Black holes: cosmic signal shakes Earth after 7 billion years

Imagine the energy of eight suns released in an instant.

This is the gravitational “shock wave” that extended from the largest merger ever observed between two black holes.

The signal from this event traveled for about seven billion years to reach Earth, but it was still strong enough to set off laser detectors in the US and Italy in May of last year.

The researchers say that the colliding black holes produced a single entity with a mass 142 times that of our Sun.

This is noteworthy. Science has long tracked the presence of black holes in the sky that are slightly smaller or even much larger. But this new observation inaugurates a new class of so-called intermediate-size black holes in the 100-1,000 solar (or solar) mass range.

The analysis is the latest in the international LIGO-VIRGO collaboration, which operates three super-sensitive gravitational wave detection systems in the Americas and Europe.

Media playback is not supported by your device

What is a black hole?

• A black hole is a region of space where matter has collapsed in on itself.
• The gravitational pull is so strong that nothing, not even the light from the event, can escape.
• Black holes will emerge from the explosive disappearance of certain large stars
• But some are truly gigantic and have billions of times the mass of our Sun.
• It is unknown how these monsters formed, which are found in the centers of galaxies
• Black holes are detected by the way they influence their environment
• They produce observable gravitational waves as they spiral around each other.

The collaboration’s laser interferometer instruments “listen” for vibrations in space-time that are generated by truly cataclysmic cosmic events, and on May 21, 2019, they were all triggered by a sharp signal lasting just a tenth of a second.

Computer algorithms determined that the source is the final stage moments of two spiraling black holes, one with a mass 66 times that of our Sun and the other with 85 solar masses.

The distance to the merger was calculated to be the equivalent of 150 billion trillion kilometers.

“It’s really amazing,” said Professor Nelson Christensen of the Côte d’Azur Observatory in France. “This signal has been propagating for seven billion years. So this event happened ‘just before halftime’ for the Universe, and now it mechanically moved our detectors here on Earth,” he explained to BBC News.

Gravitational waves: waves in spacetime

• Gravitational waves are a prediction of the general theory of relativity.
• It took decades to develop the technology to detect them directly.
• They are waves in the fabric of space-time generated by violent events.
• Accelerated masses will produce waves that travel at the speed of light.
• Detectable sources include merging black holes and neutron stars
• LIGO-VIRGO fire lasers in long L-shaped tunnels; the waves disturb the light
• Wave Detection Opens the Universe to Completely New Research

The involvement of an 85-solar-mass object in the collision has made the collaborating scientists feel that their understanding of how black holes form from the death of a star can’t explain anything on this scale.

Stars, when they use up their nuclear fuel, will experience an explosive core collapse to produce a black hole, if they are large enough. But the physics that are supposed to operate inside stars suggests that the production of black holes in the particular mass range between 65 and 120 solar masses is impossible. The dying stars that could produce such entities actually rip apart and leave nothing behind.

If the science is correct on this point, then the most likely explanation for the existence of an 85-solar-mass object is that it itself was the result of an even earlier black hole union.

And that, believes Professor Martin Hendry, from the University of Glasgow, UK, has implications for how the Universe evolved.

“We are talking here about a hierarchy of mergers, a possible way to make black holes bigger and bigger,” he said. “So who knows? This 142 solar mass black hole may have merged with other very massive black holes, as part of an accumulation process that reaches into those supermassive black holes that we think are at the heart of galaxies.”

The LIGO-VIRGO collaboration reports on the May 21, 2019 event (listed as GW190521) in two scholarly articles.

One is in the journal Physical Review Letters and describes the discovery. The second can be found in The Astrophysical Journal Letters and discusses the physical properties of the signal and the scientific implications.

GW190521 is one of more than 50 gravitational wave activators currently under investigation in laser laboratories.

The pace of research has increased rapidly since the collaboration conducted its first Nobel Prize-winning gravitational wave detection in 2015.

“We are increasing the sensitivity of the detectors and, yes, we could end up doing more than one detection a day. We will have a shower of black holes! But this is beautiful because we will learn much more about them,” said Prof. Alessandra Buonanno, director from the Max Planck Institute for Gravitational Physics in Potsdam, he told BBC News.

• A laser is fed into the machine and its beam splits along two paths
• Separate paths bounce back and forth between damped mirrors
• Finally, the two parts of light are recombined and sent to a detector.
• Gravitational waves passing through the lab must disturb the setup.
• The theory holds that they should very subtly stretch and squeeze their space
• This should show up as a change in the length of the light arms.
• The photodetector captures this signal in the recombined beam

[email protected] and follow me on Twitter: @BBCAmos