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{{short description|Flashes of gamma rays from distant galaxies}}
▲[[File:Gamma ray burst.jpg|thumb|300px|Artist's illustration showing the life of a [[star#Massive stars|massive star]] as [[nuclear fusion]] converts lighter elements into heavier ones. When fusion no longer generates enough pressure to counteract gravity, the star rapidly collapses to form a [[black hole]]. Theoretically, energy may be released during the collapse along the axis of rotation to form a GRB.]]
In [[gamma-ray astronomy]], '''gamma-ray bursts''' ('''GRBs''') are immensely energetic explosions that have been observed in distant [[Galaxy|galaxies]], described by [[NASA]] as "the most powerful class of explosions in the universe".<ref>{{Cite web |last=Reddy |first=Francis |date=2023-03-28 |title=NASA Missions Study What May Be a 1-In-10,000-Year Gamma-ray Burst - NASA |url=https://www.nasa.gov/universe/nasa-missions-study-what-may-be-a-1-in-10000-year-gamma-ray-burst/ |access-date=2023-09-29 |website=nasa.gov |language=en-US}}</ref> They are the most energetic and luminous [[Electromagnetic pulse|electromagnetic events]] since the [[Big Bang]].<ref>{{cite web|title=Gamma Rays|url=http://missionscience.nasa.gov/ems/12_gammarays.html|work=NASA|url-status=dead|archive-url=https://web.archive.org/web/20120502232209/http://missionscience.nasa.gov/ems/12_gammarays.html|archive-date=2012-05-02}}</ref> Bursts can last from ten milliseconds to several hours.<ref>{{Cite web|last=Atkinson|first=Nancy|date=2013-04-16|title=New Kind of Gamma Ray Burst is Ultra Long-Lasting|url=https://www.universetoday.com/101486/new-kind-of-gamma-ray-burst-is-ultra-long-lasting/|access-date=2022-01-03|website=Universe Today|language=en-US}}</ref><ref name="Kouveliotou" /> After an initial flash of [[gamma ray]]s, a longer-lived "afterglow" is usually emitted at longer wavelengths ([[X-ray]], [[ultraviolet]], [[visible spectrum|optical]], [[infrared]], [[microwave]] and [[radio waves|radio]]).<ref>[[#VedrenneAtteia|Vedrenne & Atteia 2009]]</ref>
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