JWST has captured beautiful clouds of star formation in other galaxies : ScienceAlert

There is a lot going on in the space between the stars.

There, the thin dust and gas that fill the voids sometimes come together to form dense clouds. This is where stars are born, forming from clumps of material that collapse and ignite under gravity to light up the universe.

Shrouded in nebula, the actual process of star formation is still largely a mystery. But JWST, with its unprecedented resolution in infrared wavelengths, sees what our eyes cannot.

Images from the space telescope are being used to piece together the secrets of how and where star formation takes place in 19 nearby spiral galaxies, and to map the gas and dust swirling around.

The project is called Physics at High Angular resolution in Nearby Galaxies (PHANGS), and 21 papers describing the first findings on four of these galaxies have just been published in a special issue of The Astrophysical Journal Letters.

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“With JWST, you can create incredible maps of nearby galaxies at very high resolution that provide incredibly detailed images of the interstellar medium,” says physicist Karin Sandstrom of the University of California, San Diego.

The reason JWST is able to see into parts of galaxies that are opaque to other telescopes is not only because it is the most powerful space telescope ever built, but also because it sees the universe in infrared. Shorter wavelengths of light, such as optical, scatter small particles, and therefore tend not to penetrate thick clouds. Longer wavelengths, such as infrared, have a much greater chance of slipping through the dust unimpeded.

Previous infrared space telescopes, such as Spitzer, have hinted at the infrared treasures hidden in these clouds, but JWST’s spectacular resolution gives us an unprecedented view inside.

A comparison of M74 (also known as NGC 628 or the Phantom Galaxy) images from the Spitzer Space Telescope (l) and JWST (r). (SST: NASA/JPL-CalTech/JWST: NASA, ESA, CSA, STScI)

The PHANGS project is specifically designed for this, studying a selection of 19 nearby spiral galaxies with properties similar to the Milky Way, oriented in space so that we see them face-to-face. This orientation allows us to get the best overview of the distribution of dust and gas in the galaxies, and can more accurately map where star formation does and does not occur.

In just the first four galaxies studied for PHANGS – M74, NGC 7496, IC 5332 and NGC 1365 – scientists have been able to pick out fine structures in incredible detail, including features extending from the galactic centers called bars, and “tracks” of cold gas between the spiral arms – regions thought to be rich in star formation.

NGC 1365, one of the galaxies studied in the first phase of the PHANGS project. (NASA, ESA, CSA and J. Lee/NOIRLab, A. Pagan/STScI)

“The clarity with which we see the fine structure certainly surprised us,” says Ohio State University astronomer Adam Leroy.

According to astrophysicist Nadine Neumayer of the Max Planck Institute for Astronomy in Germany, “The new PHANGS-JWST data give us a fascinating insight into the star formation of surrounding spiral galaxies at the highest resolution.”

These images finally allow scientists to confirm that star formation is indeed taking place between the well-defined spiral arms: they pinned baby stars in their tracks.

They also found some mysteries, such as the heart of galaxy M74, also known as NGC 628 or the Phantom Galaxy. Here, the galactic nucleus, which consists of a cluster of stars surrounding a supermassive black hole, sits in a 1,300-light-year-wide cavity completely devoid of gas and dust. How this region was evacuated is a puzzle.

The mysterious empty heart of M74, the Phantom Galaxy. (ESA/Webb, NASA & CSA, J. Lee and the PHANGS-JWST team)

Other teams focused on the chemistry of the interstellar medium, investigating the presence of polycyclic aromatic hydrocarbons (PAHs). These molecules are easily ionized and uniformly distributed, making them an excellent tracer of the entire interstellar medium.

Together, these first results suggest that PHANGS has a lot to tell us about how galaxies make new stars.

“One of the things I’m most excited about is now that we have this high-resolution tracer of the interstellar medium, we can map all kinds of things, including the structure of the diffuse gas, which has to become denser and molecular for star formation to happen,” says Sandstrom .

“We can also map the gas around newly formed stars where there is a lot of ‘feedback’ such as from supernova explosions. We really get to see the whole cycle of the interstellar medium in great detail. It’s at the heart of how a galaxy comes to form stars.”

The 21 papers are published in a special issue of The Astrophysical Journal Letters.

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