Published: Saturday, May 18, 2020
Three images captured by JWST of the Orion Nebula show the familiar star-forming region in an exciting new light
Image credit: NASA/ESA/CSA E. Dartois and E. Habart (PDRs4All ERS Team)
Orion Nebula is a well-known and well-studied celestial body, but the new images taken by the James Webb Space Telescope show it in a new and vibrant way.
The Orion Nebula (also known as M42) is located approximately 1,500 light-years from Earth, towards the constellation Orion. It is the nearest large star-forming and stellar nursery in our solar system.
The Orion Nebula is visible to the naked-eye under dark skies. But the JWST images reveal it in unprecedented detail. The powerful space telescope focused on the “Orion Bar,” a diagonal, ridgelike feature of dust and gas in the lower left quadrant M42.
Images collected by the JWST PDRs4All Program are more valuable than just their beauty. The data collected by the JWST’s PDRs4All program will enable scientists to explore the messy and chaotic conditions associated with star formation.
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The images are so detailed that we’ll be studying them for years to come. Els Peeters, Western University astrophysicist, and PDRs4All principal investigator said that the data were incredible and would serve as benchmarks in astrophysics for many decades. “We have only explored a small fraction of the data so far. This has already led to several major and surprising discoveries.”
The Orion Nebula is a mess when it comes to star birth
When dense patches of dust and gas collide under their own weight, a star is formed. This creates a protostar, which is then wrapped in the natal cocoon made of dust and gas.
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The protostars will continue to collect material from their natal envelops until they gather enough mass in order to trigger nuclear fusion. This process is what defines a main sequence star, like our sun. It will have undergone this process around 4.65 billion years ago.
It’s more complex than you might think, as these dense patches don’t collapse all at once, nor are they all of the same size.
Peeters explained that the process of star formation was messy, because it involves stars at various stages of development embedded in their natal clouds. Also, many physical and chemical processes interact with each other.
Photo-dissociation zones or PDRs (the PDRs in PDRs4All) are a key part of understanding gas and dust that exists between stars, or the “interstellar media” from which new stars form. PDRs’ chemistry and physics are determined by the interaction of ultraviolet radiation with dust and gas.
This bombardment of radiation creates structures such as the Orion Bar. It is the edge of a bubble that has been carved by the stars powering the nebula.
The same structural details which give these images an aesthetic appeal reveal a more complex structure than what we initially thought. Background and foreground gas and dust make the analysis harder. PDRs4All member Emile Habart, from the University of Paris Saclay, said. These images are so good that we can clearly separate the regions and show that the Orion Bar’s edge is steep like a wall. This was predicted by theories.
The JWST was able to see the Orion Bar in a way that had never been seen before. The spectrum of light it produced also allowed them to determine the chemical composition of the Orion Bar. Chemical elements emit and absorb light at specific wavelengths. This allows them to leave their fingerprints in the spectrum of light that passes through dust and gas.
The PDRs4All Team was able to determine the chemical composition of M42 and how it changes with temperature, density and radiation field strength.
This investigation led to the detection of 600 chemical fingerprints within the spectrum of the Orion Nebula. These fingerprints could be used to improve PDR models.
Peeters explained that the spectroscopic dataset covered a smaller area than the images but contained a lot more information. “A picture may be worth a 1,000 words, but astronomers say a spectrum can be worth a 1000 images,” Peeters said.
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The PDRs4All Team also addressed a long-standing problem in previous observations of Orion Nebula. This was a steep variation of emissions from dust within the Orion Bar whose origin could not be explained. This investigation revealed this emission variation was caused by a destructive process that occurred in the Orion Bar, sparked by radiation from young massive stars.
JWST image shows the region northeast from the Trapezium cluster, which is the heart of Orion Nebula. Image credit: NASA/ESA/CSA E. Dartois E. Habart PDRs4All ERS Team. “The sharp hyperspectral data contained so much more information that it pointed out the attenuation by dust and efficient destruction of the smallest particles as the underlying causes for these variations,” said team member Meriem El-Yajouri, Institut d’Astrophysique Spatiale Postdoctoral Researcher.
PDRs4All was able to extract details from the Orion Nebula about large molecules containing carbon known as polycyclic hydrocarbons (PAHs). They are among the biggest reservoirs of carbon-based material in the cosmos and may account for up to 20% of all carbon in the universe.
The study of PAHs will help us understand the possibility of life on planets around young stars.
Cami said, “We study what happens to the carbonaceous molecule long before it enters our bodies.”
PAH molecules have a long lifespan due to their resilience and durability. The JWST can use their bright emissions to show that, despite the PAHs’ toughness, the ultraviolet light of young stars is still able to alter the emissions.
Peeters said, “It’s an embarrassment.” Even though large molecules were thought to be extremely sturdy, UV radiation changed the properties of the molecules responsible for the emission.
The results showed that ultraviolet radiation can break down smaller carbon molecules, while it can also change the emission of larger molecules. The Orion Nebulas show these effects in different extremes. They move from shielded to more exposed areas.
The Orion Bar’s edge-on geometry allows us to observe in great detail the physical and chemical reactions that occur as we move away from the harsh, ionized area into the more shielded region where molecular gases can form. This is Jan Cami, a Western University researcher and member of the PDRs4All research team.
Machine learning was used to evaluate PAHs. It revealed that, even though ultraviolet light does not break down these molecules, it can change their structure.
Cami concluded that “These papers show some kind of survival of fittest at a molecular-level in the harshest environment in space.”
The team’s work is published in six articles in the journal Astronomy and Astrophysics
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Robert Lea, a U.K. science journalist, has published articles in Newsweek, ZME Science, Newsweek, Astronomy, Newsweek, and Physics World. Robert Lea also writes for Elsevier, the European Journal of Physics and Newsweek about science communication. Rob has a Bachelor of Science degree in Physics and Astronomy from the Open University, U.K. Follow him on twitter @sciencef1rst.
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Source: Space.com