T Coronae Borealis

T Coronae Borealis (abbreviated T CrB or unofficially T Cor Bor)^[19] is the star's variable star designation and is its most commonly used name. It also has the Bright Star Catalogue designation HR 5958 and the Henry Draper Catalogue designation HD 143454.^[11]

The proper name Blaze Star^[20] has been used since its outburst in 1866, and was officially approved by the IAU Working Group on Star Names on 22 September 2025.^[21]

T CrB normally has a magnitude of about 10, which is near the limit of typical binoculars. Two well-documented outbursts have been observed, reaching magnitude 2.0 on May 12, 1866 and magnitude 3.0 on February 9, 1946,^[22] though a more recent paper shows the 1866 outburst with a possible peak range of magnitude 2.5±0.5.^[23] When at peak magnitude of 2.5, this recurrent nova is dimmer than about 100 brightest stars in the night sky,^[24] but easily visible to the naked eye.

T CrB is a binary system containing a large cool component and a smaller hot component. The cool component is a red giant that transfers material to the hot component.^[3] The hot component, which initially was the most massive and brightest of the two stars, is now a white dwarf surrounded by an accretion disc, all hidden inside a dense cloud of material from the red giant. When the system is quiescent, the red giant dominates the visible light output and the system appears as an M3 giant. The hot component contributes some emission and dominates the ultraviolet output. During outbursts, the transfer of material to the hot component increases greatly, the hot component expands, and the overall luminosity of the system increases by orders of magnitude.^{[10][25][26][27]}

The two components of the system orbit each other every 227.5528 d. The orbit is almost circular and is inclined at an angle of 61.5°. The separation between the components is 0.960 AU.^[5]

On April 20, 2016, Sky & Telescope reported a sustained brightening since February 2015 from magnitude 10.5 to about 9.2. A similar event was reported in 1938, 8 years before the  1946 outburst.^[28] By June 2018, the star had dimmed slightly but still remained at an unusually high level of activity. By mid-2023, it had faded by 0.35 magnitude or about 28%;^[a] its lowest brightness seen since 2016.^[29] A similar dimming occurred in the year before the 1946 outburst,^[30] leading some to predict an eruption before September 2024.^[31] It has repeatedly been predicted to be imminent, but several predictions have lapsed as of May 2026 and no such nova has yet been observed.^[30]