Astronomers
have finally tracked down the missing starting point of one of the two types of
solar wind.
The solar
wind is a stream of electrically charged particles that flows constantly out
from the sun in all directions. The particles can make the journey from the sun
to the Earth in fewer than 10 days and, when the wind turns into a storm,
create the magnificent auroras that dance across polar skies when they interact
with the Earth's magnetic field.
The parts
of the solar wind that emanate from the sun's equatorial region originate at
the edges of bright regions in the sun's atmosphere and are released when the magnetic
fields of two bright regions link up, scientists announced last week at the
Royal Astronomical Society's National Astronomy Meeting in Belfast, Northern
Ireland.
"It is
fantastic to finally be able to pinpoint the source of the solar wind — it has
been debated for many years and now we have the final piece of the
jigsaw," said study leader Louise Harra of University College London.
Fast and
slow
The sun
emits radiation, which is pure energy, along with the solar wind, which is
fast-moving matter. The wind's particles are accelerated by the sun's magnetic
fields, and the configuration of the magnetic fields can influence how fast the
solar wind is going when it rushes out into space.
Astronomers
recognize two types of solar wind, distinguished by their speed. The fast one is
known to originate from coronal hole regions near the sun's poles and travel at
about 1.8 million miles per hour (2.9 million kilometers per hour). The slow one
flows from the equatorial region of the sun at about 432,000 mph to 1.1 million
mph (720,000 kph to 1.8 million kph).
The fast solar
wind is so much faster because the magnetic fields that loop out from the polar
regions are always "open," meaning they don't loop back toward the
sun's surface. So "all the gas can keep streaming out, there's nothing to
stop it," Harra said.
At the
equator, on the other hand, there are both closed and open magnetic fields, and
the closed fields hold the solar
plasma back. Only when the fields open, can the solar wind stream out from
the region.
As a
result, the solar wind coming from the equatorial region is slower and
"very, very variable," Harra told SPACE.com.
Big and
'baby' regions
Using the Hinode
space observatory, Harra and her colleagues found for the first time that hot
gas spurts out at high speeds from the edges of bright, active regions along
the equator when the magnetic fields from two regions meet up.
Hinode
witnessed such a link-up when the field lines from a big active region and a
"baby" region connected and opened up.
"We
now know that interacting with smaller regions can open up the field
lines," Harra said.
These
regions can connect even when they are 500,000 kilometers apart (a distance
equivalent to placing 40 Earths side-by-side), Harra said.
For the two
regions to connect, the field lines from the two regions have to be in the
right direction and of the right strength.
The big
region "needs to find its partner to interact," Harra said.
Understanding
the solar wind and how it is formed could help scientists better predict how it
will affect the Earth and help protect the satellites in orbit around our
planet.
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