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-forming cloud of gas and dust in an incredibly 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 constellation Orion. This makes it the closest large nursery of stars and star formation 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 ridge-like feature of gas and dust in M42’s lower left quadrant, called “Orion’s Bar.”
The images collected through JWST’s PDRs4All program are valuable beyond their stunning beauty. This trove of data will allow scientists to delve into the often messy and chaotic conditions that accompany star formation.
Related: James Webb Space Telescope suggests supermassive black holes arise from heavy cosmic ‘seeds’
“These images are so detailed that we will be looking at them for many years. The data is incredible and will serve as a benchmark for astrophysics research for decades to come,” said Els Peeters, an astrophysicist at Western University and principal investigator of the PDRs4All, in a press release. . “So far, we have only explored a tiny fraction of the data, which has already resulted in several surprising and major discoveries.”
Star birth is complicated in the Orion Nebula
Star formation occurs when overly dense areas in gigantic clouds of gas and dust collapse under their own gravity. This forms a “protostar” enveloped in a natal cocoon of gas and dust left behind by its formation.
Protostars continue to gather material in their native envelopes until they have gathered enough mass to trigger the nuclear fusion of hydrogen to helium in their cores. This process defines a main sequence star like our Sun, which will have undergone this process approximately 4.6 billion years ago.
The situation is more complicated than it first appears, however, because these overly dense areas are not all the same size or mass, and they do not all collapse at the same time.
“The process of star formation is complicated because star-forming regions contain stars of varying masses at different stages of their development while still embedded in their natal cloud and because many different physical and chemical processes are in play and 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 created is the physics of photo-dissociation regions or “PDRs” (the PDR in PDRs4All). The chemistry and physics of PDRs are determined by how ultraviolet radiation from hot young stars interacts with gas and dust.
In the Orion Nebula, this bombardment of radiation creates 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 initially thought – with gases and dust in the foreground and background making the analysis a bit more difficult,” said Emile Habart, member of the PDRs4All team at the University of Paris-Saclay. . “But these images are of such quality that we can separate these regions well and reveal that the edge of the Orion Bar is very steep, like a huge wall, as theories predict.”
The JWST allowed researchers not only to see the structure of the Orion bar like never before, but the spectrum of light from the Orion bar also allowed them to determine how its chemical composition varies across it. This is possible because chemical elements absorb and emit light at characteristic wavelengths, leaving their fingerprints on the spectrum of light passing through gases and dust.
This helped reveal the large-scale chemical composition of M42, allowing the PDRs4All team to see how the temperature, density and radiation field intensity change across the Orion Nebula.
The detection of more than 600 chemical fingerprints in the spectrum of the Orion Nebula during this survey could significantly improve PDR models.
“The spectroscopic data set covers a much smaller area of the sky than the images, but it contains much more information,” Peeters said. “A picture is worth a thousand words, but we astronomers half-jokingly say that a spectrum is worth a thousand pictures.”
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 revealed that this variation in emission was the result of a destructive process of the Orion Bar spark by the radiation of young massive stars.
“The JWST hyperspectral data contains so much more information than previous observations that they clearly indicate that attenuation of radiation by dust and the effective destruction of smaller dust particles is the underlying cause of these variations,” member of the team and the Institute of Astrophysics. » said Meriem El Yajouri, postdoctoral space researcher.
The PDRs4All team was also able to uncover details about emissions from the Orion Nebula that come from large carbon molecules known as polycyclic aromatic hydrocarbons (PAHs). It is one of the largest reservoirs of carbon-based materials in the cosmos, thought to account for up to 20% of the universe’s carbon.
Because the only life in the cosmos that we know of is carbon-based, the study of PAHs is extremely relevant to our understanding of the existence of life on planets that form around young stars.
“We study what happens to carbon molecules long before carbon enters our bodies,” Cami added.
PAH molecules last a long time due to their robustness and resilience. Their emissions are bright, and JWST is able to use them to determine that even with the resistance of PAHs, ultraviolet light from young stars can modify these emissions.
“It really is an embarrassment of riches,” Peeters said. “Even though these large molecules are thought to be very robust, we found that UV radiation changes the overall properties of the molecules causing the emission.”
This revealed that ultraviolet radiation breaks up smaller carbon molecules while emissions from larger molecules are changed. These effects are seen at different extremes in Orion’s nebulae, moving from protected environments to more exposed regions.
“What makes the Orion Bar truly unique is its cutting-edge geometry, which gives us a ringside seat to study in great detail the various physical and chemical processes that occur as we move from the ionized region very exposed and harsh to the much more exposed region. protected regions where molecular gases can form,” said Jan Cami, a PDRs4All team member and researcher at Western University.
Using machine learning to evaluate PAHs revealed that even when ultraviolet light doesn’t break down these molecules, it can change their structure.
“These papers reveal a kind of survival of the fittest at the molecular level in the harshest environments of space,” Cami concluded.
The team’s research is published in a series of six articles in the journal Astronomy & Astrophysics.