The beauty and wonders of our planet’s night sky cloaks a violent, ever-changing universe of life, death, and mayhem –“with firestorms of star birth, dying stars rattling the very fabric of space in titanic explosions,” observes Hubble scientists. “Death-star-like beams of energy blasting out of overfed black holes at nearly the speed of light”, they say, “Hubble has seen them all.” A universe of which the Milky Way is one of 150 billion galaxies. A strange universe, hinted Stephen Hawking. “of shadow galaxies, shadow stars, and even shadow people.”
The Bright Cores of a Galaxy
Each “eye” in this piercing image, said Julianne Dalcanton , a University of Washington professor of astronomy and chair of the Department of Astronomy, led the team that captured the image, “is the bright core of a galaxy, one of which slammed into another. The outline of the face is a ring of young blue stars. Other clumps of new stars form a nose and mouth.”
Hubble observed this unique system as part of a “snapshot” program that takes advantage of occasional gaps in the telescope’s observing schedule to squeeze in additional pictures. The entire system is catalogued as Arp-Madore 2026-424, or AM 2026-424, from the Arp-Madore “Catalogue of Southern Peculiar Galaxies and Associations.”
Halton Arp, an artist’s son with a swashbuckling air, published his compendium of 338 unusual-looking interacting galaxies–“The Atlas of Peculiar Galaxies”– in 1966. Arp’s dogged insistence that astronomers had misread the distances to quasars cast doubt on the Big Bang theory of the universe, eventually led to his exile from his peers and the telescopes he loved. He later partnered with astronomer Barry Madore to extend the search for unique galactic encounters in the southern sky, listing several thousand galaxies in the survey, published in 1987.
Arp’s “Unknown Physics”
Arp, reported Dennis Overbye for The New York Times, “found that galaxies with radically different redshifts, and thus at vastly different distances from us, often appeared connected by filaments and bridges of gas. This suggested, he said, that redshift was not always an indication of distance but could be caused by other, unknown physics.”
Head-On Collision Created this Arp-Madore System
Although galaxy collisions are common — especially back in the young universe — most are not head-on smashups, like the collision that likely created this Arp-Madore system. The violent encounter gives the system an arresting “ring” structure for only a short amount of time, about 100 million years. The crash pulled and stretched the galaxies’ disks of gas, dust and stars outward. This action formed the ring of intense star formation that shapes the nose and face.
“A Roll of the Dice”–Rare Ring Galaxies
Ring galaxies are rare; only a few hundred of them reside in our larger cosmic neighborhood. The galaxies have to collide at just the right orientation to create the ring. The galaxies will merge completely in about 1 billion to 2 billion years, hiding their messy past.
The side-by-side juxtaposition of the two central bulges of stars from both galaxies also is unusual. Because the bulges that make the eyes appear to be the same size, it is evidence that two galaxies of nearly equal proportions were involved in the crash, rather than more common collisions where small galaxies are gobbled up by their larger neighbors.
Dalcanton and her collaborators plan to use this innovative Hubble program to take a close look at many other unusual interacting galaxies. The goal is to compile a robust sample of nearby interacting galaxies, which could offer insight into how galaxies grew over time through galactic mergers. By analyzing these detailed Hubble observations, astronomers could then choose which systems are prime targets for follow-up with NASA’s James Webb Space Telescope, scheduled to launch in 2021.