Primordial Black Holes ( PBHs ) are gravitationally collapsed objects that may have been created by density fluctuations in the early universe and could have arbitrarily small masses down to the Planck scale .
Hawking showed that due to quantum effects , a black hole has a temperature inversely proportional to its mass and will emit all species of fundamental particles thermally .
PBHs with initial masses of \sim 5.0 \times 10 ^ { 14 } g should be expiring in the present epoch with bursts of high-energy particles , including gamma radiation in the GeV – TeV energy range .
The Milagro high energy observatory , which operated from 2000 to 2008 , is sensitive to the high end of the PBH evaporation gamma-ray spectrum .
Due to its large field-of-view , more than 90 % duty cycle and sensitivity up to 100 TeV gamma rays , the Milagro observatory is well suited to perform a search for PBH bursts .
Based on a search on the Milagro data , we report new PBH burst rate density upper limits over a range of PBH observation times .
In addition , we report the sensitivity of the Milagro successor , the High Altitude Water Cherenkov ( HAWC ) observatory , to PBH evaporation events .