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Ancient collision may have shaped the Milky Way’s barred spiral structure

The Milky Way, our cosmic abode, is a barred spiral , characterized by a central bar structure from which spirals extend. Traditionally, astronomers attributed this feature to variations in how density waves organize stars within a galaxy. However, a recent study proposes an intriguing twist, suggesting that the Milky Way's bar may have originated from an collision with another galaxy.

Despite being our home, the Milky Way remains a galaxy with aspects that elude comprehensive understanding. Mapping its intricate structure has been a challenge, but advancements from sky surveys, such as those by the Gaia spacecraft, are providing unprecedented insights. Gaia's observations reveal evidence of past collisions between the Milky Way and several other galaxies.

One notable collision, known as the Gaia Sausage, involved a dwarf galaxy colliding with the Milky Way approximately 8 to 11 billion years ago. This cosmic encounter resulted in our galaxy gaining about 50 billion solar masses and at least eight globular clusters. Gaia's observations illuminate the lingering effects of this collision in the velocity distribution of stars within our galaxy.

Remarkably, the timeframe of 8 to 11 billion years ago coincides with when the Milky Way developed its barred spiral structure. Intrigued by this temporal alignment, researchers set out to investigate a potential connection. Utilizing computer simulations, they explored how galactic collisions might lead to the formation of a barred galaxy.

While previous studies indicated that galactic collisions could give rise to a barred structure, the key focus of this research was on the specific timing of the bar's formation. Through simulations, the team found that without the Gaia Sausage collision, there could have been a 2-billion-year delay in the formation of the bar. The findings, published on the arXiv preprint server, highlight the influence of the Gaia Sausage collision on expediting the bar's formation in the early Milky Way.

Although the study doesn't definitively establish that the Milky Way's bar was directly caused by the Gaia Sausage collision, it strongly suggests that the collision played a pivotal role in triggering the bar's formation.

As ongoing sky surveys and detailed mapping of our galaxy continue, our understanding of its dynamics will deepen. For now, the intriguing proposition emerges that, in the absence of a collision, the Milky Way might have remained a simple spiral galaxy for billions of years.

Source: Universe Today

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