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The collision between our Milky Way galaxy and its biggest neighbor, the Andromeda galaxy, is expected to occur in about 4.5 billion years, and has been predicted by astronomers since 1912.
At first glance, the galactic duo, about 2.5 million light years away, appears to be on an inevitable collision course. The Milky Way and Andromeda barrel towards each other at about 223,694 miles per hour (100 kilometers per second).
However, local groups, or corners of the universe, contain 100 known small galaxies. Considering some of the biggest of them, such as the massive Magellan Cloud, or the LMC, M33, or triangular galaxy, a team of astronomers have seen how much of a role it will play in the Galaxy’s future chess board over the next 10 billion years.
After running 100,000 simulations using new data from Hubble and Gaia’s space telescopes, taking into account the gravitational pull of local group galaxies, the team discovered that there is about 50% chance of a collision between the Milky Way and Andromeda within the next 10 billion years. A study published Monday in the Journal Nature Astronomy shows that, as previously thought, there is only about 2% chance that a galaxy will collide in 4-5 billion years.
The merger of the Milky Way and Andromeda galaxies destroy both of them, eventually turning both spiral structures into one elongated galaxy, the research authors said. Other intergalactic collisions are known to “become irreversible in the centre of the remnants of the merger, supplying a central black hole that emits enormous amounts of radiation, falling irreparably into the hole.
“We thought this was the fate awaiting our Milky Way galaxy,” Frenck said. “We know now there is a very good chance we may avoid that horrible fate.”
However, according to the research authors, there are many unknown factors that make it difficult to predict the ultimate fate of our galaxy. And Frenk warns that the Milky Way is likely to collide with the LMC within two billion years, and could fundamentally change the galaxy.
The LMC orbits the Milky Way, and the M33 is an Andromeda satellite.
The mass of the LMC is only about 15% of the Milky Way. However, the team discovered that satellite galaxies have gravitational attractions perpendicular to Andromeda, which sufficiently alters the movement of the Milky Way to reduce the likelihood of mergers between the two giant galaxies. This is the same case for the M33.
“The extra mass of Andromeda’s satellite galaxy M33, Dr. Sawara, an astronomer at the University of Helsinki in Finland, said: “But it also shows that the LMC is pulling the Milky Way away from the orbit and is away from Andromeda. It doesn’t mean that the LMC will save us from its merger, but that’s a little less.”
Previous studies also assume potential values for unknown data, such as current location uncertainty, local group galaxies’ movements, and mass. In the new study, the team occupied 22 different variables, including unknowns that could contribute to the conflict.
“We ran thousands of simulations and were able to explain all the observational uncertainties,” Sawara said. “There are so many variables in each that there are errors, which accumulates in quite a large uncertainty about the outcome, leading to the conclusion that the likelihood of a direct conflict is only 50% within the next 10 billion years.”
In half of the simulations predicting what will happen in 8-10 billion years, the Milky Way and Andromeda galaxies first sailed violently with each other, then turned and then collided and fused as a single galaxy. These first close encounters between each Galaxy halo – a large envelope of gas – ultimately lead to a collision.
“In general, the merger involves strong starbursts, during which many new stars are formed, followed by a period of intense radiation caused by exploding young stars and new, active supermassive black holes, ultimately blocking star formation completely,” Sawara said. “By billions of years later, traces of the old Milkyway and Andromeda will disappear, and the remnants will become an almost uncharacteristic, oval galaxy.”
In other simulations, both galaxies passed the path without interfering with each other.
Geraint Lewis, professor of astrophysics at the University of Sydney Institute of Astronomy, found results showing significant effects of M33 and LMC. He previously wrote a study on the potential conflict between Andromeda and the Milky Way.
“I don’t know if the collision will definitely be off in the future, but this clearly shows that what people say is that there is a collision that destroys the Milky Way and Andromeda. “But even if there is a rather close encounter rather than crushing the front, the gravitational tear that each of them claims to each other could leave two large galaxies in a disappointing state.”
Although it is important to include the gravitational effect of LMC on the Milky Way, considering uncertainty is the most important aspect of the new research, said Scott Lucchini, a postdoctoral fellow for theory and calculation at the Harvard & Smithsonian Institute at the Astrophysics Center.
“Here, they were able to sample from the uncertainty of the galaxy’s position, velocity and mass to obtain the relative probabilities of different outcomes,” Lucchini wrote in an email. “This really gives us a big picture of what will happen in the future.”
Galaxies are full of complexity. Their shapes can be distorted, interactions can change trajectories and lose mass in a variety of ways. Such complexity makes predictions difficult, Lucchini said.
It essentially leaves the fate of the Milky Way “completely open,” the research author wrote in a new paper.
However, increasing data from the Gaia Space Telescope in the summer of 2026 will provide measurements that will improve some of the uncertainties regarding the speed and direction of Andromeda moving across the sky, Sawara said.
Researchers say the fate of the sun can have a greater impact on Earth’s future than the movement of the galaxy.
Our sun is 4.5 billion years ago. According to NASA, when they begin to die in another five billion years, they swell into Mercury, Venus, and the red giant that potentially swallows Earth.
“The simple answer is that the end of the sun is much worse for our planet than it’s collision with Andromeda,” Sawara said. “The merger means the end of our galaxy, but it is not necessarily the end of the Sun or Earth. Our work also shows previous research, but argues that the fate of the solar system accurately predicted that the post-merger fate was clearly premature.
The team did not model the merger between the LMC and the Milky Way in detail, but discovered “virtual certainty” that will occur in the next 2 billion years. However, the effect could be more minor than the merger of the Milky Way and Andromeda.
“The merger (between the Milky Way and the LMC) does not destroy our galaxy, but it changes deeply and affects our central, ultra-large black holes and galaxy halos,” wrote Frenk in an email. He also co-authored a 2019 paper on potential mergers.
