T Coronae Borealis

T Coronae Borealis

Location of T Coronae Borealis (circled in red)
Observation data Epoch J2000      Equinox J2000
Constellation	Corona Borealis
Right ascension	15h 59m 30.1622s[1]
Declination	+25° 55′ 12.613″[1]
Apparent magnitude (V)	2.0–10.8[2]
Characteristics
Evolutionary stage	Red giant + white dwarf[3]
Spectral type	M3III+p[4]
Variable type	recurrent nova[2]
Astrometry
Radial velocity (Rv)	−27.75±0.04[5] km/s
Proper motion (μ)	RA: −4.461 mas/yr[1] Dec.: 12.016 mas/yr[1]
Parallax (π)	1.0920±0.0275 mas[1]
Distance	2,990 ± 80 ly (920 ± 20 pc)
Absolute magnitude (MV)	+0.16 (min.)[6]
Orbit[5]
Period (P)	227.5528±0.0002 days
Semi-major axis (a)	0.960 AU
Eccentricity (e)	0.009±0.003[7]
Inclination (i)	61.5°
Periastron epoch (T)	2459978.37±0.08
Semi-amplitude (K1) (primary)	23.90±0.05 km/s
Details
Red giant
Mass	0.93[5] M☉
Radius	63.5±0.3[8] – 71.1[5] R☉
Luminosity	583±4[8] L☉
Surface gravity (log g)	0.672+0.009 −0.007[8] cgs
Temperature	3,561±3[8] K
Metallicity [Fe/H]	+0.20+0.05 −0.03[8] dex
Rotational velocity (v sin i)	4.75±0.26[5] km/s
White dwarf
Mass	1.35[5] M☉
Radius	0.0045[9] R☉
Luminosity	~100[10] L☉
Other designations
Blaze Star, T CrB, AAVSO 1555+26, BD+26°2765, HD 143454, HIP 78322, HR 5958, SAO 84129, 2MASS J15593015+2555126[11]
Database references
SIMBAD	data

T Coronae Borealis is a binary star and a recurrent nova about 3,000 light-years (920 parsecs) away in the constellation Corona Borealis.[12] It has the official proper name Blaze Star, T Coronae Borealis is the variable-star designation. The system was first observed in outburst in 1866 by John Birmingham,[13] though it had been observed earlier in quiescence as a 10th magnitude star.[14] It may have been observed in 1217 and in 1787 as well.[15][16] In February 1946, Michael Woodman, a 15-year-old schoolboy from Wales, observed a flare‐up, subsequently writing to the Astronomer Royal and leading to the theory that the star flares every 80 years,[17] with the next nova expected to occur before 2027.

T Coronae Borealis (abbreviated T CrB or unofficially T Cor Bor)[18] is the star's variable star designation. It also has the Bright Star Catalogue designation HR 5958 and the Henry Draper Catalogue designation HD 143454.[11]

The proper name Blaze Star[19] has been used since its outburst in 1866, and was officially approved by the IAU Working Group on Star Names on 22 September 2025.[20]

The light curve of T Coronae Borealis during the time surrounding its 1946 eruption, plotted from AAVSO data

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,[21] though a more recent paper shows the 1866 outburst with a possible peak range of magnitude 2.5±0.5.[22] Even when at peak magnitude of 2.5, this recurrent nova is dimmer than about 100 brightest stars in the night sky,[23] but easily visible to the naked eye.

Diagram of T Coronae Borealis based on a description given by Kraft[3] using the updated mass ratio given by Stanishev[10]

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 is 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 luminosity of the system increases by orders of magnitude.[10][24][25][26]

AAVSO light curve of recurrent nova T CrB from Jan 1, 2008 to Nov 17, 2010, showing rotating ellipsoidal variability. Up is brighter and down is fainter. Day numbers are Julian day.

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 radius of the orbit of the primary component around the center of mass 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, followed by another outburst in 1946.[27] 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.[28] A similar dimming occurred in the year before the 1946 outburst,[29] leading some to predict an eruption before September 2024.[30] As of February 2026, such a nova has not yet been observed, although some have predicted it is imminent.[29]

Predictions of the next nova (in order of when the prediction was made):

• Wallerstein, George; Tanya Harrison; Ulisse Munari; Andrew Vanture (May 11, 2008). "The Metallicity and Lithium Abundances of the Recurring Novae T CrB and RS Oph". Publications of the Astronomical Society of the Pacific. 120 (867). University of Chicago Press: 492–497. Bibcode:2008PASP..120..492W. doi:10.1086/587965. ISSN 1538-3873. OCLC 40768120. S2CID 106406607.
• MacRobert, Alan M. (April 6, 2012). Naeye, Robert (ed.). "R and T Coronae Borealis: Two Stellar Opposites". Sky & Telescope. Sky Publishing. ISSN 0037-6604. OCLC 1765612. Archived from the original on April 6, 2012.

• Blaze Star, The Worlds of David Darling
• AAVSO: Check Recent Observations (get recent magnitude estimates for T CrB)