The Orion Molecular Cloud Complex is hundreds of light years in diameter. Some parts of it, like the Orion Nebula, are visible to the naked eye, while others can be seen in binoculars and small telescopes.
Flame Nebula (NGC 2024). Image: Adam Block/Mount Lemmon SkyCenter/University of Arizona
The Flame Nebula is home to a cluster of several hundred very young stars. 86 percent of these stars have circumstellar disks. The youngest members are concentrated near the cluster’s centre, while the older members lie in the outer regions. This was revealed in a study using data from NASA’s Chandra X-ray Observatory, the Spitzer Space Telescope, the United Kingdom Infrared Telescope, and the 2MASS telescope, which showed that the stars at the cluster’s centre were only about 200,000 years old, while those in the outer regions were around 1.5 million years old.
A study of NGC 2024 and the Orion Nebula Cluster, another region where many stars are forming, suggest that the stars on the outskirts of these clusters are older than those in the central regions. This is different from what the simplest idea of star formation predicts, where stars are born first in the center of a collapsing cloud of gas and dust when the density is large enough. The research team developed a two-step process to make this discovery. First, they used Chandra data on the brightness of the stars in X-rays to determine their masses. Next, they found out how bright these stars were in infrared light using data from Spitzer, the 2MASS telescope, and the United Kingdom Infrared Telescope. By combining this information with theoretical models, the ages of the stars throughout the two clusters could be estimated. According to the new results, the stars at the center of NGC 2024 were about 200,000 years old while those on the outskirts were about 1.5 million years in age. In Orion, the age spread went from 1.2 million years in the middle of the cluster to nearly 2 million years for the stars toward the edges. Image: NASA (X-ray: NASA/CXC/PSU/K.Getman, E.Feigelson, M.Kuhn & the MYStIX team; Infrared:NASA/JPL-Caltech)
There are several possible explanations for this. Star formation may be continuing to occur in the central regions of the nebula because the clouds of star forming gas are thicker there than in the outskirts. It is also possible that older stars are in the outer regions simply because they have had more time to move away from the centre. Another theory proposes that young stars are forming in massive filaments of gas that fall toward the cluster’s centre.
Location of the Flame Nebula (NGC 2024) in Orion. Image: Wikisky
The Flame Nebula is illuminated by the bright star Alnitak, Zeta Orionis, the easternmost star in Orion’s Belt. Alnitak is a multiple star system consisting of a hot blue supergiant and two fourth magnitude companions. The supergiant has a visual magnitude of 2.0 and, with an absolute magnitude of -6.0, it is the brightest O-class star in the sky. The star system has a combined visual magnitude of 1.77.
Flame Nebula. Image: ESO/J. Emerson/VISTA. Acknowledgment: Cambridge Astronomical Survey Unit
The components of the Alnitak system are members of the Orion OB1 association, a group of several dozen hot giant O and B-type stars found within the Orion Molecular Cloud Complex. The association is divided into several subgroups. The members of the Orion OB1a subgroup include stars northwest of Orion’s Belt, which have an estimated age of about 12 million years. The stars of Orion’s Belt – Alnitak, Alnilam and Mintaka – and stars in the vicinity form the Orion OB1b subgroup and have an average age of 8 million years. The Orion OB1c subgroup consists of the stars in Orion’s Sword, located just under the Belt. These stars are between 3 and 6 million years old. The youngest members of the Orion OB1 association form the Orion OB1d subgroup. These include the stars in the Orion Nebula (M42) and De Mairan’s Nebula (M43).
The Flame Nebula in X-ray. Pre–main-sequence stars X-ray emission is hundreds to thousands of times higher than X-ray emission from main-sequence stars like the Sun, making X-ray observations an effective means of identifying young stars. Image: NASA/CXC/PSU/K.Getman, E.Feigelson, M.Kuhn & the MYStIX team
Flame Nebula – NGC 2024
Distance: 1,350 light years (415 parsecs)
Apparent magnitude: +2
Right ascension: 05h 41m 54s
Apparent size: 30′ x 30′
Designations: Flame Nebula, NGC 2024, Sharpless 277, W 12, LBN 953, PMN J0541-0154, SNR G206.5-16.4
This VISTA image shows the spectacular star-forming region known as the Flame Nebula, or NGC 2024, in the constellation of Orion (the Hunter) and its surroundings. In views of this evocative object in visible light the core of the nebula is completely hidden behind obscuring dust, but in this VISTA view, taken in infra-red light, the cluster of very young stars at the object’s heart is revealed. The wide-field VISTA view also includes the glow of the reflection nebula NGC 2023, just below centre, and the ghostly outline of the Horsehead Nebula (Barnard 33) towards the lower right. The bright bluish star towards the right is one of the three bright stars forming the Belt of Orion. The image was created from VISTA images taken through J, H and Ks filters in the near-infrared part of the spectrum. The image shows the full area of the VISTA field and is one degree by 1.5 degrees in extent. The total exposure time was 14 minutes. Image: ESO/J. Emerson/VISTA. Acknowledgment: Cambridge Astronomical Survey Unit
This spectacular visible light wide-field view of part of the famous belt of the great celestial hunter Orion shows the region of the sky around the Flame Nebula. The whole image is filled with glowing gas clouds illuminated by hot blue young stars. It was created from photographs in red and blue light forming part of the Digitized Sky Survey 2. The field of view is approximately three degrees. Image: ESO and Digitized Sky Survey 2
Sparkling at the edge of a giant cloud of gas and dust, the Flame Nebula, also referred to as NGC 2024, is in fact the hideout of a cluster of young, blue, massive stars, whose light sets the gas ablaze. Located 1300 light-years away towards the constellation of Orion, the nebula owes its typical colour to the glow of hydrogen atoms, heated by the stars. The latter are obscured by a dark, forked dusty structure in the centre of the image and are only revealed by infra-red observations. Image: ESO/IDA/Danish 1.5 m/R. Gendler, J.-E. Ovaldsen, C. Thöne and C. Féron
A Tour of Flame Nebula – Chandra X-ray Observatory
Flame Nebula: VISTA Telescope Zoom In
Flame Nebula: VISTA Telescope Pan Over
Flame Nebula: Infrared-Visual Crossfade