Tiny Mirrors to Help VIRUS Spot Trails of Dark Energy

Precision Glass & Optics recently delivered specialized optical mirrors for use in building VIRUS, a key instrument for the Hobby-Eberly Telescope Dark Energy Experiment (HETDEX), a $36 million project that will study dark energy, the force that causes the expansion of the universe to speed up, rather than slow down.

Because dark energy comprises more than 70 percent of the universe, understanding it is considered one of the top challenges in physics today, according to HETDEX researchers. The VIRUS instrument will be assembled, aligned and tested at Texas A&M and at the University of Texas. Darren DePoy and Jennifer Marshall will lead the effort at Texas A&M. Gary Hill and Sarah Tuttle will lead the effort at the University of Texas.

VIRUS-P, a prototype of the VIRUS spectrograph system. Inset shows some of the optical coatings made by mirror supplier Precision Glass & Optics (PG&O). (Main photo courtesy of Martin Harris/McDonald Observatory; inset courtesy of PG&O.)

The VIRUS (Visible Integral-Field Replicable Unit Spectrographs) system is composed of 150 tiny, identical spectrographs, and the mirrors provided by Precision Glass & Optics for the instrument’s collimator fold mirror cover the wavelength range of 345 to 700 nm. To meet the requirements for VIRUS, the reflective coatings on the borosilicate glass comprising the mirrors have an operational lifetime of 20 years.

The astronomical instrument is designed to gather light from distant galaxies and split it into individual spectra. Each spectrum will reveal an object’s chemical composition, its temperature, and the speed at which the universe is stretching between the detected galaxies and Earth. VIRUS will capture spectra from 33,000 points on the sky simultaneously, permitting astronomers to produce a 3-D map of a large volume of space. Researchers can then find how fast the universe expanded at different periods in history, which will help reveal the role that dark energy has played during different eras. HETDEX will search for any evidence that the strength of dark energy changes over time and will provide the most precise measurement of the geometry of the universe, which is related to the physics of the universe at the moment of Big Bang.

DePoy said that because VIRUS is designed for spectroscopic observations of a large number of objects simultaneously, the instrument is well suited for measuring the subtle effects that dark energy has on the structure of the universe.

For more information, visit: www.hetdex.org