SCIENCE
The fast radio burst (FRB) mystery has captured the imagination of astronomers and the broader public alike. The DSA is tackling the two most important questions posed by the discovery of FRBs: (1) what makes them, and; (2) what is the nature of the intergalactic material through which they travel to us? Our group of graduate students, postdocs, research staff, and faculty are pursuing these questions through detailed multiwavelength observations of the distant host galaxies of DSA-detected FRBs, and of galaxies between us and the FRB sources. This effort will be augmented by follow-up efforts by the broader astronomical community enabled by the rapid release of FRB positions from the DSA.
Image: ESO
What Makes FRBs?
Dynamic spectrum of FRB 190523, detected and localized to a galaxy at a distance of 2.4 Gpc by the DSA-10 precursor instrument to the DSA-110. (Image: V. Ravi)
FRB are likely emitted from compact (tens of km), highly magnetized (more than a million times stronger than the strongest magnetic field on Earth) regions. Of all the astronomical objects we know about, neutron stars are the best possible candidates. Although we know of several neutron-star formation channels (e.g., supernovae, binary white dwarf mergers), we do not know which channels make the FRB sources. To find out, our team will characterize the host galaxies of DSA FRBs using optical telescopes at the Palomar and W. M. Keck Observatories, and determine whether or not the FRB sources are associated with special objects within the galaxies like supermassive black holes. Our measurements will also reveal the true distances to the FRBs sources, providing information on the FRB occurrence rate and emitted energies.
What is the Nature of the Intergalactic Material Through Which FRBs Travel to Us?
All FRBs accurately encode the total amounts of matter along their sightlines. Remarkably, even after setting aside dark matter, 80%—90% of the normal matter in the Universe is not observed by astronomers. This matter is thought to be hot (over a million degrees Kelvin) and diffusely distributed in between galaxies. Understanding how this intergalactic matter is distributed in halos surrounding galaxies and in the cosmic web is critical for our understanding or how galaxies form out of and interact with intergalactic gas. We will address this problem by identifying the distances to the host galaxies of a hundred DSA FRBs, and by also identifying intervening galaxies intersected by the FRBs on their several billion-year journeys to the Earth.
[A] Radio localization of FRB 190523 by the DSA-10, a precursor instrument to the DSA-110. [B] Keck/LRIS optical image of the field. [C] and [D]: Localization contours of FRB 190523 overlaid on Keck/LRIS optical images in different bands, indicating the most probable host galaxy (S1) at a redshift of 0.66. (Image: V. Ravi)
Other Science Goals
The DSA fulfills a unique role within the suite of radio telescopes available to astronomers. When complete, it will have the sensitivity of a radio dish with a 50-meter diameter but with 100 times the field of view, and the resolving power of a dish 2.5 kilometers in diameter. Our group is exploring additional scientific questions that the DSA is suited to answer. One area of active interest is the nature of the most extreme structures in the interstellar gas of the Milky Way. These structures are only observed through their transient effects on distant radio sources (like actively growing supermassive black holes). By regularly monitoring thousands of such sources, the DSA can build a world-leading data set on these mysterious interstellar structures.