Spitzer Spies Monster Galaxy Pileup

Four galaxies are slamming into each other and kicking up billions of stars in one of the largest cosmic smash-ups ever observed.

The clashing galaxies, spotted by NASA's Spitzer Space Telescope, will eventually merge into a single, behemoth galaxy up to 10 times as massive as our own Milky Way. This rare sighting provides an unprecedented look at how the most massive galaxies in the universe form.

"Most of the galaxy mergers we already knew about are like compact cars crashing together," said Kenneth Rines of the Harvard-Smithsonian Center for Astrophysics, Cambridge, Mass. "What we have here is like four sand trucks smashing together, flinging sand everywhere." Rines is lead author of a new paper accepted for publication in Astrophysical Journal Letters.

Collisions, or mergers, between galaxies are common in the universe. Gravity causes some galaxies that are close together to tangle and ultimately unite over a period of millions of years. Though stars in merging galaxies are tossed around like sand, they have a lot of space between them and survive the ride. Our Milky Way galaxy will team up with the Andromeda galaxy in five billion years.

Mergers between one big galaxy and several small ones, called minor mergers, are well documented. For example, one of the most elaborate known minor mergers is taking place in the Spiderweb galaxy – a massive galaxy that is catching dozens of small ones in its "web" of gravity. Astronomers have also witnessed "major" mergers among pairs of galaxies that are similar in size. But no major mergers between multiple hefty galaxies – the big rigs of the galaxy world – have been seen until now.

The new quadruple merger was discovered serendipitously during a Spitzer survey of a distant cluster of galaxies, called CL0958+4702, located nearly five billion light-years away. The infrared telescope first spotted an unusually large fan-shaped plume of light coming out of a gathering of four blob-shaped, or elliptical, galaxies. Three of the galaxies are about the size of the Milky Way, while the fourth is three times as big.

Further analysis of the plume revealed it is made up of billions of older stars flung out and abandoned in an ongoing clash. About half of the stars in the plume will later fall back into the galaxies. "When this merger is complete, this will be one of the biggest galaxies in the universe," said Rines.

The Spitzer observations also show that the new merger lacks gas. Theorists predict that massive galaxies grow in a variety of ways, including gas-rich and gas-poor mergers. In gas-rich mergers, the galaxies are soaked with gas that ignites to form new stars. Gas-poor mergers lack gas, so no new stars are formed. Spitzer found only old stars in the quadruple encounter.

"The Spitzer data show that these major mergers are gas-poor, unlike most mergers we know about," said Rines. "The data also represent the best evidence that the biggest galaxies in the universe formed fairly recently through major mergers."

Some of the stars tossed out in the monstrous merger will live in isolated areas outside the borders of any galaxies. Such abandoned stars could theoretically have planets. If so, the planets' night skies would be quite different from our own, with fewer stars and more visible galaxies.

In addition to Spitzer, Rines and his team used a telescope formerly known as the Multiple Mirror Telescope and now called MMT near Tucson, Ariz., to confirm that the four galaxies are intertwined, and NASA's Chandra X-ray Observatory to weigh the mass of the giant cluster of galaxies in which the merger was discovered. Both Spitzer and a telescope known as WIYN at Kitt Peak, also near Tucson, Ariz., were used to study the plume. WIYN is named after the University of Wisconsin, Indiana University, Yale University and the National Optical Astronomy Observatory, which own and operate the telescope.

Other authors of this paper include Rose Finn of Siena College, Loudonville, N.Y.; and Alexey Vikhlinin of the Harvard-Smithsonian Center for Astrophysics.

Source: NASA, Jet Propulsion Laboratory

Related stories:

Cosmic Lens Reveals Distant Galactic Violence
(PhysOrg.com) -- By cleverly unraveling the workings of a natural cosmic lens, astronomers have gained a rare glimpse of the violent assembly of a young galaxy in the early Universe. Their new picture suggests that the galaxy has collided with another, feeding a supermassive black hole and triggering a tremendous burst of star formation.
Caltech astronomers describe the bar scene at the beginning of the universe
Bars abound in spiral galaxies today, but this was not always the case. A group of 16 astronomers, led by Kartik Sheth of NASA's Spitzer Science Center at the California Institute of Technology, has found that bars tripled in number over the past seven billion years, indicating that spiral galaxies evolve in shape.
Hubble Space Telescope Spies Galaxy/Black Hole Evolution in Action
A set of 29 Hubble Space Telescope (HST) images of an exotic type of active galaxy known as a "post-starburst quasar" show that interactions and mergers drive both galaxy evolution and the growth of super-massive black holes at their centers.
The Antennae Galaxies move closer
The Antennae Galaxies are among the closest known merging galaxies. The two galaxies, also known as NGC 4038 and NGC 4039, began interacting a few hundred million years ago, creating one of the most impressive sights in the night sky. They are considered by scientists as the archetypal merging galaxy system and are used as a standard against which to validate theories about galaxy evolution.
Galaxies Gone Wild
Interacting galaxies are found throughout the Universe, sometimes as dramatic collisions that trigger bursts of star formation, on other occasions as stealthy mergers that result in new galaxies. A series of 59 new images of colliding galaxies has been released from the several terabytes of archived raw images from the NASA/ESA Hubble Space Telescope to mark the 18th anniversary of the telescope’s launch. This is the largest collection of Hubble images ever released to the public simultaneously.
Milky Way seen to be a galactic cannibal
A stream of debris across the sky is the result of intergalactic cannibalism, researchers from The Australian National University conclude, and it is the not the first time our galaxy has had one of its neighbours for breakfast.
Galaxy may hold hundreds of rogue black holes
If the latest simulation of what happens when black holes merge is correct, there could be hundreds of rogue black holes, each weighing several thousand times the mass of the sun, roaming around the Milky Way galaxy.
Anatomy of a cosmic bird
Using ESO's Very Large Telescope, an international team of astronomers has discovered a stunning rare case of a triple merger of galaxies. This system, which astronomers have dubbed 'The Bird' - albeit it also bears resemblance with a cosmic Tinker Bell - is composed of two massive spiral galaxies and a third irregular galaxy.

News discussion:

one example!? in Space & Earth science news