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1Repair Windows errors before they cause bigger problems2Fix the driver behind crashes, sound loss and screen glitches3Clear out junk files and repair common Windows errorsMagnetars produce powerful X-ray flares by rapidly releasing energy stored in their extreme magnetic fields. A sudden magnetic-field instability—possibly triggered or accompanied by a fracture in the star’s crust—can generate an intense flash of X-rays and gamma rays. In giant flares, radiation and electron–positron pairs may remain trapped near the star, creating a longer, pulsing tail. Scientists have not established one definitive trigger for every flare.
What powers a magnetar flare?
The energy source is magnetic, not simply the star’s rotation. A magnetar is a neutron star with an exceptionally strong magnetic field, and that field stores enough energy to power abrupt, intense high-energy eruptions. As the field changes, stress can build both in the magnetosphere—the region around the star shaped by its field—and in the solid crust.
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The crust and magnetic field are coupled. A change in magnetic stress can contribute to crustal failure, while a crustal disruption can in turn alter the field. The exact order of events in a flare remains unsettled.
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How a giant flare unfolds
1. Stress accumulates
The magnetic field evolves and stores energy. Stress may build in the field around the star, in its crust, or across both connected regions.
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2. An instability releases energy
The leading picture involves a sudden rearrangement of the magnetic field. Magnetic reconnection—when field lines change their arrangement and release energy—is one proposed mechanism. A fracture or shift in the crust, often described as a starquake, could initiate or accompany that rearrangement. These processes are candidates, not a confirmed universal sequence. NASA’s account of the April 2020 event and a 2023 NASA-hosted Gamma-Ray Transient Network report both describe the trigger as unresolved.
3. A sharp high-energy flash appears
A giant flare begins with a brief, bright spike of X-rays and gamma rays. For the April 15, 2020 event, NASA reported that Fermi’s Gamma-ray Burst Monitor resolved the first pulse on a 77-microsecond timescale; the complete initial X-ray/gamma-ray pulse lasted about 140 milliseconds. These are different measurements: the first describes the appearance time of an individual pulse, while the second is the duration of the initial event. Fermi recorded X-rays reaching 3 million electron volts (MeV) in that event, according to NASA’s 2021 report.
4. Trapped radiation can produce a longer tail
After the initial spike, a giant flare can continue as a fluctuating tail. One model holds that the magnetic field confines a hot, dense mixture of radiation and electron–positron pairs—a fireball—in the magnetosphere. The observed spectra are consistent with a confined, Comptonized fireball in a magnetic flux tube, according to the NASA-hosted science report. This is an interpretation of the measurements, not a direct image of the fireball.
As the magnetar rotates, the emitting region moves in and out of view, so the tail’s brightness can pulse. Rotation therefore shapes what observers see after the release; it does not by itself explain the flare’s sudden energy source.
Do starquakes cause magnetar flares?
They may play a role, but the evidence does not show that every flare is caused by a crust-breaking quake. There are several plausible causal arrangements: a crustal fracture could disturb the magnetic field; evolving magnetic stress could crack the crust; or crust and field could respond together as a coupled system. A NASA account of Fermi observations describes this crust–field coupling and discusses oscillations that may reveal the star’s response.
Quasi-periodic oscillations—repeated variations in the late X-ray emission—are interpreted as possible seismic vibrations of the neutron star. They help constrain models, but do not by themselves prove which process triggered the flare. The 2005 ESA discussion of the 2004 SGR 1806-20 event cited a model-based estimate of a fracture about five kilometres across. That estimate concerns this particular event and is not a general measurement of magnetar cracks.
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What observations can—and cannot—tell us
Researchers compare candidate mechanisms against the flare’s timing and pulse structure, oscillations, rotational modulation, and changing spectrum. A 2014 Fermi Symposium abstract discusses relativistic tearing as a candidate reconnection trigger. Such proposals help explain how a rapid release might occur, but the observed features have not singled out one confirmed trigger.
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The April 2020 flare, designated GRB 200415A, provided unusually fine timing data. Commenting on observations of GRB 200415A, associate scientist Oliver Roberts said: “For the first time, GRB 200415A and distant flares like it allow our instruments to capture every feature and explore these powerful eruptions in unparalleled depth.” That level of detail improves the constraints on flare models; it does not mean the trigger has been solved.
Counts of known magnetars and giant flares depend on the date and scope of the source. NASA reported 29 cataloged Milky Way magnetars, two of which had produced giant flares, in its 2021 account. A separate NASA article in 2014 referred to three giant flares observed over the preceding 40 years. Those are dated historical snapshots, not current totals.
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