Space Telescope Sees Stars Born in Collision of 2 Galaxies

The Hubble Space Telescope has peered into the heart of a colossal collision between two galaxies for a close-up view of the debris of a head-on wreck: at least 1,000 clusters of newborn stars. The brightest clusters may contain up to a million stars each.

This burst of creation inside the core of the galactic crackup offers stark evidence for astronomers’ growing belief that the universe is a violent place. “The old idea was that galaxies begin as giant clouds,” said Caltech astrophysicist Shri Kulkarni. “Now people see that galaxies bashing into each other is an important part of star and galaxy formation.”

This intimate look at star birth sparked by galaxy collisions should help astronomers answer some of the biggest outstanding mysteries in science--including how stars and galaxies are created.

“What gets stars to form?” asked UCLA astronomer Andrea Ghez. “Do you need a shock to trigger it? One idea is that star formation gets triggered when galaxies interact.”

While the Hubble images do not necessarily break new scientific ground, they do offer a tantalizing “laboratory” to study the process of star formation, Kulkarni said.

“The degree of detail in these images is astounding,” said Brad Whitmore of the Space Telescope Science Institute in Baltimore, one of the researchers responsible for the images.

The pictures also offer tangible evidence that tight clusters of stars can be created from relatively recent cosmic events. The images capture light traveling toward Earth from 63 million light-years away, and therefore 63 million years ago--almost yesterday in cosmic terms. Previously, astronomers thought globular clusters were among the oldest collections of stars in the universe.

Such clusters in the Milky Way date to the beginnings of the galaxy 15 billion years ago, and perhaps formed even before the galaxy, according to Caltech astronomer Chuck Steidel. “Now [evidence suggests that] you can make them in collisions. Maybe ramming big objects together is the best way” to make globular clusters.

When galaxies collide, the gas and stars in them get squeezed together. The gravital pressure inside sparks nuclear fires, and newborn stars light up like strings of fireworks, grouped into clusters.

Earlier Hubble images revealed that the collection of galaxies in the universe is far more diverse than ever imagined. Instead of sedate “island universes,” as galaxies were first described, they are now known to be constantly crashing into each other, merging, evolving. Indeed, nearly a third of the galaxies seen in the early Hubble images appear to be interacting with their neighbors in some way.

Such marriages tend to produce new galaxies with drastically altered shapes. Spiral galaxies like the Milky Way, some astronomers believe, transform into more uniform elliptical galaxies in the wake of collisions.

The newly observed collision in the Antennae Galaxies is old news in Earth years, having occurred 63 million years ago, not long after dinosaurs roamed the planet. However, the same fate may await our own Milky Way when it collides with neighboring Andromeda billions of years in the future. Andromeda is more than 2 million light-years and 12 million trillion miles away. The two galaxies are heading toward each other at 300,000 mph.

The new images should help astronomers understand what will happen when they meet. “The discovery will help us put together a chronological sequence of how colliding galaxies evolve,” Whitmore said.