General_relativity

General relativity, also known as the general theory of relativity, and as Einstein's theory of gravity, is the geometric theory of gravitation published by Albert Einstein in 1915 and is the current description of gravitation in modern physics. General relativity generalizes special relativity and refines Newton's law of universal gravitation, providing a unified description of gravity as a geometric property of space and time, or four-dimensional spacetime. In particular, the curvature of spacetime is directly related to the energy and momentum of whatever is present, including matter and radiation. The relation is specified by the Einstein field equations, a system of second-order partial differential equations.

Newton's law of universal gravitation, which describes classical gravity, can be seen as a prediction of general relativity for the almost flat spacetime geometry around stationary mass distributions. Some predictions of general relativity, however, are beyond Newton's law of universal gravitation in classical physics. These predictions concern the passage of time, the geometry of space, the motion of bodies in free fall, and the propagation of light, and include gravitational time dilation, gravitational lensing, the gravitational redshift of light, the Shapiro time delay and singularities/black holes. So far, all tests of general relativity have been shown to be in agreement with the theory. The time-dependent solutions of general relativity enable us to talk about the history of the universe and have provided the modern framework for cosmology, thus leading to the discovery of the Big Bang and cosmic microwave background radiation. ..
>> https://en.wikipedia.org/wiki/General_relativity

* relatively related:
https://en.wikipedia.org/wiki/Kerr_metric
https://en.wikipedia.org/wiki/Penrose_process
https://physicsopenlab.org/2017/09/07/spectral-lines-broadening/

* Credits: Wikimedia Commons

Black Hole Tidal Disruption Event

When a star wanders too close to a black hole, the intense gravity will stretch the star out until it becomes a long river of hot gas, as shown in this animation. The gas is then whipped around the black hole and is gradually pulled into orbit, forming a bright disk.

https://nustar.caltech.edu/

* Credit: Science Communication Lab/DESY

XMM-Newton catches giant black hole’s X-ray oscillations

The European Space Agency's XMM-Newton has detected rapidly fluctuating X-rays coming from the very edge of a supermassive black hole in the heart of a nearby galaxy. The results paint a fascinating picture that defies how we thought matter falls into such black holes, and points to a potential source of gravitational waves that ESA’s future mission, LISA, could see.

XMM-Newton is showing us that black holes devour matter in more complex ways than astronomers first thought. Black holes are predictions of Albert Einstein’s theory of general relativity. They are gravitational monsters that imprison any piece of matter or energy that crosses their ‘surface’, a region of spacetime known as the event horizon.

During its final descent into the black hole, a process known as accretion, the doomed matter forms a disc around the black hole. The gas in the accretion disc heats up and gives off mostly ultraviolet (UV) light.

The UV rays interact with a cloud of electrically charged gas, or plasma, that surrounds the black hole and accretion disc. This cloud is known as the corona and the interactions give the UV rays energy, boosting them up to X-rays, which XMM-Newton can capture.

XMM-Newton has been observing the supermassive black hole 1ES 1927+654 since 2011. Back then, everything was pretty normal. But in 2018, things changed.

1ES 1927+654 suffered a large outburst that appeared to disrupt its surroundings because the X-ray corona disappeared. Gradually, the corona returned, and by early 2021 normality appeared to have been restored.

https://www.esa.int/Science_Exploration/Space_Science/XMM-Newton/XMM-Newton_catches_giant_black_hole_s_X-ray_oscillations

>> there is more >>
https://www.esa.int/Science_Exploration/Space_Science/XMM-Newton/From_boring_to_bursting_a_giant_black_hole_awakens

Credits:
Discovery of extreme Quasi-Periodic Eruptions in a newly accreting massive black hole by L. Hernandez-García et al. is published today in Nature Astronomy. DOI 10.1038/s41550-025-02523-9

#space #blackhole #astroart #astrophotography #photography _awakens#astronomy #science #nature #NASA #ESA

Journey of an observer falling inside a(n ideal) Kerr black hole and emerging in a parallel universe. (The black hole has a mass of roughly one million solar masses (Schwarzschild radius = 10 light seconds) and an angular momentum at 80% of maximality (a/M=0.8). The observer has an energy of 1.2 times its mass and zero angular momentum along the black hole's axis.)

The upper left quadrant is the observer's front view (for a somewhat arbitrary definition of "front"), the upper right quadrant is their rear view. The lower left quadrant displays the trajectory on a polar plane cut (external horizon is red, internal horizon is green, static limit is dashed and is not seen in the video, cut discontinuity is purple, and trajectory is blue) and in a Penrose diagram (outer (I) blocks are shown in blue, inner (III) blocks are shown in pink, and intermediate (II) blocks are shown in light or dark grey according as they are white hole or black hole regions; the trajectory is again shown in blue). The bottom right quadrant shows the Boyer-Lindquist coordinates and their derivative with respect to the proper time (s) of the observer.

In the video, a blue sphere is placed outside the black hole at some distance, a purple sphere is placed in negative space (i.e., beyond the singularity cut), and the outer and inner horizons are various shades of red and green in the same color scheme as in the Penrose diagram (lighter shades are white hole horizons, darker shades are black hole horizons). All spheres are checkered in an identical way, with twenty-four longitudinal stripes and twelve latitudinal (or polar) stripes, consistent with the black hole's axis. (The longitudinal stripes on the horizons rotate with the black hole.) The ring singularity itself is not visible as such, but appears as the edge rim of the purple region.

*Video and Text Credits:
David Madore

The Spinning Black Hole

"Black holes are macroscopic objects with masses varying from a few solar masses to millions of solar masses.To the extent they may be considered as stationary and isolated, to that extent, they are all, every single one of them, described exactly by the Kerr solution.
This is the only instance we have of an exact description of a macroscopic object.

Macroscopic objects, as we see them all around us, are governed by a variety of forces, derived from a variety of approximations to a variety of physical theories.

In contrast, the only elements in the construction of black holes are our basic concepts of space and time.
They are, thus, almost by definition, the most perfect macroscopic objects there are in the universe. And since the general theory of relativity provides a single unique two-parameter family of solutions for their description, they are the simplest objects as well."
—S. Chandrasekhar

Images below explained from left to right downwards:

1. Black holes are tremendous objects whose immense gravity can distort and twist space-time, the fabric that shapes our universe.

2. Scientists measure the spin rates of supermassive black holes by spreading the X-ray light into different colors.

3. This image taken by the ultraviolet-light monitoring camera on the European Space Agency's (ESA's) XMM-Newton telescope shows the beautiful spiral arms of the galaxy NGC1365.

4. NASA's Nuclear Spectroscopic Telescope Array, or NuSTAR, has helped to show, for the first time, that the spin rates of black holes can be measured conclusively.

Credit: NASA/JPL-Caltech/ESA/CfA/INAF

https://www.jpl.nasa.gov/news/nasas-nustar-helps-solve-riddle-of-black-hole-spin/

* You may want to download and study this scientific elaboration:

PROJECT F
The Spinning Black Hole
https://www.eftaylor.com/pub/SpinNEW.pdf

@pennine
UK is a founding member of #esa and continues to be a major member state. This satellite was built by a consortium of European businesses led by Airbus UK.