The project took 20 years and studied more than 2 million galaxies and quasars, covering 11 billion years of history.
The starry sky has been measured like never before thanks to the Sloan Digital Sky Survey, an international project in which scientists took part from the National Autonomous University of Mexico (UNAM) and the University of Guanajuato (UG).
They principally collaborated on the eBOSS (Extended Baryon Oscillation Spectroscopic Survey) experiment, the objective of which was to undertake a cosmological census using telescopes and powerful data analysis computers.
What was the outcome? The best map of the universe ever made, which includes more than 2 million galaxies and quasars (the weakening nuclei of galaxies), covering 11 billion years of cosmic history.
According to Octavio Valenzuela Tijerino, a researcher in the Institute of Astronomy (IA) at UNAM, the number of astronomical objects studied allowed scientists to achieve for the first time a 1% and 3% order of accuracy for calculated distances and expansion speed, respectively.
“It’s very unusual in the history of cosmology and science,” says this scientist, who participated in the eBOSS national data analysis team, in an interview for Tec Review.
This group analyzed relatively old galaxies (sets of stars) known, in astronomical circles, as large red galaxies.
“As they’re old stellar populations, they no longer undergo many transformations, so all the observed changes were related to the universe and not to the internal metabolism of the galaxies themselves,” explains Valenzuela Tijerino.
Mariana Vargas Magaña, a researcher at the UNAM Physics Institute (IF), was responsible for filtering the astronomical sample. That means distinguishing and discarding very close stars which are often confused with galaxies or cause other effects.
“I started my doctorate with this experiment. My first steps as a researcher began here. I grew academically as a result of this collaboration. For me, finishing this is like the end of an era. It was quite a big mental transition,” says the scientist in an interview for Tec Review.
She says her work is called observational cosmology, which involves analyzing great magnitudes of data. It is something relatively new in the country and needs promoting in academic contexts.
“At UNAM, we’ve tried to motivate students to do this type of physics, which is new for them, because access to this data has not always been available in Mexico. To analyze the data, you have to know a lot about statistics and programming,” says Vargas Magaña.
She had the support of Sébastien Fromenteau, a French researcher attached to the UNAM Institute of Physical Sciences (ICF) who, in an interview for Tec Review, emphasized the complete dedication required for the project.
“A lot of prior research was done to determine what kinds of galaxies we had. Afterwards, there were a huge amount of numerical simulations to do. It is very satisfying to see that, after so many years of work, without holidays or weekends, something has finally been achieved,” says the French scientist.
It is important to mention that the entire eBOSS project took 20 years. Dozens of international researchers from universities in more than 10 countries such as the United States, Chile, Brazil, Spain, England, France, and China have taken part in it.
It is a great example of a collaborative project which has contributed to the training of new, internationally renowned scientists and has permitted technology transfer, to the benefit of participating countries.
Alma Xóchitl González Morales, a researcher in the Physics Department at UG, also stands out within the group, as she is the only person in Mexico not attached to UNAM to take part in the project.
She explains in an interview for Tec Review that the results were consistent with the standard Big Bang-based cosmological model: the theory of accelerated expansion of the universe following an explosion approximately 14 billion years ago.
However, she clarifies that it was only possible to study a small part of the cosmos in this investigation.
“Actually, the content of this map, the largest so far, reveals that we haven’t even been able to study everything in the observable universe,” says González Morales.
Axel Ricardo De la Macorra Pettersson Moriel, a researcher at UNAM’s IF, says that although the study does not reveal an astronomical paradigm shift, it is important to continue working on the conclusions of eBOSS, which were recently published in 20 different scientific articles.
“It hasn’t been a revolution in itself, but it has given us much greater accuracy and the ability to discriminate between different, alternative models. There has been no major surprise. We need to study the results in more detail,” explains this academic.
However, De la Macorra Pettersson Moriel believes that theoretical surprises cannot be ruled out entirely, “because the full impact of the data may have not been completely unraveled yet.”
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According to Octavio Valenzuela, even though the applications of this study are far from evident, there are three fields in which we will begin to see benefits for society.
Interpretation of the eBOSS observations was done using some of the most powerful computers in the world, including those in Mexico.
Each nation took on the parts of the problem that it could tackle. In Mexico, IBM collaborated with Summit, the most powerful supercomputing system in the world at the time.
“This involved the adaptation of the system and, consequently, there was a transfer of technological knowledge to students, technicians and researchers who, in turn, shared it with people who now apply it to biology and medicine. This has also taken place, for example, in Covid-19 propagation models.”
The refinement of cosmic cartography involves accurate knowledge of the fundamental laws of physics. Although, for the moment, no specific application is known for this research, the history of science reveals the course to follow.
“When the laws of thermodynamics were determined, it became a trivial thing to build refrigerators, and now we all have them at home. They’re so common that we can say there’s not too much complicated science there. However, you had to understand how energy, heat and temperature behaved to get to that point. I think the same will happen with eBOSS.”
Decades ago, it was believed the universe was so large that it could never be measured. However, current physics already has certain parameters related to the evolution of the cosmos.
“We’re now studying the history of the universe in great detail. This has great philosophical value, especially for complex problems like Covid-19, economic questions, and other types of technological issues.”
“If something as abstract and apparently as impossible as mapping the universe can be proposed, and an experiment can be designed to solve that problem, everything else is also possible.”
Cosmology, according to De la Macorra, is currently experiencing a golden age and, in the future, its influence will be felt even more.
“We have never advanced so much in understanding the universe. There has never been so much international interest in investing money in different experiments. There are more satellites to be launched; more probes to be made. It’s a great pleasure to have been able to participate in the biggest cosmology project of recent years. Furthermore, it means that Mexico will participate in the next project, taking everything one step further: we will measure between 50 and 60 million (astronomical) objects over the course of four years. But right now, we are celebrating the eBOSS results,” he said.