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Galaxies in gridlock

NASA / JPL-Caltech / STScI / ESA
This image of a pair of colliding galaxies called NGC 6240 shows them in a
rare, short-lived phase of their evolution just before they merge into a
single, larger galaxy. Click on the image for a larger version.

Nothing draws a crowd like a spectacular crash - whether it's a NASCAR auto race or a galactic collision. Over the past month, Internet users voted for a cosmic smash-up as their favorite target for a future close-up from the Hubble Space Telescope, and this week you can feast your eyes on two fantastic images of galaxies in gridlock.

The first "train wreck" comes from NASA's Spitzer Space Telescope. This is a biggie: Two huge galaxies, each anchored by a central black hole that's millions of times as massive as the sun, are moving toward an imminent pile-up. Exactly how imminent? Millions of years after the scene captured in this image - a time span that's a mere blink of the eye on the cosmic scale.

"One of the most exciting things about the image is that this object is unique," Stephanie Bush of the Harvard-Smithsonian Center for Astrophysics, says in a news release about the observations. "Merging is a quick process, especially when you get to the train wreck that is happening. There just aren't many galactic mergers at this stage in the nearby universe."

Spitzer's image of NGC 6240, which is 400 million light-years away in the constellation Ophiuchus, highlights the bursts of infrared radiation as the dust and gas from the two galaxies slam together. All that pressure creates new generations of hot stars, blazing away in infrared wavelengths even though the radiation in visible wavelengths is obscured by dust clouds. Because of this phenomenon, these starry swirls are known as luminous infrared galaxies.

In the news release, the Spitzer science team point to the streams of stars being ripped off the galaxies - "tidal tails" that extend into space in all directions. And this is just the warmup act: Bush and her colleagues expect the galactic black holes to hit head-on. That would upgrade NGC 6240's status to that of an ultra-luminous infrared galaxy, thousands of times as bright in infrared as our own Milky Way.

The findings are detailed in The Astrophysical Journal. In addition to Bush, the paper's co-authors include Zhong Wang, Margarita Karovska and Giovanni Fazio, all of the Harvard-Smithsonian Center for Astrophysics.

This week's other galactic crash was witnessed by the European Southern Observatory's Very Large Telescope in Chile. Two galaxies are piling into each other 70 million light-years away in the constellation Libra, and just as in the case of NGC 6240, the clashing clouds of gas and dust are sparking waves of stellar fireworks.

ESO
This color composite image from the ESO Very
Large Telescope in Chile shows Arp 261. Click on
the picture for a larger version.


These galaxies, collectively known as Arp 261, aren't as big as the monsters in NGC 6240. They're on the scale of dwarf galaxies, similar to the Magellanic Clouds orbiting the Milky Way. In this week's image advisory, the ESO says the focus of research in this picture actually isn't the wide-screen view of smashing galaxies, but a detailed look at an unusually long-lasting, X-ray-emitting supernova. This image adds little white bars to highlight the location of the supernova.

The picture also includes other objects at a wide range of distances. If you click on a higher-resolution view, you'll be able to make out a sprinkling of background galaxies on the right side of the picture. Those galaxies may be 50 to 100 times farther away than Arp 261, the ESO says.

Toward the top left corner of the picture, you can see two red-green-blue streaks. Those are two small asteroids in our solar system's main asteroid belt. The streaks are multicolored because the ESO's picture was taken through different color filters - and the asteroids were moving through the telescope field even as the exposures were switched from one filter to the next.

If you're looking for more simply smashing pictures, don't miss today's report about Saturn's quadruple-moon transit, as well as our regular roundup of the best space views in the cosmos.

Correction for 3:30 p.m. ET March 18: I fixed a bad link to the Saturn transit story ... Sorry about that! After reading all the perceptive comments below, I've also edited the item to straighten something out about the timing of events at NGC 6240. We will likely see an even more spectacular pile-up there millions of years from now, but because the galaxies are so distant, and because the speed of light is finite, that phase of the pile-up will have happened hundreds of millions of years earlier.