‘Household Tree’ of The Milky Method Reveals The Destiny of The Mysterious Kraken Galaxy

The Milky Method has collided and merged with a number of different galaxies over its lengthy lifespan, however piecing collectively its historical past has been a painstaking job.

A brand new evaluation of dense star clusters orbiting the Milky Method has now given us essentially the most full galactic merger historical past but. And in these knowledge is a beforehand unknown merger occasion that occurred 11 billion years in the past, and fully altered our galaxy’s form. Astronomers have named that galaxy – subsumed by the Milky Method – the Kraken.

The clusters of stars in query are referred to as globular clusters, typically thought of “fossils” of the early Universe. They’re very dense, spherical clusters of roughly 100,000 to 1 million very previous stars, some practically as previous because the Universe itself. In any globular cluster, all its stars shaped on the similar time, from the identical cloud of gasoline, which suggests we will use their chemical composition to work out their origins.

However that is just one a part of the puzzle. The Milky Method has round 150 globular clusters, and understanding and reconstructing their orbital movement, and their present form (some are torn aside into lengthy, stellar streams), can even assist piece collectively the place they got here from.

And that is what a group of astronomers has now finished, utilizing a synthetic neural community to simulate globular clusters orbiting Milky Method-like galaxies. These simulations, referred to as E-MOSAICS, mannequin the entire lifespan of globular clusters, from formation by way of evolution to destruction.

“The primary problem of connecting the properties of globular clusters to the merger historical past of their host galaxy has at all times been that galaxy meeting is an especially messy course of, throughout which the orbits of the globular clusters are fully reshuffled,” mentioned astronomer Diederik Kruijssen of the College of Heidelberg, Germany. 

“We examined the algorithm tens of 1000’s of instances on the simulations and have been amazed at how precisely it was capable of reconstruct the merger histories of the simulated galaxies, utilizing solely their globular cluster populations.”

The following step was to feed the software program actual knowledge. Lately, the Gaia satellite tv for pc has been working diligently to map the Milky Method galaxy with excessive precision and element not simply in area, but additionally time. This has given us essentially the most correct knowledge but on the positions and motions of galactic objects, ensuing in some fascinating discoveries about our dwelling galaxy.

Utilizing the Gaia knowledge, the group grouped collectively globular clusters primarily based on their orbital movement. That is as a result of the clusters which have comparable orbits across the Milky Method are thought to have come from the identical place; that’s, a galaxy that was subsumed by the Milky Method in some unspecified time in the future in its previous.

(Kruijssen et al., MNRAS, 2020)

When these knowledge have been processed by the group’s software program, the outcomes carefully agreed with 5 galactic collisions.

4 of them have been recognized – the Gaia-Enceladus galaxy, often known as the Gaia Sausage, devoured up by the Milky Method round 9 billion years in the past; the Helmi streams, from a merger round 10 billion years in the past; the Sequoia galaxy, merging with the Milky Method round 9 billion years in the past; and the Sagittarius dwarf galaxy, which has repeatedly punched by way of the Milky Method for billions of years.

The fifth occasion was pieced collectively from a not too long ago found group of “low vitality” globular clusters. In line with the software program’s evaluation, these all carefully match the properties of a beforehand unknown – and extremely necessary – collision with what the group has dubbed the Kraken galaxy.

“The collision with Kraken should have been essentially the most important merger the Milky Method ever skilled,” Kruijssen mentioned.

“Earlier than, it was thought that a collision with the Gaia-Enceladus-Sausage galaxy, which occurred some 9 billion years in the past, was the most important collision occasion. Nevertheless, the merger with Kraken occurred 11 billion years in the past, when the Milky Method was 4 instances much less large. In consequence, the collision with Kraken should have actually reworked what the Milky Method seemed like on the time.”

Utilizing this info, the group put collectively a ‘household tree’ describing essentially the most up-to-date collision historical past of the Milky Method – the 5 main collisions with galaxies containing over 100 million stars, which occurred between 6 and 11 billion years in the past; and round 15 smaller merger occasions with galaxies containing over 10 million stars.

This tree ought to kind the premise for ongoing and future efforts to grasp the epic occasions that modified our galaxy’s historical past.

“The particles of greater than 5 progenitor galaxies has now been recognized,” Kruijssen mentioned. “With present and upcoming telescopes, it must be attainable to search out all of them.”

The analysis has been revealed within the Month-to-month Notices of the Royal Astronomical Society.