A team of scientists has found evidence of the first stars that ever existed in the Universe, which gives us a better understanding of their nature. Using the European Southern Observatory’s Very Large Telescope (VLT), they discovered three distant gas clouds with a chemical composition that matches what we expect from the explosions of the first stars.
“For the first time ever, we were able to identify the chemical traces of the explosions of the first stars in very distant gas clouds,” says Andrea Saccardi, a PhD student who led the study, in a statement.
These first stars, which formed 13.5 billion years ago, were different from the stars we see today. They contained only hydrogen and helium, the simplest chemical elements in nature. These massive stars quickly died in powerful explosions called supernovae, which released heavier elements into the surrounding gas for the first time. Later generations of stars were born from this enriched gas and produced even heavier elements as they died. However, the first stars are long gone, so scientists study them indirectly by detecting the chemical elements they dispersed after their death.
Turning to quasars for data
For the study, astronomers analyzed data from a large survey of quasars. Quasars emit a lot of light, which scientists can use to study the universe’s history and structure. They’re powered by supermassive black holes at the centers of galaxies. The data was collected using a powerful telescope called the VLT X-shooter in Chile.
Researchers looked at the light coming from 100 quasars, which were chosen because they were very far away (about 10-12 billion light-years). The light from these quasars passes through gas clouds between us and the quasar, and these gas clouds absorb some of the light. By studying the absorption lines in the quasar’s light spectrum, scientists can learn about the gas clouds’ properties, like their chemical composition and density.
To analyze the data, the team used a software called Astrocook, which helps identify the absorption lines and match them to known elements. They focused on gas clouds with a specific range of hydrogen density because these clouds can give insights into the diffuse gas around galaxies and cosmic filaments (large-scale structures in the universe).
They found 54 absorption systems in their data, 16 of which were sub-DLAs (a type of gas cloud with a particular hydrogen density) and 21 were LLSs (another type of gas cloud). To determine the chemical composition of these gas clouds, they used computer models to correct for ionization, which is the process of an atom losing or gaining electrons.
The researchers then calculated the metallicity (the amount of heavier elements) of the gas clouds, which helps understand their origin and evolution. They found a wide range of metallicities, with some gas clouds being very metal-poor (with low amounts of heavier elements). This information can help researchers learn more about the history and structure of the universe.
‘Fingerprints’ of the first stars with gas clouds
Study authors found that some of the gas clouds they studied had higher amounts of carbon compared to iron. They compared these carbon-rich clouds to the chemical makeup of ancient stars in our galaxy and found that they matched up well. This suggests that the gases in these distant clouds might have come from the same places where the first stars were born.
The study also looked at the presence of other elements like oxygen, magnesium, and silicon in these gas clouds. They found that these elements also had similar patterns to those found in very old stars, which supports the idea that these clouds of gas are related to the birthplaces of ancient stars.
One interesting finding was that these carbon-rich gas clouds seem to be similar to a specific type of ancient star called CEMP-no stars. These stars are thought to have been influenced by the first stars that formed in the universe. The researchers suggest that these carbon-rich gas clouds could be the gaseous counterparts of these ancient CEMP-no stars, which helps us understand more about the early universe and the formation of the first stars.
Essentially, the astronomers pinpointed the “fingerprints” our stars from the infancy of the Universe.
“Our discovery opens new avenues to indirectly study the nature of the first stars, fully complementing studies of stars in our galaxy,” explains Stefania Salvadori, a co-author of the study.
This study looked at the chemical makeup of 37 gas systems found in the distant universe. They analyzed the data and found some interesting results:
- The gas systems have different levels of metal content, with two main groups: one with a lot of iron and another with very little iron.
- Some of these gas systems have high levels of carbon and other elements, similar to very old stars in our galaxy and nearby dwarf galaxies.
- The carbon-rich gas systems have similarities to a specific type of old star, called “CEMP-no” stars, which are thought to be connected to the first stars that formed in the Universe.
These findings suggest that these gas systems could be good places to look for clues about the early universe and the first stars. It paves the way for next-generation telescopes and instruments, like ESO’s upcoming Extremely Large Telescope (ELT) and its high-resolution ArmazoNes high Dispersion Echelle Spectrograph (ANDES). “With ANDES at the ELT, we will be able to study many of these rare gas clouds in greater detail, and we will be able to finally uncover the mysterious nature of the first stars,” adds Valentina D’Odorico, a co-author of the study.