by The Orion Nebula may be a familiar and well-studied celestial object, but new images from the James Webb Space Telescope (JWST) show this star-shaped cloud of gas and dust in a remarkably new and vibrant light.
The Orion Nebula, also known as “Messier 42” (M42), is located approximately 1,500 light years from Earth in the direction of the Orion constellation. It is therefore the nearest large star-forming and stellar nursery to our solar system.
Visible to the naked eye under dark skies, the Orion Nebula has been studied throughout human history, but the JWST images show it in unprecedented detail. In particular, the powerful space telescope zoomed in on the diagonal feature, like a ridge of gas and dust in the lower left quadrant of M42 called “the Orion Bar.”
The images collected as part of JWST’s PDRs4All program are valuable for more than their stunning beauty. This trove of data will enable scientists to grapple with the often confusing and chaotic conditions of star formation.
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“These images have incredible data that we will be scrutinizing for years to come. The data is incredible and will serve as benchmarks for astrophysics research for years to come,” said the Western University astrophysicist and investigator PDRs4All Els Peeters in a statement. “So far, we’ve only explored a small portion of the data, and this has already led to some surprising and major discoveries.”
Star birth in the Orion Nebula is a mess
Star formation occurs when dense patches of massive clouds of gas and dust collapse under their own gravity. This creates a “protostar” wrapped in a prenatal cocoon of gas and dust left over from its formation.
Protostars continue to gather material from their natal envelope until they have accumulated enough mass to fuel nuclear fusion of hydrogen into helium in their cores. This process defines a main sequence star like our sun, which went through this process about 4.6 billion years ago.
The situation is more complicated than it might seem at first, however, because not all of these intense patches are of the same size or mass, and they do not all fall at the same time.
“The star formation process is messy because star-forming regions have stars of different masses at different stages of their development while still embedded in their natal cloud and because there are many different physical and chemical processes at work that influence each other ,” Peeters said. .
One of the most important aspects of understanding the gas and dust between stars or “interstellar medium” from which other stars are formed is the physics of photodissociation regions or “PDRs” (the PDR in PDRs4All). The chemistry and physics of PDRs is determined by how ultraviolet radiation from hot young stars interacts with gas and dust.
In the Orion Nebula, this radiation bombardment is creating structures like the Orion Bar, which is essentially the edge of a large bubble carved out by some of the massive stars that power the nebula.
“The same structural details that give these images their aesthetic appeal reveal a more complex structure than we first thought – with foreground and background gas and dust making the analysis a bit more difficult,” said team member Emile Habart PDRs4All from the University of Paris-Saclay. . But these images are of such a quality that we can separate these regions well and reveal that the edge of the Orion Bar is very sharp, like a giant wall, as predicted by theories.”
The JWST allowed researchers to not only see the structure of the Orion Bar like never before, but the spectrum of light from the Orion Bar also allows them to determine how its chemical composition varies around the globe. This is possible because chemical elements absorb and emit light at specific wavelengths, leaving their fingerprints on the spectrum of light passing through gas and dust.
This helped reveal the large-scale chemical composition of M42, allowing the PDRs4All team to see how temperature, density and radiation field strength change through the Orion Nebula.
Finding more than 600 chemical fingerprints in the spectrum of the Orion Nebula during this investigation could greatly improve the models of PDRs.
“The spectroscopic data set covers a much smaller area of the sky compared to the images, but there is a ton of additional information,” said Peeters. “A picture is worth a thousand words, but we astronomers half-heartedly say that a spectral image is worth a thousand.”
The James Webb Space Telescope leaves other telescopes in the dust
The PDRs4All team also tackled a long-standing problem with previous observations of the Orion Nebula, namely a large variation in dust emissions in the Orion Bar, the origin of which could not be explained. This investigation showed that this variation in emissions was the result of a destructive process in the Orion Bar spark radiating from young massive stars.
“The sharp spectral data from JWST contains so much more information than previously observed that it clearly showed that the attenuation of radiation by dust and the effective destruction of the smallest dust particles is the root cause of these changes,” team member and Institut d’Astrophysique. Spatiale postdoctoral researcher Meriem El Yajouri said.
The PDRs4All team was also able to include data on emissions from the Orion Nebula that come from large carbon molecules called polycyclic aromatic hydrocarbons (PAHs). These happen to be among the largest reservoirs of carbon-based materials in the cosmos, estimated to be responsible for up to 20% of the carbon in the universe.
As the only carbon-based life in the cosmos that we know of, the study of PAHs is extremely relevant to our understanding of the existence of life on planets that form around young stars.
“We are studying what happens to carbon molecules long before the carbon makes its way into our body,” said Cami.
The PAH molecules are long lasting due to their sturdiness and resilience. Their emissions are bright, and the JWST is able to use these to determine that ultraviolet light from young stars can change those emissions even when they are as intense as the PAHs.
“It’s an embarrassment of riches,” Peeters said. “Although these large molecules are thought to be very sturdy, we found that UV radiation changes the overall properties of the molecules that cause the emission.”
This showed that ultraviolet radiation breaks apart smaller carbon molecules and changes the emission of larger molecules. These effects are seen in varying extremes throughout the Orion Nebula, moving from shielded environments to more exposed regions.
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“What makes the Orion Bar truly unique is its edge-on geometry, which gives us a ringside seat to study in exquisite detail the various physical and chemical processes that occur as we move from the highly exposed ionized region to to the highly exposed ionized area. protected regions where molecular gas can form,” said Jan Cami, PDRs4All team member and Western University researcher.
By using machine learning to evaluate HIAs, it was revealed that even when ultraviolet light does not break these molecules, it can change their structure.
“These papers reveal that the fittest at the molecular level are somehow safe in the harshest environments in space,” Cami said.
The team’s research is published over a series of six papers in the journal Astronomy & Astrophysics
