Our Milky Way galaxy has an elegant spiral shape with long arms
filled with stars, but exactly how it took this form has long puzzled
scientists. New observations of another galaxy are shedding light on how
spiral-shaped galaxies like our own get their iconic shape.
Magnetic fields play a strong role in shaping these galaxies,
according to research from the Stratospheric Observatory for Infrared
Astronomy, or SOFIA. Scientists measured magnetic fields along the
spiral arms of the galaxy called NGC 1068, or M77. The fields are shown as streamlines that closely follow the circling arms.
“Magnetic fields are invisible, but they may influence the evolution
of a galaxy,” said Enrique Lopez-Rodriguez, a Universities Space
Research Association scientist at the SOFIA Science Center at NASA’s
Ames Research Center in California’s Silicon Valley. “We have a pretty
good understanding of how gravity affects galactic structures, but we’re
just starting to learn the role magnetic fields play.”
The M77 galaxy is located 47 million light years away in the
constellation Cetus. It has a supermassive active black hole at its
center that is twice as massive as the black hole at the heart of our
Milky Way galaxy. The swirling arms are filled with dust, gas and areas
of intense star formation called starbursts.
SOFIA’s infrared observations reveal what human eyes cannot: magnetic
fields that closely follow the newborn-star-filled spiral arms. This
supports the leading theory of how these arms are forced into their
iconic shape known as “density wave theory.” It states that dust, gas
and stars in the arms are not fixed in place like blades on a fan.
Instead, the material moves along the arms as gravity compresses it,
like items on a conveyor belt.
The magnetic field alignment stretches across the entire length of
the massive, arms — approximately 24,000 light years across. This
implies that the gravitational forces that created the galaxy’s spiral
shape are also compressing its magnetic field, supporting the density
wave theory. The results are published in the Astrophysical Journal.
“This is the first time we’ve seen magnetic fields aligned at such large scales with current star birth in the spiral arms,” said Lopez-Rodriquez. “It’s always exciting to have observational evidence that supports theories.”
Celestial magnetic fields are notoriously difficult to observe. SOFIA’s newest instrument,
the High-resolution Airborne Wideband Camera-Plus, or HAWC+, uses
far-infrared light to observe celestial dust grains, which align
perpendicular to magnetic field lines. From these results, astronomers
can infer the shape and direction of the otherwise invisible magnetic
field. Far-infrared light provides key information about magnetic fields
because the signal is not contaminated by emission from other
mechanisms, such as scattered visible light and radiation from
high-energy particles. SOFIA’s ability to study the galaxy with far
infrared light, specifically at the wavelength of 89 microns, revealed
previously unknown facets of its magnetic fields.
Further observations are necessary to understand how magnetic fields
influence the formation and evolution of other types of galaxies, such
as those with irregular shapes.
SOFIA, the Stratospheric Observatory for Infrared Astronomy, is a
Boeing 747SP jetliner modified to carry a 106-inch diameter telescope.
It is a joint project of NASA and the German Aerospace Center, DLR.
NASA’s Ames Research Center in California’s Silicon Valley manages the
SOFIA program, science and mission operations in cooperation with the
Universities Space Research Association headquartered in Columbia,
Maryland, and the German SOFIA Institute (DSI) at the University of
Stuttgart. The aircraft is maintained and operated from NASA’s Armstrong
Flight Research Center Building 703, in Palmdale, California. The HAWC+
instrument was developed and delivered to NASA by a multi-institution
team led by the Jet Propulsion Laboratory in Pasadena, California.
Media Contact
Felicia Chou
NASA Headquarters, Washington
202-358-0257
felicia.chou@nasa.gov
Editor: Kassandra Bell
Source: NASA/SOFIA
