The Life Cycle of Dust

This proposal advocates for a collective science initiative within Canada to better understand the nature of interstellar dust through its entire life cycle.  Interstellar dust grains (solid particles) are a fundamental probe of the Universe.  Dust is present across multiple scales that probe the physical properties of (1) dense and diffuse clouds in the multi-phase ISM in galaxies, (2) the atmospheres of evolved stars, (3) the ejecta of stellar remnants,  (4) circumstellar disks, and (5) the high-redshift universe. 

Even though dust is such a key component in how we perceive entire galaxies, characterize stellar evolution, and trace both star and planet formation, we don't have good physical and chemical constraints on the dust grains themselves.  What are dust grains made out of?  What is their size distribution?  What is their structure?  These questions are a key problem in using dust as a probe of the universe.  These questions are also non-trivial, because dust grains are expected to vary widely in their composition, size, and structure in the ISM and in different galactic environments.  This white paper highlights the challenges that are faced in observational and theoretical studies of the dust life cycle and the direction the Canadian community should take to meet these challenges using current, upcoming, and future technologies.

A robust model of dust requires multi-wavelength observations of different stages of dust in its life cycle, because dust can obscure radiation through extinction and scattering processes and emit radiation from their own thermal energy.  Canada is a world leader in studies of the key stages of dust from star and planet formation, stellar populations, galaxy evolution, and cosmology.  We have extensive expertise using current facilities, such as the Canada-France-Hawaii Telescope (CFHT),  James Clerk Maxwell Telescope (JCMT), and Herschel Space Observatory to conduct multi-wavelength studies of dust extinction, emission, polarization, and scattering processes necessary to characterize the properties of dust.  As such, Canadian astronomers are well positioned to lead research projects to investigate dust properties throughout its life cycle.

A full understanding of dust in all of its forms and stages requires statistical studies of dust properties over multiple wavelengths and across stellar evolution, star and planet formation, and redshift.  Canada has a rich history of developing and supporting instrumentation ideal for dust studies at optical and near-infrared wavelengths (e.g., WIRCam at CFHT), far-infrared wavelengths (e.g., SPIRE onboard Herschel), submillimeter wavelengths (e.g., POL-2 at JCMT), and millimeter wavelengths (e.g., the Band 3 receivers for ALMA).  The Canadian community is also actively involved in future instrument upgrades to these facilities and future technologies and research initiatives that will provide invaluable data for constraining the properties of dust grains: ALMA, BLAST-TNG, CASTOR, CCAT-p, JWST, ngVLA, Origins, SKA, SPICA, WFIRST.

No one facility can solve dust.  Dust properties across the life cycle can only be constrained from multi-wavelength technologies that probe a wide range of properties and span a wide range of angular scales, from dust in high-redshift galaxies and tiny protoplanetary disks to dust in nearby supernova remnants and diffuse clouds.  For this LRP2020 white paper, we recommend that Canada invest in multi-scale, multi-wavelength projects so that Canadian astronomers have access to world-class facilities to tackle the question of dust composition, size, and structure from the local solar neighbourhood to the distant universe.  These projects will enable Canadian astronomers to bridge the gaps between dust production and evolution, and place important constraints on dust models so we can build meaningful and robust conclusions of the universe.