Scientists Found a Black Hole That Shouldn’t Exist. Now Physics Has a Problem.

Here’s what you’ll learn when you read this story:

• Over the past decade, the LIGO-Virgo-KAGRA (LVK) network has detected hundreds of black hole mergers, but none quiet as large as GW231123.

• At 225 solar masses, the black hole resulting from the merger far exceeds previous record holder GW190521, which weighed in at 140 solar masses.

• This black holes involved in this merger were actually so large that they challenge some of our understanding of stellar evolution.

The Laser Interferometer Gravitational-wave Observatory, or LIGO, made major headlines in 2015 when scientists confirmed the first ever detection of gravitational waves—ripples in spacetime caused by highly energetic deep space phenomena (think: black hole mergers, supernovae, and neutron star collisions). This particular detection originated from a black hole merger that created a new black hole 62 times the mass of our Sun.

The LIGO-Virgo-KAGRA (LVK) network of gravitational wave detectors hasn’t let off the gas in the decade since, and has made hundreds of confirmed gravitational-wave detections, including the first neutron star merger in 2017 and the largest black hole merger (clocking in at 140 solar masses) in 2021.

Now, in a preprint uploaded to the arXiv server, LVK scientists have provided evidence that there’s a new heavyweight champion—a merger that produced a new 255-solar-mass black hole. Designated GW231123 for the date it was discovered (November 23, 2023, during the fourth observing run of the LVK network), this black hole is actually too big, according to our current best understanding of physics.

“This is the most massive black hole binary we’ve observed through gravitational waves, and it presents a real challenge to our understanding of black hole formation,” Mark Hannam, a member of the LVK Collaboration from Cardiff University, said in a press statement. “Black holes this massive are forbidden through standard stellar evolution models.”

To form this black hole, the two black hole predecessors likely had to measure around 100 and 140 times the mass of the Sun, respectively. This means they potentially lie in what’s known as the “upper-mass gap”—a range of masses in which black holes aren’t thought to form from stars directly (the resulting supernovae of these hugely massive stars should leave behind no stellar remnant at all).

“One possibility is that the two black holes in this binary formed through earlier mergers of smaller black holes.” Hannam said.

However, these black holes’ masses aren’t the only mystery, as both were spinning between 80 and 90 percent of their top speed limit. This makes them the highest spinning black holes ever recorded by LVK.

“The black holes appear to be spinning very rapidly—near the limit allowed by Einstein’s theory of general relativity,” Charlie Hoy, another member of the LVK from the University of Portsmouth, said in a press statement. “That makes the signal difficult to model and interpret. It’s an excellent case study for pushing forward the development of our theoretical tools.”

Because the detectors are sensitive to black holes of around 100 solar masses, detecting one more than double that size certainly pushes LIGO to its limits. According to Science News, the LVK network was only able to detect the smallest blip from this merger, with only around 0.1 seconds detected at the tail end of the collision.

LIGO’s decades-long mission to detect gravitational waves has given scientists a whole new understanding of the universe, and nearly a decade after its first detection, it shows no signs of stopping.

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