Astronomers find ‘fossil galaxy’ buried deep in the Milky Way

We know a lot about long-extinct creatures like dinosaurs thanks to their fossilized bones that act as time capsules, revealing not only their size and shape, but also clues to their diet, behavior, or even patterns of life. ‘coupling. Likewise, astronomers can learn more about the galactic history of the Milky Way billions of years ago by studying stellar relics.

In a new study, researchers describe a newly discovered “fossil galaxy”, which until now has been hidden deep within our Milky Way.

Large galaxies such as the Milky Way, which contains over 100 billion stars, take a long time to accumulate matter and reach their gargantuan size. In addition to developing their own stars in galactic nurseries, large galaxies also merge with smaller galaxies over time, increasing their mass.

In its 12 billion year history, the Milky Way has undergone a dozen such fusions, devouring a neighbor’s stars and mixing them into an ever-growing stew of requisitioned suns. With each galactic merger, the shape, size and motion of our galaxy have changed, forming its now iconic spiral.

But it’s possible to unwind that spiral and into the reverse-engineering process of previous Milky Way mergers.

Just a week after Dr Diederik Kruijssen of the Center for Astronomy at the University of Heidelberg (ZAH) reported newly identified globular clusters that match the properties of a previously unknown collision with what the team dubbed the ‘Kraken’ galaxy, a new study now reports another hidden galaxy.

Using data from the Galactic Evolution Experiment (APOGEE) from Sloan Digital Sky Surveys’ Apache Point Observatory, astronomers have found the remains of an ancient collision between the Milky Way and a primitive galaxy. The event, which took place 10 billion years ago when our galaxy was still in its infancy, is responsible for about a third of the Milky Way’s spherical halo.

“To find a fossil galaxy like this, we had to look at the detailed chemical makeup and motions of tens of thousands of stars,” said Ricardo Schiavon from John Moores University in Liverpool (LJMU) in the UK. in a press release. “This is particularly difficult to do for the stars in the center of the Milky Way, because they are hidden from view by clouds of interstellar dust. APOGEE allows us to pierce this dust and see more deeply than ever the heart of the Milky Way.

Astronomers nicknamed the galactic fossil Heracles, after the ancient Greek hero also called Hercules, who was bestowed with the gift of immortality during the creation of the Milky Way – at least according to myth.

In order to distinguish Heracles’ stars from all of the billions of Milky Way objects, astronomers had to measure the chemical composition and velocities of stars using APOGEE. A few hundred of these stars had radically different chemical makeup and speeds from all the others. The only reasonable explanation is that these objects belonged to a galaxy other than the Milky Way.

“These stars are so different that they could only have come from another galaxy. By studying them in detail, we could trace the precise location and history of this fossil galaxy, ”Danny Horta of LJMU, lead author of the new study published in the Monthly notices from the Royal Astronomical Society, said in a statement.

This is just the tip of the iceberg. In the future, the fifth phase of the Sloan Digital Sky Survey and its “Milky Way Mapper” will measure spectra for ten times as many stars across the galaxy. Who knows what cosmic fossils astronomers will be able to discover then.

“As a cosmic home, the Milky Way is already special to us, but this ancient galaxy buried within makes it even more special,” says Schiavon.

And as you must be wondering, the next merger is expected in 2.5 billion years with the neighboring Andromeda galaxy.