The Milky Way has merged with many other galaxies in its long lifespan, but stealing its history together has been a loving act.
A new analysis of galactic clusters around the galaxy has now given us the most complete galactic merger history ever. And that data includes a previously unknown merger event that occurred 11 billion years ago, and completely changed the shape of our galaxy. Astronomers have named the galaxy – accepted by the Milky Way – Kraken.
The clusters of stars in question are called globular clusters, often considered the “fossils” of the early universe. They are very ga ense, spherical clusters with about 100,000 to 1 million very old stars, some of which are almost as old as the universe itself. In any globular cluster, all its stars form at the same time with the same cloud of gas, which means that we can use their chemical composition for their original function.
But that’s just one part of the puzzle. The galaxy has about 150 globular clusters, and is functional and reconstructing their orbital motion, and their current shape (some are long, torn into stellar rivers), can also help from where they came from.
A team of astronomers has now done this, using an artificial neural network to simulate globular clusters orbiting galaxies like galaxies. These simulations, called e-mosaics, form the entire lifespan of globular clusters, from evolution to destruction.
“The main challenge in linking the properties of global clusters to the merger history of their host galaxy has always been that galaxy assembly is a highly disorganized process, during which the orbit of global clusters changes completely,” said astronomer Diederick Cruise. University of Heidelberg, Germany.
“We’ve tested the algorithm thousands of times on simulations and they were amazed at how accurately they are able to reconstruct the merged history of simulated galaxies, using only their globular cluster populations.”
The next step was to feed the software real data. In recent years, the Gaia satellite has been working diligently to create high ision in-depth and detailed maps of galaxies not only in space but also over time. This has given us the most accurate data yet about the position and motion of the galaxy of objects, which has led to some interesting discoveries about our home galaxy.
Using Gaia data, the team grouped the globular clusters together based on their orbital motion. This is because clusters with similar orbits around the galaxy are thought to have come from the same place; That is, a galaxy that was moved by a galaxy at some point in its past.
(Cruisesen et al., MNRAS, 2020)
When this data was processed by the team’s software software, the results were closely agreed with the five galactic collisions.
Four of them were known – the Gaia-Enceladus galaxy, also known as the Gaia Sausage, which was collapsed by a galaxy about 9 billion years ago; From mergers about 10 billion years ago, helmy currents; The Sequoia Galaxy, merged with the Milky Way about 9 billion years ago; And the Sagittarius dwarf galaxy, which has been repeatedly pushed by galaxies for billions of years.
The fifth event was found by a group of recently discovered “low energy” globular clusters. According to software analysis, all of this closely matches the fact that the Kraken Galaxy has been dubbed into a team of previously unknown – and most importantly – collisions.
“The collision with Kraken could be the galaxy’s most significant merger ever,” Cruisessen said.
“Previously, it was thought that the collision with the Gaia-Enceladus-Sausage galaxy, which formed about 9 billion years ago, was the largest collision ever. As a result, the collision with Kraken, which looked like a galaxy at the time, must have changed. “
Using this information, the team put together a ‘family tree’, describing the history of the galaxy’s most advanced collisions – five million collisions with more than 100 million stars that occurred 6 to 11 billion years ago. ; And about 15 small merger events with more than 10 million stars.
This tree should form the basis of ongoing and future efforts to understand the epic events that changed the history of our galaxy.
“More than five prehistoric galaxies have been identified,” Cruisessen said. “With current and future telescopes, it should be possible to find them all.”
Research has been published in Monthly instructions of the Royal Astronomical Society.
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