Dragonfly is an innovative, multi-lens array designed for ultra-low surface brightness astronomy at visible wavelengths. Commissioned in 2013 with only three lenses, the array is growing in size and proving capable of detecting extremely faint, complex structure around galaxies. The most recent upgrade—completed in 2016—saw Dragonfly grow to 48 lenses in two clusters.

According to Cold Dark Matter (CDM) cosmology, structure in the Universe grows from the “bottom up”, with small galaxies merging to form larger ones. Evidence of such mergers can be seen in faint streams and filaments visible around the Milky Way Galaxy and the nearby M31 galaxy.

But the CDM model predicts that we should see more of this structure than is currently observed. However, images obtained using even the largest, most advanced telescopes today contain scattered light that may be hiding this faint structure.

Dragonfly is designed to reveal the faint structure by greatly reducing scattered light and internal reflections within its optics. It achieves this using commercially available Canon 400mm lenses with unprecedented nano-fabricated coatings with sub-wavelength structure on optical glasses.

Also, Dragonfly images a galaxy through multiple lenses simultaneously—akin to a dragonfly’s compound eye—enabling further removal of unwanted light. The result is an image in which extremely faint galaxy structure is visible.

The array began imaging targets in 2013 from its home at the New Mexico Skies hosting facility. Images have shown Dragonfly is at least ten times more efficient than its nearest rival and will be able to detect faint structures predicted by current merger models.

The original co-principal-investigators for Dragonfly are U of T’s Prof. Roberto Abraham and Yale University’s Prof. Pieter van Dokkum, and they have recently been joined by Harvard’s Charlie Conroy as the third co-principal-investigator. At the U of T, the Dragonfly team also includes graduate students Jielai Zhang and Deborah Lokhorst.

Funding for Dragonfly was provided by Abraham’s NSERC Discovery Grant, with initial funds provided by the Dunlap Institute and Yale University, and NSERC equipment grants awarded in 2014 and 2016.

Dragonfly in the news:

Washington Post: A new class of galaxy has been discovered, one made almost entirely of dark matter

CNN.com: “Dark Twin” of the Milky Way Galaxy discovered

Forbes.com: Newly Discovered Galaxy is Almost Entirely Made of Dark Matter

FOX News: Found: Dragonfly 44: a Strange Galaxy Made Mostly of Dark Matter

WIRED: Meet Dragonfly 44, the galaxy made of 99.9% dark matter

Nautil.us: How to Discover a Galaxy with a Telephoto Lens, Nautilus, 28 Jan 2016

Recent Dragonfly papers:

The Dragonfly Nearby Galaxies Survey

Spectroscopic Confirmation of the Existence of Large, Diffuse Galaxies in the Coma Cluster

A High Stellar Velocity Dispersion and ~100 Globular Clusters for the Ultra-Diffuse Galaxy Dragonfly 44

Forty-seven Milky Way-sized, Extremely Diffuse Galaxies in the Coma Cluster

The discovery of seven extremely low surface brightness galaxies in the field of the nearby spiral galaxy M101

First results from the Dragonfly Telephoto Array: the apparent lack of a stellar halo in the massive spiral galaxy M101

Ultra Low Surface Brightness Imaging with the Dragonfly Telephoto Array


The galaxy Dragonfly 44, first identified with the Dragonfly array, is 99.99% dark matter. Image: P. van Dokkum; Roberto Abraham; J. Brodie


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Half of Dragonfly in 2016. Image: P. Van Dokkum; R. Abraham


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Dragonfly in 2015. Image: P. Van Dokkum; R. Abraham