Insert Hollywood Starlet Joke *Here*
A new image from NASA's Spitzer Space Telescope offers a rare
view of an imminent collision between the cores of two merging
galaxies, each powered by a black hole with millions of times the
mass of the sun.
The galactic cores are in a single, tangled galaxy called NGC
6240, located 400-million light years away in the constellation
Ophiuchus. Millions of years ago, each core was the dense center of
its own galaxy before the two galaxies collided and ripped each
other apart. Now, these cores are approaching each other at
tremendous speeds and preparing for the final cataclysmic
collision. They will crash into each other in a few million years,
a relatively short period on a galactic timescale.
The spectacular image (above)
combines visible light from NASA's Hubble Space Telescope and
infrared light from Spitzer. It catches the two galaxies during a
rare, short-lived phase of their evolution, when both cores of the
interacting galaxies are still visible but closing in on each other
fast.
"One of the most exciting things about the image is that this
object is unique," said Stephanie Bush of the Harvard-Smithsonian
Center for Astrophysics, Cambridge, Mass., lead author of a new
paper describing the observation in an upcoming issue of the
Astrophysical Journal. "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."
NGC 6240 is already putting out huge amounts of infrared light,
an indication that a burst of star formation is underway. The extra
infrared radiation is common in interacting galaxies; as the two
galaxies interact, dust and gas swept up by the collision form a
burst of new stars that give off infrared light. Such galaxies are
called luminous infrared galaxies. Spitzer's infrared array camera
can image the extra heat from newly formed stars, even though their
visible light is obscured by thick dust clouds around them.
The blob-like shape of the galaxy is due to the sustained
violence of the collision. Streams of millions of stars are being
ripped off the galaxy, forming wispy "tidal tails" that lead off
NGC 6240 in several directions. But things are about to get even
more violent as the main event approaches and the two galactic
cores meld into one.
In the center of NGC 6240, the two black holes in the cores will
whip up a frenzy of radiation as they careen towards one another
head-on, likely transforming the galaxy into a monster known as an
ultra-luminous infrared galaxy, thousands of times as bright in
infrared as our Milky Way.
No two galactic mergers are the same. "Not only are there few
objects at this stage, but each object is unique because it came
from different progenitor galaxies," said Bush. "These observations
give us another layer of information about this galaxy, and
galactic mergers in general."
Infrared light taken by Spitzer's infrared array camera at 3.6
and 8.8 microns (red) shows cold dust and radiation from star
formation; visible light from Hubble (green and blue) shows hot gas
and stars.
Other authors of this paper include Zhong Wang, Margarita
Karovska and Giovanni Fazio, all of the Harvard-Smithsonian Center
for Astrophysics.