Science

Details of the star nursery in the “sword of Orion” blown up by the stars

A detailed image of a stellar nursery illuminated by ultraviolet radiation from massive young stars shows how the intense radiation heats and shapes the fuel for star formation.

This zone of ultraviolet exposure, known as the photodissociation region (PDR), is located in the Orion Bar region in the Orion Nebula, located at the center of the “Orion Sword” dangling from Orion’s Belt.

Although this nebula, a dense cloud of cold gas that is a site of intense star formation, appears to be a single star to the naked eye, its true nature as a luminous nursery of stars becomes clear when viewed through a telescope.

Related: Hubble Space Telescope paints stellar outflows in new portrait of Orion Nebula

In this image, massive young stars in this zone can be seen bombarding the nebula and its cold gas—the fuel for star formation—with ultraviolet radiation, heating and shaping it.

Because it is the closest massive star-forming region to Earth, astronomers consider the study of the Orion Nebula an important tool for understanding the circumstances surrounding the birth of our solar system.

Observing the PDR as it is heated by starlight could help better understand the impact of the large amount of ultraviolet light emitted by young stars on the physics and chemistry of their local environment, as well as the shape and structure of the gas clouds they reside in. were born.

“These regions are important because they allow us to understand how young stars affect the gas and dust cloud in which they are born, especially in places where stars such as the Sun are formed,” said Emily Habart, astrophysicist at the University of Paris-Saclay. (will open in a new tab) “Observing areas of photodissociation is like looking into our past.”

The Orion Belt PDR study will be a roadmap for further exploration using the James Webb Space Telescope (JWST), known as the PDRs4All program.

Mosaic of the Orion Bar made by the Hubble Space Telescope (left) and an infrared thermal map of the Orion Bar made by the Keck Observatory’s NIRC2 instrument (right). (Image credit: NASA/STScI/Rice Univ./C.O’Dell et al./Habart et al./WM Keck Observatory) (will open in a new tab)

To capture this new high-detail image, PDRs4All team astronomers surveyed the region using the Second Generation Near Infrared Camera (NIRC2) in combination with the Keck II telescope’s adaptive optics system. Both instruments are located at the W. M. Keck Observatory, located on the Maunakea volcano on the island of Hawaii.

In the image, the various substructures that make up the Orion Bar can be identified in unprecedented detail. These include ridges, globules, and filaments of gas, as well as disks around young stars that form when starlight forms the gas and dust of a nebula, called “proplydes.”

“Never before have we been able to observe on a small scale how the structures of interstellar matter depend on their environment, in particular, how planetary systems can form in environments heavily irradiated by massive stars,” Habart said. “This may allow us to better understand the legacy of the interstellar medium in planetary systems, namely our origins.”

The team will be particularly interested in seeing in PDR images where the gas transitions from a hot ionized state (devoid of electrons) to a warm atomic gas and then back to a cold molecular gas capable of collapsing to form stars.

For Keck Observatory astronomer Carlos Alvarez, one of the most exciting elements of this study is that Keck plays a fundamental role in the era of JWST astronomy.

“It was exciting to be the first, along with my colleagues from the James Webb Space Telescope PDRs4All team, to see the clearest images of the Orion Barrier ever taken in the near infrared,” he said in a statement. (will open in a new tab) “[The] JWST will be able to dive deeper into the Orion bar and other PDRs, and Keck will play an important role in confirming JWST’s early scientific results. Together, the two telescopes can provide a unique insight into PDR gas characteristics and chemistry, helping us understand the nature of these spectacular star-struck regions.”

The team’s research has been accepted for publication in the journal Astronomy & Astrophysics and is currently available to read as a preprint. (will open in a new tab) in the arXiv paper repository.

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