The heaviest known neutron star — or the lightest known black hole

Gravitational-wave observatories have witnessed a black hole, 23 times as massive as the Sun, gobbling up an enigmatic object. At 2.6 solar masses, it is thought to be too large to be a neutron star, the only other type of orb that current detectors are sensitive to. But if it is a black hole, it would be the lightest ever observed. The massive stars that collapse to form black holes should leave behind remnants at least twice that size, standard astrophysical models suggest. Astronomers tried to find clues by looking for light from the merger, but to no avail.

Neutrinos reveal final secret of Sun’s nuclear fusion

The theories for why the Sun shines date back to the 1930s, but one crucial bit of evidence was missing. Now, physicists have found direct evidence for a type of reaction, involving carbon and nitrogen nuclei, in which four protons fuse into a helium nucleus. The smoking gun? Neutrinos, elementary particles the reaction releases. These zip straight out from the Sun’s core, reaching Earth just 8 minutes later. The carbon–nitrogen pathway is not the only type of fusion in the Sun, and it’s not even the main one — neutrinos from all the other reactions had been detected before — but it is thought to be the dominant energy source for larger stars.

Vast neolithic circle of deep shafts found near Stonehenge

Archæologists have discovered a 2-kilometre ring of prehistoric shafts about 3 kilometres from Stonehenge. There are at least 20 of the 4,500-year-old shafts, each more than 5 metres deep and 10 metres in diameter. The startling discovery, in one of the world’s most studied archæological landscapes, comes thanks to modern techniques including ground-penetrating radar.

Dark Matter Experiment Finds Unexplained Signal

The world’s most sensitive dark-matter experiment might have found a hint of the stuff — although the data it has collected so far could be a statistical fluctuation or a spurious signal. The data collected in 2017-18 by the underground XENON1T experiment have revealed an excess in the number of particles hitting its liquid xenon, with a relatively low energy. The finding suggests the possible existence of a hypothetical particle called the axion. But another possible explanation is the presence of radioactive impurities. An upgraded version of the detector called XENONnT could solve the riddle next year.

Bizarre nearby star offers clues to origins of mysterious fast radio bursts

For a fraction of a second in late April, a hyper-magnetised star in the Milky Way suddenly blasted out radio energy. Now scientists say that this sudden, strange blip could help to explain one of astronomy’s biggest puzzles: what powers the hundreds of other mysterious fast radio bursts (FRBs) that have been spotted much farther away in the Universe. Many astronomers think that fast radio bursts — brief but powerful cosmic flashes that flare for just milliseconds — come from magnetars, but haven’t found the link.

Archæologists discover 'amazing' details of Roman city

Archaeologists have mapped a full ancient city with ground-penetrating radar. Falerii Novi, a 30-hectare settlement near Rome that was occupied between 241 BC and AD 700, is now almost entirely buried under agricultural land. The team towed their radar antennas with a quad bike. Their finds include a mysterious public monument — possibly linked to pre-Roman religions — and an extensive network of water pipes that was evidently planned and laid before the city was built.

Oldest Mayan monument ever found

A huge artificial plateau that is 1.4 kilometres long and 10–15 metres high has been discovered in Mexico. Archaeologists spotted the monumental construction from the air using lidar, a remote-sensing method that maps the ground using lasers. Dubbed Aguada Fénix, the extensive structure was built between 1000 and 800 BC, and precedes the peak of the Maya empire by more than a millennium.

Revolutionary microscopy sees individual atoms for first time

A game-changing technique for imaging molecules has produced its sharpest pictures yet — and, for the first time, has discerned individual atoms in a protein. The cryo-electron microscopy breakthrough, reported by two laboratories late last month, will ultimately help researchers to understand how proteins work in health and disease, and will lead to better drugs with fewer side effects.

Ancient DNA offers clues to physical origins of Dead Sea Scrolls

DNA fingerprinting is helping researchers to understand the patchwork of archæological fragments known as the Dead Sea Scrolls. Through genetic analysis, researchers have been able to reconstruct the origin of some of the ancient parchments. In particular, they realised that two pieces once considered part of the same manuscript were in fact made from different animal hides — one from sheep and the other from cow.

Topological insulators enter the fourth dimension

Physicists have created a virtual crystal with four spatial dimensions that acts as a topological insulator — a material that conducts electricity on only its outer boundary. To do so, the team wired up connections among electrical circuits to simulate those in a four-dimensional (4D) crystal. (Just as cubes have six square faces, hypercubes have eight cubic ‘faces’ — so when hypercubes are stacked in 4D, each one is in contact with eight neighbours.) A similar scheme could extend to even more dimensions of space, leading to the observation of new phenomena. Exotic topological insulators could find applications in future quantum computers.

The most ancient land animal ever found

An inch-long creature similar to a millipede looks to be the oldest animal known to have lived on land. Fossil imprints of Kampecaris obanensis from the island of Kerrera in Scotland have been radiometrically dated to around 425 million years ago, in the Silurian period. The arthropod probably fed on decomposing plants on a lakeside. Even earlier land animals, from the Cambrian era, are known to have existed, but only indirectly, from their tracks.