Astronomers Detect New Gamma-Ray Beacons in Space

The Quest for Cosmic Gamma-Rays

Scientists aimed to determine if specific globular clusters (dense, spherical collections of millions of stars) with high stellar encounter rates (the speed at which stars in a cluster approach each other) emit gamma-rays.

Gamma-rays are the most energetic form of light, like ultra-powered X-rays. These clusters rapidly form "close binary systems" where two stars orbit very near each other, often leading to objects like millisecond pulsars (MSPs) – rapidly spinning dead stars that emit beams of radiation. Researchers believed these MSPs could be the source of the gamma-rays.

Methodology: Hunting for High-Energy Light

The study looked at gamma-ray data from seven globular clusters previously not known to be gamma-ray sources but predicted to be, due to their high stellar encounter rates.

They used data from the Fermi Gamma-ray Space Telescope, a space observatory that detects gamma-rays. For each cluster, they analyzed gamma-ray signals collected between August 2008 and August 2010, carefully removing background noise from other sources and diffuse (spread out) gamma-ray emissions.

Remarkable Discoveries and Puzzling Offsets

The team discovered gamma-ray emission from:

• Liller 1
• NGC 6624
• NGC 6752

They also found strong evidence for gamma-ray emission from M80, NGC 6139, and NGC 6541.

Liller 1 shone brightest, with a gamma-ray luminosity (total energy emitted per second) of 5.9 quintillion trillion ergs per second (5.9 × 10^35 erg s^-1), making it the most powerful gamma-ray globular cluster found so far. The gamma-ray "glow" from these clusters often appeared slightly offset from the cluster’s main center, suggesting the source of emission isn't always perfectly at the cluster's heart.

"The discovery of several more γ-ray emitting GCs reported in this work has allowed population studies to be carried out in order to better understand the relationship between the γ-ray properties of GCs and other parameters of GCs," the authors stated.

This means finding more gamma-ray clusters helps scientists see patterns and connections between how these clusters behave and why they emit such powerful light. The displaced gamma-ray emission could be explained by models where MSPs are spread out, or charged particles are diffusing, like smoke spreading out from a bonfire.

Future Research

The study noted that limited photon statistics (the number of photons collected) made it hard to pinpoint the exact characteristics of the gamma-ray energy. Future research can use this expanded list of gamma-ray emitting globular clusters to further explore how these clusters generate such extreme energy.

These glittering cosmic cities continue to reveal their explosive secrets through the highest-energy light.