Showing posts with label Einstein’s General Theory of Relativity. Show all posts
Showing posts with label Einstein’s General Theory of Relativity. Show all posts

Thursday, April 16, 2020

ESO Telescope Sees Star Dance Around Supermassive Black Hole, Proves Einstein Right

Artist’s impression of Schwarzschild precession

Orbits of stars around black hole at the heart of the Milky Way

Wide-field view of the centre of the Milky Way

Sagittarius A* in the constellation of Sagittarius


Videos

ESOcast 219 Light: Star Dance Around Supermassive Black Hole
ESOcast 219 Light: Star Dance Around Supermassive Black Hole

Artist’s animation of S2’s precession effect
Artist’s animation of S2’s precession effect

Zooming in on the heart of the Milky Way
Zooming in on the heart of the Milky Way

The star S2 makes a close approach to the black hole at the centre of the Milky Way
The star S2 makes a close approach to the black hole at the centre of the Milky Way

Interview with Reinhard Genzel (in English)
Interview with Reinhard Genzel (in English)

Interview with Reinhard Genzel (in German)
Interview with Reinhard Genzel (in German)

Another artist’s impression of S2’s precession effect
Another artist’s impression of S2’s precession effect


Observations made with ESO’s Very Large Telescope (VLT) have revealed for the first time that a star orbiting the supermassive black hole at the centre of the Milky Way moves just as predicted by Einstein’s general theory of relativity. Its orbit is shaped like a rosette and not like an ellipse as predicted by Newton's theory of gravity. This long-sought-after result was made possible by increasingly precise measurements over nearly 30 years, which have enabled scientists to unlock the mysteries of the behemoth lurking at the heart of our galaxy.

“Einstein’s General Relativity predicts that bound orbits of one object around another are not closed, as in Newtonian Gravity, but precess forwards in the plane of motion. This famous effect — first seen in the orbit of the planet Mercury around the Sun — was the first evidence in favour of General Relativity. One hundred years later we have now detected the same effect in the motion of a star orbiting the compact radio source Sagittarius A* at the centre of the Milky Way. This observational breakthrough strengthens the evidence that Sagittarius A* must be a supermassive black hole of 4 million times the mass of the Sun,” says Reinhard Genzel, Director at the Max Planck Institute for Extraterrestrial Physics (MPE) in Garching, Germany and the architect of the 30-year-long programme that led to this result.

Located 26 000 light-years from the Sun, Sagittarius A* and the dense cluster of stars around it provide a unique laboratory for testing physics in an otherwise unexplored and extreme regime of gravity. One of these stars, S2, sweeps in towards the supermassive black hole to a closest distance less than 20 billion kilometres (one hundred and twenty times the distance between the Sun and Earth), making it one of the closest stars ever found in orbit around the massive giant. At its closest approach to the black hole, S2 is hurtling through space at almost three percent of the speed of light, completing an orbit once every 16 years. “After following the star in its orbit for over two and a half decades, our exquisite measurements robustly detect S2’s Schwarzschild precession in its path around Sagittarius A*,” says Stefan Gillessen of the MPE, who led the analysis of the measurements published today in the journal Astronomy & Astrophysics.

Most stars and planets have a non-circular orbit and therefore move closer to and further away from the object they are rotating around. S2’s orbit precesses, meaning that the location of its closest point to the supermassive black hole changes with each turn, such that the next orbit is rotated with regard to the previous one, creating a rosette shape. General Relativity provides a precise prediction of how much its orbit changes and the latest measurements from this research exactly match the theory. This effect, known as Schwarzschild precession, had never before been measured for a star around a supermassive black hole.

The study with ESO’s VLT also helps scientists learn more about the vicinity of the supermassive black hole at the centre of our galaxy. “Because the S2 measurements follow General Relativity so well, we can set stringent limits on how much invisible material, such as distributed dark matter or possible smaller black holes, is present around Sagittarius A*. This is of great interest for understanding the formation and evolution of supermassive black holes,” say Guy Perrin and Karine Perraut, the French lead scientists of the project.

This result is the culmination of 27 years of observations of the S2 star using, for the best part of this time, a fleet of instruments at ESO’s VLT, located in the Atacama Desert in Chile. The number of data points marking the star’s position and velocity attests to the thoroughness and accuracy of the new research: the team made over 330 measurements in total, using the GRAVITY, SINFONI and NACO instruments. Because S2 takes years to orbit the supermassive black hole, it was crucial to follow the star for close to three decades, to unravel the intricacies of its orbital movement.

The research was conducted by an international team led by Frank Eisenhauer of the MPE with collaborators from France, Portugal, Germany and ESO. The team make up the GRAVITY collaboration, named after the instrument they developed for the VLT Interferometer, which combines the light of all four 8-metre VLT telescopes into a super-telescope (with a resolution equivalent to that of a telescope 130 metres in diameter). The same team reported in 2018 another effect predicted by General Relativity: they saw the light received from S2 being stretched to longer wavelengths as the star passed close to Sagittarius A*. “Our previous result has shown that the light emitted from the star experiences General Relativity. Now we have shown that the star itself senses the effects of General Relativity,” says Paulo Garcia, a researcher at Portugal’s Centre for Astrophysics and Gravitation and one of the lead scientists of the GRAVITY project.

With ESO’s upcoming Extremely Large Telescope, the team believes that they would be able to see much fainter stars orbiting even closer to the supermassive black hole. “If we are lucky, we might capture stars close enough that they actually feel the rotation, the spin, of the black hole,” says Andreas Eckart from Cologne University, another of the lead scientists of the project. This would mean astronomers would be able to measure the two quantities, spin and mass, that characterise Sagittarius A* and define space and time around it. “That would be again a completely different level of testing relativity," says Eckart.


More Information

This research was presented in the paper “Detection of the Schwarzschild precession in the orbit of the star S2 near the Galactic centre massive black hole” to appear in Astronomy & Astrophysics (DOI: 10.1051/0004-6361/202037813).

The GRAVITY Collaboration team is composed of R. Abuter (European Southern Observatory, Garching, Germany [ESO]), A. Amorim (Universidade de Lisboa - Faculdade de Ciências, Portugal and Centro de Astrofísica e Gravitação, IST, Universidade de Lisboa, Portugal [CENTRA]), M. Bauböck (Max Planck Institute for Extraterrestrial Physics, Garching, Germany [MPE]), J.P. Berger (Univ. Grenoble Alpes, CNRS, Grenoble, France [IPAG] and ESO), H. Bonnet (ESO), W. Brandner (Max Planck Institute for Astronomy, Heidelberg, Germany [MPIA]), V. Cardoso (CENTRA and CERN, Genève, Switzerland), Y. Clénet (Observatoire de Paris, Université PSL, CNRS, Sorbonne Université, Université de Paris, Meudon, France [LESIA], P.T. de Zeeuw (Sterrewacht Leiden, Leiden University, The Netherlands and MPE), J. Dexter (Department of Astrophysical & Planetary Sciences, JILA, Duane Physics Bldg.,University of Colorado, Boulder, USA and MPE), A. Eckart (1st Institute of Physics, University of Cologne, Germany [Cologne] and Max Planck Institute for Radio Astronomy, Bonn, Germany), F. Eisenhauer (MPE), N.M. Förster Schreiber (MPE), P. Garcia (Faculdade de Engenharia, Universidade do Porto, Portugal and CENTRA), F. Gao (MPE), E. Gendron (LESIA), R. Genzel (MPE, Departments of Physics and Astronomy, Le Conte Hall, University of California, Berkeley, USA), S. Gillessen (MPE), M. Habibi (MPE), X. Haubois (European Southern Observatory, Santiago, Chile [ESO Chile]), T. Henning (MPIA), S. Hippler (MPIA), M. Horrobin (Cologne), A. Jiménez-Rosales (MPE), L. Jochum (ESO Chile), L. Jocou (IPAG), A. Kaufer (ESO Chile), P. Kervella (LESIA), S. Lacour (LESIA), V. Lapeyrère (LESIA), J.-B. Le Bouquin (IPAG), P. Léna (LESIA), M. Nowak (Institute of Astronomy, Cambridge, UK and LESIA), T. Ott (MPE), T. Paumard (LESIA), K. Perraut (IPAG), G. Perrin (LESIA), O. Pfuhl (ESO, MPE), G. Rodríguez-Coira (LESIA), J. Shangguan (MPE), S. Scheithauer (MPIA), J. Stadler (MPE), O. Straub (MPE), C. Straubmeier (Cologne), E. Sturm (MPE), L.J. Tacconi (MPE), F. Vincent (LESIA), S. von Fellenberg (MPE), I. Waisberg (Department of Particle Physics & Astrophysics, Weizmann Institute of Science, Israel and MPE), F. Widmann (MPE), E. Wieprecht (MPE), E. Wiezorrek (MPE), J. Woillez (ESO), and S. Yazici (MPE, Cologne).

ESO is the foremost intergovernmental astronomy organisation in Europe and the world’s most productive ground-based astronomical observatory by far. It has 16 Member States: Austria, Belgium, the Czech Republic, Denmark, France, Finland, Germany, Ireland, Italy, the Netherlands, Poland, Portugal, Spain, Sweden, Switzerland and the United Kingdom, along with the host state of Chile and with Australia as a Strategic Partner. ESO carries out an ambitious programme focused on the design, construction and operation of powerful ground-based observing facilities enabling astronomers to make important scientific discoveries. ESO also plays a leading role in promoting and organising cooperation in astronomical research. ESO operates three unique world-class observing sites in Chile: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope and its world-leading Very Large Telescope Interferometer as well as two survey telescopes, VISTA working in the infrared and the visible-light VLT Survey Telescope. Also at Paranal ESO will host and operate the Cherenkov Telescope Array South, the world’s largest and most sensitive gamma-ray observatory. ESO is also a major partner in two facilities on Chajnantor, APEX and ALMA, the largest astronomical project in existence. And on Cerro Armazones, close to Paranal, ESO is building the 39-metre Extremely Large Telescope, the ELT, which will become “the world’s biggest eye on the sky”.


Links


Contacts

Reinhard Genzel
Director, Max Planck Institute for Extraterrestrial Physics
Garching bei München, Germany
Tel: +49 89 30000 3280

Stefan Gillessen
Max-Planck Institute for Extraterrestrial Physics
Garching bei München, Germany
Tel: +49 89 30000 3839
Cell: +49 176 99 66 41 39

Frank Eisenhauer
Max-Planck Institute for Extraterrestrial Physics
Garching bei München, Germany
Tel: +49 89 30000 3563
Cell: +49 162 3105080

Paulo Garcia
Faculdade de Engenharia, Universidade do Porto and Centro de Astrofísica e Gravitação, IST, Universidade de Lisboa, Portugal
Porto, Portugal
Cell: +351 963235785

Karine Perraut
IPAG of Université Grenoble Alpes/CNRS
Grenoble, France

Guy Perrin
LESIA – Observatoire de Paris - PSL
Meudon, France

Andreas Eckart
1st Institute of Physics, University of Cologne
Cologne, Germany
Tel: +49 221 470 3546

Bárbara Ferreira
ESO Public Information Officer
Garching bei München, Germany
Tel: +49 89 3200 6670
Cell: +49 151 241 664 00
Email: pio@eso.org

Source: ESO/News

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Wednesday, July 31, 2019

Einstein’s General Theory of Relativity is Questioned But Still Stands ‘For Now’

An artist visualization of the star S0-2 as it passes by the supermassive black hole at the Galactic Center. 
Credit: Nicolle R. Fuller, National Science Foundation 

Maunakea, Hawaii – More than 100 years after Albert Einstein published his iconic general theory of relativity, it is beginning to fray at the edges, said Andrea Ghez, UCLA professor of physics and astronomy. Now, in the most comprehensive test of general relativity near the monstrous black hole at the center of our galaxy, Ghez and her research team report July 25 in the journal Science that Einstein’s theory of general relativity holds up.

“Einstein’s right, at least for now,” said Ghez, a co-lead author of the research. “We can absolutely rule out Newton’s law of gravity. Our observations are consistent with Einstein’s general theory of 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.”

Einstein’s 1915 general theory of relativity holds that what we perceive as the force of gravity arises from the curvature of space and time. The scientist proposed that objects such as the sun and the Earth change this geometry. Einstein’s theory is the best description of how gravity works, said Ghez, whose UCLA-led team of astronomers has made direct measurements of the phenomenon near a supermassive black hole — research Ghez describes as “extreme astrophysics.”


The laws of physics, including gravity, should be valid everywhere in the universe, said Ghez, who added that her research team is one of only two groups in the world to watch a star known as S0-2 make a complete orbit in three dimensions around the supermassive black hole at the center of the Milky Way. The full orbit takes 16 years, and the black hole’s mass is about four million times that of the sun.

The researchers say their work is the most detailed study ever conducted into the supermassive black hole and Einstein’s general theory of relativity.

The key data in the research were spectra that Ghez’s team analyzed this April, May, and September as her “favorite star” made its closest approach to the enormous black hole. Spectra, which Ghez described as the “rainbow of light” from stars, show the intensity of light and offer important information about the star from which the light travels. Spectra also show the composition of the star.

These data were combined with measurements Ghez and her team have made over the last 24 years.

Spectra — collected at the W. M. Keck Observatory in Hawaii using a spectrograph built at UCLA by a team led by colleague James Larkin — provide the third dimension, revealing the star’s motion at a level of precision not previously attained (images of the star the researchers took at the Keck Observatory provide the two other dimensions). Larkin’s instrument takes light from a star and disperses it, similar to the way raindrops disperse light from the sun to create a rainbow, Ghez said.

“What’s so special about S0-2 is we have its complete orbit in three dimensions,” said Ghez, who holds the Lauren B. Leichtman and Arthur E. Levine Chair in Astrophysics. “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.”


Ghez’s research team was able to see the co-mingling of space and time near the supermassive black hole. “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.

“Making a measurement of such fundamental importance has required years of patient observing, enabled by state-of-the-art technology,” said Richard Green, director of the National Science Foundation’s division of astronomical sciences. For more than two decades, the division has supported Ghez, along with several of the technical elements critical to the research team’s discovery.

 “Through their rigorous efforts, Ghez and her collaborators have produced a high-significance validation of Einstein’s idea about strong gravity.”

Keck Observatory Director Hilton Lewis called Ghez “one of our most passionate and tenacious Keck users.” “Her latest groundbreaking research,” he said, “is the culmination of unwavering commitment over the past two decades to unlock the mysteries of the supermassive black hole at the center of our Milky Way galaxy.”

The researchers studied photons — particles of light — as they traveled from S0-2 to Earth. S0-2 moves around the black hole at blistering speeds of more than 16 million miles per hour at its closest approach. Einstein had reported that in this region close to the black hole, photons have to do extra work. Their wavelength as they leave the star depends not only on how fast the star is moving, but also on how much energy the photons expend to escape the black hole’s powerful gravitational field. Near a black hole, gravity is much stronger than on Earth.

Ghez was given the opportunity to present partial data last summer, but chose not to so that her team could thoroughly analyze the data first. “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.”

An artist visualization of the star S0-2 getting closer to the supermassive black hole at the center of the Milky Way and causing a gravitational redshift that is predicted by Einstein’s General Relativity. By observing this redshift, we can test Einstein’s theory of gravity. Credit: Nicolle R. Fuller, National Science Foundation 

Ghez, a 2008 recipient of the MacArthur “Genius” Fellowship, studies more than 3,000 stars that orbit the supermassive black hole. Hundreds of them are young, she said, in a region where astronomers did not expect to see them.

It takes 26,000 years for the photons from S0-2 to reach Earth. “We’re so excited, and have been preparing for years to make these measurements,” said Ghez, who directs the UCLA Galactic Center Group. “For us, it’s visceral, it’s now — but it actually happened 26,000 years ago!”

This is the first of many tests of general relativity Ghez’s research team will conduct on stars near the supermassive black hole. Among the stars that most interest her is S0-102, which has the shortest orbit, taking 11 1/2 years to complete a full orbit around the black hole. Most of the stars Ghez studies have orbits of much longer than a human lifespan.

Ghez’s team took measurements about every four nights during crucial periods in 2018 using the Keck Observatory — which sits atop Hawaii’s dormant Mauna Kea volcano and houses one of the world’s largest and premier optical and infrared telescopes. Measurements are also taken with an optical-infrared telescope at Gemini Observatory and Subaru Telescope, also in Hawaii. She and her team have used these telescopes both on site in Hawaii and remotely from an observation room in UCLA’s department of physics and astronomy.

Black holes have such high density that nothing can escape their gravitational pull, not even light. (They cannot be seen directly, but their influence on nearby stars is visible and provides a signature. Once something crosses the “event horizon” of a black hole, it will not be able to escape. However, the star S0-2 is still rather far from the event horizon, even at its closest approach, so its photons do not get pulled in.)

Ghez’s co-authors include Tuan Do, lead author of the Science paper, a UCLA research scientist and deputy director of the UCLA Galactic Center Group; Aurelien Hees, a former UCLA postdoctoral scholar, now a researcher at the Paris Observatory; Mark Morris, UCLA professor of physics and astronomy; Eric Becklin, UCLA professor emeritus of physics and astronomy; Smadar Naoz, UCLA assistant professor of physics and astronomy; Jessica Lu, a former UCLA graduate student who is now a UC Berkeley assistant professor of astronomy; UCLA graduate student Devin Chu; Greg Martinez, UCLA project scientist; Shoko Sakai, a UCLA research scientist; Shogo Nishiyama, associate professor with Japan’s Miyagi University of Education; and Rainer Schoedel, a researcher with Spain’s Instituto de Astrofısica de Andalucıa.

The National Science Foundation has funded Ghez’s research for the last 25 years. More recently, her research has also been supported by the W. M. Keck Foundation, the Gordon and Betty Moore Foundation and the Heising-Simons Foundation.

In 1998, Ghez answered one of astronomy’s most important questions, helping to show that a supermassive black hole resides at the center of our Milky Way galaxy. The question had been a subject of much debate among astronomers for more than a quarter of a century.

A powerful technology that Ghez helped to pioneer, called adaptive optics, corrects the distorting effects of the Earth’s atmosphere in real time. With adaptive optics at Keck Observatory, Ghez and her colleagues have revealed many surprises about the environments surrounding supermassive black holes. For example, they discovered young stars where none was expected to be seen and a lack of old stars where many were anticipated. It’s unclear whether S0-2 is young or just masquerading as a young star, Ghez said.

In 2000, she and colleagues reported that for the first time, astronomers had seen stars accelerate around the supermassive black hole. In 2003, Ghez reported that the case for the Milky Way’s black hole had been strengthened substantially and that all of the proposed alternatives could be excluded.

In 2005, Ghez and her colleagues took the first clear picture of the center of the Milky Way, including the area surrounding the black hole, at Keck Observatory. And in 2017, Ghez’s research team reported that S0-2 does not have a companion star, solving another mystery.




About Adaptive Optics
W. M. Keck Observatory is a distinguished leader in the field of adaptive optics (AO), a breakthrough technology that removes the distortions caused by the turbulence in the Earth’s atmosphere. Keck Observatory pioneered the astronomical use of both natural guide star (NGS) and laser guide star adaptive optics (LGS AO) on large telescopes and current systems now deliver images three to four times sharper than the Hubble Space Telescope. Keck AO has imaged the four massive planets orbiting the star HR8799, measured the mass of the giant black hole at the center of our Milky Way Galaxy, discovered new supernovae in distant galaxies, and identified the specific stars that were their progenitors. Support for this technology was generously provided by the Bob and Renee Parsons Foundation, Change Happens Foundation, Gordon and Betty Moore Foundation, Mt. Cuba Astronomical Foundation, NASA, NSF, and W. M. Keck Foundation.


About W.M. Keck Observatory
The W. M. Keck Observatory telescopes are the most scientifically productive on Earth. The two, 10-meter optical/infrared telescopes atop Maunakea on the Island of Hawaii feature a suite of advanced instruments including imagers, multi-object spectrographs, high-resolution spectrographs, integral-field spectrometers, and world-leading laser guide star adaptive optics systems. The data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. The authors recognize and acknowledge the very significant cultural role that the summit of Maunakea has always had within the Native Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain.

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