Is Betelgeuse getting ready to explode?

Since 1604, astronomers have awaited the Milky Way’s next naked-eye supernova.

In the year 1054, the brightest supernova in recorded history, as seen from Earth, took place. Nearly 1000 years later, the Crab Nebula, pulsar, and supernova remnant can all be seen as the aftermath of this supernova event.

Many look to Betelgeuse, a nearby red supergiant star, as a potential candidate.

The black hole at the center of the Milky Way should be comparable in size to the physical extent of the red giant star Betelgeuse: larger than the extent of Jupiter’s orbit around the Sun. Betelgeuse was the first star of all beyond our Sun to be resolved as more than a point of light, but other red supergiants, such as Antares and VY Canis Majoris, are known to be larger and may actually be further on the path to becoming a type II supernova than Betelgeuse is.

Although it’s only ~8-10 million years old, Betelgeuse is in its final evolutionary stage.

This illustration shows the anatomy of the interior of a red supergiant, like Betelgeuse or Antares. Although the full extent of Betelgeuse is even larger than Jupiter’s orbit around the Sun, the extent of Antares goes almost to Saturn as measured by the end of the upper chromosphere. Its luminous Wind Acceleration Zone goes all the way out almost to the extent of Uranus’s orbit.

Its core fuses elements in layers, with carbon, neon, and/or oxygen fusing in the center.

Artist’s illustration (left) of the interior of a massive star in the final stages, pre-supernova, of silicon-burning. (Silicon-burning is where iron, nickel, and cobalt form in the core.) A Chandra image (right) of the Cassiopeia A supernova remnant today shows elements like Iron (in blue), sulfur (green), and magnesium (red). Betelgeuse is expected to follow a very similar pathway to previously observed core-collapse supernovae, although we do not know which of carbon, neon, and oxygen fusion are occurring inside it.

Meanwhile, its outer layers vary tremendously: in size, temperature, and brightness.

This simulation of a red supergiant’s surface, sped up to display an entire year of evolution in just a few seconds, shows how a “normal” red supergiant evolves during a relatively quiet period with no perceptible changes to its interior processes. The enormity of its surface and the volatility of the tenuous outer layers leads to tremendous variability on short but irregular timescales.

At some critical moment, Betelgeuse will exhaust its core’s nuclear fuel, dying in a type II supernova.

At some critical stage in the evolution of a red giant, an inner “ash” core of iron, nickel and cobalt will implode, leading to a “shock breakout” event at the surface of the star: the first eruption of a core-collapse supernova. 20 minutes later, the full fury of the shockwave reaches the surface and the doomed star blasts apart as a supernova explosion.

When this occurs, it will reach a maximum brightness of 10,000,000,000 Suns.

In 2011, one of the stars in a distant galaxy that happened to be in the field of view of NASA’s Kepler mission spontaneously and serendipitously went supernova. This marked the first time that a supernova was caught occurring in the act of transitioning from a normal star to a supernova event, with a surprising ‘breakout’ temporarily increasing the star’s brightness by a factor of about 7,000 over its previous value.

Several millions of neutrinos will appear in Earth’s neutrino detectors.

Neutrino and antineutrino detectors operate by having a large “target” for neutrinos/antineutrinos to interact with inside of a tank surrounded by photomultiplier tubes, which allow scientists to reconstruct the event characteristics that happened at the source.

In Earth’s skies, this explosion will match the full Moon’s brightness, but be concentrated at a single point.

The constellation Orion as it would appear if Betelgeuse went supernova in the very near future. The star would shine approximately as brightly as the full Moon, but all the light would be concentrated to a point, rather than extended over a disk that covers approximately half a degree. Peak brightness should be achieved roughly two weeks after the initial explosion.

It could happen tomorrow, or up to ~100,000 years from now.

The Wolf-Rayet star WR 124 and the surrounding nebula M1-67, as imaged by Hubble, both owe their origin to the same originally massive star that blew off its hydrogen-rich outer layers. The central star is now far hotter than what came before, as Wolf-Rayet stars typically have temperatures between 100,000 and 200,000 K, with some stars cresting even higher. Could a star like this, rather than Betelgeuse, be our galaxy’s next naked-eye supernova? Only time will tell.

In 2019/2020, Betelgeuse dimmed severely in a notable astronomical event.

Betelgeuse has given off large amounts of gas and dust over its history, filling the interstellar medium surrounding it with matter, which gets illuminated in infrared light. This image was taken in December of 2019, based on data obtained with the VISIR instrument aboard the ESO’s Very Large Telescope.

But it then re-brightened, having merely “belched” a significant cloud of dust.

In late 2019, Betelgeuse dimmed by a large amount in brightness, having fallen to a low of about one-third of its normal brightness from early 2019 to early 2020. In April 2020, however, Betelgeuse returned to its normal range of brightnesses, with the culprit being a large “burp” of dust having been emitted by the star.

However, since mid-April 2023, it’s newly brightened further.

This graph shows the apparent brightness of Betelgeuse from 2015-2023, with data from the American Association for Variable Star Observers (AAVSO). The large dimming event from 2019-2020 stands out on the graph, but the recent brightening is very surprising.

It’s presently our 7th brightest star, surpassing Achernar, Procyon, and Rigel.

Although Betelgeuse is an intrinsically variable star, it does not normally shine as bright as it has been from mid-to-late April, 2023 until the present over such a sustained period in a very long time. Currently shining at 142% of its normal brightness, many wonder what is going on in Betelgeuse’s interior.

Both collapse,

In the inner regions of a star that undergoes a core-collapse supernova, a neutron star begins to form in the core, while the outer layers crash against it and undergo their own runaway fusion reactions. Neutrons, neutrinos, radiation, and extraordinary amounts of energy are produced, with neutrinos and antineutrinos carrying the majority of the core-collapse supernova’s energy away.

and the final pre-supernova (silicon-burning) phase will generate detectable antineutrinos.

The electromagnetic output (left) and the spectrum of neutrino/antineutrino energies (right) produced as a very massive star comparable to Betelgeuse evolves through carbon, neon, oxygen, and silicon-burning on its way to core-collapse. Note how the electromagnetic signal barely varies at all, while the neutrino signal crosses a critical threshold on the way toward core-collapse.

That only provides hours of advance warning, however.

A supernova explosion enriches the surrounding interstellar medium with heavy elements. This illustration, of the remnant of SN 1987a, showcases how the material from a dead star gets recycled into the interstellar medium. In addition to light, we also detected neutrinos from SN 1987a. With the LIGO and Virgo detectors now functional, it’s possible that the next supernova within the Milky Way will yield a triple multi-messenger event, delivering particles (neutrinos), light, and gravitational waves all together.

Supernovae occur, but “when” is otherwise unpredictable.

This Wolf–Rayet star is known as WR 31a, located about 30,000 light-years away in the constellation of Carina. The outer nebula is expelled hydrogen and helium, while the central star burns at over 100,000 K. In the relatively near future, many suspect that this star will explode in a supernova much like WR 124, enriching the surrounding interstellar medium with new, heavy elements. It cannot be predicted which evolved, massive star in our galaxy will be the Milky Way’s next supernova.

Mostly Mute Monday tells an astronomical story in images, visuals, and no more than 200 words. Talk less; smile more.