Meet THESEUS
The European Space Agency has funded an initial study for a high-energy space observatory dubbed the Transient High Energy Sky and Early Universe Surveyor (THESEUS). If fully funded, THESEUS would launch in 2032. THESEUS should find lots of distant GRBs by determining their accurate locations as well as their distances, all without having to rely on ground-based observations. The spacecraft would carry not only a gamma-ray and X-ray detector to spot a GRB when it occurs, but an infrared telescope to immediately observe the same location, get a spectrum, and determine distance.
THESEUS will have the capability of observing in one year the same number of GRBs that have been observed with Swift in 10 years, says Maria Giovanna Dainotti, a Stanford University astronomer and an assistant professor at Jagiellonian University in Poland.
And by looking not only in gamma rays but also in X-rays, O’Brien says, astronomers will find many more extremely distant objects. That’s because, as the universe expands, light becomes stretched out, or redshifted, to lower wavelengths. Gamma rays from bursts at the greatest distances are thus stretched to lower energies, appearing as X-rays.
A new standard?
Astronomers’ ultimate goal is to find a way to make GRBS “standardizable” in the same way that Type Ia supernovae are, says Brad Cenko, an astronomer at NASA Goddard Space Flight Center in Maryland. This, he says, would allow us to use them as standard candles to measure to greater distances than is possible today the locations and motions of galaxies, revealing how the universe is expanding over time.
Additionally, the farther a galaxy lies from us, the earlier into the universe’s history we’re looking when we observe it. Using distant GRBs as standard candles, astronomers believe we could look back to times as early as about 500 million to 1 billion years after the Big Bang — when the first galaxies were just starting to form.
Extending standard candles to greater distances and looking further back in time should also help astronomers solve the mystery surrounding dark energy — the force that’s causing the expansion of the universe to accelerate.
Because dark energy’s contribution varies with time, finding GRBs at greater distances would help researchers get a better understanding of how dark energy evolved over cosmic time. But the crux of such research depends on making GRBs work as standard candles.