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Category: physics

In the center of our galaxy, hundreds of stars closely orbit a supermassive black hole. Most of these stars have large enough orbits that their motion is described by Newtonian gravity and Kepler’s laws of motion. But a few orbit so closely that their orbits can only be accurately described by Einstein’s theory of general relativity. The star with the smallest orbit is known as S62. Its closest approach to the black hole has it moving more than 8% of light speed.

Our galaxy’s is known as Sagittarius A* (SgrA*). It is a mass of about 4 million suns, and we know this because of the stars that orbit it. For decades, astronomers have tracked the motion of these stars. By calculating their orbits, we can determine the mass of SgrA*. In recent years, our observations have become so precise that we can measure more than the black hole’s mass. We can test whether our understanding of is accurate.

The most studied star orbiting SgrA* is known as S2. It is a bright, blue giant star that orbits the black hole every 16 years. In 2018, S2 made its closest approach to the black hole, giving us a chance to observe an effect of relativity known as gravitational redshift. If you toss a ball up into the air, it slows down as it rises. If you shine a into the sky, the light doesn’t slow down, but gravity does take away some of its energy. As a result, a beam of light becomes redshifted as it climbs out of a gravitational well. This effect has been observed in the lab, but S2 gave us a chance to see it in the real world. Sure enough, at the , the light of S2 shifted to the red just as predicted.

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The end of the universe as we know it will not come with a bang. Most stars will slowly fizzle as their temperatures fade to zero.

“It will be a bit of a sad, lonely, cold place,” said theoretical physicist Matt Caplan, who added no one will be around to witness this long farewell happening in the far far future. Most believe all will be dark as the comes to an end. “It’s known as ‘heat death,’ where the universe will be mostly black holes and burned-out ,” said Caplan, who imagined a slightly different picture when he calculated how some of these might change over the eons.

Punctuating the darkness could be silent fireworks—explosions of the remnants of stars that were never supposed to explode. New theoretical work by Caplan, an assistant professor of physics at Illinois State University, finds that many white dwarfs may explode in in the distant far future, long after everything else in the universe has died and gone quiet.

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This magnitude 7.1 earthquake started deep underground, in a gash on the Atlantic seafloor, a little more than 650 miles off the coast of Liberia, in western Africa. It rushed eastward and upward, then did an about-face and boomeranged back along the upper section of the fault at incredible speeds‑so fast it caused the geologic version of a sonic boom.

The ferocity of shaking from an earthquake is usually focused in the direction the temblor is traveling. But a boomerang quake, or a “back-propagating rupture” in scientific terms, may spread the intense shaking across a wider zone. It remains uncertain how common boomerang earthquakes are—and how many travel at such great speeds. But the new study, published today in the journal Nature Geoscience, is a major step toward untangling the complex physics behind these events and understanding their potential hazards.

“Studies like this help us understand how past earthquakes ruptured, how future earthquakes may rupture, and how that relates to the potential impact for faults near populated areas,” says Kasey Aderhold, a seismologist with the Incorporated Research Institutions for Seismology, via email.

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Dozens of times over the last decade NASA scientists have launched laser beams at a reflector the size of a paperback novel about 240,000 miles (385,000 kilometers) away from Earth. They announced today, in collaboration with their French colleagues, that they received signal back for the first time, an encouraging result that could enhance laser experiments used to study the physics of the universe.

The NASA scientists aimed for is mounted on the Lunar Reconnaissance Orbiter (LRO), a spacecraft that has been studying the moon from its orbit since 2009. One reason engineers placed the reflector on LRO was so it could serve as a pristine target to help test the reflecting power of panels left on the moon’s surface about 50 years ago. These older reflectors are returning a , which is making it harder to use them for science.

Scientists have been using reflectors on the moon since the Apollo era to learn more about our nearest neighbor. It’s a fairly straightforward experiment: Aim a at the reflector and clock the amount of time it takes for the light to come back. Decades of making this one measurement has led to major discoveries.

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International team develops a new method to determine the origin of stardust in meteorites.

Analysis of meteorite content has been crucial in advancing our knowledge of the origin and evolution of our solar system. Some meteorites also contain grains of stardust. These grains predate the formation of our solar system and are now providing important insights into how the elements in the universe formed.

Working in collaboration with an international team, nuclear physicists at the U.S. Department of Energy’s (DOE’s) Argonne National Laboratory have made a key discovery related to the analysis of “presolar grains” found in some meteorites. This discovery has shed light on the nature of stellar explosions and the origin of chemical elements. It has also provided a new method for astronomical research.

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(Inside Science) — What do a volcanologist, a pulmonologist, and a glassmaker have in common? They all worry about bubbles. The physics of how bubbles form, behave and pop is crucial to understanding natural phenomena as well as many industrial processes. According to a new study appearing in the journal Science, scientists have been getting that physics wrong for at least a couple of decades.

The new findings suggest that instead of being driven by gravity, the collapse of bubbles that form on the surface of thick liquids is driven by surface tension, in a complex, unintuitive way. And to find the truth, all the researchers had to do was turn their experiment upside down.

The physics of a bubble depends on how thick — viscous — its fluid is. If a bubble floating on the surface of water is poked and popped, surface tension makes the bubble retract quickly and violently, vanishing in about a millisecond. But in a very viscous liquid, a surface bubble may take up to one full second to collapse. This gives researchers extra time to observe a complex interplay between forces that is perfect for studying the fundamental physics at work in bubble collapse.

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Ultrashort laser pulses induce unusual sound waves via a structural instability in a material.

RIKEN physicists have initiated unusual sound waves in a flake using ultrashort pulses of laser light and then created videos of their movement using electron microscopy. This advance should help engineers to achieve higher precision control of heat flow and sound in nanodevices using light.

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Scientists can use some pretty wild forces to manipulate materials. There’s acoustic tweezers, which use the force of acoustic radiation to control tiny objects. Optical tweezers made of lasers exploit the force of light. Not content with that, now physicists have made a device to manipulate materials using the force of… nothingness.

OK, that may be a bit simplistic. When we say nothingness, we’re really referring to the attractive force that arises between two surfaces in a vacuum, known as the Casimir force. The new research has provided not just a way to use it for no-contact object manipulation, but also to measure it.

The implications span multiple fields, from chemistry and gravitational wave astronomy all the way down to something as fundamental and ubiquitous as metrology — the science of measurement.

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