One day a little more than five years ago, Ely Kovetz was having lunch with his colleagues at Johns Hopkins University in Baltimore, discussing a tantalizing rumor. Like many in the physics community, Kovetz had heard the buzz about a possible signal from a newly operational US physics observatory. The observatory was designed to pick up disturbances in the fabric of spacetime, ripples created by, among other things, black holes crashing into each other. Most intriguingly, the signal appeared to have been created by massive objects, far heavier than anyone expected. That pointed at some eyebrow-raising possibilities.
“The first thought in everybody’s mind was, ‘What? This can’t be. This is impossible!’” recalls Kovetz, a physicist at Ben-Gurion University in Israel and a visiting scholar at Johns Hopkins. But then a more exciting suspicion began to creep in. Maybe, they thought, this could be a sign of primordial black holes.
Black holes from the dawn of time! It sounds like the title of a sci-fi B movie, but fractions of a second after our universe was born, a swarm of ravenous black holes could have spontaneously formed from the fiery energy permeating the cosmos. Supported by math and theory but never definitively observed, these primordial black holes are a possibility that has fascinated physicists for nearly half a century, gaining or losing popularity as new observations seemed to support or exclude their existence.
The puzzling 2015 signals from the US observatory, known as LIGO (Laser Interferometer Gravitational-Wave Observatory), and dozens more detections by the observatory and its European counterpart, Virgo, have fueled a surge of renewed interest in the idea, with hundreds of papers published on them in just the last five years.
Primordial black holes, if they exist, would be massive entities that give off no light, rendering them invisible. Since they would be scattered throughout the universe, they could help make sense of a wide variety of strange observations that have so far defied explanation. One of the main reasons researchers are drawn to these odd black holes is that they could solve one of the biggest, most vexing mysteries in astrophysics: the identity of dark matter.
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