SPACE
Hubble Images Show Massive Galactic Smashups

Astronomers believe galaxies have been running into each other for billions of years. There's even evidence our own Milky Way galaxy has swallowed a smaller companion, with more to come, both big and small.

These titanic "interactions" often trigger pyrotechnic eruptions of star formation, and sometimes they eject streams of stars into the loneliness of intergalactic space. Yet astronomers say creatures living in those galaxies would hardly notice a thing.

New Images

In celebration of the 18th anniversary of the Hubble Space Telescope's launch into orbit, the Space Telescope Science Institute in Baltimore on Thursday released a collection of 59 new images of galactic collisions.

Together with related computer simulations and animations, the collection is the largest group of Hubble images ever released to the public. Why now?

"Galaxy interactions are still a very active field of research," said Massimo Stiavelli, an astronomer at the institute. "The formation of galaxies and their evolution will also be a focus of Hubble's successor, the James Webb Space Telescope."

Besides, he added, the images are often quite dramatic and beautiful, with clouds of stars being tossed about like dust in a whirlpool, or pulled apart like taffy.

Scientists studying the evolution of the universe love this stuff. "Interactions between galaxies were probably very common early in the universe, because we think galaxies actually formed that way -- through collisions or mergers of smaller chunks to make bigger objects," Stiavelli said. "The pictures illustrate the variety of ways this can happen."

No Stellar Train Wrecks

Mergers of two similar spiral galaxies, for example, tend to disrupt the spiral movements of stars in the two original galaxies, creating new elliptical galaxies, which space telescope institute astronomer Brad Whitmore calls "a trash pile of stars in a heap."

Curiously, because stars are so small relative to the vast gulfs between them, there are no stellar train wrecks. "While the galaxies can collide, the individual stars never do," Stiavelli said. The galaxies pass right through each other.

However, if there's gas within the galaxies, the merger will bring two gas "shock fronts" into collision. That compresses the gas, making it denser and triggering star formations that can light up the galaxies like fireworks.

These "interactions" tend to occur over tens of millions to hundreds of millions of years, Whitmore said. So anyone living on a planet circling a star within one of those galaxies would see nothing remarkable in a lifetime.

Life Would Go On

"If there is another galaxy very close, you wouldn't see it move because the time scales are very long," Stiavelli said. But if our star were ejected from the galaxy, our descendants would eventually see the parent galaxies in one part of the sky, while the rest appeared much darker and emptier.

Life would go on much as usual amid colliding galaxies, he added, unless bursts of star formation also triggered gamma ray bursts -- extremely powerful blasts of radiation that some studies suggest are associated with massive young stars.

"If that happens too close -- and being in the same galaxy may be too close -- then that could harm life on the planet," he said.

Get Captain Kirk on the line.

To explore the new Hubble gallery of galactic collisions, visit: baltimoresun.com/sciencematters.