Dust is both an astronomer’s dream and nightmare.
Dark, dusty molecular clouds like this image of Barnard 59, part of the Pipe Nebula found in our Milky Way, collapse over time to give rise to new stars, with the densest regions inside forming the most massive stars. However, even though there are many stars behind it, the starlight cannot penetrate the dust; it is absorbed until more of the nebula is ionized. Only with longer wavelength light, such as in the mid-infrared region, will this dust appear bright, rather than dark, when heated.
This dense material, which lines the galactic spiral arms, leads directly to the formation of new stars.
This Hubble Space Telescope image, taken by the Hubble WFC3 camera in ultraviolet, optical, and near-infrared light, shows the bright, dust-lined star-forming arms of the nearby spiral galaxy NGC 1566. The galaxy is 40 million light-years away, with a small but extremely bright galactic nucleus .
But it is also opaque: it prevents us from seeing the light sources inside.
This nearby dust-rich spiral galaxy, NGC 1433, is only 32 million light-years away. The luminous, bright core makes it a Seyfert galaxy, which contains a small molecular outflow and spiral structure in its central molecular gas. Outside the core, dust dominates Hubble’s view of this galaxy.
To truly understand how dust affects galaxy evolution, multi-wavelength views are necessary.
The Andromeda Galaxy, the nearest large galaxy to Earth, displays a tremendous amount of detail depending on which wavelength or set of wavelengths the light is viewed at. Even the optical view on the top left is composed of many different filters. Viewed together, they reveal an incredible array of phenomena present in this spiral galaxy. Multi-wavelength astronomy can provide unexpected insights into almost any astronomical object or phenomenon, revealing details in one wavelength that are completely invisible in another.
ALMA detects individual molecules and ions in galaxies at very long wavelengths.
The Atacama Large Millimeter/Submillimeter Array (ALMA) consists of a series of radio telescopes. The array has the ability to collect light as the sum of the collecting areas of the individual dishes, but has the resolution of the distance separating the dishes. It can be used to identify molecular signatures such as neutral and ionized hydrogen, carbon monoxide and other common molecules and ions found in space.
Hubble and ground-based observatories can directly measure stars, starlight, and energized regions.
This view of the Phantom Galaxy, also known as Messier 74/NGC 628, combined blue, visible and near-infrared images from Hubble, along with a specific hydrogen emission line, to create this composite. While it was previously our best look at the Phantom Galaxy that revealed many interesting features, JWST’s views of it have already revealed much more.
But only with JWSTand specifically its MIRI device, dust can be detected directly.
This top-down view shows the same spiral galaxy IC 5332 from the front in visible and near-infrared light (top) from Hubble, along with a mid-infrared view (bottom) from JWST. The complex, filamentary structure of the dust, heated by nearby star-forming activity, shines brightly in JWST’s view.
The Pphysics at Hhigh ANDangular resolution v Near GalaxiaWITH The survey (PHANGS) aims to explain the entire galactic life cycle of matter.
A spiral galaxy typically consists of four main gas regions in the disc: diffuse atomic gas, dense molecular gas, stars and star clusters, and ionized regions of matter resulting from energetic injections from star-forming regions, young stars, and stellar cataclysms. JWST, along with other PHANGS data sources, helps reveal various aspects of this life cycle.
They sampled 19 nearby spiral galaxies, showing their insides in unprecedented detail.
This MIRI view from JWST and the PHANGS collaboration of the spiral galaxy NGC 1566 shows hot, dusty and nuclear features that are completely invisible to other observatories observing at optical/UV and even radio wavelengths. This network of dust filaments is ubiquitous in spirals, but JWST data are needed to map and understand it.
The dust almost perfectly follows the spiral arms where new stars form.
NGC 1433, shown earlier with primarily optical (Hubble) views, shows its rich dust structures with the MIRI JWST instrument. The central bright area contains a spiral structure, an energy outflow, and is enveloped by an outer dust spiral that extends in two directions into the outer arms. These features not only capture the “dark” regions found in optical views, but also reveal heating due to nearby young stars.
Galaxies with rich central bulges harbor seedbeds of activity within.
This top/bottom comparison shows the nearby barred dusty spiral galaxy NGC 7496 in optical (top) and mid-infrared (bottom) views. Bright spikes in the infrared are an indication of nuclear central activity and potentially reveal an active supermassive black hole. The dark features in the top image caused by light blocking dust are what are illuminated in the bottom image.
Young, newly formed stars heat the dust and cause it to radiate.
This optical view of barred spiral galaxy NGC 1365 shows various features: star formation, the central supermassive black hole, elongated spiral arms, the massive central bar, and dust-rich features that block light from the stars behind them. Our Milky Way is a barred spiral, which makes NGC 1365 particularly important to our home galaxy.
Glowing dust cavities are the result of overlapping shells/bubbles where stars inject energy.
In this MIRI image of the galaxy NGC 1365, clumps of dust and gas in the interstellar medium have absorbed light from forming stars and emitted it back as infrared light. This illuminates an intricate network of cavernous bubbles and fibrous shells. The center of the galaxy has an active supermassive black hole and many overlapping shells of ionized material, while the central bar also shows its extremely dusty nature.
MIRI detects polycyclic aromatic hydrocarbons: organic molecules rich in carbon.
This mid-infrared view of the heart of the phantom galaxy, Messier 74, shows dust heated by nearby star-forming regions. At the center, the gasless core allows the material there to glow brightly at mid-infrared wavelengths, while the “bubbles” blown along the spiral arms represent cavities carved by energetic phenomena.
The the network of dust fibers shows a huge variety of functions across the galaxies.
This three-panel animation shows three different views of the center of the Phantom Galaxy, M74 (NGC 628). The familiar color image is the Hubble (optical) view, the second panel shows near-infrared views from both Hubble and Webb, while the middle infrared panel shows the warm dust that will later form new stars, containing data from JWST itself.
The JWST views give us indirect glimpses into the earliest stages of stellar life cycles.
Star-forming regions are driven by gravitational collapse, turbulent flows, and energy from radiation, which carves both small- and large-scale features into spiral galaxies. At the scale of stellar/star-forming regions to galactic and galactic group/cluster scales, its effects can be felt and seen by cosmic structures.
Mostly, Silent Monday tells an astronomical story in images, visuals and no more than 200 words.
