It may sound like a fantastic ice cream flavor, but a quadruple galactic crunch is really a rare cosmic event recently spotted by astronomers: Four galaxies made of old stars in the process of merging into one mega-galaxy.

Galactic Crunch
NASA/JPL-Caltech/T. Pyle (SSC)

Unlike many galactic collisions, however, this merger seems to be triggering no new stars to form — which is a little weird.

"When we look in detail…the colors are exactly what you’d expect from old stars," said Kenneth Rines of the Harvard-Smithsonian Center for Astrophysics.

That observation suggests the galaxies are not dust-rich spiral galaxies like our own, but sphere-like "elliptical" galaxies with little dust but lots of aged stars. Rines and his colleagues will be publishing their discoveries about the CL0958+4702 cluster in a coming issue of Astrophysical Journal Letters.

"Conventional wisdom is that whenever we have galaxies merging, you have new stars," said Rines. That’s because galactic mergers usually cause the dust of galaxies to collide and condense into new stars. At the same time, stars in merging galaxies generally just fly harmlessly past each other.

The four-way collision was detected in infrared light by the Spitzer Space Telescope.

The galaxies appear as four bright orbs surrounded by a warm halo of old stars, five billion light-years away. The halo was probably created when the stars were flung into intergalactic space by the wild gyrations of the galaxies as they spiral into each other.

Eventually, they will create a single galaxy ten times the mass of the Milky Way.

"We know how far apart they are and how fast they are moving," said Rines.

From that, the researchers calculate the merger will probably take 100 million years. The final galaxy will look like a fuzzy ball of old stars: sort of a great big cosmic dust bunny.

Another sign that no dust is involved in the collision is that there are no signs of super-massive black holes in the centers of any of the four galaxies in the process of eating dust.

When a black hole is devouring matter, the matter gives off lots of ultraviolet light and X-rays — none of which is seen in this case. The only X-rays coming from the CL0958+4702 collision are from the sparse dust and gas there being sped up to a degree that translates into very high temperatures — one to ten million degrees.

"It’s a similar temperature to the center of the sun," said Rines. At those temperatures, gases glow in X-rays.

The lack of bright new stars or feeding black holes is exactly what makes these collisions hard to find, explained astronomer Pieter van Dokkum of Yale University.

"It’s hard to recognize these mergers and hard to find them," said van Dokkum. "The special thing about this one is that it’s big and it’s four galaxies."

Via: Discovery Channel