When it comes to massive events, Galaxies colliding is pretty high up on the list. Imagine billions of stars from two galaxies intermingling as two systems merge.
This is exactly what the Herschel space observatory has taken images of in this relatively rare event. The two galaxies together are called HXMM01 and are located about 11 billion light-years away from Earth. The merging galaxies are creating some 2,000 stars per year which is a lot when compared to our Milky Way galaxy which only creates about two to three stars per year.
This discovery is important as it gives us a rare glimpse into the early years of the universe and actually helps give us a clearer picture of how the largest galaxies in the universe are created. The most popular theory is that these massive systems are created by a larger galaxy picking up smaller ones, but this discovery shows us that they may actually be created by two massive galaxies colliding instead.
You can read the full article in detail on this subject from JPL/NASA.