Einstein’s GR corroborated: space and time do co-mingle near a black hole

Einstein’s GR modeling of gravity corroborated: space and time do co-mingle near a black hole (20 Jan 2020)

6 objects orbiting the center of our galaxy & supermassive black hole as cross (CNN)

by Ashley Strickland, CNN; July 25, 2019

https://edition.cnn.com/2019/07/25/world/einstein-theory-general-relativity-star-scn/index.html

Einstein's general relativity stands, study says - for now

 (CNN)Albert Einstein's theory of general relativity, which suggests that gravity is due to the curvature of space and time, is more than 100 years old. And it's holding up as researchers analyze the behavior of gravity in space -- but it may not last forever, according to a new study.

The 1915 theory was tested when University of California, Los Angeles astronomy and physics professor Andrea Ghez and her team measured gravity near the black hole at the center of our home galaxy, the Milky Way.

Their study was published Thursday in the journal Science.

"Einstein's right, at least for now," said Ghez, a co-lead author of the study, in a statement. "We can absolutely rule out Newton's law of gravity. Our observations are consistent with Einstein's theory of general relativity. However, his theory is definitely showing vulnerability. It cannot fully explain gravity inside a black hole, and at some point we will need to move beyond Einstein's theory to a more comprehensive theory of gravity that explains what a black hole is."

But at the moment, the theory is the best description of how gravity works, Ghez said.

Her team was one of only two in the world to observe the complete 16-year orbit of a star called S0-2 around the supermassive black hole at the galactic center.

Their observations spanned three dimensions. The star made its closest approach to the black hole in April, May and September 2018, moving at 16 million miles per hour. Spectral data spanning wavelengths of light provided insight about the star's composition, which was combined with measurements the team had gathered over the past 24 years.

The spectral data was collected by a spectrograph built at the university and collected at the W.M. Keck Observatory in Hawaii. This allowed the researchers to determine precise measurements of the star's motion as one dimension and combine those with images and observations of the star taken at Keck.

"What's so special about S0-2 is we have its complete orbit in three dimensions," Ghez said. "That's what gives us the entry ticket into the tests of general relativity. We asked how gravity behaves near a supermassive black hole and whether Einstein's theory is telling us the full story. Seeing stars go through their complete orbit provides the first opportunity to test fundamental physics using the motions of these stars."

The researchers were able to see how space and time commingled near the black hole, she said.

"In Newton's version of gravity, space and time are separate, and do not co-mingle; under Einstein, they get completely co-mingled near a black hole," she said in the statement.

Richard Green, director of the National Science Foundation's Division of Astronomical Sciences, noted that "Making a measurement of such fundamental importance has required years of patient observing, enabled by state-of-the-art technology. Through their rigorous efforts, Ghez and her collaborators have produced a high-significance validation of Einstein's idea about strong gravity."

Because of its distance from the black hole, the star doesn't get pulled into it.

The team tracked particles of light called photons that traveled from the star to Earth over 26,000 years. It took years of planning for Ghez and her team to be ready to make the measurements of the photons.

"For us, it's visceral, it's now -- but it actually happened 26,000 years ago," she said.

Ghez studies more than 3,000 stars that orbit the black hole at the center of our galaxy. Going forward, she wants to test more of the stars near the black hole, including S0-102, which has a short orbit of 11½ years. Most of the other stars have an orbit that exceeds the average human lifespan.

"We're learning how gravity works. It's one of four fundamental forces and the one we have tested the least," she said. "There are many regions where we just haven't asked, how does gravity work here? It's easy to be overconfident and there are many ways to misinterpret the data, many ways that small errors can accumulate into significant mistakes, which is why we did not rush our analysis."

Ref/ Tuan Do, Aurelien Hees, Andrea Ghez, et al. Relativistic redshift of the star S0-2 orbiting the Galactic Center supermassive black hole. Science, Vol. 365, Issue 6454, pp. 664-668. 16 Aug 2019. DOI: 10.1126/science.aav8137

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Gravitational anomaly found under the Moon’s far side

 2000 miles wide gravitational anomaly under the Moon’s far side (June 2019)

 

This false-color graphic shows the topography of the far side of the Moon. The warmer colors indicate high topography and the bluer colors indicate low topography. The South Pole-Aitken (SPA) basin is shown by the shades of blue. The dashed circle shows the location of the mass anomaly under the basin. [NASA/Goddard Space Flight Center/University of Arizona]

The GRAIL paired spacecrafts are tuned to detect gravitational anomalies, and were in operation most of 2012 to map the moon G field ; they allowed us to discover a 2000 miles wide gravitational anomaly under the Moon’s far side, precisely buried several miles deep beneath the South Pole-Aitken basin.

Baylor University’s researchers just published their findings after a thorough study of the GRAIL/NASA data – NASA’s Gravity Recovery and Interior Laboratory (GRAIL) mission – in the journal Geophysical Research Letters.

The two GRAIL spacecrafts are set to fly one in front of the other to detect very small density fluctuations in the Moon’s gravitational field. The leading spacecraft (called “Ebb”), when flying over a region of higher gravitational density, will slightly accelerate just a moment before the trailing spacecraft (“Flow”) will get to register that higher density (and thus gets accelerated in its turn). In between those two events, the distance between the two spacecrafts has been increased. Thus, by minutely measuring the distance between the two GRAIL spacecrafts, scientists are able to map precisely the gravitational field of the surface above which they fly.

Peter B. James, lead author of the Baylor University’s study, compared the “unexpected mass” they found burried underground the basin to “a pile of metal five times larger than the Big Island of Hawaii.”

Ian O’Neill, in his article on astroengine.com (ref. below) agrees with Peter James et al that this mysterious mass could bring us the key to the mystery of the moon formation 4 billion years ago. He ponders :

“How did all that material end up buried inside the Moon’s mantle? The South Pole-Aitken basin was created four billion years ago in the wake of a massive asteroid impact. In fact, the basin is known to be one of the biggest impact craters in the solar system. If this crater was formed by an impact, it stands to reason that the gravitational anomaly is being caused by the dense metallic remains of the massive asteroid that met its demise when the Earth-Moon system was in the throes of formation.” In other words, “it’s likely the massive metallic corpse of an ancient asteroid.”

Peter James et al write: “One of the explanations of this extra mass is that the metal from the asteroid that formed this crater is still embedded in the Moon’s mantle.” Another explanation, according to the authors, is that this burried mass could be an accumulation of “dense oxides associated with the last stage of lunar magma ocean solidification.”

O’Neill concludes : “It just so happens that we currently have a mission at the basin, exploring this strange and unexplored place. On Jan. 3, the Chinese Chang’e 3 mission achieved the first soft touchdown on the lunar far side, landing inside Von Kármán crater and releasing a robotic rover, Yutu-2, to explore the landscape. At time of writing, the mission is ongoing.”

Let’s stay tuned on this exciting discovery and what it will unveil about our moon!

--------------------------------------------------------  Refs --------------------------------------------------------------

·         There’s Something Massive Buried Under the Moon’s Far Side, by Ian O'Neill at https://astroengine.com/2019/06/11/theres-something-massive-buried-under-the-moons-far-side/

·         Peter B. James, et al. Deep Structure of the Lunar South Pole‐Aitken Basin. Geophysical Research Letter. First published: 05 April 2019. https://doi.org/10.1029/2019GL082252

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