A plain-language summary of Dissecting the Local Environment of FRB 190608 in the Spiral Arm of its Host Galaxy (Chittidi, Simha et al. 2021, The Astrophysical Journal; arXiv).
TL;DR: using the Hubble Space Telescope, we found that this burst came from a patch of young stars on a spiral arm of an otherwise calm, ordinary galaxy.
The context
This is a companion study to (the one I led), which mapped the gas along its path. This one asked how much of the gas was in the burst’s own galaxy.
One way to find out is detective work: look closely at the scene. If bursts keep turning up where stars have recently formed, whatever makes them is probably young. If they turn up among old stars, it is probably old.
This burst was also a good test case for a second question. It had passed through more gas than usual for its distance.
What did we do?
- We took sharp images of the home galaxy with the Hubble Space Telescope, which showed its spiral arms in detail. It also showed where the ultraviolet light was coming from in the galaxy, a sign that there are relatively young (less than 100 million years old) massive stars are forming there.
- We used the Keck telescope in Hawaii to split the galaxy’s light into colours at every point across it. That shows where gas is glowing because young stars are heating it, and how fast the galaxy is spinning.
What did we find?
- The burst came from a spiral arm, right on a clump where stars are forming.
- The galaxy’s own gas accounts for a large share of all the gas the burst passed through, about a third of the full budget of its 1.5-billion-year journey put together.
- From how the galaxy rotates, we estimated that the stars at the burst’s location formed no more than about 20 million years ago. That is young: the Sun is more than 200 times older.
Why does it matter?
It ties this burst to young stars, which fits the leading idea that bursts come from the remains of massive stars that live fast and die young.
Together with the companion study, it also gave the first complete account of a burst’s journey, from its birthplace to Earth.
Words you’ll see in the paper
- Host galaxy: the galaxy a burst came from.
- Interstellar medium (ISM): the gas between the stars inside a galaxy.
- Progenitor: whatever object produced the burst.
- Star formation rate: how quickly a galaxy, or a patch of it, is making new stars.