Betelgeuse in 2015, before recent dimming. Distance from Earth to the sun Betelgeuse in 2015, before recent dimming. Distance from Earth to the sun Betelgeuse in 2015, before recent dimming. Distance from Earth to the sun Betelgeuse in 2015, before recent dimming. Distance from Earth to the sun

A Fading Giant

Around 700 years ago, the red star Betelgeuse began to fade. The light from that unusual dimming is only now reaching Earth, some 700 light-years away.

Betelgeuse is normally one of the 10 brightest stars in the sky, but is now fainter than ever recorded.

Magnitude 0 0.5 1.0 Betelgeuse now ▶ 1.5 1995 2000 2005 2010 2015 2020 Magnitude 0 0.5 1.0 1.5 Betelgeuse now ▶ 2000 2005 2010 2015 2020 Magnitude 0 0.5 1.0 1.5 Betelgeuse now ▶ 2010 2015 2020 Magnitude 0 0.5 1.0 Betelgeuse now ▶ 1.5 2015 2020

Betelgeuse typically fades and brightens in short cycles of 14 months and longer cycles of about six years. Overlapping cycles might explain the dimming, or clouds of debris might be obscuring the starlight.

Or the star might be about to explode.

Orion’s Shoulder

Betelgeuse is a red supergiant in the constellation Orion, and is more of a swollen, churning blob than a crisp sphere like our sun.

A simulation of a red supergiant. B. Freytag, S. Höfner, S. Liljegren (Uppsala University)

The star has only 10 to 20 times the mass of the sun, but Betelgeuse is so vast and diffuse that in our solar system it would engulf the orbits of Jupiter and all the inner planets.

Bellatrix Betelgeuse Betelgeuse ORION Orion Nebula Rigel Saiph Bellatrix Betelgeuse Betelgeuse ORION Orion Nebula Rigel Saiph Bellatrix Betelgeuse Betelgeuse ORION Orion Nebula Rigel Saiph Bellatrix Betelgeuse ORION Orion Nebula Rigel Saiph Orion and the stellar nursery of the Orion Nebula Photo by Rogelio Bernal Andreo

An Element Factory

Betelgeuse is a young star near the end of its life. It formed about 8 million years ago, when the far distant ancestors of humans were just beginning to split away from the great apes.

The newborn star spent millions of years fusing hydrogen into helium, then helium into heavier elements.

PERIODIC TABLE OF THE ELEMENTS Lighter elements created in stars Hydrogen Helium H He Iron Fe Heavier elements created in supernovas Hydrogen Helium H He Iron Lighter elements created in stars Fe PERIODIC TABLE OF THE ELEMENTS Heavier elements created in supernovas Hydrogen Helium H He Iron Lighter elements created in stars Fe PERIODIC TABLE OF THE ELEMENTS Heavier elements created in supernovas

Betelgeuse will keep burning until the atoms in its core finally fuse into iron and the star runs out of fuel. When that will happen is unknown — perhaps next year, perhaps 100,000 years from now.

The star will collapse violently and then explode. The resulting supernova will release staggering amounts of energy and create a burst of even heavier elements as it casts debris out into space.

For a while the dying star will be visible in the daytime and shine as bright as the moon.

Betelgeuse before dimming. ESO/Digitized Sky Survey

Supernova 1987A

The most recent nearby supernova bloomed in the southern hemisphere in Feb. 1987 and has been closely studied for over 30 years.

NASA/Space Telescope Science Institute

Today the remnants of that supernova are visible as a blurry cloud of debris expanding inside an older, bright ring.

NASA/ESA/R. Kirshner and P. Challis, Harvard-Smithsonian Center for Astrophysics/Digitized Sky Survey

A New Star in 1604

The last visible supernova in our Milky Way galaxy appeared in 1604 and faded the following year.

Johannes Kepler compiled a book of observations of the new star.

California Institute of Technology

The elements that formed in Kepler’s supernova are still expanding outward. Some day those atoms may shape other stars and planets, just as our bodies are made from elements forged billions of years ago in unseen supernovas.

NASA/Chandra X-ray Center/Smithsonian Astrophysical Observatory/D. Patnaude







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Betelgeuse image by ALMA (European Southern Observatory/National Astronomical Observatory of Japan/National Radio Astronomy Observatory)/E. O’Gorman/P. Kervella. Magnitude data from the American Association of Variable Star Observers. Sources: NASA; ESA; AAVSO; The Astronomer’s Telegram.



