Betelgeuse Dimming and Brightening

The bright orange star at the shoulder of the Orion constellation has captivated stargazers for centuries, but its behavior in recent years has shifted from routine to erratic. Betelgeuse is a red supergiant that typically brightens and dims in a predictable cycle. However, recent events—specifically a dramatic dimming in 2019 followed by a surprising brightening in 2023—have astronomers scrambling to understand what is happening inside this dying star. This erratic pulsing offers scientists a front-row seat to the final stages of stellar evolution and fuels the debate on when Betelgeuse will finally go supernova.

The Great Dimming of 2019

To understand the current erratic behavior, you must look back to late 2019. For decades, Betelgeuse appeared as one of the top ten brightest stars in the night sky. In October 2019, it began to fade significantly. By February 2020, it had dropped to approximately 40% of its normal brightness, reaching a magnitude of +1.61. This was the faintest the star had been since measurements began over a century ago.

Initial speculation ran wild. Many enthusiasts hoped this was the “calm before the storm,” indicating a supernova was imminent. However, data from the Hubble Space Telescope and other observatories revealed a different cause.

The Dust Cloud Theory

Andrea Dupree, a senior astrophysicist at the Center for Astrophysics (Harvard & Smithsonian), led the research that solved the mystery. The star had experienced a massive Surface Mass Ejection (SME). In simple terms, Betelgeuse “burped” out a massive chunk of its surface material. This material shot out into space, cooled down, and formed a dense cloud of dust. From our perspective on Earth, this dust cloud blocked the light from the star, making it appear dimmer than usual.

The Recent Brightening and Erratic Pulsing

Following the Great Dimming, Betelgeuse did not simply return to normal. Instead, it swung to the opposite extreme. Throughout 2023 and into 2024, the star became unusually bright, at times shining at 150% of its normal luminosity. It briefly overtook Rigel (Orion’s foot) and Capella to become the seventh-brightest star in the sky.

This brightening is a direct consequence of the 2019 ejection. The star is currently recovering from that trauma. The ejection left the star with a cool patch on its surface and disrupted its internal rhythm. Imagine a bell that has been struck hard; it continues to ring and vibrate long after the initial hit. Betelgeuse is currently “ringing” as its photosphere tries to stabilize.

A Broken Rhythm

Before 2019, Betelgeuse had a very reliable heartbeat. It pulsed on a primary cycle of about 400 days. Since the ejection, that 400-day cycle has seemingly vanished. Currently, the star is pulsing on a much shorter, faster rhythm of approximately 185 days. This shift in frequency is what the snippet refers to as “erratic pulsing.” Astronomers use this data to model the internal pressure and convection currents of the star, looking for signs of instability that lead to core collapse.

Predicting the Supernova

The question everyone wants answered is: When will it explode?

A supernova occurs when a massive star runs out of fuel. Without the outward pressure of nuclear fusion to hold it up, gravity wins. The core collapses in a fraction of a second, resulting in a colossal explosion.

The Carbon vs. Helium Debate

The timing depends entirely on what the star is currently burning in its core.

• Helium Burning: Most astrophysicists believe Betelgeuse is currently fusing helium into carbon. If this is the case, the star has roughly 100,000 years of life left.
• Carbon Burning: A controversial paper published in 2023 by Hideyuki Saio and colleagues suggested the 185-day pulse indicates the star is already burning carbon. If true, the star could explode within a few decades.

However, the consensus among the wider scientific community remains with the helium model. The erratic behavior is viewed as surface instability caused by the 2019 mass ejection rather than a sign of core collapse. While the star is certainly near the end of its life in cosmic terms, it is likely not going to explode next Tuesday.

What We Will See

When Betelgeuse does finally go supernova, it will be a spectacle unlike anything modern humanity has witnessed.

• Brightness: It will shine as bright as the half-moon.
• Visibility: It will be visible during the day for several months.
• Shadows: At night, the light from the exploding star will be strong enough to cast distinct shadows on Earth.

Understanding the Red Supergiant

To grasp why these changes matter, it helps to understand the scale of Betelgeuse. This is not a star like our Sun. It is a monster.

• Size: If you placed Betelgeuse at the center of our solar system, its surface would extend past the orbit of Jupiter. It is roughly 700 to 1,000 times wider than the Sun.
• Distance: It sits approximately 650 light-years away. This is close enough to be studied in detail but far enough that its explosion poses no danger to Earth.
• Structure: Unlike the Sun, which is a dense ball of plasma, Betelgeuse is a diffuse, vacuum-like cloud of hot gas. Its surface is not solid or smooth; it boils with massive convection cells. Some of these boiling bubbles are larger than our entire solar system.

How Astronomers Track the Changes

Continuous monitoring is required to make sense of the erratic pulsing. Professional observatories like the Very Large Telescope (VLT) in Chile use adaptive optics to image the surface of the star directly. They can actually see the bright and dark spots shifting on the star’s face.

However, amateur astronomers provide a massive amount of critical data. Organizations like the AAVSO (American Association of Variable Star Observers) collect thousands of brightness estimates from backyard telescopes. Because Betelgeuse is so bright, it is difficult for sensitive space telescopes like James Webb to look at it without being blinded. This makes amateur visual observations and ground-based data vital for tracking the daily and weekly changes in the star’s magnitude.

Frequently Asked Questions

Is Betelgeuse going to explode soon? It is unlikely to explode in our lifetime. While the star is erratic, most data suggests it is still in the helium-burning phase, meaning it has roughly 100,000 years left. However, in astronomical terms, this is very “soon.”

Will the supernova hurt Earth? No. Betelgeuse is about 650 light-years away. For a supernova to strip Earth’s ozone layer or cause radiation damage, the star would need to be within 50 light-years. We will get a spectacular light show, but no physical harm.

Why does the star look red? The color comes from its surface temperature. Betelgeuse is much cooler than our Sun (about 3,500 Kelvin compared to the Sun’s 5,778 Kelvin). Cooler stars emit more light in the red part of the spectrum, while hotter stars appear blue or white.

How can I see Betelgeuse? Look for the constellation Orion. It is usually visible in the evening sky from late autumn to early spring in the Northern Hemisphere. Betelgeuse is the bright, orange-red star at the top left (the shoulder) of the hunter figure. Compare its brightness to Rigel (the blue star at the bottom right) to see the difference.