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Flame Nebula
Flame Nebula
Flame Nebula
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NGC 2024
Emission nebula
The Flame Nebula in visible light (broadband). The star above it is Alnitak. The nebulae to the upper left are IC 431 and IC 432.
Observation data: J2000.0 epoch
Right ascension05h 41m 54s
Declination−01° 51′ 0.0″
Distance1350[1] ly   (415 pc)
Apparent magnitude (V)10
Apparent dimensions (V)30'x30'
ConstellationOrion
Physical characteristics
Radius6 ly
DesignationsNGC 2024 and Sharpless 277
See also: Lists of nebulae

The Flame Nebula, designated as NGC 2024 and Sh2-277, is an emission nebula in the constellation Orion. It is about 1350 light-years away.[1] At that distance, the Flame Nebula lies within the Orion B cloud of the larger Orion Molecular Cloud Complex.

The bright star Alnitak (ζ Ori), the easternmost star in the Belt of Orion, appears very close to the Flame Nebula in the sky. But the star and nebula are not physically associated with one another. The Flame Nebula contains a young cluster of stars which includes at least one hot, luminous O-type star labeled IRS 2b.[2] The dense gas and dust in the foreground of the nebula heavily obscures the star cluster inside the nebula, making studies at infrared wavelengths most useful.

The energetic ultraviolet light emitted by the central O-type star IRS 2b into the Flame Nebula causes the gas to be excited and heated. The glow of the nebula results from the energy input from this central star. Within the nebula and surrounding the central hot star is a cluster of young, lower-mass stars,[3] 86% of which have circumstellar disks.[4] X-ray observations by the Chandra X-ray Observatory[5][6] show several hundred young stars, out of an estimated population of 800 stars.[7] X-ray and infrared images indicate that the young stars are concentrated near the center of the cluster.[8][9]

The center of the Flame Nebula seen by JWST NIRCam, revealing proplyds in new detail and revealing two new candidates.

The Flame Nebula was observed with ALMA and this study found two populations, which are separated by a molecular cloud. The eastern population is 0.2-0.5 Myr old and has a disk fraction of 45±7%. The western population is slightly older at 1 Myr and has a lower disk fraction of 15±4%.[10] This disk fraction is lower than the one observed in the mid-infrared,[4] but the ALMA survey also observed a smaller region.[10] The eastern part contains the O8 star IRS 2b and the western part contains the B0.5V star IRS 1. Hubble observations have shown that the Flame Nebula contains 4 clear proplyds and 4 candidate proplyds. Three of these are in the older western region and are pointing towards IRS 1. The other 5 are in the younger eastern region and are pointing towards IRS 2b.[11]

[edit]
  • Optical image in B, V and R filters, from La Silla Observatory
    Optical image in B, V and R filters, from La Silla Observatory
  • Infrared image, from 2MASS
    Infrared image, from 2MASS
  • Near-infrared image, from VISTA
    Near-infrared image, from VISTA
  • Visible light wide-field view of region of Orion's Belt and the Flame Nebula
    Visible light wide-field view of region of Orion's Belt and the Flame Nebula
  • NGC 2024 seen by the Chandra X-ray Observatory
    NGC 2024 seen by the Chandra X-ray Observatory
  • Flame Nebula and Horsehead Nebula
    Flame Nebula and Horsehead Nebula
  • Horsehead and Flame Nebulae in H-alpha
    Horsehead and Flame Nebulae in H-alpha
  • The Flame Nebula (NGC 2024) - based on Chandra X-Ray and Spitzer Infrared images
    The Flame Nebula (NGC 2024) - based on Chandra X-Ray and Spitzer Infrared images

References

[edit]
[edit]
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Flame Nebula

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from Grokipedia
The Flame Nebula, also designated as NGC 2024, is an and prominent star-forming region situated in the constellation Orion, approximately 1,400 light-years from . It forms part of the expansive , near the iconic and the bright star in , and is characterized by dense concentrations of interstellar gas and dust that foster the birth of new stars. Discovered in the late by , the nebula spans several light-years and appears as a fiery, irregular glow in visible light due to of by embedded young stars, while dark lanes of obscuring dust create its distinctive flame-like silhouette. With an estimated age of less than 1 million years, the Flame Nebula represents a young, dynamic environment where turbulent processes drive the collapse of molecular clouds into protostars, including massive that heat surrounding dust to emit brightly in wavelengths. Observations reveal intricate structures such as pillars of dense brown dust with wispy plumes and swirling patterns of cooler material, which may influence formation by dispersing protoplanetary disks through intense and stellar winds from nearby high-mass . In far- views from telescopes like Herschel, the nebula's dense cores shine prominently, highlighting hidden pockets of obscured at optical wavelengths. Recent advancements from the (JWST) have pierced the nebula's dusty veil using near-infrared imaging, detecting a population of low-mass objects including down to about 3 masses, with sensitivity reaching 0.5 masses across a 9.68 arcminute² field. These observations, building on data, indicate a turnover in the (IMF) below 12 masses, suggesting a fundamental limit to turbulent fragmentation in near 3 masses and fewer free-floating planetary-mass objects than expected. Such findings underscore the Flame Nebula's role as a key laboratory for studying the early stages of stellar and substellar evolution in our galaxy.

Overview and Location

General Description

The Flame Nebula, designated as NGC 2024 and Sharpless 2-277, is an energized by radiation from young, massive stars, which ionizes the surrounding gas and produces prominent red emissions. This causes the nebula to glow brightly in the red portion of the , as electrons recombine with protons to form neutral atoms. Visually, the Flame Nebula exhibits a striking, flame-like characterized by bright ionized regions interspersed with prominent dark dust lanes that obscure background , giving it a dramatic, fiery appearance in optical images. It spans approximately 30 by 30 arcminutes in apparent size, making it a conspicuous feature adjacent to the iconic . As a key stellar nursery within the Orion B molecular cloud, the Flame Nebula hosts embedded protostars and Herbig-Haro objects, regions where jets from newborn stars interact with surrounding gas to form bright emission knots. Less than 1 million years old, it represents one of the youngest active star-forming regions observable from Earth, actively producing new stars and brown dwarfs amid dense concentrations of gas and dust.

Coordinates and Distance

The Flame Nebula occupies equatorial coordinates of 05ʰ 41ᵐ 43ˢ and −01° 50′ 30″ (J2000 ). Its corresponding galactic coordinates are longitude 206.5° and latitude −16.3°. Distance measurements place the nebula approximately 1,340 light-years (410 parsecs) from Earth, derived from trigonometric parallaxes obtained by the mission and corroborated by spectroscopic data of embedded young stars. This estimate aligns with the nebula's position within the broader , where DR3 astrometric data from 2022 has refined the parallax-based distances for member stars, yielding a mean value of about 410 pc for the associated cluster with reduced uncertainty compared to prior releases. As part of the Orion OB1 association—specifically the Orion B subgroup—the Flame Nebula shares kinematic and spatial properties with nearby star-forming regions, including a similar distance to the (M42), facilitating comparative studies of their embedded populations.

Physical Properties

Size and Morphology

The Flame Nebula (NGC 2024) spans an apparent angular size of approximately 30 arcminutes in . At its distance of about 1,400 light-years (430 parsecs), this corresponds to a physical of around 3.8 parsecs, or approximately 12 light-years. The nebula's morphology is characterized by an elongated, flame-like outline formed by bright emission regions interspersed with prominent dark absorption lanes, including Bok globulettes—small, dense clouds that obscure background light. These features create a complex gaseous architecture, with bright ridges of ionized hydrogen gas contrasting against the darker molecular material. Internally, the structure reveals cavities and pillars sculpted by the stellar winds and from embedded young stars, eroding the surrounding and producing an expanding H II bubble with distinct eastern and western loops. observations highlight finger-like protrusions along these pillars, revealing denser filaments amid the diffuse gas. Density variations are significant, with core regions reaching up to 10410^4 to 10510^5 particles per cm³, while outflows and fronts contribute to the nebula's asymmetric shapes, as detailed in multiwavelength images from the and .

Composition and Spectrum

The Flame Nebula, an within the Orion B , is primarily composed of (about 74% by mass, or ~92% by number of atoms) and (about 24% by mass, or ~8% by number of atoms), with trace amounts of heavier elements such as oxygen, , and carbon. The exists predominantly in neutral (H I) form in the outer envelopes but is ionized (H II) in the central regions due to radiation from embedded massive stars. is partially ionized, with observations detecting around 3% ionized through recombination lines like He76α. Dust grains interspersed within the gas make up a small fraction of the total mass but play a significant role in the nebula's appearance and physics. These include and carbonaceous particles, which cause substantial in visible wavelengths—visual magnitudes (A_V) ranging from 5.5 to 25—rendering the nebula opaque at optical bands while allowing greater transparency in the . The nebula's spectrum is dominated by emission lines from ionized gas recombination and forbidden transitions in low-density zones. Prominent features include the Hα line at 656.3 nm, arising from hydrogen recombination in the H II regions, which gives the nebula its characteristic red glow. Forbidden lines such as [O III] at 500.7 nm are also observed, particularly in the central areas, indicating photoionized oxygen in regions of lower . Ionization is driven primarily by the O8 V IRS 2b, a massive early-type with an of 22,000–34,000 K that emits sufficient photons (approximately 7.3 × 10^47 s⁻¹ in the Lyman continuum) to sustain the H II region. The ionized gas reaches temperatures around 10,000 K, typical for such regions. In contrast, cooler molecular cores, detected through rotational lines of CO isotopologues like ¹²CO(1–0), exhibit kinetic temperatures of 20–50 K, tracing denser, shielded gas.

Formation and Evolution

Star-Forming Processes

The star-forming processes in the Flame Nebula (NGC 2024) are dominated by the of dense cores within the , a fundamental mechanism where regions exceeding their mass become unstable and contract under self-gravity, leading to the formation of protostars. This process has been particularly active following a cloud-cloud collision between two molecular components, which compressed the gas and triggered the birth of high-mass O- and B-type stars in a compact area spanning approximately 0.3 pc. The collision is evidenced by complementary velocity structures in 13CO observations, indicating relative motions of about 2-3 km/s that drove the compression necessary for collapse. The nebula contains over 100 young stellar objects (YSOs), many classified as Class 0 and Class I protostars embedded in infalling envelopes and surrounded by circumstellar accretion disks that facilitate ongoing mass buildup. These protostars, such as the FIR 1-5 sources, exhibit bipolar outflows and collimated jets, observable in near-infrared and molecular line emissions, which clear and regulate accretion rates up to 10^{-5} M_\sun yr^{-1}. Radiation from the central massive stars provides crucial feedback, as their photons ionize and heat the surrounding medium, driving photoevaporation that erodes protoplanetary disks and sculpts dense pillars of gas and while potentially suppressing further collapse in exposed areas. The estimated star formation rate in the region reflects efficient production of both high-mass stars (above 8 M_\sun) and low-mass counterparts, alongside candidates for with masses as low as 2-3 M_Jup and free-floating planetary-mass objects down to 0.5 M_Jup detected via recent infrared imaging. This rate underscores the nebula's role as a prolific site within the Orion B cloud, where feedback balances ongoing collapse to sustain a diverse . Recent observations indicate that magnetic fields, with strengths of ~0.1-0.3 mG, play a role in supporting the dense filament and regulating fragmentation during .

Age and Dynamical History

The Flame Nebula, or NGC 2024, is estimated to be less than 1 million years old, with its stellar population exhibiting a core-halo age gradient where pre-main-sequence (PMS) in the dense core have a age of approximately 0.2 million years, while those in the outer halo reach up to 1.5 million years. This age is inferred from the evolutionary stages of young stellar objects (YSOs), including their positions on Hertzsprung-Russell diagrams and the dynamical timescales of molecular outflows, which indicate recent and ongoing . The dynamical history of NGC 2024 began with the collision of two s within the Orion B giant approximately 0.3 million years ago, compressing the gas and triggering the initial collapse of dense cores. This cloud-cloud collision, with a of about 2.7 km s⁻¹ and a spatial separation of roughly 0.6 pc, increased the column by a factor of two, leading to the rapid formation of protostars. Shortly thereafter, the ignition of the first massive O- and early B-type stars ionized the surrounding gas, creating the expanding that defines the nebula's current structure. NGC 2024 remains embedded in the broader Orion B , where these internal dynamical processes dominate over external influences. Stellar feedback from the young massive stars is expected to disperse gas in 1–2 million years, transitioning the embedded cluster into a loosely bound . This dispersal will be driven by ultraviolet radiation and stellar winds that erode the molecular material, halting further and allowing the surviving low-mass stars to expand outward.

Observation History

Discovery and Early Studies

The Flame Nebula, designated NGC 2024, was discovered by British astronomer William Herschel on January 1, 1786, during his sweeps of the northern sky and cataloged as IV.28 in his initial list of nebulae. It was later included in John Herschel's General Catalogue of Nebulae and Clusters (1864) based on observations by both father and son, and standardized as NGC 2024 by J.L.E. Dreyer in the New General Catalogue published in 1888. This early visual detection identified it as a diffuse object within the Orion constellation, appearing as a hazy extension near the bright star ζ Orionis (Alnitak). The nebula was later redesignated Sh2-277 in the 1959 Sharpless Catalogue of H II Regions by American astronomer Stewart Sharpless, which compiled northern sky emission nebulae based on radio and optical data. Early telescopic observations revealed NGC 2024 as a faint, fuzzy patch visible to amateur astronomers with small instruments under , often requiring to discern its outline against the glare of . The first photographic evidence emerged in the late 1880s, when long-exposure plates of the Orion region captured its flame-like silhouette amid the surrounding dust clouds, including the nearby (B33). These pioneering images, taken with early dry-plate technology, demonstrated the nebula's irregular morphology and its embedding within the broader Orion B , sparking interest in its gaseous nature. Spectroscopic studies in the early confirmed NGC 2024's status as an , identifying bright emission lines indicative of by nearby hot stars. During the 1920s and 1930s, Robert J. Trumpler at conducted further of stars and gas in the Orion region, revealing NGC 2024's characteristics—ionized hydrogen clouds shaped by from embedded O-type stars—and its association with the diffuse complex. Trumpler's analyses, incorporating measurements, also highlighted interstellar absorption effects, providing foundational insights into the nebula's dynamical environment up to the mid-.

Modern Telescopic Observations

The has provided pivotal insights into the Flame Nebula through high-resolution imaging since the late 1990s. Early observations using the Wide Field Planetary Camera 2 (WFPC2) in 1999 captured detailed views of intricate dust lanes and embedded protostars, highlighting the nebula's complex structure illuminated by nearby massive stars. Later, in 2013, imaging with the (WFC3) revealed embedded young stellar clusters previously obscured by dust, showcasing the region's active star-forming environment. These observations demonstrated how ultraviolet radiation from central O-type stars shapes the nebula's morphology, with dust features appearing as dark silhouettes against glowing gas. Advancements in infrared astronomy during the 2000s further illuminated the Flame Nebula's cooler components. NASA's conducted mid- surveys as part of the Massive Young Star-Forming Complex Study in and X-ray (MYStIX) project, mapping dust emission and identifying approximately 800 young stellar objects (YSOs), many of which are concentrated in the nebula's core. These data revealed an age gradient, with stars at the center as young as 200,000 years old, contrasting with older peripheral members up to 1.5 million years, challenging uniform models. Complementing Spitzer, the European Space Agency's performed far-infrared observations in 2010–2011, targeting cold dust temperatures below 20 K and additional YSOs hidden in dense envelopes. Using the PACS and instruments at wavelengths of 70–500 μm, Herschel mapped the nebula's extended filaments, uncovering dense concentrations of material that glow brightly in far-infrared, indicative of ongoing collapse and protostellar activity. These surveys identified cooler, less evolved YSOs, enhancing the census of efficiency in the region. The (JWST) marked a new era in 2025 with unprecedented depth into the Flame Nebula's interior. Observations released in March 2025, utilizing the Near-Infrared Camera (NIRCam) and (MIRI) across 1.15–4.3 μm and longer mid-infrared bands up to 21 μm, pierced dense to detect faint and planetary-mass objects down to 0.5 masses. JWST's resolution of approximately 0.1 arcseconds resolved structures in pillars of gas and , revealing fragmentation processes and outflow signatures from low-mass objects not visible in prior telescopes. This data confirmed a scarcity of objects below 2 masses, suggesting a formation threshold influenced by the nebula's turbulent environment.

Proximity to Horsehead Nebula

The , particularly the dark feature known as Barnard 33 silhouetted against the , lies just south of the Flame Nebula (NGC 2024), with their centers separated by approximately 40 arcminutes and both embedded within the same filamentary structure of the Orion B complex. This close spatial proximity places them in a shared star-forming environment about 1,300–1,500 light-years from Earth, where turbulent gas and dust dynamics connect the regions through networks of cool filaments. Both nebulae are illuminated by the ultraviolet radiation from the nearby O9.7 supergiant Alnitak (ζ Orionis), which ionizes the surrounding hydrogen gas to create the bright emissions characteristic of the area. The Horsehead manifests as a dark silhouette against the glowing red backdrop of IC 434, formed by dense dust blocking the light, in stark contrast to the Flame Nebula's vivid, flame-like emission structure driven by its active H II region. Their common origin traces back to the collapse and fragmentation of the Orion B cloud, fostering interconnected star formation processes across the filament. The combined region spans roughly 1 degree in the vicinity of , encompassing a transitional zone where the Horsehead's photo-dissociation region (PDR)—where photons dissociate molecules—directly borders the expansive ionized H II zone of the Flame Nebula, illustrating their physical interdependence.

Illuminating Stars and Clusters

The primary illuminator of the Flame Nebula is the massive O-type star (ζ Orionis), classified as spectral type O9.5 Iab with an estimated mass of approximately 33 solar masses and a surface of around 29,500 K. This hot star emits copious photons that ionize the nebula's gas, stripping electrons and causing the emission of visible light through recombination processes. Embedded within the Flame Nebula is the young stellar cluster, comprising several hundred members that include both high-mass stars and lower-mass pre-main-sequence objects such as stars. Prominent among the massive stars are IRS 1, a B0.5 V type, and IRS 2b, classified as O8 V, which contribute significantly to the local radiation field and ionization alongside . The cluster features a central stellar of about 0.1 pc−3^{-3}, along with variable stars and emitting sources linked to accretion activity in the young stellar objects. NGC 2024 has an estimated age of 0.3–0.5 million years in its core, indicative of ongoing , as determined from age gradients across the cluster. Surveys using the near-infrared catalog and have been instrumental in identifying cluster members, revealing approximately 50 emitting young stellar objects consistent with active accretion and magnetic activity.

References

  1. https://science.nasa.gov/missions/hubble/hubble-spots-swirls-of-dust-in-the-flame-nebula/
  2. https://sci.esa.int/web/herschel/-/51703-a-horsehead-a-flame-and-hidden-gems-in-orion-b
  3. https://science.nasa.gov/missions/webb/nasas-webb-peers-deeper-into-mysterious-flame-nebula/
  4. https://iopscience.iop.org/article/10.3847/2041-8213/adb96a
  5. https://www.eso.org/public/images/eso0949e/
  6. https://www.esa.int/ESA_Multimedia/Images/2025/03/Flame_Nebula_in_visible_and_infrared_light
  7. https://simbad.cds.unistra.fr/simbad/sim-basic?Ident=NGC+2024
  8. https://www.aanda.org/articles/aa/full_html/2024/04/aa48376-23/aa48376-23.html
  9. https://www.aanda.org/articles/aa/full_html/2011/11/aa16915-11/aa16915-11.html
  10. https://theskylive.com/sky/deepsky/ngc2024-object
  11. https://www.constellation-guide.com/flame-nebula/
  12. https://science.nasa.gov/missions/hubble/hubble-finds-flame-nebulas-searing-stars-may-halt-planet-formation/
  13. https://www.spitzer.caltech.edu/image/ssc2014-04a-the-flame-nebula
  14. https://www.aanda.org/articles/aa/pdf/2003/22/aah4248.pdf
  15. https://science.[nasa](/page/NASA).gov/missions/hubble/hubble-spots-swirls-of-dust-in-the-flame-nebula/
  16. https://www.telescopenerd.com/celestial-objects/flame-nebula.htm
  17. https://www.aanda.org/articles/aa/pdf/2024/04/aa48376-23.pdf
  18. https://ui.adsabs.harvard.edu/abs/2021PASJ...73S.256E/abstract
  19. https://academic.oup.com/pasj/article/73/Supplement_1/S256/5859081
  20. https://arxiv.org/pdf/1403.2742
  21. https://arxiv.org/pdf/1912.11607
  22. https://www.deepskycorner.ch/obj/ngc2024.en.php
  23. https://adsabs.harvard.edu/full/1959ApJS....4..257S
  24. https://www.galactic-hunter.com/post/ic-434-the-horsehead-flame-nebulae
  25. https://iopscience.iop.org/article/10.1088/0004-637X/787/2/109
  26. https://arxiv.org/abs/1211.2935
  27. https://www.esa.int/Science_Exploration/Space_Science/Herschel/Herschel_and_Hubble_see_the_Horsehead_in_new_light
  28. https://www.astronomytrek.com/stars/alnitak/
  29. https://www.jpl.nasa.gov/images/pia13448-a-flame-in-orions-belt/
  30. https://iopscience.iop.org/article/10.1086/378085
  31. https://www.aanda.org/articles/aa/abs/2003/22/aah4248/aah4248.html
  32. https://academic.oup.com/mnras/article/501/3/3502/6043222
  33. https://iopscience.iop.org/article/10.1088/0004-637X/787/2/107
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