A 3D model predicts the X-ray emission of the next nearby nova, T Coronae Borealis. The study: “Predicting the X-ray signatures of the imminent T Coronae Borealis outburst through 3D hydrodynamic modeling” of S. Orlando (INAF – OAPA) appeared on A&A

A new star may soon light up our sky, becoming visible even at naked eye. It is T Coronae Borealis, a recurrent nova located just under 3000 light-years away from us. In fact, it is the closest known object of this class to Earth.

A nova is a system characterized by periodic explosions accompanied by sudden increases in brightness. These are binary systems composed of an evolved star (a red giant) and a compact object, typically a white dwarf. The latter accretes material from its companion: the gas drawn from the giant forms an accretion disk before falling onto the surface of the white dwarf.
The eruption occurs when the accumulated material reaches temperatures and pressures high enough to trigger an uncontrolled thermonuclear reaction.

T Coronae Borealis is therefore the nearest recurrent nova, at a distance of about 3000 light-years—roughly half that of the next closest object of the same class, RS Ophiuchi (5300 light-years).
But its proximity is not the only reason for its scientific interest. Its last recorded eruptions occurred in 1866 and 1946, about 80 years apart. If this interval hides a true periodicity, the next eruption could therefore occur in 2026, becoming visible at naked eye in the constellation of the Corona Borealis.
This possibility is supported by several recent observations showing an increase in the accretion rate onto the white dwarf, variations in optical brightness, and enhanced high-energy activity.

Many astronomers are preparing for this potential event. Among them is the team led by astrophysicist S. Orlando (INAF – Osservatorio Astronomico di Palermo), who recently published three-dimensional simulations of the explosion aimed at predicting the X-ray emission from T Coronae Borealis.
To obtain realistic simulations, the morphology and physical properties of the system were constrained using available inter-eruption observations, particularly in the radio band. In addition to the white dwarf and the red giant, the model includes the accretion disk, the circumbinary material produced by the giant wind — with a mass-loss rate of about four billionths of a solar mass per year and a density of roughly one million particles per cubic centimeter — as well as an equatorial overdensity in the shape of a torus.

The simulations reveal that, because of the presence of the disk and the equatorial overdensity, the shock wave generated by the explosion will be strongly asymmetric, propagating preferentially along the poles with a bipolar geometry. The red giant, impacted by the blast, will further distort the shape of the shock front.

The X-ray emission will thus develop in three main phases, corresponding to different components of the system being hit by the shock wave:

an initial phase (lasting a few hours) of high-energy X-ray emission produced by the material in the accretion disk;
an intermediate phase (lasting a few weeks) dominated by lower-energy emission from the ejecta expelled during the explosion;
a final, longer-lasting phase in which the X-ray emission will arise from the circumbinary medium.

The simulations, their interpretation, and the model’s predictions are presented in the paper “Predicting the X-ray signatures of the imminent T Coronae Borealis outburst through 3D hydrodynamic modeling”, recently published in Astronomy & Astrophysics.

T Coronae Borealis is also the subject of a long-term monitoring campaign with the automated telescope of INAF – Astronomical Observatory of Palermo, aimed at tracking its variability up to the next outburst.

The cover image (click here to view it in full) shows the evolution of the shock wave in T Coronae Borealis as predicted by the model.
Each panel represents the system and the ejected fragments at different times, as indicated in the top-right corner.
Colors represent the density of the material, while the transparent gray surface marks the position of the shock front.
Also visible are the red giant (in orange), the accretion disk around the white dwarf (in violet), the equatorial overdensity (in light blue), and arrows indicating the direction of the material’s motion.

It should be noted that the scale of the panels increases with time, which makes the relative sizes of the red giant and the other components appear progressively smaller.

There are also 3D models available for virtual reality viewing: one depicts one of the models used in the paper (https://skfb.ly/ptZNy), while the second offers an artistic visualization of T Coronae Borealis (https://skfb.ly/pzB6Z).