LONG BEACH, Calif. -- Space is typically thought of
as a very quiet place. But one team of astronomers has
found a strange cosmic noise that booms six times louder
The roar is from the distant cosmos. Nobody knows
what causes it.
Of course, sound waves can't travel in a vacuum
(which is what most of space is), or at least they
can't very efficiently. But radio waves
Radio waves are not sound waves, but they are still
electromagnetic waves, situated on the low-frequency end
of the light
Many objects in the universe, including stars and
quasars, emit radio waves. Even our home galaxy, the
Milky Way, emits a static hiss (first detected in 1931
by physicist Karl Jansky). Other galaxies also send out
a background radio
But the newly detected signal, described here today
at the 213th meeting of the American Astronomical
Society, is far louder than astronomers expected.
There is "something new and interesting going on in
the universe," said Alan Kogut of NASA's Goddard Space
Flight Center in Greenbelt, Md.
A team led by Kogut detected the signal with a
balloon-borne instrument named ARCADE (Absolute
Radiometer for Cosmology, Astrophysics, and Diffuse
In July 2006, the instrument was launched from NASA's
Columbia Scientific Balloon Facility in Palestine,
Texas, and reached an altitude of about 120,000 feet
(36,500 meters), where the atmosphere thins into the
vacuum of space.
ARCADE's mission was to search the sky for faint
signs of heat from the first generation of stars, but
instead they heard a roar from the distant reaches of
"The universe really threw us a curve," Kogut said.
"Instead of the faint signal we hoped to find, here was
this booming noise six times louder than anyone had
Detailed analysis of the signal ruled out primordial
stars or any known radio sources, including gas in the
outermost halo of our own galaxy.
Other radio galaxies also can't account for the noise
– there just aren't enough of them.
"You'd have to pack them into the universe like
sardines," said study team member Dale Fixsen of the
University of Maryland. "There wouldn't be any space
left between one galaxy and the next."
The signal is measured to be six times brighter than
the combined emission of all known radio sources in the
For now, the origin of the signal remains a
"We really don't know what it is,"said team member
Michael Seiffert of NASA's Jet Propulsion Laboratory in
And not only has it presented astronomers with a new
puzzle, it is obscuring the sought-for signal from the
earliest stars. But the cosmic static may itself provide
important clues to the development of galaxies when the
universe was much younger, less than half its present
age. Because the radio waves come from far away,
traveling at the speed of light, they therefore represent
an earlier time in the universe.
"This is what makes science so exciting," Seiffert
said. "You start out on a path to measure something – in
this case, the heat from the very first stars – but run
into something else entirely, some unexplained."