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Starts With A Bang

Is Betelgeuse getting ready to explode?

A new, unexpected brightening, just 3 years after a massive dimming event, has astronomers watching Betelgeuse. Is a supernova imminent?
Betelgeuse visualization
Observation of the red supergiant star, Betelgeuse, revealed a vast plume of gas almost as large as our Solar System and a gigantic bubble boiling on its surface. In 2019-2020, a great plume of material erupted from Betelgeuse. With a recent brightening event now occurring, could a supernova be imminent?
Credit: ESO/L. Calçada
Key Takeaways
  • Betelgeuse, normally the 10th brightest star in the sky, has brightened over the past month to creep up to 7th place on the list of brightest stars.
  • Although Betelgeuse is an intrinsically variable star, we don't yet know: is this just a normal phase in its variability, or is it preparing to go supernova?
  • An unexpected source, the humble neutrino, will be the only indication we have as far as advance warning goes. The truth is, it could go at any time.

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

Crab nebula multiwavelength
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.
Credit: NASA, ESA, G. Dubner (IAFE, CONICET-University of Buenos Aires) et al.; A. Loll et al.; T. Temim et al.; F. Seward et al.; VLA/NRAO/AUI/NSF; Chandra/CXC; Spitzer/JPL-Caltech; XMM-Newton/ESA; and Hubble/STScI

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

Betelgeuse alpha orionis direct image
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.
Credit: Andrea Dupree (Harvard-Smithsonian CfA), Ronald Gilliland (STScI), NASA and ESA

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

red supergiant anatomy
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.
Credit: NRAO/AUI/NSF, S. Dagnello

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

interior of a core-collapse supernova and element locations
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.
Credits: NASA/CXC/M.Weiss (illustration, left) NASA/CXC/GSFC/U. Hwang & J. Laming (image, right)

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

red supergiant outer layers simulation
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.
Credit: Bernd Freytag, Susanne Höfner & Sofie Liljegren

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

exploding star shockwave evolve from red supergiant
Many of the cataclysms that occur in space are typical supernovae: either core-collapse or Type Ia. The most massive stars of all have hundreds of times the mass of the Sun and live just 1 or 2 million years, total, before running out of fuel and dying in such a cataclysm.
Credit: NASA Ames, STScI/G. Bacon

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

a line graph showing the speed of a rocket.
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.
Credit: NASA Ames/W. Stenzel

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

antineutrino detector daya bay
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.
Credit: Roy Kaltschmidt, Lawrence Berkeley National Laboratory; Daya Bay Antineutrino detector

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

Betelgeuse supernova
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.
Credit: HeNRyKus/Wikimedia Commons

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

Hubble WR 124
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.
Credit: ESA/Hubble & NASA; Acknowledgement: Judy Schmidt (

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

Betelgeuse dust gas 2019
The nebula of expelled matter created around Betelgeuse, which, for scale, is shown in the interior red circle. This structure, resembling flames emanating from the star, forms because the behemoth is shedding its material into space. The extended emissions go beyond the equivalent of Neptune’s orbit around the Sun. Betelgeuse alone has about a 1-in-4,000 chance of having already died.
Credit: ESO/P. Kervella/M. Montargès et al.; Acknowledgement: Eric Pantin

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

Betelgeuse 2019 2020 dust
Whereas Betelgeuse, as shown here, dimmed and then re-brightened due to a surface event intrinsic to the star itself, other mechanisms for stellar dimming, including dust, debris, and other light-blocking phenomena, are more common around lower-mass, young stellar systems.
Credit: ESO/M. Montargès et al.

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

Betelgeuse Brightness 2015-2023
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.
Credit: Rami Maddow/Twitter

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

Betelgeuse brightness May 2023
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.
Credit: @betelbot/Twitter

Both collapse,

diagram of core-collapse supernova anatomy
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.
Credit: TeraScale Supernova Initiative/Oak Ridge National Lab

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

brightness and neutrino flux as a massive star evolves
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.
Credit: A. Odrzywolek, 2015

That only provides hours of advance warning, however.

Sn 1987a remnant
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. However, precisely what’s occurring at the center of the remnant is obscure, as even JWST’s powerful NIRCam imager cannot fully penetrate the light-blocking dust to see inside.
Credit: ESO/L. Calçada

Supernovae occur, but “when” is otherwise unpredictable.

wolf rayet wr 31a
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.
Credit: ESA/Hubble & NASA; Acknowledgement: Judy Schmidt

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


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