Planning some Halloween fun? Let the cosmos help. The universe was made for Halloween with its numbing emptiness, subzero dark and curdled nebulae. In celebration of the day, this new image from the Hubble Space Telescope captures two galaxies of equal size in a collision that appears to resemble a ghostly face.
Although galaxy collisions are common — especially in the early universe when the distances between galaxies was much smaller — most are not head-on impacts like the one that likely created this Arp-Madore system 704 million light-years from Earth. Given all the empty space between stars, it’s highly unlikely any stars crashed into each other in the slam, but the violent encounter has created a striking wreath of stars around the duo. The galaxies’ mutual gravities have pulled and stretched their disk of gas, dust and stars outward to form a ring of intense star formation in the shape of a “nose” and “face.”
Ring galaxies are rare, and only a few hundred of them reside in our cosmic neighborhood. The galaxies have to collide at just the right orientation so that they interact to create the ring. In time they will merge together completely into a single much larger galaxy, hiding the evidence of the cataclysmic catastrophe.
The side-by-side pairing of the two central bulges (eyes) of stars in the galaxies is a bit unusual. Astronomers believe that since the bulges appear to be the same size, the crashing galaxies were equally massive. This is different from the more common collisions in which small galaxies are gobbled up by their larger neighbors.
This galaxy system is catalogued as Arp-Madore 2026-424 (AM 2026-424) in the Arp-Madore “Catalogue of Southern Peculiar Galaxies and Associations”. Astronomer Halton Arp published his compendium of 338 unusual-looking interacting galaxies in 1966. He later partnered with astronomer Barry Madore to extend the search for unique galactic encounters in the southern sky. Several thousand galaxies are listed in this 1987 survey. Nearly all feature the how galaxies act on other galaxies during encounters or collisions to warp each other’s shapes. Gas and dust clouds in one galaxy slamming into those of another compress the material and fire up waves of new star formation that light up as rings and arcs of hot, blue newborn suns.
On Halloween night, trick-or-treaters can watch the returning crescent moon shine to the left of Jupiter during prime candy-harvesting hours. While the crescent is shiny bright, the remainder of the moon’s outline will glow spookily with earthshine — light reflected off our own planet to the moon and back. However you see it — scary, beautiful or both — will be up to your imagination.