https://en.wikipedia.org/wiki/Betelgeuse#After_core_hydrogen_exhaustion wrote:
<<Betelgeuse's time spent as a red supergiant can be estimated by comparing mass loss rates to the observed circumstellar material, as well as the abundances of heavy elements at the surface. Estimates range from 20,000 years to a maximum of 140,000 years. Betelgeuse appears to undergo short periods of heavy mass loss and is a runaway star moving rapidly through space, so comparisons of its current mass loss to the total lost mass are difficult. The surface of Betelgeuse shows enhancement of nitrogen, relatively low levels of carbon, and a high proportion of
13C relative to
12C, all indicative of a star that has experienced the first dredge-up. However, the first dredge-up occurs soon after a star reaches the red supergiant phase and so this only means that Betelgeuse has been a red supergiant for at least a few thousand years. The best prediction is that Betelgeuse has already spent around 40,000 years as a red supergiant, having left the main sequence perhaps one million years ago.
The current mass can be estimated from evolutionary models from the initial mass and the expected mass lost so far. For Betelgeuse, the total mass lost is predicted to be no more than about one M
☉, giving a current mass of 19.4–19.7 M
☉, considerably higher than estimated by other means such as pulsational properties or limb-darkening models.
All stars more massive than about 10 M
☉ are expected to end their lives when their core collapses, typically producing a supernova explosion. Up to about 15 M
☉, a type II-P supernova is always produced from the red supergiant stage. More massive stars can lose mass quickly enough that they evolve towards higher temperatures before their cores can collapse, particularly for rotating stars and models with especially high mass loss rates. These stars can produce type II-L or type IIb supernovae from yellow or blue supergiants, or type Ib/c supernovae from Wolf-Rayet stars. Models of rotating 20 M
☉ stars predict a peculiar type II supernova similar to SN 1987A from a blue supergiant progenitor. On the other hand, non-rotating 20 M
☉ models predict a type II-P supernova from a red supergiant progenitor.
The time until Betelgeuse explodes depends on the predicted initial conditions and on the estimate of the time already spent as a red supergiant. The total lifetime from the start of the red supergiant phase to core collapse varies from about 300,000 years for a rotating 25 M
☉ star, 550,000 years for a rotating 20 M
☉ star, and up to a million years for a non-rotating 15 M
☉ star. Given the estimated time since Betelgeuse became a red supergiant, estimates of its remaining lifetime range from a "best guess" of under 100,000 years for a non-rotating 20 M
☉ model to far longer for rotating models or lower-mass stars. Betelgeuse's suspected birthplace in the Orion OB1 Association is the location of several previous supernovae. It is believed that runaway stars may be caused by supernovae, and there is strong evidence that OB stars μ Columbae, AE Aurigae and 53 Arietis all originated from such explosions in Ori OB1 2.2, 2.7 and 4.9 million years ago.
A typical type II-P supernova emits 2×10
46 J of neutrinos and produces an explosion with a kinetic energy of 2×10
44 J. As seen from Earth, it would have a peak apparent magnitude of about −12.4. It may outshine the full moon and would be easily visible in daylight. This type of supernova would remain at roughly constant brightness for 2–3 months before rapidly dimming. The visible light is produced mainly by the radioactive decay of cobalt, and maintains its brightness due to the increasing transparency of the cooling hydrogen ejected by the supernova.
Due to misunderstandings caused by the 2009 publication of the star's 15% contraction, apparently of its outer atmosphere, Betelgeuse has frequently been the subject of scare stories and rumors suggesting that it will explode within a year, leading to exaggerated claims about the consequences of such an event. The timing and prevalence of these rumors have been linked to broader misconceptions of astronomy, particularly to doomsday predictions relating to the Mayan calendar. Betelgeuse is not likely to produce a gamma-ray burst and is not close enough for its x-rays, ultraviolet radiation, or ejected material to cause significant effects on Earth. Following the dimming of Betelgeuse in December 2019,reports appeared in the science and mainstream media that again included speculation that the star might be about to go supernova – even in the face of scientific research that a supernova is not expected for perhaps 100,000 years. Some outlets reported the magnitude as faint as +1.3 as an unusual and interesting phenomenon, like Astronomy magazine, the National Geographic, and the Smithsonian magazine. Some mainstream media, like The Washington Post, ABC News in Australia, and Popular Science, reported that a supernova was possible but unlikely, whilst other outlets portrayed a supernova as a realisitic possibility. CNN, for example, chose the headline "A giant red star is acting weird and scientists think it may be about to explode," while The New York Post declared Betelgeuse as "due for explosive supernova." Phil Plait has again written to correct what he calls "Bad Astronomy," noting that Betelgeuse's recent behaviour "[w]hile unusual ... isn't unprecedented. Also, it probably won't go bang for a long, long time."
Following Betelgeuse's supernova, a small dense remnant will be left behind, either a neutron star or black hole. Betelguese does not have a core massive enough for a black hole so the remnant is predicted to be a neutron star of approximately 1.5 M
☉.>>