search for extraterrestrial intelligence is focused largely on
detecting signals sent from afar. But in 1960, physicist Freeman Dyson proposed a way to directly search for artifacts of alien civilisations.
envisioned that population pressure and the demand for energy would
drive civilisations to dismantle planets and use the debris to surround
a star, creating a massive solar collector.
number of Dyson sphere structures have been proposed, including a
solid, rotating ring and a spherical shell of debris. These structures
might be habitable themselves, or they might be used as remote solar
structures would partially or fully block the star's visible and
ultraviolet light, but they would still be detectable. A Dyson sphere
or ring would be warmed by the star's energy and would radiate infrared
light that could be detected from Earth.
Some researchers have previously searched for signs of the spheres in data from the Infrared Astronomical Satellite (IRAS), which launched in 1983 and made an infrared map of the entire sky.
took data in different modes, sometimes looking at its sources through
a handful of colour filters, and sometimes looking at sources with its
spectrograph, which carefully studied a wide range of colours.
previous searches focused on sources that had been studied with the
colour filters. They looked for objects that radiate most of their
light at relatively long infrared wavelengths. That would be the case
if a Dyson sphere located at about the Earth's orbital distance from
its star absorbed the energy emitted by a Sun-like star and then
re-emitted it as heat.
with only a few colours available to scrutinise for the temperature
signature of a Dyson sphere, the previous studies could not whittle
down the list of 250,000 IRAS sources to a few good candidates.
Richard Carrigan, a retired physicist who had worked at the Fermi
National Accelerator Laboratory in Batavia, Illinois, has combed
through data from the probe's spectrograph, which provides a more
detailed portrait of the source's light.
with more than 10,000 infrared spectra taken by IRAS, Carrigan
identified only 17 possible "spheres", four of which seem most
all the objects have features that could just as easily be explained by
clouds of hydrogen gas, dust engulfing ancient stars, or even asteroids
in our own solar system, Carrigan told New Scientist.
"There are very few candidates that come close to fitting the bill," Carrigan says.
different kinds of astrophysical objects could masquerade as Dyson
spheres," says infrared astronomer Charles Beichman of Caltech. "I
think the search . . . is looking for a needle in a field of haystacks,
when you're not even sure there's a needle there. But he's done a very
nice job of working through the available data."
approach is good at whittling down sphere candidates from many sources,
agrees astronomer Dan Werthimer of the University of California,
Berkeley, and chief scientist of SETI@Home, a project that harnesses
the idle time of people's computers to search for possible
extraterrestrial radio signals.
"It gets it down to a manageable number of stars you can follow up on," Werthimer told New Scientist. "That's been a big problem with these Dyson sphere searches."
17 sphere candidates Carrigan has identified have been added to SETI's
list of interesting objects, to be investigated for radio and laser
signals. "If we're lucky, maybe one of these things will pan out and be
the first evidence of an alien civilisation," Werthimer says.
But Werthimer adds more promising evidence for Dyson spheres could come from NASA's Spitzer Space Telescope.
was not precise enough to identify individual stars, particularly in
crowded parts of the sky, such as the plane of the Milky Way. "You
might have 10 or 20 sources within the IRAS beam, but what you're
getting is the sum of all that flux, not the signature of a single
Dyson sphere," says astronomer Ed Churchwell of the University of
survey may offer better prospects for Dyson structure searches. The
all-sky infrared map contains more than 100 million objects and has
some 60 times IRAS's resolution, Churchwell told New Scientist. A final version of the survey's data may be available as early as the end of 2008.
Copyright: New Scientist