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Peering Inside the Pillars of Creation

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Pillars of Creation
The Pillars of Creation, as captured in a high-resolution HST image taken in 2014 as a tribute to the original Hubble photograph from 1995. A new study explores how magnetic fields influence these pillars. [NASA/ESA/Hubble Heritage Team (STScI/AURA)]

On 1 April 1995, Hubble captured one of its most well-known images: a stunning photo of towering features known as the Pillars of Creation, located in the Eagle Nebula just 7,000 light-years away. A new study explores how these iconic columns are influenced by the magnetic fields within them.

Pillars from Shocks

Pillars of Creation magnetic fields

An illustrative figure of the BISTRO magnetic-field vectors observed in the Pillars of Creation, overlaid on a Hubble composite of the pillars. [Pattle et al. 2018]

In the Hubble image, we see the result of young, hot stars that have driven a photoionization shock into the cloud around them, forming complex structures in the dense gas at the shock interfaces. These structures — in this case, dense columns of neutral gas and dust — are then bombarded with hot radiation from the young stars, giving the structures a misty, ethereal look as they photoevaporate.

Though we have a rough picture, the specifics of how the Pillars of Creation were formed and how they evolve in this harsh radiation environment aren’t yet fully understood. In particular, the role of magnetic fields in shaping and sustaining these pillars is poorly constrained, both observationally and theoretically.

To address this problem, a team of scientists led by Kate Pattle (University of Central Lancashire, UK and National Tsing Hua University, Taiwan), has now made the first direct observations of the magnetic-field morphology within the Pillars of Creation.

Pillars of Creation formation schematic

The authors’ proposed formation scenario: a) an ionization front approaches an overdensity in the molecular gas, b) the front is slowed at the overdensity, causing the magnetic field lines to bend, c) the compressed magnetic field supports the pillar against radial collapse, but can’t support against longitudinal erosion. [Adapted from Pattle et al. 2018]

Observing Fields

Pattle and collaborators imaged the pillars as a part of the B-Fields in Star-Forming Region Observations (BISTRO) project, which uses a camera and polarimeter mounted on the James Clerk Maxwell Telescope in Hawaii. The high-resolution, submillimeter-wavelength polarimetric observations allowed the team to measure the orientations of the magnetic fields within the pillars.

Pattle and collaborators found that the magnetic fields inside the Pillars of Creation are actually quite organized: they generally run along the length of the pillars, perpendicular to and decoupled from the field in the surrounding cloud. The authors use their observations to estimate the strength of the fields: roughly 170–320 µG in the pillars.

Magnetic Support

What do these results tell us? First, the strength of the fields is consistent with a formation scenario in which very weakly magnetized gas was compressed to form columns. The authors propose that the Pillars of Creation were formed when an ionization front — driven by radiation from nearby young, hot stars — encountered a dense clump as it moved through the cloud of molecular gas. The overdensity slowed the front, causing the magnetic field to bend as the surrounding gas moved. The compressed magnetic field then supported the resulting column from collapse.

Pattle and collaborators argue that the magnetic fields in the Pillars of Creation are supporting the pillars radially against collapse even now. They may also be preventing the pillar ends from breaking off into disconnected clumps known as cometary globules, a process that could eventually disintegrate the pillars.

So what’s BISTRO up to now? The project is continuing to survey magnetic fields in the dense gas of other nearby high-mass star-forming regions. This may help confirm the results found for the Pillars of Creation, bringing us another step closer to understanding how magnetic fields influence the some of the striking features that Hubble and other telescopes have revealed in our astronomical backyard.

Citation

Kate Pattle et al 2018 ApJL 860 L6. doi:10.3847/2041-8213/aac771