British scientists have tied the tightest knot ever tied. Until now, scientists have been able to create only simple molecular knots with three or five crossings of strands. Now researchers, in a study in Science, have described a way to tie a much more complicated, and therefore much stronger, knot. A team of researchers mixed oxygen, nitrogen and carbon in a solution with metal ions. The organic molecules wrap themselves around sticky iron ions and chloride ions, crossing in just the right ways and at just the right points. The loose ends were then sealed together chemically, forming a completely tied knot with eight crossings. The number of crossings made the knot much tighter than anything that had ever been achieved before at the molecular level. The entire loop is tiny, the length of 192 atoms.

Astronomers try to pin down mass of galaxy

Astronomers have arrived at what they believe to be the most accurate measure yet of the mass of the Milky Way: about 4.8 x 10(11) times the mass of the sun, or “solar masses,” to use a standard unit of mass in astronomy. This comes to about 9.5 x 10(41) kilograms — that is, 95 followed by 40 zeros. The number, of course, is inexact, as no direct measure of all the billions of stars and other objects in the Milky Way could be taken. But in a paper to be published in the Astrophysical Journal, scientists used methods of measurement that involve complex mathematical and statistical techniques called hierarchical Bayesian analysis, as well as direct measurements of the velocity of globular clusters, the tightly packed spherical groups of 10,000 to 100,000 old stars that move through the galaxy. Just as the mass of the sun can be calculated by measuring its gravitational pull on Earth, the mass of the Milky Way can be calculated by measuring its gravitational pull on the globular clusters. The estimate includes everything within 125 kiloparsecs of the center of the galaxy — that is, within 3.9 x 10(18) kilometers.

Ruby sea dragon glimpsed in wild

Famous for their flamboyant, leaflike appendages and mesmerizing movements, sea dragons are aquatic works of art. Since the 19th century, marine biologists had thought that only two types existed — the leafy and weedy — until they discovered a third among museum specimens in 2015: the ruby sea dragon. For the first time, scientists have observed one in the wild, swimming in the waters around the Recherche Archipelago in Western Australia. It looks like a stretched-out sea horse, with a hump like a camel and a tail it can curl. Unlike its kin, the ruby sea dragon lacks the appendages that help camouflage it in kelp and sea grass.

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