milky way

Webb’s Infrared Eye Reveals the Heart of the Milky Way

The full view of the NASA/ESA/CSA James Webb Space Telescope’s NIRCam (Near-Infrared Camera) instrument reveals a 50 light-years-wide portion of the Milky Way’s dense centre. An estimated 500,000 stars shine in this image of the Sagittarius C (Sgr C) region, along with some as-yet unidentified features. Image Credit: NASA, ESA, CSA, STScI, S. Crowe (UVA)

The JWST is taking a break from studying the distant Universe and has trained its infrared eye on the heart of the Milky Way. The world’s most powerful space telescope has uncovered some surprises and generated some stunning images of the Milky Way’s galactic center (GC.) It’s focused on an enormous star-forming region called Sagittarius C (Sgr C).

Sgr C is about 25,000 light-years from Earth and 300 light-years away from our galaxy’s supermassive black hole, Sagittarius A* (Sgr A*.) This image contains about 500,000 stars.

The cyan area is a massive region of ionized hydrogen, but its size is a bit of a surprise. Typically, hot young stars ionize the hydrogen gas in a situation like this, but this region is so large that young stars can’t really account for it.

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The deep black region directly above the ionized hydrogen is an infrared-dark cloud (IDC). It’s a part of the molecular cloud that’s extremely dense and cold. Even though the JWST is extremely powerful and has the capacity to discern faint infrared sources, it can’t see what’s not there. Light from the stars beyond the IDC isn’t reaching the Webb. So even though it appears less densely populated than other parts of the image, the opposite is true. The Webb is mostly seeing stars in the foreground.

This image of Sagittarius C (Sgr), captured by Webb’s Near-Infrared Camera (NIRCam), shows compass arrows, a scale bar, and a colour key for reference. This image shows invisible near-infrared wavelengths of light that have been translated into visible-light colours. The colour key shows which NIRCam filters were used when collecting the light. Image Credit: NASA, ESA, CSA, STScI, S. Crowe (UVA)

IDCs were only discovered about 30 years ago, and their nature is still kind of mysterious. They may be where extremely massive stars are born. Only more research can confirm that.

A cluster of young protostars is emerging from the cloud. They appear as a red clump near the bottom of the IDC. One of the stars in the cluster is a previously unknown protostar that’s greater than 30 times the mass of the Sun.

The galactic core is known as a chaotic place. High-velocity compact clouds (HVCCs) move around and sometimes collide with one another in the region. Supernova explosions might have propelled some of these clouds, causing them to collide and triggering another round of star birth.

When viewed in radio waves, supernova remnants (SNRs) pop into view. So do mysterious threads, which are likely related to shifting, intertwining magnetic fields in the region.

The diagonal line of bright objects in this image of the heart of our Milky Way Galaxy are all powerful sources of radio waves. Sgr C is just one of the regions in the Milky Way’s chaotic center. The bright center is the home of the supermassive black hole, Sagittarius A*. The dense, bright circles are the nurseries of new, hot stars, and the bubbles are the graveyards of massive stars that exploded as supernovae. The thread-like shapes are not yet understood but probably trace powerful magnetic field lines. This giant image was assembled from observations made by the Very Large Array (VLA). Image Credit: By NRAO/AUI/NSF and N.E. Kassim, Naval Research Laboratory – https://public.nrao.edu/gallery/labeled-map-of-our-galaxys-center/, CC BY 3.0, https://commons.wikimedia.org/w/index.php?curid=83336763

The Milky Way’s center draws a lot of attention. Astronomers and astrophysicists have been studying it for decades. Before the JWST was ever launched, researchers observed it in radio waves, as in the above image from the Karl Jansky Very Large Array.

NASA’s Chandra X-Ray Observatory has also imaged the region. X-rays reveal different sources and a different type of detail than the VLA or the JWST does. The image below is a composite of Chandra X-ray data and radio wave data from MeerKat.

This 2021 image of the Milky Way’s center shows the larger environment that Sgr C inhabits. It’s made from 370 Chandra images as well as radio images. It shows how threads of superheated gas and magnetic fields are weaving a tapestry of energy at the center of the Milky Way. The green circles are supernova remnants. Image Credit: X-ray: NASA/CXC/UMass/Q.D. Wang; Radio: NRF/SARAO/MeerKAT

Some things in the image still await further study and more detailed explanations, like the rose-coloured region on the right of the image. Like many topics in astrophysics and astronomy, and like many regions in space, the JWST is giving us a new, more detailed look. According to astronomers, the Webb has provided a wealth of new data on Sgr C and the rest of the Milky Way’s centre.

Evan Gough