| Abstract: |
Cosmic dust, together with gas, is one of the major constituents of the Interstellar Medium (ISM). Although
dust particles (grains) amount to only ∼1% of the total mass of the ISM in our galaxy (and even a smaller
fraction in low-mass galaxies), dust is responsible for absorbing and scattering 50% of all the energy produced
by stars in the Universe today (and around 75% at z=2, the peak of Star Formation). Ignoring the effects
of dust leads to a significant underestimate of the effective stellar content in galaxies and this, in turn, has a
severe impact on our understanding of the Star Formation process across Cosmic Times. Furthermore, dust
grains are the catalyst for the formation of molecular hydrogen, the fuel for star formation itself, and, after
stars form, they serve as the seeds for planet formation. Finally, dust grains facilitate the synthesis of water as
well as complex organic molecules, thus being crucial for biogenesis.
While we have reasonably good knowledge of the size and chemical composition of dust grains in the
diffuse, low density (∼0.1–1 atom per cubic centimeter) ISM, there is a general lack of information regarding
dust properties for the dense medium (∼1,000 molecules per cubic centimeter), which is typical of star
forming regions, and on how these vary from one galaxy to another, and within galaxies. Furthermore, JWST
has recently detected dust in the early Universe, but how this dust formed and evolved, in order to have the
diversity of environments we observe today, is not yet clear.
With its ability to observe at a wide range of wavelengths, from the UV to the IR, combined with its
exquisite spatial and spectral resolution, HWO will measure the variations of the extinction curve, within
and outside our Galaxy, more accurately than ever before, thereby filling our long-standing gap in knowledge on dust evolution. This improved knowledge will also lead to advancements in our understanding of
galaxy evolution—in particular with respect to chemical and radiative-transfer processes, and ISM cooling
and heating (via the photoelectric effect)—as well as of the distribution of neutral hydrogen with redshifts.
This article is an adaptation of a science case document developed for HWO’s ISM and Star Formation
Steering Committee. |
