ASTRONOMERS have discovered a new source of microwaves in our Galaxy, the
first such discovery for nearly 20 years. The radiation comes from space dust
that fills the voids between stars. The discovery should allow astronomers to
measure the cosmic microwave background radiation鈥攖he afterglow of the big
bang鈥攎ore accurately than ever before.
Cosmologists who study the microwave background are particularly interested
in pinpointing microwave emissions from our Galaxy because they mess up their
measurements. 鈥淚 see the [microwave emissions from our] Galaxy as garbage that I
have to take out from my data,鈥� says Angelica de Oliveira-Costa from the
University of Pennsylvania. She hopes that working out which emissions are
coming from the Milky Way will help her see the background radiation more
clearly.
De Oliveira-Costa and her colleagues were studying a type of microwave
emission known as free-free radiation and found that emissions from the Milky
Way were brighter than they expected. 鈥淪uddenly we realised that maybe we had
something else,鈥� she says.
Advertisement
To explain the finding, astrophysicists revived an idea from the 1950s
suggesting that tiny dust grains with an uneven distribution of electric charge
would be set spinning by charged particles that raced past. This would make them
radiate microwaves at the same frequency as the rate of rotation. Astrophysicist
Douglas Finkbeiner from Princeton University in New Jersey and his colleagues
compared the rogue emissions with maps they had already made of 10 dust clouds
in the Milky Way. 鈥淲e chose nice clouds of dust with sharp edges and distinctive
features,鈥� he says. The areas of the sky from which the microwaves came matched
the dust clouds exactly. Their findings will be published in a future issue of
The Astrophysical Journal.
With NASA鈥檚 MAP (Microwave Anisotropy Probe) satellite poised to make the
most accurate observations yet, he says understanding the role of microwaves
from the Galaxy will be crucial.