A collision between our galaxy — the Milky Way — and another 2 -3 billion years ago may have caused a rapid period of star formation, creating over half the stars in the galactic disc.
A team of scientists have analysed data from the Gaia satellite, discovering that an extreme star formation burst occurred in the Milky Way between two and three billion years ago. The process could have created more than 50 % of the stars that form the galactic disc.
The team — led by researchers of the Institute of Cosmos Sciences of the University of Barcelona (ICCUB, UB-IEEC) and the Besançon Astronomical Observatory — extracted their results from the combination of the distances, colours and magnitude of the stars measured by Gaia, then comparing them with models that predict their distribution in our Galaxy.
The study has been published in the journal Astronomy & Astrophysics.
Disturbing the rhythm of star formation
The rhythm of star formation in the Milky Way — fuelled by deposited gas — should decrease slowly and continuously until all the existing gas is exhausted.
The results of the study show that even though the process took place over the first 4,000 million years of the disc formation — a severe star formation burst, or “stellar baby boom” inverted this trend.
A collision and merger between the Milky Way and a satellite galaxy — rich in gas — could have injected new fuel and thus, reactivated the process of stellar formation. This mechanism would also explain the distribution of distances, ages and masses estimated from the data taken from the European Space Agency Gaia satellite.
Roger Mor, ICCUB researcher and primary author of the article, says: “The time scale of this star formation burst together with the great amount of stellar mass involved in the process, thousands of millions of solar mass, suggests the disc of our Galaxy did not have a steady and paused evolution, it may have suffered an external perturbation that began about five billion years ago.”
Mor continues: “We have been able to find this out due having -for the first time- precise distances for more than three million stars in the solar environment.
“Thanks to these data we could discover the mechanisms that controlled the evolution of our galactic disc more than 8–10 billion years ago. Which is not more than the bright band we see in the sky on a dark night and with no light pollution.”
The team’s findings have been made possible thanks to a combination of a great amount of unprecedented precision data, and the availability of a great amount of hours in computing in the computer facilities funded by the FP7 GENIUS European project (Gaia European Project for Improved data User Services) — in the Center for Scientific and Academic Services of Catalonia (CSUC).
Various studies have used Gaia data to build cosmological models predict that our galaxy could have grown due to mergers with other galaxies. One of these mergers could be the cause of the rapid star formation burst that was detected in this study.
Francesca Figuerars, lecturer at the Department of Quantum Physics and Astrophysics of the UB, ICCUB member and co-author of the study, says: “Actually, the peak of star formation is so clear, unlike what we predicted before having data from Gaia, that we thought necessary to treat its interpretation together with experts on cosmological evolution of external galaxies.”
Santi Roca-Fàbrega is an expert on simulations of galaxies similar to the Milky Way: “the obtained results match with what the current cosmological models predict, and what is more our Galaxy seen from Gaia’s eyes is an excellent cosmological laboratory where we can test and confront models at a bigger scale in the universe.”
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Gaia — the gift that keeps giving
The study in question wouldn’t have been possible without the wealth data provided by the Gaia mission — operated by the European Space Agency — which has thus far surveyed over 2 million stars. Xavier Luri, director of ICCUB and co-author states: “The role of scientists and engineers of the UB has been essential so that the scientific community enjoys the excellent quality of data from the Gaia release.”
More than 400 scientists and engineers from around Europe are part of the consortium in charge of preparing and validating these data. Luri continues: “Their collective work brought the international scientific community a release that is making us rethink many of the existent scenarios on the origins and evolution of our galaxy.”
In one year, more than 1,200 peer review articles published in journals show the effect Gaia data in almost all fields of astrophysics — ranging from the recent detection of new stellar clusters and new asteroids, to the affirmation of the star extragalactic origin in our Galaxy — right through to the calculation of the Milky Way’s mass.
Carme Jordi, UB researcher and member of the Gaia Science Team, notes: “The satellite continues to operate optimally and this July the five nominal years of scientific operation will be completed.”
ESA has approved of the extension of the Gaia mission until late 2020 — one more year than expected — and engineering teams estimate that there is enough fuel the satellite to continue working until 2024.
Jordi concludes: “There is no doubt this mission has passed a technological unprecedented challenge in space missions of all time.”
Original research: R. Mor, A. C. Robin, F. Figueras, S. Roca-Fàbrega and X. Luri. “Gaia DR2 reveals a star formation burst in the disc 2–3 Gyr ago”. Astronomy and Astrophysics, Volume 624, April 2019. DOI: 10.1051/0004–6361/201935105