Star Formation

Feast Your Eyes on this Star-Forming Region, Thanks to the JWST

Nature is stingy with its secrets. That’s why humans developed the scientific method. Without it, we’d still be ignorant and living in a world dominated by superstitions.

Astrophysicists have made great progress in understanding how stars form, thanks to the scientific method. But there’s a lot they still don’t know. That’s one of the reasons NASA built the James Webb Space Telescope: to coerce Nature into surrendering its deeply-held secrets.

In our time, the scientific method can’t accomplish much without powerful scientific instruments, and the JWST is one of the most powerful ever devised. It has the power to examine star formation regions in more detail than any other telescope, teasing out previously unseen details and processes. As it does so, it gathers some startling images.

In this image, the blue tendrils are emissions from dusty silicates, a common type of dust, and polycyclic aromatic hydrocarbons (PAHs.) PAHs are organic compounds that scientists think could be some of life’s building blocks. The more diffuse red regions are made of warm dust heated by the massive, bright stars in the region’s center. The faint arcs in the image may be created by light reflecting off the central stars. The brightest patches and filaments indicate regions brimming with abundant protostars.

This image is just one way that the JWST can examine star-forming regions. But nature sends clues out in multiple wavelengths, and it’s up to us to decipher it. The leading image was taken with the space telescope’s Mid-Infrared Instrument (MIRI.) Back in January, the telescope imaged the same region with its NIRCam instrument, and it sees in the near-infrared portion of the spectrum.

This is the JWST’s NIRCam image of the same region, NGC 346. This image cuts through more of the gas and dust to reveal more individual stars. Combining the images gives astronomers a more complete idea of the star-forming region. Image Credit: NASA, ESA, CSA, STScI, A. Pagan (STScI); CC BY 4.0

There’s a near-infinite selection of targets that the JWST could study during its mission. Why NGC 346?

The star-forming region is in the Small Magellanic Cloud, and the SMC has a much lower metallicity than the Milky Way. That means it’s made of mostly hydrogen and helium and very little else. It’s similar to the ancient Universe. It takes generations of stars living and dying to create heavier elements—or metals—so the SMC’s low metallicity is similar to the early Universe. In the early Universe, there wasn’t enough time for many stars to live and die and spread their heavy elements out into space.

Studying star formation in the SMC and NGC 346 is an analog for studying star formation in the early Universe. Specifically, it’s similar to the Universe’s ‘Cosmic Noon’ about two or three billion years after the Big Bang when star formation peaked.

Peak star formation occurred during the ‘Cosmic Noon’ about 2 or 3 billion years ago. Image Credit: ESA (acknowledgement: work performed by ATG under contract to ESA), CC BY-SA 3.0 IGO

“A galaxy during cosmic noon wouldn’t have one NGC 346, as the Small Magellanic Cloud does; it would have thousands,” said Margaret Meixner, an astronomer at the Universities Space Research Association. “But even if NGC 346 is now the one and only massive cluster furiously forming stars in its galaxy, it offers us a great opportunity to probe the conditions that were in place at cosmic noon.”

Comparing star formation in metal-poor regions to star formation in the higher-metallicity Milky Way is one way of prying loose some of nature’s secrets. Astronomers have studied NGC before in the infrared, but they could only examine stars with between five to eight solar masses. But the Webb obliterates that observational limit.

The JWST can probe protostars as small as 10% of one solar mass. This gives astrophysicists a more granular way to compare star formation between low-metallicity and higher-metallicity environments and quantify the differences. Webb is also able to see dust around these small stars, whereas previous observations revealed only gas. So they’re not only seeing infant stars forming, they’re also seeing the building blocks of eventual planets.

“We’re seeing the building blocks, not only of stars but also potentially of planets,” said Guido De Marchi of the European Space Agency when the NIRCam image was released. “And since the Small Magellanic Cloud has a similar environment to galaxies during cosmic noon, it’s possible that rocky planets could have formed earlier in the universe than we might have thought.”

The JWST is changing astronomy. Previously, we had no way to begin to determine if planets formed alongside stars in the Cosmic Noon, but the JWST is giving us a way to probe that important period in the life of the Universe.

Astronomers have observed NGC 346 with many different telescopes, including the Hubble. Viewing the Hubble’s image of NGC 346 highlights the strength of both space telescopes and how their images can work together.

This Hubble Space Telescope image shows different details in NGC 346. It highlights how a torrent of radiation from the hot stars in NGC 346, at the centre of the image, eats into denser areas around it. It’s almost hard to believe this is a natural object. Image Credit: NASA, ESA and A. Nota (ESA/STScI, STScI/AURA)

The star formation taking place inside NGC 346 is hidden by multiple veils, each one corresponding to different wavelengths of light. The following video shows how each telescope and instrument removes a specific veil obscuring NGC 346. By observing regions like NGC 346 with different instruments and in different wavelengths, astronomers have a better chance of uncovering nature’s star-formation secrets.

The JWST has only been observing for about 15 months. In this period of time, it’s proven to be our most effective telescope. It’s slowly and methodically working to reveal Nature’s secrets.

We’re already wondering where we’d be without it.

Evan Gough

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