This artist’s conception portrays four extremely red galaxies that lie almost 13 billion light-years from Earth. Discovered using the Spitzer Space Telescope, these galaxies appear to be physically associated and may be interacting. One galaxy shows signs of an active galactic nucleus, shown here as twin jets streaming out from a central black hole. Image: David A. Aguilar (CfA) |
In the distant reaches of the universe, almost 13 billion light-years
from Earth, a strange species of galaxy lay hidden. Cloaked in dust and dimmed
by the intervening distance, even the Hubble Space Telescope couldn’t spy it.
It took the revealing power of NASA’s Spitzer Space Telescope to uncover not
one, but four remarkably red galaxies. And while astronomers can describe the
members of this new “species,” they can’t explain what makes them so
ruddy.
“We’ve
had to go to extremes to get the models to match our observations,” says
Jiasheng Huang of the Harvard-Smithsonian
Center for Astrophysics
(CfA). Huang is lead author on the paper announcing the find, which was published
online by the Astrophysical Journal.
Spitzer
succeeded where Hubble failed because Spitzer is sensitive to infrared light—light
so red that it lies beyond the visible part of the spectrum. The newfound
galaxies are more than 60 times brighter in the infrared than they are at the
reddest colors Hubble can detect.
Galaxies can
be very red for several reasons. They might be very dusty. They might contain
many old, red stars. Or they might be very distant, in which case the expansion
of the universe stretches their light to longer wavelengths and hence redder
colors (a process known as redshifting). All three reasons seem to apply to the
newfound galaxies.
All four
galaxies are grouped near each other and appear to be physically associated,
rather than being a chance line up. Due to their great distance, we see them as
they were only a billion years after the Big Bang.
“Hubble
has shown us some of the first protogalaxies that formed, but nothing that
looks like this. In a sense, these galaxies might be a ‘missing link’ in
galactic evolution” says co-author Giovanni Fazio of the CfA.
Next,
researchers hope to measure an accurate redshift for the galaxies, which will
require more powerful instruments like the Large Millimeter Telescope or
Atacama Large Millimeter Array. They also plan to search for more examples of
this new “species” of extremely red galaxies.
“There’s evidence for others in other regions of the sky. We’ll analyze
more Spitzer and Hubble observations to track them down,” says Fazio.
