Fast Radio Bursts (FRBs) are incredibly powerful blasts of energy from deep space. They remain one of the astronomical enigmas, shrouded in mysteries. Despite hitting the Earth every minute, their origin is still unknown.
Researchers at Carnegie Mellon University have discovered the distortion in data that affects how FRBs are observed and interpreted. One of the reasons behind these biases is the variations in data collection from optical telescopes and radio telescopes.
Optical telescopes are more likely to detect brighter objects, while radio telescopes tend to detect FRBs from galaxies that fully face the Earth.
Additionally, the study has highlighted another bias: inclination. Based on the angles seen from Earth, a galaxy is termed an ‘edge-on galaxy’ or ‘face-on galaxy’. To demonstrate this, imagine looking at a coin from different angles.
Astronomers have noticed the frequent bursts of FRBs from face-on galaxies, while the FRBs from edge-on galaxies witnessed scarcity. Authors have stated that this had led to a significant underestimation of the FRB rates reported.
“In the universe, galaxies do not have a preferred orientation, so from Earth, we should view them at random angles. But when we studied a sample of galaxies from which FRBs have come, we discovered an excess of face-on galaxies and a paucity of edge-on galaxies.” said the lead author Mohit Bhardwaj.
New observation of a supernova explosion that was witnessed in the year 1181
Bhardwaj and the authors have pointed to these two factors as undermining estimations of FRBs, meaning that FRBs are more abundant and frequent than we previously thought and estimated.
“We now need to revisit all the analyses that we have done and take into account this inclination-related selection bias and then see whether the conclusions we have drawn still make sense,” Bhardwaj said.
To support their hypothesis, the team used data from the Dark Energy Spectroscopic Instrument (DESI) survey and the Panoramic Survey Telescope and Rapid Response System (Pan-STARRS) survey to measure the inclination angles of 23 FRB host galaxies.
Their analysis supported their hypothesis, and most FRBs were from disks of their host galaxies. The disks of galaxies are the regions where ongoing star formation occurs.
This inclination-based bias for detecting FRBs could challenge almost all prior FRB theories. The bias could even disfavor globular clusters as the dominant source of FRBs.
For the inclination-related selection bias, Bhardwaj proposes that FRB signals are scattered as they pass through the host galaxy. If the signals pass through large fractions of host galaxies, they are likely to be scattered and weakened.
In face-on galaxies, the signals wouldn’t have to travel through as much of the galaxy, making them less likely to be weakened. Meanwhile, in edge-on galaxies, FRBs covering large distances weaken, and they aren’t detected by telescopes.
Astronomers discovered a new, complex molecule in the depths of interstellar space
Journal Reference
- Bhardwaj, M., Lee, J., & Ji, K. (2024). Selection bias obfuscates the discovery of fast radio burst sources. Nature, 1-5. DOI: 10.1038/s41586-024-08065-w