This latest Picture of the Month from the NASA/ESA/CSA James Webb Space Telescope features Messier 77 (M77), a barred spiral galaxy famous and appreciated among astronomers for its combination of relative proximity and spectacular features to study. It is located 45 million light-years away in the constellation Cetus (The Whale). This new image from Webb’s Mid-Infrared Instrument (MIRI) highlights its swirling spiral arms, the dust in its disc and its piercingly bright core like never before.
At the heart of M77 is a compact region filled with hot gas that handily outshines the rest of the galaxy put together, even overcoming the light-gathering capacity of Webb’s cameras. This is an active galactic nucleus (AGN), and it’s powered by M77’s central supermassive black hole, which is eight million times as massive as our Sun. Gas in the galaxy’s central regions is pulled by the strong gravity into a tight and rapid orbit around the black hole, where it crashes together and heats up, releasing tremendous amounts of radiation.
The bright orange lines appearing to radiate out from the centre of M77 are not actually a feature of the galaxy: they are a type of distortion that arises from the optical design of the telescope. Called diffraction spikes, they are created because the intense light from the unresolved AGN is bent (“diffracted”) very slightly at the edges of Webb’s hexagonal mirror panels and around one of the struts that hold up its secondary mirror. This distinctive six-plus-two-pointed pattern is the same for any image taken by Webb. For diffraction spikes to appear, the light source has to be very bright and very concentrated, so they’re most often seen on stars. But in some galaxies, as here, the nucleus is bright and compact enough to make diffraction spikes appear as well.
M77 is not just known for its easily visible AGN, but also as a prolific star-forming galaxy. The near-infrared image of M77 reveals a bar spanning across the central region, which doesn’t appear in visible-light images of the galaxy. The bar is enclosed by a bright ring, called a starburst ring, formed by the inner ends of M77’s two spiral arms. Starburst regions in galaxies are typified by extremely high star-formation rates. This ring is more than 6 000 light-years across and displays intense and widespread starbursts, visible in this image by the densely concentrated orange bubbles all around the ring. Since M77 is relatively close to Earth, this starburst ring is a very well-studied example of the phenomenon.
As an active spiral galaxy, M77’s disc is filled with gas and dust which is both a product of and fuel for future star formation. Webb’s MIRI fills out our view of the galaxy with the glow of interstellar dust grains emitted at longer wavelengths, shown here in blue. The dust forms a huge vortex of smoky, swirling filaments with cavities in between. The glowing orange bubbles carved out by newly formed star clusters are also prominently visible out along the galaxy’s arms.
Beyond Webb’s quite focused view, M77’s arms join into a faint extended ring of hydrogen gas thousands of light-years wide, where yet more star formation is taking place. Vast, tenuous filaments of hydrogen gas stretch across this ring and out into intergalactic space, forming an outermost layer around the galaxy. For the tentacle-like appearance of these filaments, M77 is also named the Squid Galaxy.
The data used to create this image are from an observing programme (#3707) that surveyed massive, nearby, star-forming galaxies to create a rich dataset useful for many scientific investigations. As can be seen here, the stunning resolution of Webb’s instruments reveals star clusters and rich reservoirs of gas, which can be used to explore the cycle of star formation, life and death in these and other galaxies.
Source: ESA/Webb/potm
Links
- Messier 77 (MIRI + NIRCam image)
- Messier 77 (NIRCam image)
- Image on ESA website
- Space Sparks episode
- Pan video
- Transition video
