Tag

General Relativity

All articles tagged with #general relativity

space21 hours ago•45 min saved

Cosmic Glitch Suggests Gravity Fades at the Universe’s Largest Scales

Researchers from the University of Waterloo and University of British Columbia propose a minimal modification to gravity—a 'cosmic glitch'—where gravity is about 1% weaker on cosmological scales (billions of light-years) than predicted by general relativity, captured by the parameter Ωg. Analyses of Planck 2018 data yield Ωg ≈ -0.0087 ± 0.0046 and a Hubble constant near 68.6 km/s/Mpc; in some data combinations this can lessen the Hubble tension, but the improvement isn't universal across all datasets. The model preserves GR on smaller scales and could be tested by future CMB and large-scale structure surveys (DESI, Euclid). If confirmed, it would hint at physics beyond general relativity at cosmic distances.

via The Brighter Side of News|

#cosmic-glitch-in-gravity #general-relativity #gravity

science4 days ago•12 min saved

The 1919 Eclipse That Made Einstein Famous

During the May 29, 1919 total solar eclipse, astronomers photographed star positions near the Sun to test Einstein’s prediction that light bending by the Sun’s gravity would amount to about 1.75 arcseconds. Two expeditions—Sobral, Brazil, and Príncipe—produced measurements with mixed data quality, but the best results (notably from Sobral’s four‑inch telescope) aligned with Einstein’s value and disagreed with Newton. After careful reductions and later reanalyses, the evidence favored Einstein, boosting his fame and cementing relativity. The episode also foreshadowed modern gravitational lensing research; today, more precise methods continue to test gravity, but the 1919 plates remain a landmark in scientific history.

via Fstoppers|

#1919-eclipse #eddington #einstein

space6 days ago•2 min saved

S301: Milky Way’s Fastest Star Skims the Central Black Hole

Astronomers have found S301, the Milky Way’s fastest star, zooming around the central black hole Sagittarius A* at about 25,000 km/s on a tight 8.7-year orbit, coming within roughly 12 AU of the hole. Its extreme proximity could enable a direct measurement of the black hole’s spin and a stringent test of Einstein’s general relativity, using the ESO Very Large Telescope Interferometer to track the orbit back to 2017 and observe the 2031 pericentre passage; spin measurements could come within a decade.

via The Guardian|

#black-hole-spin #general-relativity #s301

science27 days ago•53 min saved

Relativity's Road to Time Travel: From Time Dilation to Timelike Loops

Einstein’s special and general relativity show time is not fixed: moving clocks run slower and strong gravity slows time, enabling travel into the future. Some solutions to Einstein’s equations—such as Kerr spacetime around rotating masses—mathematically permit backward time travel via closed timelike curves, but these regions are inherently unstable and no practical method of time travel exists.

via Yahoo|

#closed-timelike-curves #general-relativity #relativity

science28 days ago•7 min saved

Black Hole Singularity Might Be a 3D Surface, Not a Point

A forthcoming Physical Review D paper argues that Schwarzschild (and likely Kerr) singularities are better described as flat, three-dimensional spacelike surfaces rather than points. This means two observers falling in from opposite directions cannot converge on the same spacetime event, a result that could reshape how general relativity breaks down inside black holes and redefine the starting point for quantum gravity research.

via ScienceAlert|

#black-hole #general-relativity #quantum-gravity

science1 month ago•11 min saved

Star S2's relativistic whirl around Milky Way's black hole tests Einstein's gravity

For nearly 30 years, astronomers tracked the star S2 as it orbits the Milky Way’s center around Sagittarius A*, a supermassive black hole about 4 million solar masses. At its closest approach it reaches ~7,650 km/s (~0.025c), enabling precise tests of general relativity in strong gravity via relativistic effects like gravitational redshift, transverse Doppler shift, and Schwarzschild precession. The findings—made with ESO's GRAVITY and Keck, by Genzel and Ghez’s teams—helped secure the Nobel Prize in Physics 2020 and complement the Event Horizon Telescope’s 2022 image of the black hole’s shadow.

via Space Daily|

#astronomy #black-hole #general-relativity

science-space1 month ago•11 min saved

Time Slows to a Standstill at Black Hole Edges, Then Crosses the Horizon

Black holes warp time as well as space: near the event horizon, a distant observer sees infalling matter slow and freeze at the edge due to gravitational time dilation, while the object itself experiences finite proper time to cross the horizon. This freezing is a coordinate effect, not a literal halt in the falling object’s reality. Gravitational time dilation has been measured on Earth and in GPS systems, confirming relativity beyond black holes. Observations like the Event Horizon Telescope and LIGO support horizon physics but do not show a literal frozen image, and quantum-gravity effects (e.g., Hawking radiation) remain unobserved and unresolved.

via Space Daily|

#black-hole #event-horizon #general-relativity

space1 month ago•15 min saved

Moon drifting away at 3.8 cm per year, confirmed by millimetre-precision laser ranging

Laser pulses bounced off Moon retroreflectors left by Apollo and Lunokhod missions measure the Moon’s recession from Earth at about 3.8 cm per year with millimetre accuracy, a result that tests general relativity and informs Earth–Moon dynamics; the rate depends on ocean tides and continental layout, and future reflectors from Artemis missions will enable sharper measurements.

via Space Daily|

#apollo-reflectors #general-relativity #lunar-laser-ranging

science1 month ago•27 min saved

LARES-2 tightens Earth's frame-dragging test to ~0.1% accuracy

The LARES-2 laser-ranging satellite, combined with LAGEOS and GRACE data, delivers the most precise measurement of Earth's frame-dragging to about one part in a thousand, providing a stringent confirmation of general relativity in the near-Earth environment and placing tight limits on alternative gravity models such as Chern–Simons gravity, while also improving the understanding of Earth tides through high-precision satellite analysis with GEODYN/UTOPIA and ILRS data.

via Nature|

#chern-simons-gravity #frame-dragging #general-relativity

science1 month ago•5 min saved

First Magnetar Birth Seen in Chirping Supernova

Astronomers monitored SN 2024afav for about 200 days and observed four distinct brightness bumps—the object's light curve chirp—best explained by a newborn magnetar with a tilted accretion disk that undergoes Lense-Thirring precession, a relativistic effect that modulates emitted light. This provides the first direct evidence that magnetars power some superluminous supernovae, supporting Dan Kasen's 2010 theory; the magnetar spins ~4.2 milliseconds with a magnetic field around 3×10^14 gauss. The discovery, published in Nature, confirms GR's role in a stellar explosion and suggests future surveys (e.g., Rubin Observatory) will uncover many more chirping events.

via ScienceDaily|

#general-relativity #lense-thirring #magnetar

space1 month ago•104 min saved

Einstein-powered microlensing uncovers a distant exoplanet in TESS data

NASA's TESS has detected Gaia23bra b using gravitational microlensing—a method based on Einstein's general relativity—marking a rare microlensing planet found in TESS data. Hints first appeared in Gaia data in 2023; Gaia23bra b weighs about 1.6 Jupiter masses and orbits an orange-dwarf star roughly 40,000 light-years away, far beyond TESS's typical transit range. This discovery shows microlensing can reveal planets that transit methods miss and foreshadows Roman Space Telescope-led microlensing surveys, which could uncover many more such worlds.

via Space|

#exoplanets #gaia23bra-b #general-relativity

space-and-spaceflight1 month ago•17 min saved

Gravastar Idea: A Dark-Energy ‘Mini-Universe’ Inside a Black Hole Mimic

Physicists propose gravastars—ultra-compact stars with a thin shell of ordinary matter and an interior powered by dark energy—that externally resemble black holes but lack singularities or event horizons. A new model shows how such objects could form from gravitational collapse and, in the process, trigger a Big Bang–like expansion inside a self-contained mini-universe. The scenario hinges on ideal, finely tuned conditions and does not replace black holes as the default outcome of collapse.

via Gizmodo|

#black-holes #dark-energy #general-relativity

space1 month ago•5 min saved

Star Collapse May Forge a Mini-Universe: Gravastars as Black Hole Alternatives

A new study proposes gravastars—ultra-compact objects formed when collapsing stars create a miniature universe inside, with dark-energy interiors that halt collapse and mimic black holes without horizons or singularities—offering a GR-consistent alternative to black holes. Yet the mechanism requires fine-tuning, questions of stability remain, and it’s unclear how such objects could be distinguished observationally; formation remains a key open problem.

via Universe Today|

#black-holes #but-we-only-need-five-ensure-only-five-so-remove-extra #cosmology

space1 month ago•43 min saved

Time Emerges from Quantum Entanglement, Not a Universal Backdrop

A theoretical study revisits the Page and Wootters idea and argues that time may not be a fundamental backdrop but arises from the entangled relationship between a clock and a system. Using a two-system model (a clock and an oscillator), the work shows that when these subsystems are properly entangled, ordinary quantum motion can emerge and, in the macroscopic/classical limit, the familiar time of classical physics and Schrödinger dynamics appears. The research also notes the clock’s limits in fully quantum regimes and emphasizes the need for the clock to behave classically for time to emerge, while stressing that experimental confirmation remains out of reach and the idea remains speculative.

via The Brighter Side of News|

#emergent-time #general-relativity #page-and-wootters-mechanism

science1 month ago•49 min saved

Loudest Black-Hole Merger Sheds Light on Event Horizons

Scientists analyzed GW250114—the loudest binary black-hole gravitational-wave signal observed to date, from a merger of two ~32-solar-mass black holes detected by LIGO, Virgo, and KAGRA. They identified a direct-waves component near the horizon and used it to measure the remnant black hole’s rotation and surface gravity, offering a new way to study event horizons and test general relativity in the extreme gravity regime.

via Yahoo|

#black-hole #event-horizon #general-relativity