Today’s expected announcement may not be just one great discovery but two because of the black holes that are rumoured to have created the signal

It is now widely expected that the detection of gravitational waves using the Ligo (Laser Interferometer Gravitational-wave Observatory) observatories will be announced today at 15:30 GMT at a press conference that has been called at the National Press Club, Washington DC.

Although everything is still rumour at this point, the “details” have begun to leak. If they are true, then they certainly explain a few things that seemed confusing at first. In particular, they suggest that the gravitational waves were produced by a pair of highly unusual black holes colliding.

Anticipation mounts ahead of gravitational wave announcement - live Read more

The black hole news on its own would be a great discovery, but combined with the detection of the gravitational waves it is an academic double whammy that has astronomers and physicists reeling with excitement.

Black holes are the most mysterious objects in the universe but one thing we do know is that they come in two main varieties. Stellar black holes are those that form after stars explode, and typically have masses of between 3-15 times that of the sun. At the other end of the scale there are supermassive black holes that squat in the centre of galaxies and possess masses of millions and billions times that of the sun.

What is a black hole? Read more

However, the black holes expected to be announced today are said to have masses of 29 and 36 suns. These are highly unusual masses – above the usual stellar black hole regime but far below the supermassive ones – and may explain why researchers were confident that it wasn’t a test signal injected into the data.

It also explains the sudden appearance in early January of a number of theoretical papers that were talking about the collision of a pair of 30-solar mass black holes, a scenario outside the boundaries of what had been thought common before. Derek Fox of Penn State University brought one particular paper to light on Twitter.

The description of an unusual gravitational wave scenario tipped off some physicists that a detection announcement was imminent.

Let’s assume for the moment that the rumours are true. Where do these 30-solar mass black holes come from? This is where it gets even more interesting, because astronomers do not really know.

Gravitational waves: everything you need to know Read more

In recent years, a class of intermediate mass black holes has been discovered. Although their numbers are comparatively low at the moment, they appear to possess masses of between 100-1000s of solar masses. However, the lower end of that boundary is poorly known. Could these new discoveries be some of those?

It has been suggested that intermediate mass black holes are the remnants of the very first stars to be born in the universe. Known as population III stars, they existed more than 13 billion years ago and are thought to have each been much larger than the stars of today. Hence, they might reasonably be expected to leave behind larger black holes.

If the Ligo scientists do indeed confirm the 30-solar mass rumours today then astronomers will have much to celebrate. To see such a signal so quickly after the detectors reached the correct sensitivity implies that such collisions are common, which implies that such black holes are common.

We will have a window onto a wholly unanticipated population of black holes: a way to look at the dead hearts of the very first stars that formed in the universe. Also, of course, we will have the great discovery of gravitational waves, another extraordinary triumph for Einstein’s monumental general theory of relativity.

Confirmation and surprise: the triumph of theory and the serendipity of observation. What’s not to love about that?

Follow all the action on our live blog from 2.15pm GMT this afternoon.

Stuart Clark is the author of The Unknown Universe (Head of Zeus), and co-host of the podcast The Stuniverse (Bingo Productions).