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NIST’s research reactor suffered little damage, but will be offline for months

At one time, many physicists resisted the notion of a black hole, a ghostly, self-sustaining gravitational field so intense that not even light can escape. Now, theorists have few alternatives to these creepy holes in the universe. Any alternative to a black hole must be some dark, dense material orb that9s bigger than a black hole of the same mass. One hypothetical possibility is a gravastar: a thin material shell filled with dark energy, the mysterious space-stretching stuff that appears to be accelerating the expansion of the universe. Another possibility would be a boson star, which would consist of exotic, massive Higgs bosons or nearly massless hypothetical particles called axions. Theorists say the study of black hole alternatives would expand if observers saw evidence that the current description of black holes isn9t correct.

A potential chink in physicists9 understanding of fundamental particles and forces now looks more real. New measurements confirm a fleeting subatomic particle called the muon may be ever so slightly more magnetic than theory predicts, a team of more than 200 physicists reported this week. That small anomaly—just 2.5 parts in 1 billion—is a welcome threat to particle physicists9 prevailing theory, the standard model, which has long explained pretty much everything they9ve seen at atom smashers and left them pining for something new to puzzle over. Announced on 7 April, the new result from Muon g-2 experiment at Fermi National Accelerator Laboratory confirms an excess that the same experiment reported in the early 2000s, when it ran at Brookhaven National Laboratory, showing that the excess most likely wasn9t a statistical fluke or an experimental artifact. The extra magnetism of the muon could be evidence of new fundamental particles lurking in the vacuum around it and distorting its properties.

Just 5 years ago, physicists opened a new window on the universe when they first detected gravitational waves, ripples in space itself set off when massive black holes or neutron stars spiral together. Even as discoveries pour in, researchers are already planning bigger, more sensitive detectors. And a Ford versus Ferrari kind of rivalry has emerged, with scientists in the United States simply proposing detectors 10 times bigger than the ones they have now, and researchers in Europe pursuing a more radical design that would combine six detectors in a single underground observatory. Researchers say detectors 10 times more sensitive than the ones they have now could detect all black hole mergers within the observable universe and spot hundreds of mergers of neutron stars, laying bare the nature of the ultradense matter in neutron stars. But, it9s early days for the U.S. project, which is called the Cosmic Explorer, and the European project, which is known as the Einstein Telescope.

In 1986, TV journalist Dan Rather was attacked in New York City by an assailant who demanded cryptically, "Kenneth, what9s the frequency?" The query became a pop culture meme and the title of a hit pop song on it. Now, it could be the motto for the team about to deliver this year9s most anticipated result in particle physics. As early as March, the Muon g-2 experiment at Fermi National Accelerator Laboratory will report a new measurement of the magnetism of a particle called the muon, a heavier, short-lived cousin of the electron. Since 2001, the experiment has hinted that the muon is slightly more magnetic than theory predicts, an excess that could imply the existence of novel massive particles that might be producible with an atom smasher. The experiment entails measuring a single frequency with exquisite precision, and to ensure they don9t fool themselves into claiming a false discovery, g-2 researchers are taking cloak and dagger measures involving locked cabinets, sealed envelopes, and a second, secret frequency that will be revealed only at the last moment.

Four years ago, when experimenters spotted pentaquarks—exotic, short-lived particles made of five quarks—some physicists thought they had glimpsed the strong nuclear force, which binds the atomic nucleus, engaging in a bizarre new trick. New observations have now expanded the zoo of pentaquarks, but suggest a tamer explanation for their structure. The findings, from the Large Hadron Collider beauty experiment (LHCb), a particle detector fed by the LHC at CERN, the European particle physics laboratory near Geneva, Switzerland, suggest pentaquarks are not bags of five quarks binding in a new way, but are more like conventional atomic nuclei, with a particle called a baryon that contains three quarks bound to another called a meson, which has two. Researchers say it9s too early to say which model of pentaquarks is correct, but the new observations move the needle toward the molecular picture.

As children once did before Christmas, astrophysicists have been eagerly awaiting the arrival of a catalog, this one listing not toys, but cataclysmic collisions of objects such as black holes—the ghostly ultraintense gravitational fields left behind when massive stars collapse. Last week, it arrived, courtesy of the world9s network of three huge gravitational wave detectors, which sense the infinitesimal ripples in space itself set off when, say, to massive black holes spiral into each other. Physicists previously spotted 11 events including a merger of two neutron stars, which shed light on how the universe forges heavy elements. Now, the team has cataloged 37 additional black hole mergers, another neutron star merger, and a possible merger of a black hole and neutron star. The sample enables physicists to begin statistical analyses, which are already showing that black holes are more varied than scientists had expected, providing new insights into how black holes may pair in the first place.

For decades, some theoretical physicists have speculated that in the heart of a neutron star, a bizarre type of matter might emerge: a soup of the subatomic particles called quarks. Now, a new analysis indicates the recipe for such "cold quark matter" needs revision. Atomic nuclei consist of protons and neutrons, which themselves consist of trios of particles called up and down quarks, bound tightly by the strong nuclear force. Since the 1970s, some theorists have predicted that under extreme pressures like those in neutron stars, quarks might break free to create a soup of cold quark matter. They also predicted that it should include a third flavor of quarks known as strange quarks. Stable bits of such strange quark matter—or strangelets—might emerge in cosmic rays or linger from violent astrophysical events. Now, a trio of theorists argues that cold quark matter should consist of just up and down quarks. The analysis suggests that particle accelerators on Earth might just be able to produce stable bits of the quark matter. It would also dispel a far-fetched notion the Large Hadron Collider in Switzerland could produce negatively charged strangelets that would gobble up positively charged atomic nuclei—a possibility already ruled out by cosmic ray observation. Up-down quark matter would definitively rule out the doomsday scenario, as it would be positively charged and repel atomic nuclei.

After decades of effort, physicists say they are on the verge of detecting ripples in spacetime called gravitational waves, whose existence Albert Einstein himself predicted nearly a century ago. Researchers working on the Laser Interferometer Gravitational-Wave Observatory (LIGO) will use enormous instruments in Livingston, Louisiana, and Hanford, Washington, to look for the gravitational waves set off when two neutron stars spiral into each other. LIGO ran from 2002 to 2010 and saw nothing, but those Initial LIGO instruments aimed only to prove that the experiment was technologically feasible, physicists say. Now, they9re finishing a $205 million rebuild of the detectors, known as Advanced LIGO, which should make them 10 times more sensitive and, they say, virtually ensure a detection. Such an observation would open up a whole new type of astronomy—and likely bag a Nobel Prize.