The Milky Way is a galaxy eater

The Milky Way, The galaxy in which we live seems today to be a quiet place, but we must not be fooled. That apparent calm actually hides a turbulent past.

Using data from the European Space Telescope Gaia, Indeed, an international team of astronomers has been able to identify, so far, the remains of half a dozen galaxies, all of them devoured by ours throughout its 13 billion year history. Five of the ‘victims’ were already known, but there was no news of the new one until now.

Like leftovers from an opulent banquet, remnants of the Milky Way’s past feasts are scattered everywhere in the galactic halo, an enormous spherical volume at the center of which is the galaxy’s characteristic spiral disk. .

Under the direction of Khyati Malhan, from the Max Planck Institute for Astronomy in Germany, researchers have produced a map showing the ‘crumbs’ from those ancient banquets. “The dynamical atlas of Milky Way mergers presented here – the researchers write in their paper – provides a global view of galaxy formation in action”. The work has been published in ‘The Astrophysical Journal‘.

Milky Way

When a smaller galaxy gets too close to a larger one, in this case the Milky Way, its gravity pulls the visitor in and “stretches” it into an elongated chain of stars, a ‘stellar stream’ which ends up falling into the larger galaxy, leaving debris orbiting in its halo.

The “food” leaves behind other crumbs, including smaller satellite galaxies that might have orbited the victim, or globular clusters, compact spheres made of thousands of stars tightly bound by their mutual gravity. Astronomers identified a number of stellar streams from past mergers years ago, and also used globular clusters to construct a timeline of the Milky Way’s past ‘feasts’. Although doing so is not a quick or easy task, and often requires real detective work.

In the new study, researchers took the latest data from the Gaia satellite, which accurately records the locations of a billion stars and their paths, and then analyzed the motion of 170 globular clusters (marked with star symbols in the image). , 41 stellar streams, and 46 satellite galaxies (shown as cubes). Malhan and his team were able to link 62 of those objects to one of five known merger events (shown in different colors), and identified a new, previously unknown sixth.

The new ‘victim’ of the voracity of our galaxy has been baptized as Pontus (in magenta in the image), and thus joins the previous fusions with Gaia-Enceladus, Cetus, LMS-1/Wukong(discovered in 2020), Sequoiawhich merged with the Milky Way about 9 billion years ago, and the dwarf galaxy of Sagittariuswhich has repeatedly passed through the Milky Way over the past few billion years.

kraken galaxy

Interestingly, the system missed two other known merger events, including the one that took place 11 billion years ago with the kraken galaxy and that is considered the most significant of all those that are known. The researchers believe that data could be hidden in some of the 195 objects that remain to be analyzed.

As for the newly discovered Pontus, the truth is that not much is known about it yet, although the stars that were part of it move very slowly and in the opposite direction to that of the rotation of the Milky Way. The researchers have also found evidence of other ‘hidden’ mergers, although it is too early to draw any conclusions.

The next step, explained in the article, will be to try to reconstruct a timeline of all the collisions and mergers suffered by our galaxy. The largest of which, by the way, is yet to come. It will be against our huge neighbor Andromeda and it will occur in 4.5 billion years. In that meeting, however, there will be no winners or losers and neither of the two galaxies will swallow the other. On the contrary, both will merge into a single, huge, new galaxy, which astronomers already know as Lactomeda.

Font: Jose Manuel Nieves / ABC

Reference article: https://www.abc.es/ciencia/abci-lactea-devorado-menos-otras-6-galaxias-y-dejado-esparcidos-restos-todas-partes-202202230239_noticia.html#ancla_comentarios