Ah, a golden shower joke
You can rely on El Reg!
Apparently, this sort of thing happens often and has done so for billions of years. Now, we can watch them doing it since the LIGO let's us know where to look.
Barely two years after it came online, the Laser Interferometer Gravitational-Wave Observatory (LIGO) has scored a double success. Last week, the instrument earned its creators a Nobel Prize – and this week we're told it helped spot the first neutron star collision from both its gravitational wave and radiation emissions. At …
Having scoured the Internet for more information, this article cleared up a number of things for me.
Indeed, in my original opinion, neutron stars are made of neutrons. Gold and platinum are not, so how could a merger of neutrons produce anything else but neutrons ?
Obviously, the energy involved has something to do with it. As the neutron stars collide, the residue of the explosion and the inconceivable energies involved create and eject the matter that is detected.
It is absolutely mind-blowing to imagine the sequence of events that conducted to the presence of gold on Earth. First, not too far away from our future Sun, two supermassive stars orbiting each other went supernova in the very early days of the Universe, leaving two neutron stars in the wake of the unbelievable cataclysm. These neutron stars managed to stay in orbit, then gradually came close enough to merge, causing the creation of an Earth-sized amount of gold that was spewed into the local interstellar medium.
Meanwhile, our Sun formed and its solar system followed, and was showered by the gold and platinum from the merger, some time in our past.
Then the Earth formed, capturing some meager proportion of that gold, and now we are digging the deepest tunnels ever made by Man to recover said gold.
Edit : This video is very informative as well.
The weird bit is not neutrons becoming protons, but why neutrons exist at all. Neutrons have more mass than protons and left to themselves decay to a proton, an electron and a neutrino. The half life of a lone neutron is about 15 minutes, so without some mechanism to keep them around they should all have gone before the universe was a week old.
The first excuse for neutrons comes from two places. Protons repel each other with the electromagnetic force and attract each other with the strong force. Neutrons are not affected by electromagnetism but are attracted to protons and neutrons (nucleons) by the strong force. Move two protons close to each other and the combined mass of the pair increases because of electromagnetism and decreases because of the strong force. The strong force is effectively zero at long distances but becomes stronger than electromagnetism at very close range. When the protons are close enough together the part of the mass that comes from electromagnetism is bigger than difference in mass between a proton and a neutron. One proton decays into a neutron, a positron and a neutrino. The positron and the neutrino wander off leaving a proton and a neutron bound together. The neutron cannot decay to a proton because the extra mass the new proton would need to be so close to the other proton is bigger than the difference in mass between a neutron and a proton. (The difference in mass between particles far apart and particles close together is called the binding energy).
There is a bit of quantum weirdness (called degeneracy pressure) that also makes neutrons stable in the nucleus of an atom: No two bound particles of the same type can have identical quantum numbers. The cheap way to get different sets of quantum numbers is to change the spin of one particle. As there are only two possible spins getting more than two protons or two neutrons in the same nucleus requires extra mass (reduced binding energy). That mass can be from nucleons being further from the middle of the nucleus or moving faster (in real life it is a bit of both).
Really big atoms cannot exist because keeping all the quantum numbers different takes nucleons beyond the range of the strong force. To hold a big atom together we need a long range attractive force. Crush the mass of two suns into the space of a city and there is enough gravitation binding energy hold neutrons together despite degeneracy pressure. Neutron stars are our second excuse for neutrons. The neutrons in a neutron star cannot decay into protons because they would be too close to the few remaining protons (the increase in binding energy from reduced degeneracy pressure would be less than the decrease in binding energy from electromagnetic repulsion).
For our next experiment, we need two neutron stars in orbit around each other. The pair lose energy by emitting gravitation waves. That energy comes from gravity as as the neutron stars get closer together. Conservation of angular momentum requires the neutron stars to orbit each other faster, which increases centrifugal force [The first person to say "there is no such thing as centrifugal force" has to name the direction of the force that a test tube exerts on a centrifuge]. Centrifugal force on the outside of the neutron stars counter act gravity until blobs of the neutron stars are thrown out. Once these blobs get away from the intense gravity they have no excuse to exist and start to decay into protons. The electromagnetic repulsion of the protons breaks the blobs into atoms - big ones like gold and uranium.
A good part of the mystery lies in the fact that protons and neutrons are regarded as "balls" whereas they are more like churning assemblies of quarks in which you statistically have a good chance of finding the three up and down quarks in the numbers required. They also exchange mesons with nearby particles with abandon. All this in superposition. I don't think anyone has yet thrown this through a Lattice Quantum Chromodynamics computation, as these reach only 64 points on each side of the 4-D cube, then bump against processing limits.
[The first person to say "there is no such thing as centrifugal force" has to name the direction of the force that a test tube exerts on a centrifuge].
I started reading up on this on wikipedia, and I sort of felt I was grasping something, until the equations started, then my eye rolled into the back of my head and I said "Centrifugal force, yeah, that's what it is"
... LIGO picked up a long grav wave, and gamma ray emission ...
LIGO is a gravitational-wave detector. It is incapable of detecting gamma-ray burst, or any other electromagnetic radiation. That was supplied by an entirely different gamma-ray instrument. Furthermore, LIGO by itself would not have been able to determine the location of the source - you need three detectors to triangulate it. The third detector was provided by Virgo collaboration.
You can read all about it in the original article in Physical Review Letters, which is open access - but be warned that it is pretty heavy going in places.
I know insisting on spelling out all collaborators sounds a bit like nitpicking - but recognition is the currency of science, and it does not do to attribute the work of many institutions a people to just one part of the whole collaboration - even when it is a key part.
...they must have had their own supply of neutron stars for this very purpose:
' "What's the matter with the ground? It's all cold and hard.''
``It's gold,'' said Ford.
With an amazingly balletic movement Zaphod was standing and scanning the horizon, because that was how far the gold ground stretched in every direction, perfectly smooth and solid. It gleamed like ... it's impossible to say what it gleamed like because nothing in the Universe gleams in quite the same way that a planet of solid gold does.
``Who put all that there?'' yelped Zaphod, goggle-eyed.
``Don't get excited,'' said Ford, ``it's only a catalogue.'' '
The relationships between two stars collapsing. A spray of gold to the universe. Flash after flash as the whole event gets more and more dramatic. And the slow fading into the darkness when it all ends...
Sounds almost like Hollywood, doesnt it?
(Great work those Boffins! )
> What if this event happened in our Milky Way galaxy
> which has billions of neutron stars
Size of our galaxy = aprox 1e5 light years diameter; this event was approx 1e8 light years away, so a similar event in our galaxy would be about 1e3 times closer. Due to the inverse square law, the intensity of the radiation would be 1e6 greater. But that's still tiny:
According to section 6.1 of
the total gamma ray energy released was about 3e46 erg, with a peak luminosity of about 1e47 erg/s.
(1 erg = 1e-7 J,so that's 3e39J and 1e40W respectively.)
1e5 light years = approx 1e21m. Surface area of a sphere of that radius = about 1e43 m2.
1e40W over 1e43 m2 is 1mW/m2.
That compares to solar energy reaching earth of about 1e3 W/m2, i.e. a million times more. (Not gamma rays admittedly.)
So I don't think this sort of event happening "somewhere in our galaxy" is a worry. It would need to be a lot closer.
Can anyone explain how LIGO gets an a rough idea of the direction of the gravitational wave? Its never mentioned, probably because its something beautiful mathematical, enjoyed by those few gifted individuals in the inner sanctum. Or its not mentioned because its bleeding obvious to them. Boffins seldom mention the bleeding obvious. Us mortals want some idea as to how distance and direction and detected by such a fractional wobble. They seem to know how far away and roughly where to look. How does watching an atom hardly move allow for such deductions?
Can anyone explain how LIGO gets an a rough idea of the direction of the gravitational wave?
The idea is the same as the way your ears determine where the sound came from. You observe the signal at multiple, geographically separated locations. You also record the precise time the signal arrived at each receiving station. Because gravitational waves propagate at the speed of light, the arrival times will be different at each station. You can then align the signals, giving you the relative time delays between the stations, in turn giving you an idea of where the wave came from.
If you only have two receivers, like LIGO has, you can at best figure out the cone containing the source. This is why it was so important to have the Virgo detector as well - three detectors constrain the solution to just two directions, giving you a sporting chance of finding the source in the electromagnetic spectrum as well.
As usual, it is a little more complicated: for technical reasons, the detectors are not equally sensitive for all directions of arrival. This both makes things a bit messier, and gives some, very crude, directional information as well.
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