[ad_1]
Paris (AFP) – The characteristic halo of the Milky Way is made up of stellar rubble resulting from a cosmic collision that occurred 10 billion years ago with another galaxy representing a quarter of its size, announced Wednesday. scientists stunned by their own discovery.
The idle crash of Gaia-Enceladus – named after the giant of Greek mythology, born of Earth and Sky – not only provided the raw material of the halo, the equivalent of 600 million Suns, it has also filled the distinctive disc of our galaxy, they reported in the journal Nature.
"We have basically unveiled the formation of the Milky Way," said AFP Amina Helmi, astronomer at the Kapteyn Institute of Astronomy at the University of Groningen.
"The merger led to what we now call the halo of our galaxy and, because it was so massive, to the swelling of the disc that was already present at the time."
"We did not expect most of the halo stars to have a common origin," she added.
Large galaxies do this by absorbing smaller ones.
But astronomers have long quarreled to know if the Milky Way is a diet grouping small bunches of stars, or merging with a single Big One.
Until this year, the theories of both sides were mainly based on thin reeds of speculative inference.
But all that changed with a massive data dump in April from the Gaia satellite mission.
In orbit by the European Space Agency in 2013, Gaia produced an unprecedented 3D mapping of 1.7 billion stars, of which more than one billion – one percent of the total – from the Milky Way.
Measurements repeated by the satellite make it possible to calculate precise distances and the speeds with which each star travels the universe.
– Crashing galaxies on rewind –
Looking for traces of galactic fusions with the Milky Way halo, the researchers were surprised to find that most of his stars belonged to the same immediate family.
"The chemical signature was clearly different from the" native "stars of the Milky Way," Helmi said.
"And they form a fairly homogeneous group, which indicates that they share a common origin."
By adding measurements across the entire spectrum of light, researchers have been able to reconstruct the precise movements of invading stars over time in three dimensions.
"Reading these videos back allows astronomers to study how our galaxy has been assembled and how it has evolved," said Kim Venn, astronomer at the University of Victoria in Canada.
Helmi and his colleagues calculated that the merger had occurred 10 billion years ago, about 3.8 billion years after the Big Bang, which had given birth to the Universe.
The team named the galaxy fused with the Enceladus Milky Way – offspring of Gaia, goddess of the Earth, and Uranus, god of the sky – because the giant would have caused earthquakes after being buried under Mount Etna, many how the rogue galaxy has disrupted and reshaped the Milky Way.
The Gaia satellite collects data on 100,000 stars per minute and performs about 500 million measurements per day. His first map was released in September 2016, based on an observation year of about 1.15 billion stars.
Some stars were measured more than 70 times as the satellite – circling the Sun orbiting the Earth – scanned the galaxy continuously.
Source link
