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A new study using data from the Gaia space telescope shows that the Milky Way’s last major collision occurred within the last three billion years, much later than
A new study using data from the Gaia space telescope shows that the Milky Way’s last major collision occurred within the last three billion years, much later than previously thought. By analyzing the wrinkles caused by past galactic collisions, they found that the historical timescale of these events has been significantly compressed, changing our understanding of the Milky Way’s evolution and the formation of stellar structures.
Astronomer Robin Sanderson and colleagues recently published results showing that the last major collision in the Milky Way galaxy occurred billions of years later than previously thought.
“The debate is about the Milky Way’s occupation of these stars,” Sanderson says. “Our work shows that some stars thought to be the result of an ancient merger may not exist. The pattern we see them forming has long since changed or disappeared.”
The discovery was made possible by the European Space Agency’s Gaia Billion Star Survey, which has mapped more than a thousand million stars in the Milky Way and beyond, tracking their motion, brightness, temperature and composition. The team focused on “wrinkles” in our galaxy created by other galaxies colliding with the Milky Way.
These wrinkles are like cosmic fingerprints left by past collisions, Sanderson says. By studying their patterns, cosmologists can track the chronology of these events and understand the evolutionary history of the Milky Way.
“As we get older, we get more wrinkles, but our work shows the opposite is true for the Milky Way. It’s kind of like the Benjamin Button of space, it’s getting less wrinkled over time,” says Tom Donlon, former Sanderson Group visiting scientist and lead author of the new Gaia study. “By looking at how these wrinkles spread out over time, we can track when the Milky Way had its last big collapse, and it turns out it happened billions of years later than we thought.”
By comparing their observations of the wrinkles with cosmological simulations, the team was able to determine that our last significant collision with another galaxy did not actually occur between eight and 11 billion years ago, as previously thought.
“Simulations are critical because they allow us to recreate past events that might have occurred in the Milky Way and see if they are consistent with what we observe,” Sanderson says. “In this case, they show us that the last major collision happened much later.”
For the wrinkles on stars to be as prominent as they appear in the Gaia data, they would have to have joined us at least three billion years ago, or at least five billion years later than previously thought, says co-author Professor Heidi Joe Newberg, an astronomer at Rensselaer Polytechnic Institute. “When stars wobble back and forth in the center of the Milky Way, new stellar wrinkles form. If they joined us eight billion years ago, there would have been so many wrinkles side by side that we would no longer be able to see them as separate entities,” she adds.
Several current and former Penn researchers, both graduates of the school, contributed to the work, including Arpit Arora, who created all of the models for the galactic potential used in the study, and Nond Panitanpaisal, who standardized the method used to reconstruct the structures. Emily Bregow, a former research student in the Department of Arts & Sciences, contributed to the rendering code. Danny Horta, one of Sanderson’s colleagues at the Flatiron Institute, also contributed to the work by analyzing large, ancient galaxies that merged with the Milky Way long ago.
The collision is believed to have resulted in the creation of a large number of stars with unusual orbits. Scientists had previously dated it to between eight and 11 billion years ago in a collision called the Gaia-Sociska-Enceladus merger. Instead, Newberg and Donlon’s findings suggest that the stars may have formed from a radial merger of the Virgo constellation that collided with the center of the Milky Way less than three billion years ago.
“Gaia is an extremely productive mission that is changing the way we think about space,” says Timo Prusti, Gaia Project Scientist at ESA. “These results were made possible thanks to the incredible teamwork and collaboration between a large number of scientists and engineers across Europe and beyond.”
Source: Port Altele
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