the James-Webb telescope observed spiral galaxies like never before

Nineteen images published on January 29 show spiral-shaped galaxies in a unique way, like our own, the Milky Way.

Hypnotic and intriguing, they will make your head spin. Nineteen images of spiral-shaped galaxies were published on Monday January 29 by the European (ESA) and American (NASA) space agencies. They were carried out using the instruments of the James Webb Telescope (JWST), the most powerful ever designed. The spiral shape is quite generic for galaxies: this is the case for around 60% of them, according to estimates. Our galaxy, the Milky Way, is one representative.

In these images, the stars glow blue and the shades of orange and red correspond to dust that is around the stars and between the stars. Franceinfo interviewed several scientists to better understand what was observed and photographed.

The Ghost Galaxy (NGC 628)

Located approximately 32 million light years away in the constellation Pisces, this galaxy (also called NGC 628 or M74) has already been observed by James-Webb, leading to the publication of an image in August 2022. Hubble (in visible light) and Spitzer (in infrared) telescopes had already scanned many galaxies, including this one, but the JWST instruments provide incredible detail.

These visuals are “amazing even for researchers who have studied these galaxies for decades”commented Janice Lee, scientist at the Space Telescope Science Institute in Baltimore (United States). What Annie Hughes, member of the Phangs project (Physics at High Angular resolution in Nearby GalaxieS) which monitors 90 large galaxies where stars are forming and has a front-row seat to study these new photos: “We know these objects, we know the power of the James-Webb, it has been in the works for decades. But when the images arrived, we still said, ‘Wow!’”

The James-Webb telescope operates in a register that allows us to specifically observe the very first stages of star formation. These arise in vast clouds of gas and dust, these moments of youth are usually masked. But the JWST instruments allow us to penetrate what normally escapes our sight. “When we look in the visible, the dust absorbs the light. We then see dark bands. But this dust emits in the infrared, and with the James-Webb [spécialisé dans l’infrarouge], “We can really see these dust and gas structures.”comments astrophysicist Eric Lagadec.

“We see filaments with gas and dust. We also see holes: that’s where stars exploded.”

Eric Lagadec, astrophysicist

at franceinfo

Generally speaking, there are two main types of spiral galaxies, explained astrophysicist Françoise Combes at the Collège de France in 2017: the “great design”which presents regular shapes, with “spiral arms that go from the center to the edge”and the “stochastic”, who will present “little pieces of spiral arms”but without a coherent structure.

The Phantom galaxy, which is distinguished by its great regularity and strong symmetry, is part of the first family. THE “pattern” of the galaxy NGC 628, which can evoke “lace” according to Annie Hughes, is linked to the way young stars behave and structure their environment, particularly the surrounding gases.

Among the 19 galaxy images highlighted, NGC 4254 (also called M99), located in the Berenice Hair constellation, 50 million light years from Earth, is characterized by great regularity.

The (very) bright galaxy NGC 1087

The pattern of the galaxy NGC 1087, which is in the constellation Whale, 80 million light years away, is less regular than that of the Ghost Galaxy. But Annie Hughes points out that our eye is irremediably drawn to the brilliance of his heart.

This brightness, according to her, is linked to the activity caused by the supermassive black hole which is at the center of this galaxy. The shine can be caused by two things: either there is a lot of material, or it was heated strongly during the transfer of material from the galaxy’s core to its black hole.

The spiral pattern is easier to distinguish with the following images (video), also taken as part of the Phangs project, but made with instruments from the Very Large Telescope of the European Southern Observatory (ESO), which is located in the Atacama Desert, Chile.

Barred spiral galaxies (like NGC 3351 and NGC 1512)

Located in the constellation Leo, 33 million light years from Earth, the galaxy NGC 3351, also called M95, is a spiral galaxy. And more precisely a barred spiral galaxy. A subfamily of which the Milky Way is a part. The spiral arms do not start directly from the center of the galaxy, but from a bar which passes through its center.

In the image above, this bar is blue, highlighting the presence of a cluster of stars concentrated around the center of the galaxy. These stars are all the same age and have different characteristics from those present elsewhere in the galaxy, notes Annie Hughes.

Beyond the central halo, the filaments of the spiral arms are dotted with holes, as has been observed in other cases, such as that of the Phantom galaxy. Overall, the pattern is in the same vein for NGC 1512 (below). This other barred spiral galaxy is in the Clock constellation, about 30 million light years away.

If it specializes in the observation of very distant objects, the new developments brought by the James-Webb telescope, in this section on spiral galaxies, will allow us to better understand the formation of stars.