Cosmic Crash Between Milky Way and Dwarf Galaxy Sagittarius May Have Led to Formation of Our Solar System

The emergence of our solar system could be the result of dwarf galaxy Sagittarius crashing into the Milky Way billions of years ago.

New research, based on data from the orbital telescope Gaia, suggests ripples caused by collisions may have sparked major star formations, with one such event coinciding with the formation of our own Sun, approximately 4.7 billion years ago.

It is accepted by astronomers that the neighboring galaxy Sagittarius previously made contact with the Milky Way—potentially affecting how its stars move.

But a new paper, published in Nature Astronomy, suggests the influence of this smaller galaxy may have been far greater than previously known.

"It seems that not only did Sagittarius shape the structure and influence the dynamics of how stars are moving in the Milky Way, it has also led to a build-up of the Milky Way," said scientist Carme Gallart, a co-author of the academic paper.

"It seems that an important part of the Milky Way's stellar mass was formed due to the interactions with Sagittarius and wouldn't exist otherwise," she added.

Launched in 2013, Gaia is a space telescope project managed European Space Agency (ESA) tasked with creating a 3D map of the galaxy and its star positions.

"It is known from existing models that Sagittarius fell into the Milky Way three times" explained Tomás Ruiz-Lara, researcher in Astrophysics at the Instituto de Astrofísica de Canarias (IAC) in Tenerife, Spain, and lead author of the study.

"When we looked into the Gaia data about the Milky Way, we found three periods of increased star formation that peaked 5.7 billion years ago, 1.9 billion years ago and one billion years ago, corresponding with the time when Sagittarius is believed to have passed through the disc of the Milky Way," the scientist continued.

According to the team, ripples from the crashes could have led to higher concentrations of dust and gas in areas of the Milky Way—triggering the formation of stars.

It could even be possible the sun and planets would not have existed if Sagittarius had not become trapped by the gravitational pull of the larger Milky Way galaxy.

"The sun formed at the time when stars were forming in the Milky Way because of the first passage of Sagittarius," Carme, also of the IAC, added.

"We don't know if the cloud of gas and dust that turned into the sun collapsed because of the effects of Sagittarius or not. But it is a possible scenario because the age of the sun is consistent with a star formed as a result of the Sagittarius effect."

The sun was formed billions of years ago when a cloud of dust and gas, known as a nebula, collapsed under its own gravity.

Space agency NASA describes it as the heart of our solar system as its gravity holds the planets in order while providing properties vital to life on Earth.

"The connection and interactions between the Sun and Earth drive the seasons, ocean currents, weather, climate, radiation belts and aurorae. Though it is special to us, there are billions of stars like our sun scattered across the Milky Way," NASA says.

ESA project scientist Timo Prusti praised the data provided by Gaia, which marked the positions of nearly 1.7 billion stars in its most recent release of data, published in 2018. The telescope's mission is expected to last until at least the end of 2020.

"This is the first time that we see a detailed star formation history of the Milky Way. It's a testament to the scientific power of Gaia that we have seen manifest again and again in countless ground-breaking studies in a period of only a couple of years," he said.

The research paper spearheaded by Ruiz-Lara is titled: The recurrent impact of the Sagittarius dwarf on the Milky Way star formation history.

"These findings most probably suggest that Sagittarius has... been an important actor in the build-up of the stellar mass of the Milky Way disk, with the perturbations from Sagittarius repeatedly triggering major episodes of star formation," it reads.

Milky Way
The Milky Way's Galactic Centre, Jupiter (brightest spot in the centre-left of the image) and the Small Magellanic Cloud (SMC) galaxy (right bottom corner) are seen late on May 10, 2019. MARIANA SUAREZ/AFP/Getty