The Milky Means is a spiral galaxy. Extra particularly, this can be a barred spiral galaxy, which means that inside its central area, there’s a bar form off of which the spirals emanate. About two-thirds of spiral galaxies are barred spirals, and astronomers have concept this distinction is only a variance in how density waves cluster stars in a galaxy. However a brand new find out about means that the bar of the Milky Means can have been brought about by way of an historical collision with any other galaxy.
Even if it’s our house, the Milky Means is in many ways the least understood galaxy. It’s tricky for us to map its construction intimately. Thankfully, massive sky surveys reminiscent of the only by way of the Gaia spacecraft are in any case giving us an in depth view. Probably the most issues Gaia has proven is that a number of galaxies have collided with the Milky Means up to now.
Probably the most greatest collisions is referred to as the Gaia Sausage. It’s the stays of a dwarf galaxy that struck the Milky Means about 8 – 11 billion years in the past. On account of this collision, our galaxy won about 50 billion sun lots, and a minimum of 8 globular clusters. Gaia observations display the remnants of this collision within the speed distribution of stars in our galaxy.
Pc simulation of a collision generating a barred spiral. Credit score: Merrow, et al
Curiously, 8 – 11 billion years in the past was once round the similar time that the Milky Means evolved its barred spiral construction. So the staff sought after to determine if there was once a connection. The usage of laptop simulations, they checked out how galactic collisions may lead to a barred galaxy. Previous research have proven that galactic collisions can regularly create a barred construction, so merely appearing a collision may have shaped by way of a collision isn’t a robust argument that it did. So the staff targeted at the explicit timing of the way the bar shaped. In keeping with their simulations, the staff discovered that with out the Gaia Sausage collision, there generally is a 2 billion-year prolong within the formation of a bar. The prerequisites of the early Milky Means would in many ways act to prolong bar formation. With the Gaia Sausage collision, a bar shaped a lot previous within the simulations. So whilst the find out about doesn’t end up the Milky Means’s bar was once without delay brought about by way of the Gaia Sausage collision, it does display that proof for an outdated bar construction strongly means that its formation was once brought about by way of the collision.
As extra sky surveys come on-line, and we proceed to make an in depth map of our galaxy, we can higher perceive the dynamics of our galactic construction. For now, alternatively, it sort of feels that barring a collision the Milky Means can have remained a easy spiral galaxy for billions of years.
Reference: Merrow, Alex, et al. “Did the Gaia Enceladus/Sausage merger shape the Milky Means’s bar?” arXiv preprint arXiv:2312.02318 (2023).
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