A new study by astrophysicists in Australia adds another piece to the universe’s history puzzle. By measuring the density of carbon in the gases around ancient galaxies, the team shed new light on the state of the Universe 13 billion years ago.

They found that the carbon content of warm gas rose rapidly some 13 billion years ago, possibly caused by extensive gas heating caused by the “Epoch of Reionization” phenomenon. This suggests that warm carbon has suddenly increased by 5x in just 300 million years – a blink of an eye in astronomical timescales.

Dr. Rebecca Davies, ASTRO 3D Postdoctoral Research Associate at Swinburne University of Technology, Australia, and lead author of the paper describing the discovery, said: “That’s what we’ve done here. And so we present two possible interpretations of this rapid evolution. The first is that there is an initial increase in carbon around galaxies simply because there is more carbon in the universe.”

“In the period when the first stars and galaxies form, a lot of heavy elements form because we never had carbon before we had stars. And so one possible reason for this rapid rise is that we are seeing the products of the first generation of stars.”

After the cosmological Dark Ages of the Big Bang, the lights came back on in the Age of Reionization, when the Universe was “only” a billion years old.

The cosmos was previously covered in a thick, dark gaseous fog. However, the universe was re-ionized as the first massive stars began to form and their light began to shine through space. This light may have caused the surrounding gas to warm rapidly, which was the cause of the increase in warm carbon observed in this study.

To understand when and how the first stars formed and began creating the elements present today, research into reionization is essential. However, observations have a history of being challenging.

Dr. Valentina D’Odorico of the Italian Institute of Astrophysics, the principal investigator of the observing program, said: “The research led by Dr. Davies is based on an exceptional sample of data obtained during 250 hours of observations with the Very Large Telescope (VLT) at the European Southern Observatory in Chile. This is the largest amount of observation time allocated to a single project with the X-Shooter spectrograph.”

“The 8-meter VLT allowed us to observe some of the most distant quasars, which act as flashlights and illuminate galaxies along the path from the early Universe to Earth.”

Some photons are absorbed by galaxies during the 13 billion-year journey of quasar light through the universe, leaving unique barcode-like patterns in the light that can be analyzed to learn the chemical composition and temperature of the galaxies’ gas.

This paints a picture of the historical evolution of the universe.

Dr Davies explains, “These ‘bar codes’ are captured by detectors on the VLT’s X-Shooter spectrograph. This instrument splits the light from the galaxy into different wavelengths, like passing light through a prism, allowing us to read the barcodes and measure the properties of each galaxy.”

The study captured more barcodes from ancient galaxies than ever before.

Dr. D’odorico said: “We increased the number of quasars for which we had high-quality data from 12 to 42, finally enabling detailed and accurate measurement of carbon density evolution. This major advancement was made possible by the ESO VLT, one of the most advanced telescopes on Earth and a strategic partner of Australia.”

Professor Emma Ryan-Weber, a principal investigator in the ARC Center of Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO 3D) and second author of the study, said: “The study provides an old dataset that will not be significantly improved until Class 30 telescopes come online by the end of this decade. High-quality data from even earlier in the Universe will require access to telescopes such as the Extremely Large Telescope (ELT) which is now being built in Chile.”

“Our results are consistent with recent studies showing that the amount of neutral hydrogen in intergalactic space is declining rapidly around the same time.” says Dr. Davies.

“This research also paves the way for future research with the Square Kilometer Array (SKA), which aims to directly detect the emission of neutral hydrogen during this important phase in the history of the universe.”

Professor Ryan-Weber says the research gets to the heart of ASTRO 3D’s mission to understand the evolution of elements from the Big Bang to the present day.

“It focuses on this important goal: How did the building blocks of life – in this case carbon – spread through the universe?

“People strive to understand ‘where do we come from?’ It’s incredible to think that the barcode of those 13 billion year old carbon atoms was printed on photons when the Earth didn’t even exist. Those photons traveled through the universe, into the VLT, and were then used to develop a picture of the evolution of the universe.”

Magazine reference:

  1. Rebecca Davies et al. Exploring the decrease in the C IV content of the Universe above 4.3 ≲ z ≲ 6.3 using the E-XQR-30 sample. Monthly Notices of the Royal Astronomical Society, Volume 521, Issue 1, May 2023, Pages 314-331, DOI: 10.1093/mnras/stad294