Colliding or interacting galaxies are commonplace, but the duo making up Arp 143 – NGC 2444 at left and NGC 2445 at right – are especially intriguing because of the post-collision fireworks. The galaxies presumably passed through one another in a head-on collision in the distant past, triggering a blaze of starbirth in rich gas clouds associated with NGC 2445. As seen in this image captured by the Hubble Space Telescope, the resulting triangular shape of the vast stellar nursery is caused by the less flashy NGC 2444 at left, pulling young stars and dust away in an ongoing gravitational tug of war, forming a bridge of sorts between the galaxies.
Julianne Dalcanton of the Flatiron Institute’s Center for Computational Astrophysics in New York and the University of Washington in Seattle says the triangular shape may be influenced by “an invisible, hot halo of gas that could help to pull NGC 2445’s gas away from its nucleus. So, they’re not completely free of each other yet and their unusual interaction is distorting the ring into this triangle.”
