This page contains information regarding Star Trek: Discovery, and thus may contain spoilers.
The red bursts were a series of signals of unknown provenance picked up by Federation sensors in 2257. Unlike anything Starfleet had encountered before, their precise synchronization all but ruled out natural phenomena being the cause. (DIS: "Brother")
The first appearance of the bursts occurred in perfect synchronization over a span of 24 hours in 2257. They were scattered across 30,000 light years of the Milky Way Galaxy and would have required energy beyond Starfleet's understanding to produce. (DIS: "Brother")
The Klingons also detected the bursts, and had no explanation for them. High Chancellor L'Rell confirmed to Ambassador Sarek that they were not responsible. Kol-Sha interpreted them as an ill omen for L'Rell's rule: "seven drops of blood" ready to rain down on the Klingon people. (DIS: "Brother", "Point of Light")
Spock had foreknowledge of the red bursts, which prompted him to take a leave of absence from the USS Enterprise. He left encrypted data about the bursts in his final personal log entry, in case he did not return. (DIS: "Brother")
The initial set of seven signals appearing in perfect synchronization were picked up by Federation sensors but disappeared again after just enough time to get a reading, with the exception of one signal.
The remaining signal eventually stabilized long enough to get a fix on its position, at which point the USS Enterprise captained by Christopher Pike set out to reach it. However, before anything else could be done, the Enterprise experienced a massive systems failure – later blamed by Pike on the holo-communications system. (DIS: "Brother", "An Obol for Charon")
Shortly after the bursts were detected, the Vulcan High Command directed Sarek to work with Starfleet in assembling a Federation task force. He went on to serve on this task force. (DIS: "Brother", "Light and Shadows")
Signal #1: The Interstellar asteroidEdit
At the source of the burst, Discovery found an interstellar asteroid which contained the crashed remains of the USS Hiawatha. While attempting to investigate the signal, a landing party consisting of Pike, Michael Burnham, Evan Connolly and Nhan, discovered survivors aboard the Hiawatha including Jett Reno. Despite an encounter with the red angel, the crew was unable to determine who or what generated the signal. (DIS: "Brother")
After Discovery departed the region, Starfleet sent a team to investigate the area further. They found evidence of tachyon radiation; suggesting time travel was involved. (DIS: "Saints of Imperfection")
Signal #2: TerralysiumEdit
Sometime after the initial series of bursts, a second signal was detected. The transmission was too faint to determine the exact coordinates using regular means but was eventually pinpointed to a distant region of the Beta Quadrant. Using its spore drive, Discovery was able to reach the location of this new burst, the planet of Terralysium. Once there, Discovery found a previously unknown settlement of humans. They were descendants of people saved from World War III by a mysterious entity.
Signal #3: KaminarEdit
Discovery detected a third burst in orbit of Kaminar, the homeworld of the Kelpien species, which included first officer Commander Saru. As had been the case on Terralysium, the burst had been visible from the surface; Siranna, Saru's sister and priest of their village, referred to it as a "fiery sign". (DIS: "The Sound of Thunder")
While in orbit above Kaminar investigating the residual radiation from the burst, Discovery investigated an anomaly. While investigating the anomaly in Shuttle 5, Ash Tyler and Christopher Pike were attacked by an upgraded version of a probe they'd previously launched. (DIS: "Light and Shadows")
Signal #4: Essof IVEdit
Discovery and NCIA-93 journeyed to Essof IV to attempt to capture the Red Angel. A landing party consisting of Hugh Culber, Paul Stamets, Philippa Georgiou, Spock, and Michael Burnham beamed down to the surface. While the team worked on the surface, on board NCIA-93, Ash Tyler and Leland worked to close the wormhole to prevent the Angel from leaving.
After enacting their plan to attract the Red Angel, which involved exposing Burhnam to the toxic atmosphere of the planet, they waited for the Angel to arrive. The plan worked and a burst soon appeared in orbit of the planet. The Angel arrived on the surface and revived Burnham; after which she was captured and revealed to be Burnham's mother. (DIS: "The Red Angel")