The Hydrogen Epoch of Reionization Array (HERA) is a scientific road map for exploring the large-scale structure in the baryonic universe via the 21cm line of hydrogen during cosmic reionization.

HERA Phase I projects



Phase I: currently underway Sister telescopes Murchison Widefield Array (MWA) and Precision Array for Probing the Epoch of Reionization (PAPER) are opening this new observational window on the early universe. They have shown that, careful design and new analysis techniques, foregrounds and systematics can be overcome and are now primarily limited by collecting area.

Phase II: in preparation A single array combining experience gleaned from these two arrays capable of making higher SNR measurements in much less time. This array is planned to be a grid of 14 meter PAPER-style mesh reflectors arranged in a close-packed configuration. Reflective fabric shields the drift scanning reflectors, minimizing internal reflections.  This array will be capable of robust statistical characterization and will provide the first images of large scale HI structure.


Photo of the first 19 elements of the HERA-350 array.


A hexagonal packing of 350 elements provides enough sensitivity to measure HI emission at 12>z>6 while avoiding foregrounds.

The case for cosmic reionization:

Cosmic reionization corresponds to the epoch when the neutral intergalactic medium (IGM) is reionized by the first luminous objects (stars, black holes). Probing this last unexplored phase of cosmic evolution was emphasized by the astronomy community in the 2010 Decadal Survey the primary area with extraordinary ‘discovery potential’ in the study of cosmic structure formation:

 ‘A great mystery now confronts us: When and how did the first galaxies form out of cold clumps of hydrogen gas and start to shine—when was our “cosmic dawn”? Observations and calculations suggest that this phenomenon occurred when the universe was roughly half a billion years old, when light from the first stars was able to ionize the hydrogen gas in the universe from atoms into electrons and protons—known as the epoch of reionization.’

The HERA program aims to answer the primary questions: what objects first lit up the Universe and reionized the neutral IGM? Over what redshift range did this occur? How did the process proceed, leading to the large scale galaxy structure seen today?


The HERA roadmap was the top-ranked science program from the Astro2010 Radio, Millimeter, and Submillimeter panel report and was  Mentioned as both a Discovery Area as well as a key to exploring Origins, two out of three focus areas of the top level Decadal Report. The roadmap begins with the completion of the Precision Array for Probing the Epoch of Reionization (PAPER) and Murchison Widefield Array (MWA) experiments. PAPER and MWA are ‘spearhead projects’ that lead to a consolidated array to detect and chart the epoch of reionization.



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nrao_logo_pms_300ucbseal_139_540Final SKA LOGO 2010 Paths



  • PI Aaron Parsons (Berkeley) aparsons at berkeley.edu
  • Dave DeBoer (Berkeley) ddeboer at berkeley.edu
  • Rich Bradley (NRAO) rbradley at nrao.edu
  • James Aguirre (Pennsylvania) jaguirre at sas.upenn.edu
  • Judd Bowman (ASU) judd.bowman at asu.edu
  • Chris Carilli (NRAO) ccarilli at nrao.edu
  • Jacqueline Hewitt (MIT) jhewitt at mit.edu
  • Miguel Morales (Washington) mmorales at phys.washington.edu
  • Jonathan Pober (Washington) jpober at uw.edu
  • Dan Werthimer (Berkeley) danw at ssl.berkeley.edu
  • Max Tegmark (MIT) tegmark at mit.edu
  • Steve Furlanetto (UCLA) sfurlane at ucla.edu
  • Danny Jacobs (ASU) daniel.c.jacobs at asu.edu
  • Adrian Liu (Berkeley) acliu at berkeley.edu

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