Most of Earth's Heavy Elements Come From One Place

All of the matter in the universe heavier than hydrogen or helium was made after the Big Bang in stars. However, standard nuclear fusion can only produce elements as heavy as iron; once a star tries to start fusing iron, the fusion reaction requires more energy than it puts out, causing said star to go supernova. It's during the supernova that all the heavier elements are made, however, supernovae are not the only way heavy elements come into being. The collision of two neutron stars also produces heavy elements, and according to new research, such a collision was responsible for seeding our solar with a vast quantity (something like 1 quintillion tons) of heavy elements such as gold and uranium.

According to the scientists, the specific collision happened about 1,000 light years away from the stellar nebula that our solar system formed out of, and occurred about 80 million years before the sun was born. This conclusion was reached through analysis of ancient meteorites, and the elements leftover from radioactive decay within those meteorites. Those elements were consistent with what a neutron star collision would have produced, not a supernova.

While we should be grateful for that collision all those eons ago (specifically, the iodine produced is essential for life), if such an event happened at that proximity today, it would create a gamma ray burst that would essentially torch our atmosphere, causing a mass extinction. Well, if we were unlucky enough to be on the business end of one of the poles of the black hole that would be formed in the process. Fortunately, these things don't happen very often, so no need to worry.

The Good News For General Relativity Keeps On Coming

Not too long ago, I wrote about how alternate theories to general relativity have been having a tough time as of late. Well, things just got even tougher.

The equivalence principle was on trial for this experiment. One of the basic tenets of relativity is that two objects, no matter what their mass or what they're made of, they are affected by gravity in the same way. This has been tested many times on Earth (and famously, on the Moon), but never with really dense objects. Alternative theories to relativity assume that the equivalence principle breaks down at high density, since up to now, there's been room to work.

The test involved  a neutron star-white dwarf pair, and watching the orbit of the neutron star. If there were variations in its orbit, it would have been in violation of the equivalence principle, and the various alternate theories would have some ground to stand on. But there was no variation, and once again, general relativity was proven correct. And not only that, but this test improved the accuracy of the previous best gravity test by a factor of 10. Alternate gravity theories thus have a lot less room to work.

Just How Big Are Neutron Stars, Anyway?

I know, I know, somewhere between 10 and 20 miles. We've known how big neutron stars are for a while. Well, we've roughly known, as it turns out, we don't know their size accurately enough to really figure neutron stars out. We need an exact figure, because an exact figure will tell us exactly how dense they are, and that is an important problem for particle physics. We don't know how matter behaves when pushed to the absolute limits of density, and that's what neutron stars are. They're not black holes, the laws of physics still apply, and it's possible to learn what goes on inside them. All we need to finish the neutron star puzzle (okay, probably not) is an exact radius. And luckily for physicists, an instrument called NICER (Neutron Star Interior Composition Explorer), attached to the International Space Station, will answer these big questions this summer.

So, that's something to look forward to. I don't have any spectacular conclusions, since we don't know anything yet, I just thought this was a neat article.