Four galaxies on collision course as two massive black holes approach

Two pairs of gigantic black holes, each in a different dwarf galaxy, are speeding towards each other, dragging an enormous train of gas and stars in their wake. They are set to collide and merge to form even larger galaxies, and studying them as they approach each other could help astronomers understand how the cosmic monsters lurking across the universe came to grow so large. The findings were published Nov. 8 on the preprint database arXiv, and they have been accepted for publication in The Astrophysical Journal.