According to a story published on July 10 in The Astrophysical Journal, a radio burst was detected that may have originated outside of our galaxy. Apparently, these split-second radio bursts have heard before, but always with the same telescope – Parkes Observatory in Australia. Given that only this observatory was detecting these signals, there was debate about whether they were coming from inside our galaxy, or even from Earth itself.
However, this time the radio signals were detected by a different telescope – the Arecibo Observatory in Puerto Rico – which concluded that the bursts are coming from outside the galaxy. This is also the first time one of these bursts have been found in the northern hemisphere of the sky. Exactly what may be causing such radio bursts represents a major new enigma for astrophysicists.
Victoria Kaspi, an astrophysics researcher at McGill University who participated in the research, explained:
Our result is important because it eliminates any doubt that these radio bursts are truly of cosmic origin. The radio waves show every sign of having come from far outside our galaxy – a really exciting prospect.
Fast radio bursts are a flurry of radio waves that last a few thousandths of a second, and at any given minute there are only seven of these in the sky on average, according to the Max Planck Institute for Radio Astronomy. Their cause is unknown, and the possibilities range from black holes, to neutron stars coming together, to the magnetic field of pulsars (a type of neutron star) flaring up.
The pulse was detected on Nov. 2, 2012, at the Arecibo Observatory – a National Science Foundation-sponsored facility that has the world’s largest and most sensitive radio telescope. While fast radio bursts last just a few thousandths of a second and have rarely been detected, the international team of scientists reporting the Arecibo finding estimate that these bursts occur roughly 10,000 times a day over the whole sky.
This astonishingly large number is inferred by calculating how much sky was observed, and for how long, in order to make the few detections that have so far been reported. Laura Spitler, a postdoctoral researcher at the Max Planck Institute for Radio Astronomy in Bonn, Germany and the lead author of the new paper, was also the first person to note the event. As she explained:
The brightness and duration of this event, and the inferred rate at which these bursts occur, are all consistent with the properties of the bursts previously detected by the Parkes telescope in Australia.
The bursts appear to be coming from beyond the Milky Way, based on measurement of an effect known as plasma dispersion. Pulses that travel through the cosmos are distinguished from man-made ones by the effect of interstellar electrons, which cause radio waves to travel more slowly at lower radio frequencies. The burst detected by the Arecibo telescope has three times the maximum dispersion measure that would be expected from a local source.
Efforts are now under way to detect radio bursts using radio telescopes that can observe broad swaths of the sky to help identify them. Telescopes under construction in Australia and South Africa as well as the CHIME telescope in Canada have the potential to detect fast radio bursts. Astronomers say these and other new facilities could pave the way for many more discoveries and a better understanding of this mysterious cosmic phenomenon.
For those hoping this was a possible resolution to the Fermi Paradox – i.e. that the radio bursts might have been extra-terrestrial in origin – this news is a little disappointing. But in truth, its yet another example of the deeper mysteries of the universe at work. Much like our ongoing research into the world of elementary particles, every answer gives rise to new questions.