NEW OPPORTUNITIES AWAIT

Neutron stars and kilonovae aren’t the only things multi-messenger astronomy could help reveal

While astronomers eagerly await further multi-messenger observations of kilonovae and perhaps supernovae too, there are other fields of astrophysics and cosmology in which gravitational wave detections should provide extraordinary insights. Such studies will naturally build on and illuminate more fully decades’, if not centuries’, worth of understanding from electromagnetic radiation observations, but in some cases they will also explore astronomical phenomena that simply cannot be studied by examining light of any wavelength. Black hole mergers, which don’t give off light and which LIGO has sensed several times already, are perhaps the most obvious example, but there are others.

“If our gravitational wave detectors get sensitive enough we may be able to detect signals from the very early Universe,” says Dr Michalis Agathos. “The picture that we have of the very early Universe at the moment comes mainly from the Cosmic Microwave Background. This is basically the light that streamed freely from the earliest stage when the Universe became transparent to light, about 350,000 years after the Big Bang.” Gravitational waves, however, were able to move unhindered through the opaque cosmos long before this. “If you do the calculation, you’ll see that gravitational waves started travelling freely and unperturbed from the first billionth of a trillionth of a trillionth of a second after the Big Bang. This is a really amazing prospect: if you’re able to detect gravitational waves from the very early Universe you’ll basically probe the very beginning,” says Agathos.

Might we one day detect the gravitational waves that began at almost the same instant as the Big Bang itself?