NEWS MATTER & ENERGY
ATOM & COSMOS
Atomic bomb test made a quasicrystal
Milky Way may have matured fast
In an instant, the bomb obliterated everything. The tower it sat on and the copper wires strung around it: vaporized. The desert sand below: melted. In the aftermath of the first test of an atomic bomb, in July 1945, all this debris fused together, leaving the ground of the New Mexico test site coated with a glassy substance now called trinitite. High temperatures and pressures helped forge an unusual structure within one piece of trinitite, in a grain of the material just 10 micrometers across — a bit longer than a red blood cell. That grain contains a rare form of matter called a quasicrystal, born the moment the nuclear age began, scientists report in the June 1 Proceedings of the National Academy of Sciences. Normal crystals are made of atoms locked in a lattice with a structure that repeats in a regular pattern. Quasicrystals have a structure that is orderly like a normal crystal but doesn’t repeat. This means quasicrystals can have properties that are impossible for normal crystals. First discovered in the lab in the 1980s, quasicrystals also appear in nature in meteorites (SN: 1/21/17, p. 16). The quasicrystal from the New Mexico test site is the oldest one known that was made by humans. Researchers found a quasicrystal in red trinitite that formed from melted sand and debris during the Trinity atomic bomb test.
Trinitite takes its moniker from the nuclear test, named Trinity, in which the material was created in abundance (SN: 4/10/21, p. 16). “You can still buy lots of it,” says Terry Wallace, a geophysicist and emeritus director of Los Alamos National Laboratory in New Mexico. But, Wallace notes, the trinitite that he and colleagues studied was a rarer variety, called red trinitite. Most trinitite has a greenish tinge. Red trinitite contains copper, remnants of the wires that stretched from the ground to the bomb. Quasicrystals tend to be found in materials that have experienced a violent impact and usually involve metals. Red trinitite fits both criteria. But first the team had to find some. “I was asking around for months looking for red trinitite,” says theoretical physicist Paul Steinhardt of Princeton University. But Steinhardt, who is known for trekking to Siberia to seek out quasicrystals, wasn’t deterred (SN: 3/2/19, p. 28). Eventually, mineralogist Luca Bindi of the University of Florence got some from a trinitite expert, who began collaborating with the team. Once Bindi extracted the tiny grain, the researchers scattered X-rays through it, revealing that the material had a type of symmetry found only in quasicrystals. The quasicrystal, formed of silicon, copper, calcium and iron, is “brand new to science,” says mineralogist Chi Ma of Caltech. “It’s a quite cool and exciting discovery.” The study shows that artifacts from the birth of the atomic age are still of scientific interest, says materials scientist Miriam Hiebert of the University of Maryland in College Park, who has analyzed materials from other pivotal moments in nuclear history (SN: 6/22/19, p. 16). “Historic objects and materials are not just curiosities in collectors’ cabinets but can be of real scientific value,” she says. s
Galaxy was mostly grown before it ate its small neighbor BY LISA GROSSMAN
The Milky Way as we know it today was shaped by a collision with a dwarf galaxy about 10 billion years ago. But most of the modern galaxy was already in place even at that early date, new research shows. Ages of stars left behind by the galactic outsider are a bit younger or on par with stars in the Milky Way’s main disk, researchers report May 17 in Nature Astronomy. That could mean that the Milky Way grew up faster than astronomers expected, says astrophysicist Ted Mackereth of the University of Toronto. “The Milky Way had already built up a lot of itself before this big merger happened.” The galaxy’s history is one of violent conquest. Like other large spiral galaxies in the universe, the Milky Way probably built up its bulk by colliding and merging with smaller galaxies over time. Stars from the unfortunate devoured galaxies got mixed into the Milky Way like cream into coffee, making it difficult to figure out what the galaxies were like before they merged. In 2018, astronomers realized that they could identify stars from the last major merger using detailed maps of more than a billion stars from the European Space Agency’s Gaia spacecraft. Streams of stars orbit the galactic center at an angle to the main disk of stars. Those stars’ motions and chemistries suggest they once belonged to a separate galaxy that plunged into the Milky Way about 10 billion years ago (SN: 11/24/18, p. 8). Two groups discovered evidence of the ancient galaxy at around the same time. One called the galaxy Gaia-Enceladus; the other group called it the Sausage. The name that stuck was Gaia-Enceladus/ Sausage. Mackereth and colleagues wondered
12 SCIENCE NEWS | June 19, 2021
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6/2/21 3:31 PM
DPAC/GAIA/ESA (CC BY-SA 3.0 IGO)
BY EMILY CONOVER
L. BINDI, P.J. STEINHARDT
Debris contains a material with an odd, nonrepeating structure
