Scientists may have detected the first evidence of primordial black holes – relics from the universe’s earliest moments – through the observation of gravitational waves. The Laser Interferometer Gravitational-wave Observatory (LIGO) and Virgo collaborations registered a signal on November 12th that doesn’t align with known astrophysical events, potentially indicating the merger of objects too small to be stellar remnants.
The Unusual Signal: S251112cm
Since 2012, LIGO and Virgo have confirmed gravitational waves from colliding black holes and neutron stars. However, the event designated S251112cm stood out: one of the merging objects had a mass too low to be explained by standard stellar collapse. As Durham University physicist Djuna Croon stated, “If this turns out to be real, then it’s enormous.” This would represent the first direct observation of a black hole formed not from a dying star, but from the extreme conditions of the early universe.
Primordial Black Holes: A Long-Theorized Existence
The concept of primordial black holes (PBHs) dates back decades. Unlike stellar black holes, which form from collapsing stars, PBHs are theorized to have arisen from density fluctuations in the ultra-hot plasma of the Big Bang. Their potential mass range is vast – from fractions of an atom to 100,000 times the mass of the Sun.
Why is this important? PBHs could explain some of the universe’s biggest mysteries. If they exist, they could constitute a significant portion of dark matter, the unseen substance that makes up 85% of the universe’s mass. Their existence wouldn’t require new physics beyond our current understanding, unlike many other dark matter candidates.
False Alarms and Uncertainties
However, the signal may be a false alarm. LIGO-Virgo detects spurious signals at a rate of roughly one every four years. This is especially problematic for rare events like S251112cm. The alert only narrowed the source’s location to an area 6,000 times the width of the Moon, making follow-up electromagnetic observations difficult.
Hawking Radiation and Evaporation
Even if real, the detected PBH may not be around for long. Stephen Hawking theorized that black holes emit radiation, causing them to evaporate over time. Lighter PBHs would have disappeared shortly after the Big Bang, while heavier ones might still be slowly decaying today.
The Search Continues
For now, researchers can only analyze the gravitational wave signal itself to refine their understanding. More similar detections are needed to confirm the existence of PBHs with confidence, but scientists acknowledge that such events may be exceedingly rare.
“It seems unlikely that we’ll actually know with certainty whether this alert was real or not,” Croon concluded.
Whether a genuine discovery or a statistical fluke, the S251112cm signal highlights the potential of gravitational wave astronomy to probe the universe’s earliest epochs and uncover the hidden constituents of dark matter.
