Astronomical radio source

Lore & Background

Galactic sources include the Galactic Center, which contains Sagittarius A and the supermassive black hole Sagittarius A*, as well as supernova remnants like Cassiopeia A and the Crab Nebula. Neutron stars such as pulsars emit synchrotron radiation, and rotating radio transients (RRATs) were discovered in 2006. Extra-galactic sources include radio galaxies like Centaurus A and Messier 87, quasars such as 3C 273, and the cosmic microwave background. Fast radio bursts (FRBs) were first reported by D. R. Lorimer and others, with the first observed burst known as the Lorimer burst; their nature remains speculative, with possibilities including black hole-neutron star collisions or other phenomena.

Reader's Guide

Astronomical radio sources have fundamentally expanded our understanding of the universe by revealing extreme and energetic processes invisible to optical telescopes. The discovery of radio waves from the Milky Way's center by Karl Jansky in 1932 opened a new window in astronomy, leading to the identification of pulsars, quasars, and the cosmic microwave background. Radio observations have mapped the structure of the Milky Way using emissions from neutral hydrogen and carbon monoxide, and have detected transient phenomena such as fast radio bursts and rotating radio transients. The study of radio sources continues to probe the most violent events in the cosmos, from supernova remnants and active galactic nuclei to the potential evaporation of primordial black holes via Hawking radiation. Ongoing projects like Astropulse aim to detect such elusive signals, while the search for extraterrestrial intelligence (SETI) also relies on radio observations. The field remains dynamic, with new classes of objects such as Galactic Center Radio Transients and peculiar circularly polarized waves from near the Galactic Center suggesting that many radio sources are yet to be fully understood.

Did You Know?

• The first radio waves from outer space were detected in 1932 by Karl Jansky as a steady hiss from the center of the Milky Way.
• Jupiter's radio emissions can exceed the Sun's radio output when Earth intersects the emission cone from its magnetosphere.
• The first observed fast radio burst, known as the Lorimer burst, was less than 5 milliseconds in duration and located 3° from the Small Magellanic Cloud.
• Rotating radio transients (RRATs) were discovered in 2006 and produce radio emissions for less than one second a day.