Our nearest stellar neighbour will keep shining for another four trillion years
Proxima Centauri, the closest star after the Sun at 4.25 light-years, is too dim to see without a telescope. Yet this small red dwarf will outlast the Sun by an enormous margin, staying on the main sequence for roughly four trillion more years, because it churns and burns nearly all of its fuel.
The trick is convection. Proxima's interior is fully convective, so the plasma itself carries energy outward and stirs the helium ash from fusion throughout the star instead of letting it pile up in the core. The Sun will use only about a tenth of its hydrogen before leaving the main sequence; Proxima will burn almost all of its supply, and slowly, giving off just 0.16% of the Sun's total light, over 85% of it as infrared.
It is tiny but dense. Robert Innes discovered it in 1915, and interferometry in 2002 put its diameter at about a seventh of the Sun's, or 1.5 times Jupiter's, with around 12% of the Sun's mass. That makes it about 33 times denser on average than the Sun, with surface gravity 162 times Earth's. It belongs to the Alpha Centauri system, circling the bright pair from roughly 12,950 astronomical units away once every 550,000 years or so.
The same churning powers a strong magnetic field and violent flares that can briefly brighten the whole star and reach 27 million K. On 6 May 2019 it produced the brightest flare yet recorded from it. Even when calm, its corona runs at 3.5 million K against the Sun's 2 million, and its X-ray output matches the far larger Sun's.
Two planets are confirmed. Proxima b, at least 1.06 Earth masses, circles every 11.2 days inside the zone where liquid water could exist, though the flares make its habitability very uncertain. Proxima d, smaller than Earth, orbits every 5.1 days, and a disputed third world, Proxima c, may take about 1,900 days.
Source: Proxima Centauri
