NGC 4038 (left) and NGC 4039 (right). Image source: [1]
Although it seems to be just a galaxy, in fact we are in the presence of a pair of them, known as the Galaxies of the Antennaes, which are in collision. According to theory, these majestic joints occur when two spiral galaxies attracted by their gravity, can be placed in an orbit close to each other and collide.
NGC 4038 is a spiral galaxy, and NGC 4039, a barred spiral galaxy. Now they form one of the most famous pair of galaxies, called Antennae. The tidal forces of the collision made a similar shape to the antennae of an insect, hence the name.
The two original nuclei are seen as yellow spots, but all other characteristic features have vanished. Located 63 million light-years away in the constellation Corvus, the interaction between the two led to the creation of more than a thousand bright young star clusters that are seen in white and blue over the abundant clouds of gas and dust.
At the end of its fusion, in about 400 million years, will form a supergalaxia. They were discovered by William Herschel in 1785.
More details here: Antennae Galaxies
ESO's VLT observe the Antennae Galaxies. Image source: [2]
Antennae Galaxies composite of ALMA and Hubble observations. Image source: [3]