Fast radio burst unexpectedly traced to dead and old elliptical galaxy

Location of Fast Radio Burst
Figure 4 from this paper [pdf].

The uncertainty of science: Using several radio telescopes working in tandem, astronomers have been able to identify the source galaxy of a fast radio burst (FRB) that repeatedly erupted throughout 2024, and discovered it came from a dead and old elliptical galaxy, not a younger galaxy as predicted.

[W]hile most FRBs originate well within their galaxies, the team traced FRB 20240209A to the outskirts of its home — 130,000 lightyears from the galaxy’s center where few other stars exist. “Among the FRB population, this FRB is located the furthest from the center of its host galaxy,” said Vishwangi Shah, a graduate student at McGill, who led the effort to pinpoint the FRB’s origins. “This is both surprising and exciting, as FRBs are expected to originate inside galaxies, often in star-forming regions. The location of this FRB so far outside its host galaxy raises questions as to how such energetic events can occur in regions where no new stars are forming.”

The small ellipse to the upper left of the giant elliptical galaxy (in yellow) marks the location of the FRB relative to its galaxy. Why it is so far outside remains a puzzle. The scientists consider two options: First, that the magnetar was once inside the galaxy but was kicked out at some point, and second, it simply could be inside a globular cluster that is too small to detect at this distance, two billion light years away.

Both explanations have problems and really don’t work.

Fast radio bursts not detected at certain radio wavelengths

In observations by two different radio telescopes operating at different radio wavelengths but looking at the same part of the sky, astronomers have found that an observed fast radio burst was not detected by one of those telescopes.

The Curtin University-led Murchison Widefield Array (MWA) and CSIRO’s Australian SKA Pathfinder (ASKAP) telescopes were searching the sky for fast radio bursts, which are exceptionally bright flashes of energy coming from deep space. These extreme events last for only a millisecond but are so bright that many astronomers initially dismissed the first recorded fast radio burst as an observational error.

In research published in the Astrophysical Journal Letters, astronomers describe how ASKAP detected several extremely bright fast radio bursts, but the MWA—which scans the sky at lower frequencies—did not see anything, even though it was pointed at the same area of sky at the same time.

Lead author Dr Marcin Sokolowski, from the Curtin University node of the International Centre for Radio Astronomy Research (ICRAR), said the fact that the fast radio bursts were not observed at lower frequencies was highly significant. “When ASKAP sees these extremely bright events and the MWA doesn’t, that tells us something really unexpected is going on; either fast radio burst sources don’t emit at low frequencies, or the signals are blocked on their way to Earth,” Dr Sokolowski said.

If blocked at these lower frequencies, this tells theorists something about the environment where the burst occurred. If instead the burst does not emit in those lower frequencies, it tells them something about the burst itself.