The Ancient Collision That Everyone Saw

The year is 1987, and on February 23rd, three separate neutrino observatories experienced a huge burst in detections. Although initially unsure of their origin, the next day a Supernova was discovered in the Large Magellanic Cloud, a small satellite galaxy of the Milky Way visible in the southern hemisphere.  Known as 1987A, it was the closest supernova observed in centuries, and was observed by astronomers around the world as it brightened and then slowly dimmed.  By combining the visible observations with the neutrino data, scientists learned about how supernovae occur, constrained the mass of the neutrino, and opened a new field:neutrino astronomy.

This was 20 years ago.  Today, the next frontier has been crossed, and boy were scientists ready for it.

NSF/LIGO/SONOMA STATE UNIVERSITY/A. SIMONNET

The newest gravitational wave detection from the Laser Interferometer Gravitational Wave Observatory (LIGO) occurred a few precious minutes before the collision and merger of two neutron stars, dense dead stars composed almost entirely of neutrons.  This is incredible on its own, as only distant black hole mergers have been detected up to this point.  What makes it exceptional is that the collision of two neutron stars also creates detectable light, and telescopes around the world have captured the light from the same collision that LIGO saw.

Not only do we have new gravitational wave data on a Neutron star merger that occurred 130 Million light years away (far closer than any detected gravitational waves), but we also have follow up date taken across the electromagnetic spectrum, from gamma rays all the way down.  Over 70 observatories across the globe collaborated to gather this data, allowing us to see the collision occur in many different ways.  It’s not unlike reconstructing a car accident by interviewing people who saw it from different angles.

Gravitational waves are detected in a very different way than electromagnetic waves, so how do we know they came from the same source? Derek Muller of Veritaseum does a good job of explaining.

 

 

The interesting thing about the detection is that it lasted far longer (about 100 seconds) than the millisecond detections of black hole mergers.  This is likely because the collision was much closer than the 3 billion light year distant black hole mergers.  It’s like seeing a light bulb output 40 watts of power.  If you move it further, it looks dimmer and is harder to see, closer and it’s brighter and easier to spot, but no matter what it’s still radiating the same 40 watts of energy.

Because this collision is much closer, the gravitational waves were more energetic, and the detectors picked them up earlier in the collision.  As the two neutron stars spiraled closer to each other, the intensity of gravitational waves they produced kept growing, until LIGO detected them 100 seconds before the actual merger, which is when the gamma rays were first observed.

So what’s next?  The detection of a neutron star merger let’s us see how these mergers unfold, what sort of radiation they produce, and even what elements are formed in the high-energy process.  All of this will serve to verify or disprove a variety of theories on natural nucleosynthesis, neutron star physics, and gravitational waves themselves.

We are probing deeper into the workings of the universe, and I can’t wait to see what we will find next!

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