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Magnetic Field Saves Pillars of Creation from Destruction

| Science

BISTRO magnetic field vectors overlaid on a Hubble Space Telescope three color image (502 nm, 657 nm, and 673 nm) of Pillar II. The magnetic field runs roughly parallel to the pillar’s axis. No polarization is detected at the Pillar’s tip – this depolarization is consistent with a horseshoe-shaped magnetic field on scales smaller than the observation beam.

The cloud pictured here standing like an impossibly tall tower in space is one of the Pillars of Creation in the Eagle Nebula (M16). Actually, pillars of gas like this are formed, not by extending out, but by remaining behind as the rest of the cloud is eroded away. The details of this process, particularly the role of the magnetic field, are still a topic of hot debate. Now for the first time high-resolution, submillimeter wavelength polarimetric observations have shown that the magnetic fields inside a pillar are strong enough to support it against collapse.

Young massive stars (spectral type O and early B) produce sufficient high-energy photons to ionize portions of the molecular cloud in which they form. This ionization crates a shock front pushing dense gas away from the young stars and creating a low density ionized region. These photoionized regions can exhibit complex structures, such as pillars of dense gas remaining after the shock front has passed.

The formation and evolution of pillars like this are still not well understood. New 850 micrometer observations, taken as part of the BISTRO (B-Fields in Star-forming Region Observations) Survey using the POL-2 polarimeter on the SCUBA-2 camera of the James Clerk Maxwell Telescope (JCMT) show that the internal magnetic fields run along the length of the pillar. These magnetic fields are perpendicular to, and decoupled from, the field in the surrounding photoionized cloud. This is consistent with a scenario where a pillar is formed by the compression of initially weakly magnetized gas. The estimated field strength of 170 to 320 microGauss is comparable to that required to magnetically support the pillar against pressure- and gravity-driven radial collapse. Thus the evolution and lifetime of a pillar may be strongly influenced by the strength of the magnetic fields.

The James Clerk Maxwell Telescope, located on Maunakea in Hawai`i, is operated by the East Asian Observatory. The BISTRO Survey is a large team of scientists working to understand the role of magnetic fields in the formation of stars, with members from across the partner regions of the East Asian Observatory: China, Japan, South Korea, Taiwan, and Vietnam, and from participating universities in the United Kingdom and Canada. Within Japan, contributing researchers hail from the University of Tsukuba, University of Tokyo, National Astronomical Observatory of Japan, Institute of Space and Astronautical Science, Nagoya University, Kyoto University, Kwansei Gakuin University, Tokushima University, Kagawa University, Hiroshima University, and Kagoshima University.

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