The Horsehead Nebula in Infrared

Sometimes a horse of a different color hardly seems to be a horse at all, as, for example, in this newly released image from NASA's Spitzer Space Telescope. The famous Horsehead nebula makes a ghostly appearance on the far right side of the image, but is almost unrecognizable in this infrared view. In visible-light images, the nebula has a distinctively dark and dusty horse-shaped silhouette, but when viewed in infrared light, dust becomes transparent and the nebula appears as a wispy arc.

The Horsehead is only one small feature in the Orion Molecular Cloud Complex, dominated in the center of this view by the brilliant Flame nebula (NGC 2024). The smaller, glowing cavity falling between the Flame nebula and the Horsehead is called NGC 2023. These regions are about 1,200 light-years away.

The two carved-out cavities of the Flame nebula and NGC 2023 were created by the destructive glare of recently formed massive stars within their confines. They can be seen tracing a spine of glowing dust that runs through the image.

The Flame nebula sits adjacent to the star Alnitak, the westernmost star in Orion's belt, seen here as the bright blue dot near the top of the nebula.

In this infrared image from Spitzer, blue represents light emitted at a wavelength of 3.6-microns, and cyan (blue-green) represents 4.5-microns, both of which come mainly from hot stars. Green represents 8-micron light and red represents 24-micron light. Relatively cooler objects, such as the dust of the nebulae, appear green and red. Some regions along the top and bottom of the image extending beyond Spitzer's observations were filled in using data from NASA's Wide-field Infrared Survey Explorer, or WISE, which covered similar wavelengths across the whole sky.

Image credit: NASA/JPL-Caltech

Note: For more information, see Horsehead of a Different Color.

Star Cluster NGC 2024 in the Flame Nebula

Stars are often born in clusters or groups, in giant clouds of gas and dust. Astronomers have studied two star clusters using NASA's Chandra X-ray Observatory and infrared telescopes and the results show that the simplest ideas for the birth of these clusters cannot work.

This composite image shows one of the clusters, NGC 2024, which is found in the center of the so-called Flame Nebula about 1,400 light years from Earth. In this image, X-rays from Chandra are seen as purple, while infrared data from NASA's Spitzer Space Telescope are colored red, green and blue.

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.

Explanations for the new findings can be grouped into three broad categories. The first is that star formation is continuing to occur in the inner regions. This could have happened because the gas in the outer regions of a star-forming cloud is thinner and more diffuse than in the inner regions. Over time, if the density falls below a threshold value where it can no longer collapse to form stars, star formation will cease in the outer regions, whereas stars will continue to form in the inner regions, leading to a concentration of younger stars there.

Another suggestion is that old stars have had more time to drift away from the center of the cluster, or be kicked outward by interactions with other stars. Finally, the observations could be explained if young stars are formed in massive filaments of gas that fall toward the center of the cluster.

These results will be published in two separate papers in The Astrophysical Journal and are available online (papers 1 and 2). They are part of the MYStIX (Massive Young Star-Forming Complex Study in Infrared and X-ray) project led by Penn State astronomers.

Image credit: X-ray: NASA/CXC/PSU/K.Getman, E.Feigelson, M.Kuhn and the MYStIX team; Infrared: NASA/JPL-Caltech

Note: For more information, see NASA Delivers New Insight into Star Cluster Formation and Flame Nebula: NASA's Chandra Delivers New Insight into Formation of Star Clusters.

Orion B Molecular Cloud

This image shows the Orion B molecular cloud, a vast star-forming complex in the constellation Orion, as viewed at far-infrared wavelengths with ESA's Herschel Space Observatory. At about 1300 light-years, Orion B is one of the closest regions of star formation.

This massive stellar nursery reveals itself through the glow of cosmic dust in the interstellar material that pervades it. Heated by radiation from newborn stars, the dust shines brightly at far-infrared wavelengths, revealing a tangled network of filaments.

The bright yellow, white and pink areas in the image are the densest regions, where many protostars and newborn stars are found. Darker regions correspond to colder portions of the cloud where star formation is not as active. On the right-hand side of the image, the cloud exhibits a very sharp edge where the material in Orion B is being compressed by powerful winds blowing from clusters of massive stars located beyond the field of this image. These mighty stellar winds have sculpted the iconic Horsehead Nebula, glowing brightly on the right-hand edge of the Herschel image.

Herschel's far-infrared view of Orion B also shows other pockets of star-forming gas and dust nestled in the intricate structure of this cloud: NGC 2024, also known as the Flame Nebula, and NGC 2023 on the right-hand side of the image, to the left of the Horsehead Nebula; and NGC 2071 and NGC 2068 on the left-hand side of the image.

This false-color image combines data acquired with the PACS instrument at 70 micron (shown in blue) and 160 micron (shown in green) and with the SPIRE instrument at 250 micron (shown in red).

Image credit: ESA/Herschel/PACS, SPIRE/N. Schneider, Ph. André, V. Könyves (CEA Saclay, France) for the 'Gould Belt survey' Key Programme.

Note: For more information, see A Horsehead, A Flame and Hidden Gems in Orion B and Herschel’s View of the Horsehead Nebula.

Messier 42 - The Orion Nebula

The Orion nebula is featured in this sweeping image from NASA's Wide-field Infrared Survey Explorer, or WISE. The constellation of Orion is prominent in the evening sky throughout the world from about December through April of each year. The nebula (also cataloged as Messier 42) is located in the sword of Orion, hanging from his famous belt of three stars. The star cluster embedded in the nebula is visible to the unaided human eye as a single star, with some fuzziness apparent to the most keen-eyed observers. Because of its prominence, cultures all around the world have given special significance to Orion. The Maya of Mesoamerica envision the lower portion of Orion, his belt and feet (the stars Saiph and Rigel), as being the hearthstones of creation, similar to the triangular three-stone hearth that is at the center of all traditional Maya homes. The Orion nebula, lying at the center of the triangle, is interpreted by the Maya as the cosmic fire of creation surrounded by smoke.

This metaphor of a cosmic fire of creation is apt. The Orion nebula is an enormous cloud of dust and gas where vast numbers of new stars are being forged. It is one of the closest sites of star formation to Earth and therefore provides astronomers with the best view of stellar birth in action. Many other telescopes have been used to study the nebula in detail, finding wonders such as planet-forming disks forming around newly forming stars. WISE was an all-sky survey giving it the ability to see these sites of star formation in a larger context. This view spans more than six times the width of the full moon, covering a region nearly 100 light-years across. In it, we see the Orion nebula surrounded by large amounts of interstellar dust, colored green.

Astronomers now realize that the Orion nebula is part of the larger Orion molecular cloud complex, which also includes the Flame nebula. This complex in our Milky Way galaxy is actively making new stars. It is filled with dust warmed by the light of the new stars within, making the dust glow in infrared light.

Color in this image represents specific infrared wavelengths. Blue represents light emitted at 3.4-micron wavelengths and cyan (blue-green) represents 4.6 microns, both of which come mainly from hot stars. Relatively cooler objects, such as the dust of the nebulae, appear green and red. Green represents 12-micron light and red represents 22-micron light.

Image credit: NASA/JPL-Caltech/UCLA

Note: For more information, see WISE Feels the Heat from Orion's Sword.

The Flame Nebula in Infrared

The Flame Nebula sits on the eastern hip of Orion the Hunter, a constellation most easily visible in the northern hemisphere during winter evenings. This view of the Flame nebula from WISE, NASA's Wide-field Infrared Survey Explorer, shows an expanded view over one previously released of this enormous space cloud (PIA13448).

The previous image was made from data WISE collected after its coolant began to run out, when only three of WISE's infrared bands were in operation. The Flame Nebula is a very infrared-bright region, and the reduced sensitivity during the 3-band phase of the WISE mission worked to the advantage of astronomers interested in studying the brightest parts of this region without so much glare. This new image includes more data collected from all of WISE's four infrared bands. This view takes in a vast cloud of gas and dust where new stars are being born. Three familiar nebulae are visible in the central region: the Flame nebula, the Horsehead nebula, and NGC 2023. The Flame is the brightest and largest in the image. It is being lit up by a star inside it that is 20 times the mass of the sun and would be as bright to our eyes as the other stars in Orion's belt if it weren't for all the surrounding dust, which makes it appear 4 billion times dimmer than it really is.

NGC 2023 is the bright knot below the Flame. The famous Horsehead nebula is visible poking out of the edge of the cloud, just to the right of NGC 2023 and down a touch. It takes on a very different view in infrared compared to visible light. In visible light, the horse's head is a silhouetted dark cloud in front of glowing gas. But here, we see the dust in that dark cloud glowing in infrared light.

Two of the three stars in Orion's belt are visible in this image, but despite their prominence to our eyes in the night sky, they are somewhat unremarkable as seen by WISE. Alnitak, the far left star in Orion's belt, is a multiple blue-giant star system located 736 light-years away. In this image, it is located just to the right of the central part of the Flame nebula. Alnilam, the middle star of Orion's belt, is a variable blue supergiant, located 1,980 light-years away. Despite having a radius 24 times bigger than the sun, and luminosity 275,000 times greater than the sun, it only appears as a moderately bright star near the upper right corner of this image.

Another noteworthy feature in this image is the bright red arc at the lower right. This arc surrounds the star Sigma Orionis, the upper star in the sword of Orion, which hangs from his belt. It is a blue dwarf multiple star system, located 1,070 light-years away. It is moving through space at a breathtaking speed of 5,260,000 mph (2,400 kilometers per second). At that speed, winds from the star system crash into the gas and dust outside the system and create a bow shock, where material in front of the speeding Sigma Orionis system is piling up. The energy from the bow shock heats up dust in the region and makes it glow in infrared.

Color in this image represents specific infrared wavelengths. Blue represents light emitted at 3.4-micron wavelengths, and cyan (blue-green) represents 4.6-microns, both of which come mainly from hot stars. Relatively cooler objects, such as the dust of the nebulae, appear green and red. Green represents 12-micron light and red represents 22-micron light.

Photo credit: NASA/JPL-Caltech/UCLA

Nebulae in Orion

This mosaic image taken by NASA's Wide-field Infrared Survey Explorer, or WISE, features three nebulae that are part of the giant Orion Molecular Cloud. The image covers an area of the sky about three times as high and wide as the full moon (1.5 by 1.8 degrees). Included in this view are the Flame Nebula, the Horsehead Nebula and NGC 2023.

Despite its name, there is no fire roaring in the Flame Nebula. What makes this nebula shine is the bright blue star seen to the right of the central cloud. This star, Alnitak, is the easternmost star in Orion's belt. Wind and radiation from Alnitak blasts away electrons from the gas in the Flame Nebula, causing it to become ionized and glow in visible light. The infrared glow seen by WISE is from dust warmed by Alnitak's radiation. Also known as NGC 2024 and Orion B, this nebula is classified as a molecular cloud.

The famous Horsehead Nebula appears in this image as a faint bump on the lower right side of the vertical dust ridge. In visible light, this nebula is easily recognizable as a dramatic silhouette in the shape of a horse's head. It is classified as a dark nebula because the dense cloud blocks out the visible light of the glowing gas behind it. WISE's infrared detectors can peer into the cloud to see the glow of the dust itself.

A third nebula, called NGC 2023, can be seen as a bright circle in the lower half of the image. NGC 2023 is classified as a reflection nebula, meaning that the dust is reflecting the visible light of nearby stars. But here WISE sees the infrared glow of the warmed dust itself.

Color in this image represents specific infrared wavelengths. Blue represents light emitted at 3.4-micron wavelengths, mainly from hot stars. Relatively cooler objects, such as the dust of the nebulae, appear green and red. Green represents 4.6-micron light and red represents 12-micron light.

This image was made from data collected after WISE began to run out of its supply of solid hydrogen cryogen in August 2010. Cryogen is a coolant used to make infrared detectors more sensitive. WISE mapped the entire sky by July using four infrared detectors, but during the period from August to October, 2010, while the cryogen was depleting, WISE had only three detectors operational, and the 12-micron detector was less sensitive. This turned out to be a good thing in the case of this image, because the less-sensitive detector reduced the glare of the Flame portion of the nebula enough to bring out details of the rest of the nebula.

Photo credit: NASA/JPL-Caltech/UCLA