How are galaxies and solar systems similar?

Passage through the Sagittarius dwarf galaxy

The formation of our solar system is possibly the result of a cosmic collision. This is the conclusion of a team of researchers after studying stars within a radius of 6,500 light years around the sun. In this region, the data from the Gaia space telescope show, a particularly large number of stars were formed when the Sagittarius dwarf galaxy collided with the Milky Way. Our sun could also have been formed in the course of one of these events, according to the scientists who report on their observations in the journal "Nature Astronomy".

With around one billion stars, the Sagittarius dwarf galaxy is a small, irregularly shaped companion of the Milky Way. For comparison: The Milky Way is a large spiral galaxy with around 250 billion stars. Sagittarius is currently about 70,000 light years from the Milky Way. “However, models of the orbit movement show that Sagittarius has already flown through the Milky Way three times,” explains Tomás Ruiz-Lara from the University of La Laguna on Tenerife. These clashes took place five to six, two, and a billion years ago.

Collisions of the Sagittarius dwarf galaxy with the Milky Way

On the basis of the data from the Gaia space telescope, Ruiz-Lara and his colleagues have now investigated the brightness, color and distance of stars that are up to 6500 light years away from the sun. With the help of evolution models, they calculated the age of the stars. "The Gaia data show us that there were three phases of increased star formation in the Milky Way," says Ruiz-Lara. “These phases reached their maximum 5.7, 1.9 and 1.0 billion years ago - in good agreement with the passage through the Sagittarius galaxy.” The researcher compares these events with a stone thrown into the water that caused waves generated on the surface of a lake. In a very similar way, the Sagittarius dwarf galaxy - as it passed the Milky Way - produced an undulating compression of the interstellar gas, thereby triggering the formation of many new stars.

These phases lasted a long time, even by astronomical standards - the first collision formed a particularly large number of stars 6.2 to 4.2 billion years ago. And so the formation of our sun and its planets also falls into this epoch. “The age of the sun, which is generally accepted today, is 4.7 to 4.8 billion years,” says Ruiz-Lara. “So it is conceivable that our solar system was also formed as a result of the first flight through the Sagittarius dwarf galaxy.” At the moment, however, this is still speculation and further observations are necessary.