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The multiverse theory could answer questions that remain in physics and astronomy.

For more than 20 years, a team of astronomers has tracked a single star whipping around the supermassive black hole at the center of our galaxy at up to 25 million kilometers per hour, or 3% of the speed of light. Now, the team says the close encounter has put Albert Einstein’s theory of gravity to its most rigorous test yet for massive objects, with the light from the star stretched in a way not prescribed by Newtonian gravity. In a study announced today, the team says it has detected a distinctive indicator of Einstein’s general theory of relativity called “gravitational redshift,” in which the star’s light loses energy because of the black hole’s intense gravity.

“It’s really exciting. This is such an amazing observation,” says astronomer Andrea Ghez of the University of California, Los Angeles (UCLA), who heads a rival group that is also tracking the star. “This is a direct test [of relativity] that we’ve both been preparing for for years.”

The star, called S2, is unremarkable apart from a highly elliptical orbit that takes it within 20 billion kilometers, or 17 light-hours, of the Milky Way’s central black hole—closer than any other known star. A team led by Reinhard Genzel at the Max Planck Institute for Extraterrestrial Physics (MPE) in Garching, Germany, has been tracking S2 since the 1990s, first with the European Southern Observatory’s (ESO’s) 3.6-meter New Technology Telescope in Chile’s Atacama Desert and later with ESO’s Very Large Telescope (VLT), made up of four 8-meter instruments. Ghez’s team at UCLA also began to observe the star around the same time with the twin 10-meter Keck telescopes in Hawaii.

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Observations made with ESO’s Very Large Telescope have for the first time revealed the effects predicted by Einstein’s general relativity on the motion of a star passing through the extreme gravitational field near the supermassive black hole in the centre of the Milky Way. This long-sought result represents the climax of a 26-year-long observation campaign using ESO’s telescopes in Chile.

Obscured by thick clouds of absorbing dust, the closest supermassive black hole to the Earth lies 26 000 light-years away at the centre of the Milky Way. This gravitational monster, which has a mass four million times that of the Sun, is surrounded by a small group of stars orbiting around it at high speed. This extreme environment — the strongest gravitational field in our galaxy — makes it the perfect place to explore gravitational physics, and particularly to test Einstein’s general theory of relativity.

New infrared observations from the exquisitely sensitive GRAVITY [1], SINFONI and NACO instruments on ESO’s Very Large Telescope (VLT) have now allowed astronomers to follow one of these stars, called S2, as it passed very close to the black hole during May 2018. At the closest point this star was at a distance of less than 20 billion kilometres from the black hole and moving at a speed in excess of 25 million kilometres per hour — almost three percent of the speed of light [2].

Scientists announced Wednesday that they’ve found evidence of a large body of water beneath the surface of Mars. It may not be little green men, but it’s pretty darn cool.

The announcement, which comes less than two months after the Curiosity Rover found evidence of organic molecules on Mars, adds one more piece to the puzzle for scientists searching the planet for signs that it could support life — or at least could have in the past. And while scientists have long known that Mars used to have liquid water billions of years ago, the fact that it could still have water is a big deal since there’s a possibility that this water may host living organisms.

The researchers involved in the discovery, a team of Italian astronomers and physicists, published their findings in a paper in the journal Science. In the paper, the team presents evidence collected from May 2012 to December 2015 by the MARSIS (Mars Advanced Radar for Subsurface and Ionosphere Sounding) experiment aboard the Mars Express spacecraft that shows evidence of a large body of liquid water.

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In a recent paper published to arXiv, the physicists Roland Allen and Suzy Lidstrom, of Texas A&M and Uppsala University, respectively, tackled the question about the Question by describing what they believe to be the 42 ultimate questions of life, the universe, and everything.

In a homage to ‘Hitchhiker’s Guide to the Galaxy,’ two physicists explain the biggest unknowns in science. I’ve summed them up as a tweetstorm.

Sawtooth swings—up-and-down ripples found in everything from stock prices on Wall Street to ocean waves—occur periodically in the temperature and density of the plasma that fuels fusion reactions in doughnut-shaped facilities called tokamaks. These swings can sometimes combine with other instabilities in the plasma to produce a perfect storm that halts the reactions. However, some plasmas are free of sawtooth gyrations thanks to a mechanism that has long puzzled physicists.

Researchers at the U.S. Department of Energy’s (DOE) Princeton Plasma Physics Laboratory (PPPL) have recently produced complex simulations of the process that may show the physics behind this mechanism, which is called “magnetic flux pumping.” Unraveling the process could advance the development of fusion energy.

Physics

You’re probably sitting still, right? Wrong, absolutely wrong. Not only are you on a spinning orb, but you’re also traveling around 70,000 miles per hour around a star, in a galaxy that, observations imply, is sailing through space at over a million miles per hour.

If the above numbers seem shocking, they shouldn’t be. The laws of physics look and feel the same for any object so long as it’s not accelerating, the way you can’t feel that a car is traveling at a steady 60 miles per hour unless you look out the window. But that also makes our galactic speed hard to measure from here on Earth. The million-plus mile per hour number is based on measurements of how the most distant objects in the Universe appear to move in comparison to us, but scientists want to try to measure our acceleration by looking at more nearby objects.

How large is a neutron star? Previous estimates varied from eight to 16 kilometres. Astrophysicists at the Goethe University Frankfurt and the FIAS have now succeeded in determining the size of neutron stars to within 1.5 kilometres by using an elaborate statistical approach supported by data from the measurement of gravitational waves. The researchers’ report appears in the current issue of Physical Review Letters.

Neutron stars are the densest objects in the universe, with a mass larger than that of our sun compacted into a relatively small sphere whose diameter is comparable to that of the city of Frankfurt. This is actually just a rough estimate, however. For more than 40 years, the determination of the size of neutron stars has been a holy grail in nuclear physics whose solution would provide important information on the fundamental behaviour of matter at nuclear densities.

The data from the detection of gravitational waves from merging neutron stars (GW170817) make an important contribution toward solving this puzzle. At the end of 2017, Professor Luciano Rezzolla, Institute for Theoretical Physics at the Goethe University Frankfurt and FIAS, together with his students Elias Most and Lukas Weih already exploited this data to answer a long-standing question about the maximum mass that neutron stars can support before collapsing to a black hole—a result that was also confirmed by various other groups around the world. Following this first important result, the same team, with the help of Professor Juergen Schaffner-Bielich, has worked to set tighter constraints on the size of neutron stars.

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