One hundred and thirty million years ago dinosaurs were a little more than halfway through their stay on Earth. Underneath their feet the first plants that relied on animals to spread their seeds - the first flowers - bloomed. Flowers had an enormous impact on life on Earth - greater than the dinosaurs - but during this long ago time in a galaxy far away a pair of neutron stars danced.
As with all neutron stars they had had seen remarkable times. The result of supernova explosion, all of their matter had been compresed into a city-sized sphere with a density three times higher than the nucleus of an atom. No electrons or protons, most of their interior was nothing but neutrons. While violent, the process releases many of the elements that make up you and me. In fact you are probably the result of at least a half dozen supernova explosions. Put in pin in that thought and we'll come back to it.
The pair, one of them with a mass one point one times that of our Sun, the other one point six, orbited a common center of mass for a long time radiating weak gravity waves over time progressively getting closer and closer orbiting faster and faster. The process sped up dramatically towards the end. Their last minute saw them moving close to the speed of light completing about fifteen hundred revolutions and in the process shaking the fabric of spacetime.
Then they fused.
These new fangled flowers worked out how to attract animals and the animals went about their business completely unaware that something interesting happened out there.
The signal was first detected on August 17th during a normal look at interesting event triggers from the Fermi Gamma-ray Space Telescope. Basically an orbiting cluster of large chunks of sodium iodide crystals and bismuth germanate crystals, it detects and measures gamma-rays from ranging in energy from about ten million to a hundred and fifty billion times the energy of a photon of red light.1 The Fermi looks at gamma-rays from exotic electrical storms on Earth, open air nuclear explosions, and the most violent events in the Universe. Once every few days something thought to be a gamma-ray burst from the collision of two neutron stars takes place.2 This one wasn't particularly strong, but was noted and the team went back to work.
One point seven seconds before the gamma-ray burst detected by the orbiting crystals a gravity wave rolled through Pisa, Italy changing the dimensions of everything generating a signal at the Virgo gravity wave detector at Cascina. Twenty-three thousands of a second later the wave rolled through Livingston, Louisiana and continued along shaking Hanford, Washington two thousandths of a second later. The quake in spacetime continued for over a minute. Soon the most carefully conceived data handling the world has seen indicated a gravity wave had rolled through and the gravity wave folks placed a phone call to the gamma-ray community to check if they had seen anything
The Italian site had only been active for a bit more than two weeks. With the timing of two sites you can roughly determine where in the sky something happened. Add a third and the uncertainty drops dramatically. Numbers were crunched and an alert went out to the astronomy community to point anything they had at a patch in the southern constellation Hydra. Over the next few weeks about seventy ground based and ten orbiting observatories were involved.
We've talked about LIGO and gravity waves before and soon a friend will be splashed with Swedish holy water for his part. To date there have been four solid detections. The nutshell is this is a new way of looking at the Universe. Gravity waves are ripples in spacetime, but it is so rigid that the distance between Earth and our closest star shakes about the thickness of a human hair. Designing and building working detectors is my candidate for the ultimate human technical achievement to date.
What makes this one special is there was enough information to know where to point optical telescopes and the gravity wave signal is undoubtedly associated with the electromagnetic signal. As the stars finished their dance they shook space time enough for us to hear it (I use that analogy as it is a compression and expansion of a medium just like sound is). Then the massive gamma ray burst with a light show that went on for a few weeks.
a talkie - audio and visual!
An enormous amount of information was taken as the event progress. This image samples the range from acoustical gravity wave signals and various optical signals ranging in wavelength form radio to gamma-ray.
So much has been learned. It turns out (skipping the details) it's a good way to measure the Hubble Constant and with it hone in on the expansion of the Universe. It also provides an accurate distance measure to a distant event - we have the red shift from the optical signal and luminosity from the gravity waves (again, ping me if you want details, but it gets into too much physics for this blog - for the physics types the proposal is to call these standard sirens). And Einstein was right... gravity waves travel at the speed of light.3 We now know that to considerable accuracy.
... one last thing... You may be wearing gold. A ring, a watch or some other jewelry. Gold has an atomic number of 79 making it a heavy element. The Big Bang didn't create any and the burning that goes on in normal stars doesn't either. You can produce very heavy elements in supernova explosions and this was the standard story until about five years ago. Now it's understood the violent collision of orbiting neutron stars is a rich generator of the heavies. They're blasted out in a jet that runs along the axis of rotation of the pair. An event like this generates a mass of gold a bit larger than our Moon.
Most of the gold in your jewelry is from the collision of neutron stars.
Just like what we heard and saw on the 17th of August in that first talkie of the Universe.
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0 ok - the title has problems. The acoustic part is gravity waves from the US and Italy, but the video part is from all over including Antarctica. And researchers from all over have their thumbprints on all phases. When you spend an hour writing, titles are issues.
1 you don't want to expose your body to much of this stuff. Biochemistry happens at energies close to that of visible light .. much higher and molecules are damaged and atoms ionized.
2 there are about one hundred million neutron stars in our Galaxy... way more in the Universe:) About a tenth of a percent of the stellar population
3 all massless fields travel at the speed of light.
Something quite romantic about gold, the collision of stars, and the fact this is a metal we associate with wedding and other commitment bands!
Posted by: Nancy | 10/16/2017 at 04:48 PM
I love this Steve! It is beautiful!
Now you should explain standard sirens.
Posted by: Jheri | 10/16/2017 at 05:09 PM