Think of the 100 billion stars of the Milky Way as a flat, calm pool of water. Now imagine if someone dropped a rock the size of 400 million suns into that water. The calm is shaken. Wave after wave of energy ripples across the galaxy’s surface, jostling and bobbing its stars in a chaotic dance that takes eons to settle.
Astronomers suspect that something like this could really have happened — not just once, but several times over the past billions of years.
In a new paper published September 15 in the Monthly Bulletins of the Royal Astronomical SocietyResearchers explain how a nearby mini galaxy – the Sagittarius dwarf galaxy — seems to have crashed through the Milky Way on at least two separate occasions causing stars everywhere galaxy mysteriously oscillating at different speeds.
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Using data from the European Space Agency’s Gaia space observatory, the researchers compared the movements of more than 20 million stars throughout the Milky Way, but particularly in the outer regions of the galaxy’s disk. The data revealed a mysterious wave, or vibration, that seemed to jostle stars across the galaxy.
“We can see that these stars are wobbling and moving up and down at different speeds,” says study author Paul McMillan, an astronomer at Lund University in Sweden. said in a translated statement.
Through a process the researchers equated with “galactic seismology,” the team modeled a ripple pattern that could explain the strange ripple effect unbalancing the Milky Way’s stars. They concluded that the waves were probably released hundreds of millions of years ago when the Sagittarius dwarf galaxy last passed through our galaxy – “a bit like throwing a rock into a pond,” McMillan said. It seems likely that a second, even earlier, collision between the two galaxies also occurred, the researchers added.
preliminary studies (opens in new tab) have suggested that an ancient collision with Sagittarius may have unleashed ripples in the center of the Milky Way, but this new research is the first to show that these ripples extended to the edge of the galaxy’s disk, disrupting stars at every turn. This new research should help piece together the long and violent history of our galaxy and its smaller neighbor, the researchers wrote.
Today, the Sagittarius dwarf galaxy is estimated to be about 400 times Earth’s mass — a mere shrimp compared to the Milky Way’s estimated mass of 1.5 trillion suns. Scientists suspect that Sagittarius was once much larger, but has lost up to 20% of its mass to our galaxy after repeated collisions over the past billion years.
These collisions also likely changed the shape and size of our galaxy; A 2011 study suggested that the spiral arm of the Milky Way is the result of two collisions with the Sagittarius dwarf galaxy. Another study of Gaia data, published in 2020, suggested that cosmic crashes between our galaxy and Sagittarius triggered a baby boom of new stars in the Milky Way every time the two galaxies met.
Originally published on Live Science.
