They discover the oldest known star clusters

Investigating space is also a journey through time. The further away a star is, the further back in time specialists can investigate. If one of these stars is 2.5 million light years away, this means that this glow was emitted exactly 2.5 million years ago. This trip to the past is exactly what an international team has achieved with the participation of scientists from the Institute of Astrophysics of Andalusia (IAA-CSIC) and the Institute of Physics of Cantabria (IFCA-CSIC-UC): they have discovered the most distant star clusters and ancient ones known until now, linked to a galaxy whose light was emitted when the universe was barely 460 million years old – it is estimated to be 13.8 billion years old.

“These structures are the oldest star clusters ever detected and could be precursors of the globular clusters that we currently observe in our galaxy,” explains Yolanda Jiménez, postdoctoral researcher at the IAA-CSIC and co-author of the work, published this Wednesday in the journal ‘Nature. ‘. «It is a significant work because until now there was not the slightest information. Everything that was known was much more recent,” adds José Félix Rojas, from the Planetary Sciences Group of the UPV/EHU.

Star clusters are systems of gravitationally bound stars, “like satellites of galaxies. They are bright, but not as bright as the galaxies themselves. That’s why they are not usually seen. Until now we had been able to see the closest ones, but we still had to know what they were like before and how they were formed,” highlights the expert from the Basque university.

A pearl necklace

This observation has been possible thanks to the James Webb space telescope and the so-called ‘gravitational lenses’, large accumulations of matter that stand in our line of sight of distant galaxies and act as magnifying glasses that magnify the objects behind them and sometimes distort their image. in the shape of an arch.

In this case, the galactic cluster SPT-CL J0615−5746 was responsible for magnifying the light of a galaxy called the Cosmic Gems arc from the early stages of the universe’s formation. This distant galaxy had already been previously discovered by the Hubble telescope, “but it was thanks to James Webb that we were able to reveal its fascinating structure,” underlines Jiménez.

James Webb’s observations revealed the presence of five compact points distributed along the Cosmic Gems arc, like a string of pearls. Given their characteristics, researchers believe that they could be the precursors of the globular clusters that can currently be seen in the Milky Way itself. Globular clusters are groups of thousands or tens of thousands of old, gravitationally bound stars, dispersed throughout the halo of the Milky Way and some with ages comparable to that of the galaxy itself. The Gems are also responsible for most of the ultraviolet emission of the galaxy where they are located. They are, therefore, one of the main sources of reionization in the early universe. During this stage, the first stars and galaxies began to shine, emitting radiation that ionized the existing neutral hydrogen gas. This facilitated the formation of the galaxies and cosmic structures that we observe today. “This process is key to being able to see the first stages of the cosmic dawn, the dawn of the universe,” highlights the UPV/EHU professor.

«This result is of great importance, since we currently do not know the origin of globular clusters. The discovery of the Gems provides for the first time a time scale for their formation and reveals their initial physical properties,” concludes Jiménez.