A prime history of the Milky Way and its fossil products

Just as archaeologists dig in the hopes of finding traces of the past, an international group of astronauts found their way into the thick cloud of dust around the center of the Milky Way (also known as the Milky Way). the bulge) finds primeval masses of gas and stars never seen before. They named this new class of stellar system ‘Bulge Fossil Fragments’. A research team led by Francesco Ferraro (Department of Physics and Astronomy “Augusto Righi” at the University of Bologna and a member of the National Institute of Astrophysics – INAF) conducted a study published there Astronomy of nature.

Researchers found out about this new class while analyzing Liller 1. The latter is a stellar system in the Milky Way bulge that for more than 40 years has been considered as a “global body,” ie a system made up of millions of stars of the same age (there are at least 150 global collections on the Milky Way). However, researchers looked closely at Liller 1 and found that its true identity is more interesting than they had hitherto believed. In fact, Liller 1 is a fossil fragment of one of the giant stellar lumps that came together, about 12 billion years ago, to become the main bulge of the Milky Way.

“Our results clearly show that Liller 1 is not a global collection, but a much more complex one,” said Dr. Francesco Ferraro, first author and co-ordinator of the Liller 1. It is a stellar memorial, a fossil find containing the history of the creation of the Milky Way. “

Test result

It was said that “cosmic results” already existed when researchers discovered something similar, Terzan 5, a few years ago. Terzan 5 looked like a spherical universe inside our galaxy bulge, but, on closer inspection, its properties were not compatible with the features of other spherical bodies.

However, an isolated case is just an interesting anomaly. This is why Liller 1 is so important. The shared features of Terzan 5 and Liller 1 prove that a new class of stellar systems is unknown to this day.

Fossil fragments

What are the features of the Bulge Fossil Fragments? These objects are cursed as world records, but they are completely different, if one looks at the age of the stars that make them. There are two stellar groups in these systems: one is as old as the Milky Way – it was created 12 billion years ago – and the other is much younger. On the one hand, this shows that these stellar systems appeared at early stages of the Milky Way formation; on the other hand, it shows that they are capable of inducing many events of stellar generation.

“The stellar number characteristics of Liller 1 and Terzan 5 suggest that both systems were created at the same time of the Milky Way,” explained one of the study’s authors, Barbara Lanzoni, a Professor at the University of Bologna and an INAF member. “Younger stellar populations are richer in iron and tend to accumulate in the middle of the bulge areas. In fact, this is in the context of enrichment in which the gas produced by older stars creates new ones. “

Beyond the Clouds

These conclusions were easy to come by. Liller 1 is located in one of the most hidden regions of our galaxy, where thick clouds of interstellar dust reduce star light making it up to 10,000 times weaker. Infrared light is the only way to get through these clouds. That is why Gemini South researchers chose to study Liller 1. Gemini South is a powerful telescope with a diameter of 8 meters capable of compensating for the biases in stellar images caused by the atmosphere of the Land.

The sharpness of the Gemini South statues is unmatched. Thanks to these stunning images, researchers were able to analyze the stellar population of Liller 1 in detail. Despite this initial analysis, researchers still had some work to do to get a complete picture of positioning of this stellar system. Of course, they needed to know if all the stars that showed these images with Liller 1, or if some of them were exactly in the same line of sight, but did not belong to it. They were able to resolve this issue using further observations made through the Hubble Space Telescope.

“After combining the two sets of images, we removed the non-Liller 1 stars and finally had a clear and detailed picture of this stellar system,” said Cristina Pallanca, a University researcher. Bologna and an INAF member who co-authored the study. ”Our results surprised us: Liller 1 hosts at least two stellar groups with very different ages, with the oldest having created about 12 billion years ago, the only time the Milky Way was created; the second, much younger, had been created just 1-2 billion years ago. “

A discovery that is very similar to what they found out about Terzan 5, which likewise hosts one stellar population as old as the Milky Way and a much younger one (4.5 billion years old).

“The discovery that Liller 1 and Terzan 5 share very similar features would allow it to identify a new class of stellar systems that came from some ancestors that were large enough for the gas it emitted. with supernovas to keep. structures, “adds Emanuele Dalessandro, a researcher at INAF – Space Science Observatory (OAS) in Bologna and co – author of the study.

This then confirmed the existence of the Bulge Fossil Fragments, ie stellar systems made up of the remains of large primitive materials born, 12 billion years ago, on the Milky way.

“The history of the Milky Way is written in these fossil remains. The latter are signs of an age when the Universe was very young, just 1 billion years old,” says Professor Ferraro ending. “Now we need to go deeper. Thanks to the discovery of these fossil remains, we can begin to read the history of the Milky Way and perhaps redefine our knowledge of the creation of the belly. “

“The Galactic bulge is a new class of fossil particles from the hierarchical assemblage,” the title of this study published in Astronomy of nature.

Presented by Università di Bologna