What this buys cosmology is a second, inexpensive lever on dark energy. The expansion history of the universe is the discriminating observable between competing accounts of why that expansion is accelerating, whether a cosmological constant, some evolving field or a modification of gravity itself, and hydrogen maps reconstructed across cosmic time measure exactly that history. The same datasets simultaneously constrain galaxy formation models. With close to seven years of archived observations still unprocessed and an ambition to extend the technique to an era when the universe was only about three billion years old, CHIME has effectively demonstrated that a cheap telescope and patient data analysis can compete with surveys costing a great deal more.