Astronomers have used the National Science Foundation’s Very Long Baseline
Array (VLBA) radio telescope to do a very detailed map of the magnetic field
within a star-forming cloud, an achievement that will help scientists unravel
the mysterious first steps of the stellar birth process.
“This study provides new and important data needed by theorists to understand
how magnetic fields affect the early stages of star formation,” said Anuj
Sarma, an astronomer at the University of Illinois at Urbana-Champaign. Sarma
worked with Thomas Troland of the University of Kentucky and Jonathan Romney
of the National Radio Astronomy Observatory (NRAO) in Socorro, New Mexico.
Their research results were published in the Astrophysical Journal Letters.
Stars are formed when gas in giant interstellar clouds collapses
gravitationally. Magnetic fields are believed to support such gas clouds,
helping them resist gravitational collapse, so the beginning stages of star
formation arise from a complex interplay of the magnetic fields and gravity
that is not yet well understood.
“In order to understand how star formation gets started, we need to know in
detail the structure of the magnetic fields in a star-forming cloud,” Sarma
said. “Our observations with the VLBA have provided one more big step in this
direction,” he added.
The astronomers studied a cloud of molecular gas more than 5,000 light-years
from Earth in a spiral arm of our own Milky Way Galaxy. The cloud, known as
W3 IRS5, contains seven newly-formed stars. In addition, it contains a number
of regions, somewhat smaller than the diameter of Earth’s orbit, in which
water vapor molecules act to amplify, or strengthen, radio emission. Such
regions, called masers, are a radio-wave parallel to lasers, which amplify
light.
The scientists used the VLBA to make a detailed study of the radio waves
coming from these maser regions in the gas cloud. They detected a phenomenon
called the Zeeman effect, in which a very precise frequency emitted by atoms
or molecules, called a spectral line, is split into two by a magnetic field.
Analyzing this effect allowed the astronomers to measure the strength of the
magnetic field at the locations of the maser regions.
“The bright, amplified radio emission coming from these water masers allowed
us to measure the magnetic-field strength,” Troland said.
The Expanded Very Large Array (EVLA) and the Atacama Large Millimeter Array
(ALMA), two instruments under development by the NRAO, will provide improved
sensitivity to faint radio emissions, and allow even more detailed studies
of the magnetic fields in star-forming regions.
The National Radio Astronomy Observatory is a facility of the National
Science Foundation, operated under cooperative agreement by Associated
Universities, Inc.
