Brief bursts of radio waves arriving from far-off galaxies could help astronomers estimate cosmological distances and piece together a 3D map of matter in the universe. If everything checks out, a new technique proposed by two cosmologists from the University of British Columbia will offer an independent metric – set apart from the uncertainties and systemic biases of existing methods – in plotting the large structures of the cosmos.
Fast radio bursts are radio wave signals that last only a few milliseconds and originate outside our own galaxy. They spread out and separate according to their wavelengths as they travel through space. The longer wavelengths tend to arrive later than the shorter ones, and this delay between arrival times may tell us not only the total distance traveled by the waves but also what materials (stars, gas, dark matter) lie between Earth and the source of the burst.
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Only 10 such bursts have been recorded in the eight years since the first was observed, but astronomers believe there could be thousands every day. And once-completed, the radio telescope CHIME – which stands for Canadian Hydrogen Intensity Mapping Experiment – could see tens or hundreds of these. "If they are cosmological [in origin], we can use this information to build a catalog of galaxies," said co-author Kris Sigurdson.
The researchers estimate that measurements of around 10,000 fast radio bursts would be needed to account for variations in electron density, which will otherwise result in higher-density regions appearing farther away and lower-density regions appearing closer.
Beyond that, the only major uncertainty about the new technique's viability is something called dispersion. This relates to how electromagnetic radiation travels at different speeds through space according to its wavelength and the electron density. It's the phenomenon that the fast radio burst calculations rests upon.
It is not only produced by intergalactic electron density, though, but also by environmental properties of our own galaxy and at the source of the fast radio bursts. The former can be measured and accounted for, but the latter could prove troublesome if analysis reveals big variations in fast radio burst emissions.
If it does work out, the new method would be a welcome addition to the tiny roster of existing options for estimating cosmological distances, of which redshift measurements are the leading choice (as the universe expands, stars move farther away, and we can infer distance from measuring how much the light wavelength shifts towards the red end of the spectrum) despite the inherent shortcomings in how the Hubble space telescope detects them.
A paper describing the research has been published in the journal Physical Review Letters.
Source: University of British Columbia