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Astronomy

Gemini North Discovers Long-Predicted Stellar Companion of Betelgeuse?

By ScientifiCult 21 July 2025

Gemini North Discovers Long-Predicted Stellar Companion of Betelgeuse?

Gemini North telescope in Hawai‘i reveals never-before-seen companion to Betelgeuse, solving millennia-old mystery

Using the NASA-NSF-funded ‘Alopeke instrument on the Gemini North telescope, one half of the International Gemini Observatory, partly funded by the U.S. National Science Foundation (NSF) and operated by NSF NOIRLab, astronomers have discovered a companion star in an incredibly tight orbit around Betelgeuse. This discovery answers the millennia-old question of why this famous star experiences a roughly six-year-long periodic change in its brightness, and provides insight into the physical mechanisms behind other variable red supergiants. The companion star appears blue here because, based on the team’s analysis, it is likely an A- or B-type star, both of which are blue-white due to their high temperatures.‘Alopeke is funded by the NASA-NSF Exoplanet Observational Research Program (NN-EXPLORE). Credit: International Gemini Observatory/NOIRLab/NSF/AURA Image Processing: M. Zamani (NSF NOIRLab) — Gemini North Discovers Long-Predicted Stellar Companion of Betelgeuse. Using the NASA-NSF-funded ‘Alopeke instrument on the Gemini North telescope, one half of the International Gemini Observatory, partly funded by the U.S. National Science Foundation (NSF) and operated by NSF NOIRLab, astronomers have discovered a companion star in an incredibly tight orbit around Betelgeuse. This discovery answers the millennia-old question of why this famous star experiences a roughly six-year-long periodic change in its brightness, and provides insight into the physical mechanisms behind other variable red supergiants. The companion star appears blue here because, based on the team’s analysis, it is likely an A- or B-type star, both of which are blue-white due to their high temperatures.
‘Alopeke is funded by the NASA-NSF Exoplanet Observational Research Program (NN-EXPLORE).
Credit: International Gemini Observatory/NOIRLab/NSF/AURA
Image Processing: M. Zamani (NSF NOIRLab)

Please notice that, according to the published studies, Betelgeuse’s companion might not be a star.

Astronomers have discovered a companion star in an incredibly tight orbit around Betelgeuse using the NASA and U.S. National Science Foundation-funded ‘Alopeke instrument on Gemini North, one half of the International Gemini Observatory, partly funded by the NSF and operated by NSF NOIRLab. This discovery answers the longstanding mystery of the star’s varying brightness and provides insight into the physical mechanisms behind other variable red supergiants.

Photo of the constellation Orion with annotations from IAU and Sky & Telescope. Credit: E. Slawik/NOIRLab/NSF/AURA/M. Zamani — Photo of the constellation Orion with annotations from IAU and Sky & Telescope.
Credit: E. Slawik/NOIRLab/NSF/AURA/M. Zamani

Betelgeuse is one of the brightest stars in the night sky, and the closest red supergiant to Earth. It has an enormous volume, spanning a radius around 700 times that of the Sun. Despite only being ten million years old, which is considered young by astronomy standards, it’s late in its life. Located in the shoulder of the constellation Orion, people have observed Betelgeuse with the naked eye for millennia, noticing that the star changes in brightness over time. Astronomers established that Betelgeuse has a main period of variability of around 400 days and a more extended secondary period of around six years.

Betelgeuse is one of the brightest stars in the night sky, and the closest red supergiant to Earth.Credit: IAU and Sky & Telescope — Betelgeuse is one of the brightest stars in the night sky, and the closest red supergiant to Earth.
Credit: IAU and Sky & Telescope

In 2019 and 2020, there was a steep decrease in Betelgeuse’s brightness — an event referred to as the ‘Great Dimming.’ The event led some to believe that a supernova death was quickly approaching, but scientists were able to determine the dimming was actually caused by a large cloud of dust ejected from Betelgeuse.

The Great Dimming mystery was solved, but the event sparked a renewed interest in studying Betelgeuse, which brought about new analyses of archival data on the star. One analysis led scientists to propose that the cause of Betelgeuse’s six-year variability is the presence of a companion star [1]. But when the Hubble Space Telescope and the Chandra X-Ray Observatory searched for this companion, no detections were made.

The companion star has now been detected for the first time by a team of astrophysicists led by Steve Howell, a senior research scientist at NASA Ames Research Center. They observed Betelgeuse using a speckle imager called ‘Alopeke. ‘Alopeke, which means ‘fox’ in Hawaiian, is funded by the NASA–NSF Exoplanet Observational Research Program (NN-EXPLORE) and is mounted on the Gemini North telescope, one half of the International Gemini Observatory, funded in part by the U.S. National Science Foundation and operated by NSF NOIRLab.

Speckle imaging is an astronomical imaging technique that uses very short exposure times to freeze out the distortions in images caused by Earth’s atmosphere. This technique enables high resolution, which, when combined with the light collecting power of Gemini North’s 8.1-meter mirror, allowed for Betelgeuse’s faint companion to be directly detected.

Analysis of the companion star’s light allowed Howell and his team to determine the companion star’s characteristics. They found that it is six magnitudes fainter than Betelgeuse in the optical wavelength range, it has an estimated mass of around 1.5 times that of the Sun, and it appears to be an A- or B-type pre-main-sequence star — a hot, young, blue-white star that has not yet initiated hydrogen burning in its core.

The companion is at a relatively close distance away from the surface of Betelgeuse — about four times the distance between the Earth and the Sun. This discovery is the first time a close-in stellar companion has been detected orbiting a supergiant star. Even more impressive — the companion orbits well within Betelgeuse’s outer extended atmosphere, proving the incredible resolving abilities of ‘Alopeke.

“Gemini North’s ability to obtain high angular resolutions and sharp contrasts allowed the companion of Betelgeuse to be directly detected,” says Howell. Furthermore, he explains that ‘Alopeke did what no other telescope has done before: “Papers that predicted Betelgeuse’s companion believed that no one would likely ever be able to image it.”

This discovery provides a clearer picture of this red supergiant’s life and future death. Betelgeuse and its companion star were likely born at the same time. However, the companion star will have a shortened lifespan as strong tidal forces will cause it to spiral into Betelgeuse and meet its demise, which scientists estimate will occur within the next 10,000 years.

Photo of the constellation Orion produced by NOIRLab in collaboration with Eckhard Slawik, a German astrophotographer.Credit: E. Slawik/NOIRLab/NSF/AURA/M. Zamani — Photo of the constellation Orion produced by NOIRLab in collaboration with Eckhard Slawik, a German astrophotographer.
Credit: E. Slawik/NOIRLab/NSF/AURA/M. Zamani

The discovery also helps to explain why similar red supergiant stars might undergo periodic changes in their brightness on the scale of many years. Howell shares his hope for further studies in this area:

“This detection was at the very extremes of what can be accomplished with Gemini in terms of high-angular resolution imaging, and it worked. This now opens the door for other observational pursuits of a similar nature.”

Martin Still, NSF program director for the International Gemini Observatory adds: “The speckle capabilities provided by the International Gemini Observatory continue to be a spectacular tool, open to all astronomers for a wide range of astronomy applications. Delivering the solution to the Betelgeuse problem that has stood for hundreds of years will stand as an evocative highlight achievement.”

Another opportunity to study Betelgeuse’s stellar companion will occur in November 2027 when it returns to its furthest separation from Betelgeuse, and thus easiest to detect. Howell and his team look forward to observations of Betelgeuse before and during this event to better constrain the nature of the companion.

Breathtaking views of astronomical events are a never-ending source of great excitement for the staff at Gemini North, one half of the International Gemini Observatory, supported in part by the U.S. National Science Foundation and operated by NSF NOIRLab. One such example is the lunar eclipse taking place in the distance on the right side of this image, captured in 2019. It is seemingly encased in the dark blue band above the horizon. Lunar eclipses occur when Earth moves between the Sun and the Moon. The Moon, which is only visible by the sunlight reflected off it, is darkened by the Earth’s shadow. An eclipse like this one can be viewed from anywhere on Earth where the Moon is visible, though the extent of the eclipse depends on how aligned the Moon is to Earth’s shadow and one’s viewing location. In 2022, for example, the two lunar eclipses, both total eclipses, were visible from Gemini North in Hawai‘i.Credit: International Gemini Observatory/NOIRLab/NSF/AURA/J. Chu — Breathtaking views of astronomical events are a never-ending source of great excitement for the staff at Gemini North, one half of the International Gemini Observatory, supported in part by the U.S. National Science Foundation and operated by NSF NOIRLab. One such example is the lunar eclipse taking place in the distance on the right side of this image, captured in 2019. It is seemingly encased in the dark blue band above the horizon. Lunar eclipses occur when Earth moves between the Sun and the Moon. The Moon, which is only visible by the sunlight reflected off it, is darkened by the Earth’s shadow. An eclipse like this one can be viewed from anywhere on Earth where the Moon is visible, though the extent of the eclipse depends on how aligned the Moon is to Earth’s shadow and one’s viewing location. In 2022, for example, the two lunar eclipses, both total eclipses, were visible from Gemini North in Hawai‘i.
Credit: International Gemini Observatory/NOIRLab/NSF/AURA/J. Chu

Notes

[1] Two papers released in 2024 used decades of observations of Betelgeuse from many observers around the world to predict the orbit and location of the companion star (see DOI: 10.3847/1538-4357/ad93c8 and DOI: 10.3847/1538-4357/ad87f4).

More information

This research is presented in a paper titled “Probable Direct Imaging Discovery of the Stellar Companion to Betelgeuse” to appear in The Astrophysical Journal Letters on 24 July. DOI: 10.3847/2041-8213/adeaaf

The team is composed of Steve B. Howell (NASA Ames Research Center), David R. Ciardi (NASA Exoplanet Science Institute-Caltech/IPAC), Catherine A. Clark (NASA Exoplanet Science Institute-Caltech/IPAC), Douglas A. Hope (Georgia Tech Research Institute, Georgia State University), Colin Littlefield (NASA Ames Research Center, Bay Area Environmental Research Institute), Elise Furlan (NASA Exoplanet Science Institute-Caltech/IPAC).

NSF NOIRLab, the U.S. National Science Foundation center for ground-based optical-infrared astronomy, operates the International Gemini Observatory (a facility of NSF, NRC–Canada, ANID–Chile, MCTIC–Brazil, MINCyT–Argentina, and KASI–Republic of Korea), NSF Kitt Peak National Observatory (KPNO), NSF Cerro Tololo Inter-American Observatory (CTIO), the Community Science and Data Center (CSDC), and NSF–DOE Vera C. Rubin Observatory (in cooperation with DOE’s SLAC National Accelerator Laboratory). It is managed by the Association of Universities for Research in Astronomy (AURA) under a cooperative agreement with NSF and is headquartered in Tucson, Arizona.

The scientific community is honored to have the opportunity to conduct astronomical research on I’oligam Du’ag (Kitt Peak) in Arizona, on Maunakea in Hawai‘i, and on Cerro Tololo and Cerro Pachón in Chile. We recognize and acknowledge the very significant cultural role and reverence of I’oligam Du’ag to the Tohono O’odham Nation, and Maunakea to the Kanaka Maoli (Native Hawaiians) community.

The NASA–NSF Exoplanet Observational Research Program (NN-EXPLORE) is a joint initiative to advance U.S. exoplanet science by providing the community with access to cutting-edge, ground-based observational facilities. Managed by NASA’s Exoplanet Exploration Program (ExEP), NN-EXPLORE supports and enhances the scientific return of space missions such as Kepler, TESS, HST, and JWST by enabling essential follow-up observations from the ground—creating strong synergies between space-based discoveries and ground-based characterization. ExEP is located at the Jet Propulsion Laboratory. More information at https://exoplanets.nasa.gov/exep/NNExplore/overview/.

Press release from NSF NOIRLab.

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Astronomy

Webb captures iconic Horsehead Nebula in unprecedented detail

By ScientifiCult 29 April 2024

$At the bottom of the image a small portion of the Horsehead Nebula is seen close-in, as a curved wall of thick, smoky gas and dust. Above the nebula various distant stars and galaxies can be seen up to the top of the image. One star is very bright and large, with six long diffraction spikes that cross the image. The background fades from a dark red colour above the nebula to black.$

Webb captures iconic Horsehead Nebula in unprecedented detail

The NASA/ESA/CSA James Webb Space Telescope has captured the sharpest infrared images to date of one of the most distinctive objects in our skies, the Horsehead Nebula. These observations show a part of the iconic nebula in a whole new light, capturing its complexity with unprecedented spatial resolution.

A collage of three images of the Horsehead Nebula. In the left image labelled “Euclid (Visible-Infrared)”, the Nebula is seen amongst its surroundings. A small box around it connects to the second image labelled “Hubble (Infrared)”, where the Nebula is zoomed in on. A portion of the Nebula’s head has another box, which leads with a callout to the third image, labelled “Webb (Infrared)”, of that area. — This image showcases three views of one of the most distinctive objects in our skies, the Horsehead Nebula. This object resides in part of the sky in the constellation Orion (The Hunter), in the western side of the Orion B molecular cloud. Rising from turbulent waves of dust and gas is the Horsehead Nebula, otherwise known as Barnard 33, which resides roughly 1300 light-years away.
The first image (left), released in November 2023, features the Horsehead Nebula as seen by ESA’s Euclid telescope. Euclid captured this image of the Horsehead in about one hour, which showcases the mission’s ability to very quickly image an unprecedented area of the sky in high detail.
The second image (middle) shows the NASA/ESA Hubble Space Telescope’s infrared view of the Horsehead Nebula, which was featured as the telescope’s 23rd anniversary image in 2013. This image captures plumes of gas in the infrared and reveals a beautiful, delicate structure that is normally obscured by dust.
The third image (right) features a new view of the Horsehead Nebula from the NASA/ESA/CSA James Webb Space Telescope’s NIRCam (Near-InfraRed Camera) instrument. It is the sharpest infrared image of the object to date, showing a part of the iconic nebula in a whole new light, and capturing its complexity with unprecedented spatial resolution.
Credit: ESA/Euclid/Euclid Consortium/NASA, image processing by J.-C. Cuillandre (CEA Paris-Saclay), G. Anselmi, NASA, ESA, and the Hubble Heritage Team (AURA/STScI), ESA/Webb, CSA, K. Misselt (University of Arizona) and A. Abergel (IAS/University Paris-Saclay, CNRS), M. Zamani (ESA/Webb)

Webb’s new images show part of the sky in the constellation Orion (The Hunter), in the western side of the Orion B molecular cloud. Rising from turbulent waves of dust and gas is the Horsehead Nebula, otherwise known as Barnard 33, which resides roughly 1300 light-years away.

The nebula formed from a collapsing interstellar cloud of material, and glows because it is illuminated by a nearby hot star. The gas clouds surrounding the Horsehead have already dissipated, but the jutting pillar is made of thick clumps of material that is harder to erode. Astronomers estimate that the Horsehead has about five million years left before it too disintegrates. Webb’s new view focuses on the illuminated edge of the top of the nebula’s distinctive dust and gas structure.

The Horsehead Nebula is a well-known photodissociation region, or PDR. In such a region ultraviolet light from young, massive stars creates a mostly neutral, warm area of gas and dust between the fully ionised gas surrounding the massive stars and the clouds in which they are born. This ultraviolet radiation strongly influences the gas chemistry of these regions and acts as the most important source of heat.

These regions occur where interstellar gas is dense enough to remain neutral, but not dense enough to prevent the penetration of far-ultraviolet light from massive stars. The light emitted from such PDRs provides a unique tool to study the physical and chemical processes that drive the evolution of interstellar matter in our galaxy, and throughout the Universe from the early era of vigorous star formation to the present day.

Owing to its proximity and its nearly edge-on geometry, the Horsehead Nebula is an ideal target for astronomers to study the physical structures of PDRs and the evolution of the chemical characteristics of the gas and dust within their respective environments, and the transition regions between them. It is considered one of the best objects in the sky to study how radiation interacts with interstellar matter.

At the bottom of the image a small portion of the Horsehead Nebula is seen close-in, as a curved wall of thick, smoky gas and dust. Above the nebula various distant stars and galaxies can be seen up to the top of the image. One star is very bright and large, with six long diffraction spikes that cross the image. The background fades from a dark red colour above the nebula to black. — The NASA/ESA/CSA James Webb Space Telescope has captured the sharpest infrared images to date of one of the most distinctive objects in our skies, the Horsehead Nebula. These observations show a part of the iconic nebula in a whole new light, capturing its complexity with unprecedented spatial resolution.
Webb’s new images show part of the sky in the constellation Orion (The Hunter), in the western side of the Orion B molecular cloud. Rising from turbulent waves of dust and gas is the Horsehead Nebula, otherwise known as Barnard 33, which resides roughly 1300 light-years away.
The nebula formed from a collapsing interstellar cloud of material, and glows because it is illuminated by a nearby hot star. The gas clouds surrounding the Horsehead have already dissipated, but the jutting pillar is made of thick clumps of material that is harder to erode. Astronomers estimate that the Horsehead has about five million years left before it too disintegrates. Webb’s new view focuses on the illuminated edge of the top of the nebula’s distinctive dust and gas structure.
The Horsehead Nebula is a well-known photon-dominated region, or PDR. In such a region ultraviolet light from young, massive stars creates a mostly neutral, warm area of gas and dust between the fully ionised gas surrounding the massive stars and the clouds in which they are born. This ultraviolet radiation strongly influences the gas chemistry of these regions and acts as the most important source of heat.
These regions occur where interstellar gas is dense enough to remain neutral, but not dense enough to prevent the penetration of far-ultraviolet light from massive stars. The light emitted from such PDRs provides a unique tool to study the physical and chemical processes that drive the evolution of interstellar matter in our galaxy, and throughout the Universe from the early era of vigorous star formation to the present day.
Owing to its proximity and its nearly edge-on geometry, the Horsehead Nebula is an ideal target for astronomers to study the physical structures of PDRs and the evolution of the chemical characteristics of the gas and dust within their respective environments, and the transition regions between them. It is considered one of the best objects in the sky to study how radiation interacts with interstellar matter.
This image was captured with Webb’s NIRCam (Near-InfraRed Camera) instrument.
Credit: ESA/Webb, NASA, CSA, K. Misselt (University of Arizona) and A. Abergel (IAS/University Paris-Saclay, CNRS)

Thanks to Webb’s MIRI and NIRCam instruments, an international team of astronomers have revealed for the first time the small-scale structures of the illuminated edge of the Horsehead. They have also detected a network of striated features extending perpendicular to the PDR front and containing dust particles and ionised gas entrained in the photo-evaporative flow of the nebula. The observations have also allowed astronomers to investigate the effects of dust attenuation and emission, and to better understand the multidimensional shape of the nebula.

The image is more than half-filled by a small section of the Horsehead Nebula, from the bottom up. The clouds are seen up close, showing thick, whitish streaks and dark voids, as well as textured, fuzzy-looking patterns of dust and gas. The nebula stops at a spiky edge that follows a slight curve. Above it a small number of distant stars and galaxies lie on a dark but multi-coloured background. — The NASA/ESA/CSA James Webb Space Telescope has captured the sharpest infrared images to date of one of the most distinctive objects in our skies, the Horsehead Nebula. These observations show a part of the iconic nebula in a whole new light, capturing its complexity with unprecedented spatial resolution.
Webb’s new images show part of the sky in the constellation Orion (The Hunter), in the western side of the Orion B molecular cloud. Rising from turbulent waves of dust and gas is the Horsehead Nebula, otherwise known as Barnard 33, which resides roughly 1300 light-years away.
The nebula formed from a collapsing interstellar cloud of material, and glows because it is illuminated by a nearby hot star. The gas clouds surrounding the Horsehead have already dissipated, but the jutting pillar is made of thick clumps of material that is harder to erode. Astronomers estimate that the Horsehead has about five million years left before it too disintegrates. Webb’s new view focuses on the illuminated edge of the top of the nebula’s distinctive dust and gas structure.
The Horsehead Nebula is a well-known photon-dominated region, or PDR. In such a region ultraviolet light from young, massive stars creates a mostly neutral, warm area of gas and dust between the fully ionised gas surrounding the massive stars and the clouds in which they are born. This ultraviolet radiation strongly influences the gas chemistry of these regions and acts as the most important source of heat.
These regions occur where interstellar gas is dense enough to remain neutral, but not dense enough to prevent the penetration of far-ultraviolet light from massive stars. The light emitted from such PDRs provides a unique tool to study the physical and chemical processes that drive the evolution of interstellar matter in our galaxy, and throughout the Universe from the early era of vigorous star formation to the present day.
Owing to its proximity and its nearly edge-on geometry, the Horsehead Nebula is an ideal target for astronomers to study the physical structures of PDRs and the evolution of the chemical characteristics of the gas and dust within their respective environments, and the transition regions between them. It is considered one of the best objects in the sky to study how radiation interacts with interstellar matter.
This image was captured with Webb’s MIRI (Mid-InfraRed Instrument).
Credit: ESA/Webb, NASA, CSA, K. Misselt (University of Arizona) and A. Abergel (IAS/University Paris-Saclay, CNRS)

Next, astronomers intend to study the spectroscopic data that have been obtained of the nebula to evidence the evolution of the physical and chemical properties of the material observed across the nebula.

These observations were taken in the Webb GTO programme #1192 (PI: K. Misselt) and the results have been accepted for publication in Astronomy & Astrophysics (Abergel et al. 2024).

Press release from ESA Webb.

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