The Dragonfly Telephoto Array is a ground-based

optical telescope An optical telescope gathers and focus (optics), focuses light mainly from the visible spectrum, visible part of the electromagnetic spectrum, to create a magnification, magnified image for direct visual inspection, to make a photograph, or to co ...

array developed at the Dunlap Institute for Astronomy & Astrophysics of the

University of Toronto The University of Toronto (UToronto or U of T) is a public university, public research university whose main campus is located on the grounds that surround Queen's Park (Toronto), Queen's Park in Toronto, Ontario, Canada. It was founded by ...

in Canada. The array uses a combination of

telephoto lens A telephoto lens, also known as telelens, is a specific type of a long-focus lens used in photography and cinematography, in which the physical length of the lens is shorter than the focal length. This is achieved by incorporating a special lens ...

es to observe extragalactic objects. Its main purpose is to take images of ultra-low surface brightness galaxies at visible wavelengths of light. It is well suited for this purpose because its lenses have specially coated optical glass that reduces scattered light.

Design

The telescope was designed by Roberto Abraham of the University of Toronto and Pieter van Dokkum of

Yale University Yale University is a Private university, private Ivy League research university in New Haven, Connecticut, United States. Founded in 1701, Yale is the List of Colonial Colleges, third-oldest institution of higher education in the United Stat ...

. It was commissioned in 2013 and initially had eight commercially available Canon EF 400mm f/2.8L IS II USM camera lenses. This was first increased to ten lenses, and then extended to two clusters of 24 lenses each in 2016. The array is designed to accommodate the addition of lenses to increase its effective aperture with each additional lens. With 48 lenses, the instrument has a light gathering power equivalent to a 400mm lens, or a refracting telescope with an objective lens diameter of . In March 2021 plans were announced to add 120 more lenses. By using a lens based refractor design rather than a mirror based reflector design the telescope suffers less from issues introduced by diffraction and light scattering. Reflector designs have more light scattering due to interactions with dust and any slight roughness on the mirror. Issues with diffraction occur due to the need to place obstructions in the optical path of reflecting telescopes.

Research

Astronomers used the Dragonfly Telephoto Array to discover Dragonfly 44, a galaxy that is roughly as massive as the

Milky Way The Milky Way or Milky Way Galaxy is the galaxy that includes the Solar System, with the name describing the #Appearance, galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars in other arms of the galax ...

, with 99.9% of its mass composed of

dark matter In astronomy, dark matter is an invisible and hypothetical form of matter that does not interact with light or other electromagnetic radiation. Dark matter is implied by gravity, gravitational effects that cannot be explained by general relat ...

. At the other end of the scale it was also used to discover NGC 1052-DF2, which measurements with other instruments initially suggested was a galaxy with very little dark matter. Further work indicated that NGC 1052-DF2 was closer to the earth than previous thought. If this is the case then the galaxy would appear to contain a typical amount of dark matter. Though this distance debate was continued and rebutted by a follow up observation which measured the

tip of the red-giant branch Tip of the red-giant branch (TRGB) is a primary distance indicator used in astronomy. It uses the luminosity of the brightest red-giant-branch stars in a galaxy as a standard candle to gauge the distance to that galaxy. It has been used in conjun ...

distance to NGC 1052-DF2 using Hubble Space Telescope, confirming the earlier surface brightness fluctuation measurements and resolving the ambiguous distance.

References

External links

* {{Official website, https://www.dragonflytelescope.org/ Optical telescopes