(ORDO NEWS) — The formation of the Sun, the Solar system and the subsequent emergence of life on Earth may be the result of a collision between our Milky Way galaxy and a smaller galaxy called Sagittarius, discovered in the 1990s in the orbit of our galactic home.
Astronomers know that Sagittarius repeatedly made its way through the disk of the Milky Way, since its orbit around the center of the galaxy is compressed as a result of gravitational forces. Previous research has shown that Sagittarius, the so-called dwarf galaxy, has had a profound effect on how stars move in the Milky Way. Some even claim that the 10,000-fold more massive spiral structure of the Milky Way may be the result of at least three known Sagittarius collisions over the past six billion years.
A new study based on data collected by the Gaia telescope for the first time showed that the influence of Sagittarius on the Milky Way can be even more significant. The ripples caused by the collisions seem to have triggered large episodes of star formation, one of which roughly coincided with the formation of the Sun about 4.7 billion years ago.
“From existing models it is known that Sagittarius fell into the Milky Way three times – first about five or six billion years ago, then about two billion years ago, and finally, one billion years ago,” says Thomas Ruiz-Lara, a researcher at the Institute Canary Islands Astrophysicists (IAC) in Tenerife, Spain, and lead author of a new study published in Nature Astronomy.
“When we examined Gaia’s data on the Milky Way, we found three periods of increased star formation that peaked 5.7 billion years ago, 1.9 billion years ago and 1 billion years ago, which corresponds to the time when it is believed that Sagittarius passed through the disk of the Milky Way.”
Researchers studied the luminosity, distances, and colors of stars in a sphere with a radius of about 6,500 light-years around the Sun and compared data with existing stellar evolution models.
“In the beginning, you have the Milky Way galaxy, which is relatively calm,” says Thomas. “After the initial turbulent era of star formation, partially caused by earlier mergers, the Milky Way reached a balanced state in which stars formed steadily. “Sagittarius suddenly flies in and upsets the balance, causing all previously motionless gas and dust inside the larger galaxy to move like ripples in the water.”
In some areas of the Milky Way, these ripples can lead to higher concentrations of dust and gas, while emptying others. The high density of the material in these areas will cause the formation of new stars.
“It seems that Sagittarius not only shaped the structure and influenced the dynamics of the stars in the Milky Way, but also led to the creation of the Milky Way,” says Carme Gallart, co-author of the project. “It seems that an important part of the stellar mass of the Milky Way was formed due to interaction with Sagittarius and could not exist otherwise.”
In fact, it seems possible that even the Sun and planets would not exist if the dwarf Sagittarius did not fall into the trap of the gravitational attraction of the Milky Way and eventually break through its disk.
“The sun formed at a time when stars formed in the Milky Way due to the first passage of Sagittarius,” says Karma. “We don’t know whether a particular cloud of gas and dust that has turned into the Sun has collapsed due to the influence of Sagittarius or not.”
Each collision deprived Sagittarius of some gas and dust, making the galaxy smaller after each pass. Existing data suggest that Sagittarius may have passed the Milky Way disk again quite recently, in the last several hundred million years, and is currently very close to it. In fact, a new study discovered a recent explosion of star formation, suggesting a possible new and ongoing wave of stellar birth.
According to ESA Gaia project scientist Timo Prusti, such a detailed understanding of the star formation history of the Milky Way would not have been possible before the advent of Gaia, a telescope launched in late 2013, whose two datasets in 2016 and 2018 revolutionized the study of the Milky Way.
“Some definitions of the history of star formation in the Milky Way existed earlier based on data from the Hipparcos ESA mission in the early 1990s,” says Timo. “But these observations were focused on objects in the immediate vicinity of the Sun. He could not reveal the bursts of star formation that we see now.”
“This is really the first time we have seen a detailed history of star formation in the Milky Way. This is evidence of the scientific power of the Gaia telescope, which we have shown again and again in countless pioneering studies in just a couple of years.”
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