Halo's defense system is designed to wipe out all sentient life in the galaxy. How does this work?

It can't be like nuclear bomb, otherwise it'd also destroy non-sentient life (viz. the Flood). It can't be like weapon of Star Trek: Nemesis which selectively acts on organic matter because of the same reason. How does the Halo's defense system work?

Is this something which checks for body functions of living things and read its mind (if it exists) before destruction?

  • @Willem That's not compatible with the whole framework of Halo.
    – user931
    Oct 15, 2012 at 11:47
  • Yeah, just re-watched that particulair terminal video and it turns out I was wrong, plantlife doesn't seem to be affected. ( Terminal 8: Two Betrayals )
    – Willem
    Oct 15, 2012 at 12:21
  • 9
    AFAIK there's no real-life, physical understanding of the Halo weapon. When you start talking about "superluminal communications arrays" and weapons that have an effect on upwards of 1/7th of the galaxy, I'd think it's just a black-box MacGuffin. It's supposedly an energy pulse, just like everything the Forerunners do, but who knows? We've never seen one fire from an operating state, just the partially rebuilt Alpha Halo blow itself and The Ark up by firing before it was ready.
    – rsegal
    Oct 15, 2012 at 12:25
  • 1
    @Willem - in HALO: Silentium, we see that (non-sentient) animal life is not affected either
    – The Fallen
    Apr 23, 2013 at 16:23

1 Answer 1


According to Halo.wikia.com (sourced from the Halo encyclopedia):

When activated, the Halo rings would wipe out all sentient life within three radii of the Milky Way's Galactic center, by sending out radiation, targeting certain cells in the nervous system, which includes, but is not limited to, neurons, by harmonizing all neurological frequencies.

The pulse targets the nervous system of sentient life forms via the issuing of a harmonic frequency

Presumably this operates similar to how an EMP destroys electronics - the burst of radiation destroys necessary components for operation of electronics. If all the neurons are destroyed, brain function would instantly cease, killing the organism. Presumably this means that sentient species as varied as Humans, Kig-yar, and Jiralhanae share some similar brain structures.

Edited, based on new information from HALO: Silentium (Spoilers)

The Halos also target anything, not just biological, that uses neurons. The Precursors' technology was based upon the unknown capabilities of neural physics. When the Halos fired, all Precursor architecture was destroyed as well. Presumably since the Precursors are supposed to have created life in the galaxy, they are the reason that neurons seem to be common between sentient species.

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