Milky Way collided with another galaxy

Mindy Sparks
Ноября 2, 2018

Ten billion years ago, however, when the merger with Gaia-Enceladus took place, the Milky Way itself was much smaller, so the ratio between the two was more like four to one.

"There may be other objects also contributing stars to the halo, but none is as large as this one".

The Milky Way's halo is not like the ones of other spiral galaxies. Unlike other galaxies that we can view from a distance, we sit inside the Milky Way - around 26,000 light years from its centre. Initially, the two galaxies are clearly separated, but gravity pulls them together and they merge.

Before this discovery, the team had run simulations of galactic mergers.

Recent observations from the Gaia satellite mission revealed numerous stars in the Milky Way's halo are "invaders" - or remnants of another, younger galaxy.

"It has eaten many dwarf galaxies in the past, and we've just found a major one that it ate in the past". The University of Groningen's Professor of Astronomy, Amina Helmi, has spent most of her career looking for "fossils" in our Milky Way which might offer some hints as to its evolution.

The globular cluster Omega Centauri - with as many as ten million stars - is seen in this image captured from the European Southern Observatory's La Silla Observatory.

"We became only certain about our interpretation after complementing the Gaia data with additional information about the chemical composition of stars, supplied by the ground-based APOGEE survey", says Carine Babusiaux, Université Grenoble Alpes, France, and second author of the paper. Stars from different galaxies have their own kind of fingerprint.

The researchers found that the chemical signatures of many halo stars in the Milky Way were not the same as its "native" stars.

"Playing these videos backwards allows astronomers to study how our galaxy was assembled, and how it has evolved", noted Kim Venn, an astronomer at the University of Victoria in Canada, commenting on the study.

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We are so deeply embedded in this collection that its stars surround us nearly completely, and so can be seen across most of the sky.

Helmi: That it will lead to "fireworks" in the sky.

Put into orbit by the European Space Agency in 2013, Gaia has produced an unprecedented 3-D mapping of 1.7 billion stars, including more than a billion - one percent of the total - in the Milky Way.

According to the team's simulations, as well as supplying the halo stars, the accreted galaxy could also have disturbed the Milky Way's pre-existing stars to help form the thick disc.

The team named the galaxy that melded with the Milky Way Enceladus - progeny of Gaia, goddess of Earth, and Uranus, god of the sky - because the giant was said to have caused earthquakes after being buried under Mount Etna, much in the way the rogue galaxy unsettled and resculpted the Milky Way.

Scientists have shed light on how the Milky Way came to be so milky: it crashed into another galaxy ten billion years ago and stole its stars.

This Hubble image of the Antennae galaxies is the sharpest yet of their merger.

The sheer number of odd-moving stars involved intrigued Amina and her colleagues, who suspected they might have something to do with the Milky Way's formation history and set to work to understand their origins. "By studying these stars that were present in these galaxies, you get a way of understanding the properties of galaxies". They published their results Wednesday in Nature.

"What I really like is that Gaia data was combined with the ..." A new study makes a compelling case that a central structure in the Milky Way is actually composed mostly of stars born in another galaxy, brought to us by a long-ago galactic smash-up.

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