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spacetimewithstuartgary · 2 years

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Precise insights into the supermassive black hole in the Milky Way’s heart Astronomers have made the most precise measurements yet of the motions of stars around the supermassive black hole at the center of the Milky Way. These results, obtained with the help of the Gemini North telescope, show that 99.9% of the mass contained at the very center of the galaxy is due to the black hole, and only 0.1% could include stars, smaller black holes, interstellar dust and gas, or dark matter. Astronomers have measured more precisely than ever before the position and velocity of four stars in the immediate vicinity of the supermassive black hole that lurks at the center of the Milky Way, known as Sagittarius A* (Sgr A*) [1]. These stars — called S2, S29, S38, and S55 — were found to be moving in a way that shows that the mass in the center of the Milky Way is almost entirely due to the Sgr A* black hole, leaving very little room for anything else. The team used a variety of cutting-edge astronomical facilities in this research. To measure the velocities of the stars, they used spectroscopy from the Gemini Near Infrared Spectrograph (GNIRS) at Gemini North near the summit of Maunakea in Hawai‘i, part of the international Gemini Observatory, a program of NSF’s NOIRLab, and the SINFONI instrument on the European Southern Observatory’s Very Large Telescope. The positions of the stars were measured with the GRAVITY instrument at the VLTI. [2] “We are very grateful to Gemini Observatory, whose GNIRS instrument gave us the critical information we needed,” said Reinhard Genzel, director of the Max Planck Institute for Extraterrestrial Physics and co-recipient of the 2020 Nobel Prize in physics. “This research shows world-wide collaboration at its best.” The Galactic Center of the Milky Way, located roughly 27,000 light-years from the Sun, contains the compact radio source Sgr A* that astronomers have identified as a supermassive black hole 4.3 million times as massive as the Sun. Despite decades of painstaking observations — and the Nobel Prize awarded for discovering the identity of Sgr A* [3] — it has been difficult to conclusively prove that the majority of this mass belongs only to the supermassive black hole and does not also include a vast amount of matter such as stars, smaller black holes, interstellar dust and gas, or dark matter. “With the 2020 Nobel prize in physics awarded for the confirmation that Sgr A* is indeed a black hole, we now want to go further. We would like to understand whether there is anything else hidden at the center of the Milky Way, and whether general relativity is indeed the correct theory of gravity in this extreme laboratory,” explained Stefan Gillessen, one of the astronomers involved in this work. “The most straightforward way to answer that question is to closely follow the orbits of stars passing close to Sgr A*.” Einstein’s general theory of relativity predicts that the orbits of stars around a supermassive compact object are subtly different from those predicted by classical Newtonian physics. In particular, general relativity predicts that the orbits of the stars will trace out an elegant rosette shape — an effect known as Schwarzschild precession. To actually see stars tracing out this rosette, the team tracked the position and velocity of four stars in the immediate vicinity of Sgr A* — called S2, S29, S38, and S55. The team’s observations of the extent to which these stars precessed allowed them to infer the distribution of mass within Sgr A*. They discovered that any extended mass within the orbit of the S2 star contributes at most the equivalent of 0.1% of the mass of the supermassive black hole. Measuring the minute variations in the orbits of distant stars around our galaxy's supermassive black hole is incredibly challenging. To make further discoveries, astronomers will have to push the boundaries not only of science but also of engineering. Upcoming extremely large telescopes (ELTs) such as the Giant Magellan Telescope and the Thirty Meter Telescope (both part of the US-ELT Program) will allow astronomers to measure even fainter stars with even greater precision. “We will improve our sensitivity even further in future, allowing us to track even fainter objects,” concluded Gillessen. “We hope to detect more than we see now, giving us a unique and unambiguous way to measure the rotation of the black hole.” “The Gemini observatories continue to deliver new insight into the nature of our galaxy and the enormous black hole at its center,” said Martin Still, Gemini Program Officer at the National Science Foundation. “Further instrument development during the next decade intended for broad use will maintain NOIRLab’s leadership in the characterization of the Universe around us.” Notes [1] Sagittarius A* is spoken as “Sagittarius A star.” [2] ESO’s VLT is composed of four individual colocated 8.2-meter telescopes which can combine light through a network of mirrors and underground tunnels using a technique known as interferometry, to form the VLTI. GRAVITY uses this technique to measure the position of night-sky objects with high accuracy — equivalent to picking out a quarter-dollar coin on the surface of the Moon. [3] The 2020 Nobel Prize in Physics was awarded in part to Reinhard Genzel and Andrea Ghez "for the discovery of a supermassive compact object at the centre of our galaxy". TOP IMAGE....In this illustration, stars are seen to be in close orbit around the supermassive black hole that lurks at the center of the Milky Way, known as Sagittarius A* (Sgr A*). Using Gemini North of the international Gemini Observatory, a Program of NSF’s NOIRLab and ESO’s VLT, astronomers have measured more precisely than ever before the position and velocity of four of these stars, called S2, S29, S38, and S55, and found them to be moving in a way that shows that the mass in the center of the Milky Way is almost entirely due to the Sgr A* black hole, leaving very little room for anything else. CREDIT International Gemini Observatory/NOIRLab/NSF/AURA/J. da Silva/(Spaceengine) Acknowledgement: M. Zamani (NSF's NOIRLab) LOWER IMAGE....Illustration of the black hole Sagittarius A* at the center of the Milky Way. CREDIT International Gemini Observatory/NOIRLab/NSF/AURA/J. da Silva/(Spaceengine) Acknowledgement: M. Zamani (NSF's NOIRLab)

#space #science #Astronomy #physics #news

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andrearrrrr · 3 years

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A simulation of the Schwarzschild precession, named after the German scientist Karl Schwarzschild, who provided the first precise solution to Einstein’s equations of general relativity.

Credit...European Southern Observatory

https://en.wikipedia.org/wiki/Karl_Schwarzschild

#science

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the-telescope-times · 4 years

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Artist’s impression of Schwarzschild precession

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 center of the Milky Way moves just as predicted by Einstein’s theory of general relativity. Its orbit is shaped like a rosette and not like an ellipse as predicted by Newton's theory of gravity. This effect, known as Schwarzschild precession, had never before been measured for a star around a supermassive black hole. This artist’s impression illustrates the precession of the star’s orbit, with the effect exaggerated for easier visualization.

Credit: ESO/L. Calçada

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spaceexp · 4 years

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

ESO - European Southern Observatory logo. 16 April 2020

Artist’s impression of Schwarzschild precession

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.

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

“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.

Wide-field view of the centre of the Milky Way

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.

Sagittarius A in the constellation of Sagittarius

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.

Artist’s animation of S2’s precession effect

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.

Zooming in on the heart of the Milky Way

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

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.

Interview with Reinhard Genzel

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.

Another artist’s impression of S2’s precession effect

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). https://www.aanda.org/articles/aa/full_html/2020/04/aa37813-20/aa37813-20.html 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: ESOcast 219 Light: Star Dance Around Supermassive Black Hole: https://www.eso.org/public/videos/eso2006a/ Research paper: https://www.eso.org/public/archives/releases/sciencepapers/eso2006/eso2006a.pdf Photos of the VLT: http://www.eso.org/public/images/archive/category/paranal/ MPE GRAVITY webpage: http://www.mpe.mpg.de/ir/gravity For scientists: got a story? Pitch your research paper: http://eso.org/sci/publications/announcements/sciann17277.html Images, Text, Credits: ESO/Bárbara Ferreira/1st Institute of Physics, University of Cologne/Andreas Eckart/LESIA – Observatoire de Paris - PSL/Guy Perrin/IPAG of Université Grenoble Alpes/CNRS/Karine Perraut/Faculdade de Engenharia, Universidade do Porto and Centro de Astrofísica e Gravitação, IST, Universidade de Lisboa/Paulo Garcia/Max-Planck Institute for Extraterrestrial Physics/Frank Eisenhauer/Stefan Gillessen/Reinhard Genzel/ESO/L. Calçada/spaceengine.org/Digitized Sky Survey 2. Acknowledgment: Davide De Martin and S. Guisard (www.eso.org/~sguisard)/IAU and Sky & Telescope/Videos: ESO/L. Calçada/GRAVITY Collaboration/MPE/TWENTYTWO Film GmbH. Greetings, Orbiter.ch Full article

#space #science

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kreuzaderny · 4 years

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Detection of the Schwarzschild precession in the orbit of the star S2 near the Galactic centre massive black hole

The star S2 orbiting the compact radio source Sgr A* is a precision probe of the gravitational field around the closest massive black hole (candidate). Over the last 2.7 decades we have monitored the star’s radial velocity and motion on the sky, mainly with the SINFONI and NACO adaptive optics(AO) instruments on the ESO VLT, and since 2017, with the four-telescope interferometric beam combiner instrument GRAVITY. In this paper we report the first detection of the General Relativity (GR) Schwarzschild Precession (SP) in S2’s orbit. Owing to its highly elliptical orbit(e=0.88), S2’s SP is mainly a kink between the pre-and post-pericentre directions of motion≈±1 year around pericentre passage, relative to the corresponding Kepler orbit. The superb 2017-2019 astrometry of GRAVITY defines the pericentre passage and outgoing direction. The incoming direction is anchored by 118 NACO-AO measurements of S2’s position in the infrared reference frame, with an additional 75 direct measurements of the S2-Sgr A* separation during bright states (‘flares’) of Sgr A*. Our 14-parameter model fits for the distance, central mass, the position andmotion of the reference frame of the AO astrometry relative to the mass, the six parameters of the orbit, as well as a dimensionless parameter fSP for the SP (fSP=0 for Newton and 1 for GR). From data up to the end of 2019 we robustly detect the SP of S2,δφ≈12′per orbital period.From posterior fitting and MCMC Bayesian analysis with different weighting schemes and bootstrapping we find fSP=1.10±0.19. The S2 data are fully consistent with GR. Any extended mass inside S2’s orbit cannot exceed≈0.1% of the central mass. Any compact third mass inside the central arc-second must be less than about 1000M.

#astronomy #physics

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fumpkins · 4 years

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ESO telescope sees star dance around supermassive black hole, proves Einstein right

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.

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.

###

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

* Research paper – https://www.eso.org/public/archives/releases/sciencepapers/eso2006/eso2006a.pdf

* Photos of the VLT – http://www.eso.org/public/images/archive/category/paranal/

* MPE GRAVITY webpage – http://www.mpe.mpg.de/ir/gravity

* For scientists: got a story? Pitch your research paper – http://eso.org/sci/publications/announcements/sciann17277.html

Contacts

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

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

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

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

Karine Perraut IPAG of Université Grenoble Alpes/CNRS Grenoble, France Email: [email protected]

Guy Perrin LESIA – Observatoire de Paris-Site de Meudon Paris, France Email: [email protected]

Andreas Eckart 1st Institute of Physics, University of Cologne Cologne, Germany Tel: +49 221 470 3546 Email: [email protected]

Bárbara Ferreira ESO Public Information Officer Garching bei München, Germany Tel: +49 89 3200 6670 Cell: +49 151 241 664 00 Email: [email protected]

New post published on: https://livescience.tech/2020/04/19/eso-telescope-sees-star-dance-around-supermassive-black-hole-proves-einstein-right/

#astronomy #astrophysics #SPACE/PLANETARY SCIENCE

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djcybertsai · 4 years

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Einstein wins again: star orbits black hole just like GR predicts

https://cdn.arstechnica.net/wp-content/uploads/2020/04/blackhole1-800×531.jpghttps://arstechnica.com/?p=1668764After nearly 30 years, VLT’s new observations show star moves in rosette-shaped orbit

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#albert einstein #astronomy #black hole #ESA #general relativity #Physics #Sagitarrius A*#Schwarzschild precession #Science #Very Large Telescope

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scepticaladventure · 6 years

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27 Gravitational Waves 12Sep18

Introduction This essay continues my series of essays discussing tests of Einstein’s Theory of General Relativity. More detailed descriptions of the test themselves can be found online and in the literature. See for example the literature review in May 2017 by Estelle Asmodelle from the University of Central Lancashire Ref: arXiv:1705.04397 [gr-qc] or arXiv:1705.04397v1 [gr-qc].

I have questioned whether the experimental tests exclude any other explanations for the same phenomenon. So far I have examined gravitational redshifts and gravitational light bending, the Shapiro round-trip light delay and the ‘anomalous’ precession of Mercury. The evidence so far is that while General Relativity provides a satisfying explanation for all of these experimental observations, other ways of describing the outcomes are also viable. Hence there may be more than one way to include all the evidence within a different but still complete and consistent model or theory.

In this essay I will look at the latest of the five so-called tests – gravitational waves.

Gravitational Waves Gravitational waves are generated in certain gravitational interactions and propagate as waves outward from their source at the speed of light. Their possibility was discussed in 1893 by the polymath Oliver Heaviside, using the analogy between the inverse-square laws in both gravitation and electricity.

In 1905, Henri Poincaré suggested that a model of physics using the Lorentz transformations (then being incorporated into Special Relativity) required the possibility of gravitational waves (‘ondes gravifiques’) emanating from a body and propagating at the speed of light.

Some authors claim that gravitational waves disprove Newton’s mechanics since Newton assumed that gravity acted instantaneously at a distance. I think this is unfair to Newton. Whether or not Newton explicitly claimed that gravity acted instantaneously at a distance I do not know, but it would have been a reasonable and pragmatic working assumption to make at the time. Furthermore whether he assumed instantaneous effects or delays at the speed of light makes no practical difference to the validity of Newton’s work for the type of celestial mechanics he was interested in.

In 1916, Einstein suggested that gravitational waves were a firm prediction of General Relativity. He said that that large accelerations of mass/energy would cause disturbances in the spacetime metric around them and that such disturbances would travel outwards at the speed of light. A spherical acceleration of a star would not suffice because the gravity effects would still be felt as coming from the centre of mass. The cause would have to be a large asymmetric mass that was rotating rapidly. Or better still, two very large masses that were rotating around each other.

In general terms, gravitational waves are radiated by objects whose motion involves acceleration and changes in that acceleration, provided that the motion is not spherically symmetric (like an expanding or contracting sphere) or rotationally symmetric (like a spinning disk or sphere).

A simple example is a spinning dumbbell. If the dumbbell spins around its axis of its connecting bar, it will not radiate gravitational waves. If it tumbles end over end, like in the case of two planets orbiting each other, it will radiate gravitational waves. The heavier the dumbbell, or the faster it tumbles, the greater the gravitational radiation. In an extreme case, such as when two massive stars like neutron stars or black holes are orbiting each other very quickly, then significant amounts of gravitational radiation will be given off.

Over the next twenty years the idea developed slowly. Even Einstein had his doubts about whether gravitational waves should exist or not. He said as much to Karl Schwarzschild and later started a collaboration with Nathan Rosen to debunk the whole idea. But instead of debunking the idea Einstein and Rosen further developed it and by 1937 they had published a reasonably complete version of gravitational waves in General Relativity. Note that this is 22 years after the General Theory was first published.

In 1956, the year after Einstein’s death, Felix Pirani reduced some of the confusion by representing gravitational waves in terms of the manifestly observable Riemann curvature tensor.

In 1957 Richard Feynman argued that gravitational waves should be able to carry energy and so might be able to be detected. Note that gravitational waves are also expected to be able to carry away angular or linear momentum. Feynman’s insight inspired Joseph Weber to try to build the first gravity wave detectors. However his efforts were not successful. The incredible weakness of the effects being sought cannot be over emphasized.

More support came from indirect sources. Theorists predicted that gravity waves would sap energy out of an intensely strong gravitational system. In 1974, Russell Alan Hulse and Joseph Hooton Taylor, Jr. discovered the first binary pulsar (a discovery that would earn them the 1993 Nobel Prize in Physics). In 1979, results were published detailing measurement of the gradual decay of the orbital period of the Hulse-Taylor pulsar, and these measurements fitted precisely with the loss of energy and angular momentum through gravitational radiation as predicted by calculations using General Relativity.

Four types of gravitational waves (GWs) have been predicted. Firstly, there are ‘continuous GWs,’ which have almost constant frequency and relatively small amplitude, and are expected to come from binary systems in rotation, or from a single extended asymmetric mass object rotating about its axis.

Secondly, there are ‘Inspiral GWs,’ which are produced by massive binary systems that are spiralling in towards one another. As their orbital distance lessens, their rotational velocity increases rapidly.

Then there are ‘Burst GWs,’ which are produced by an extreme event such as asymmetric gamma ray bursters or supernovae.

Lastly, there are ‘Stochastic GWs,’ which are predicted to have been created in the very early universe by sonic waves within the primordial soup. These are sometimes called primordial GWs and they are predicted to produce a GW background. Personally I doubt that this last type of GW exists.

On February 11, 2016, the LIGO and Virgo Scientific Collaboration announced they had made the first observation of gravitational waves. The observation itself was made on 14 September 2015, using the Advanced LIGO detectors. The gravity waves originated from a pair of merging black holes millions of years ago that released energy equivalent to a billion trillion stars within seconds. For the first time in human history, mankind could ‘feel and hear’ something happening in deep space and not just ‘see’ it. The black holes were estimated to be 36 and 29 solar masses respectively and circling each other at 250 times per second when the signal was first detected.

By August 2017 half a dozen other detections of gravitational waves were announced. I think all of them have been in-spiral GW’s. These produce a characteristic ‘chirp’ in which the signal becomes quicker and stronger and then stops. This is very useful for finding the signal amongst all the background noise. The flickering light pattern signal in the interferometer detector can be turned directly into a sound wave and actually does sound like a chirp.

In 2017, the Nobel Prize in Physics was awarded to Rainer Weiss, Kip Thorne and Barry Barish for their role in the detection of gravitational waves. (The same Kip Thorne who co-authored the heavyweight textbook on gravity that I have referred to so often in these essays that I gave it its own acronym - MTW).

As I first drafted this essay in 2017 there was considerable excitement in the world of astronomy because the Large Interferometer Gravity Wave Observatories (LIGO) suggested that a pair of neutron starts were in the process of collapsing. Space based telescopes were then able to look in that direction and they observed an intense burst of gamma rays. This is the first example of the two types of observational instruments working together and the dual result confirms that LIGO had been observing what they thought they were observing. Furthermore it provides evidence that gravitational waves travel at the speed of light.

Detection LIGO is a large-scale long-term physics project that includes the design, construction and operation of observatories designed to detect cosmic gravitational waves and applied theoretical work to develop gravitational-wave observations as an astronomical tool. It has been a struggle lasting many decades. It took many attempts to achieve funding for the observatories and nearly a decade to make the first successful observations. A triumph of persistence, optimism and the begrudging willingness of the USA National Science Foundation to fund a speculative fundamental science project to the tune of US$1.1 billion over the course of 40 years.

To my mind the experimental set up is reminiscent of Michelson Morley experiments 140 years ago. But it is on a much larger scale and is incredibly more sensitive, with all sorts of very clever tricks to increase the sensitivity and to get unwanted noise out of the system. Two large observatories have been built in the United States (in the states of Washington and Louisiana) with the aim of detecting gravitational waves by enhanced laser interferometry. The observatories have mirrors 4 km apart. Each arm contains resonant cavities at the end.

When a gravitational wave passes through the interferometer, the spacetime in the local area is altered. Depending on the source of the wave and its polarization, this results in an effective change in length of one or both of the beams. The effective length change between the beams will cause the light currently in the cavity to become very slightly out of phase (anti-phase) with the incoming light. The cavity will therefore periodically get very slightly out of coherence and the beams, which are tuned to destructively interfere at the detector, will have a very slight periodically varying detuning. This results in a measurable signal.

Or, to put it another way: After approximately 280 trips up and down the 4 km long evaluated tube arms to the far mirrors and back again, the two beams leave the arms and recombine at the beam splitter. The beams returning from two arms are kept out of phase so that when the arms are both in coherence and interference (as when there is no gravitational wave or extraneous disturbance passing through), their light waves subtract, and no light should arrive at the final photodiode. When a gravitational wave passes through the interferometer, the distances along the arms of the interferometer are repeatedly shortened and lengthened, creating a resonance and causing the beams to become slightly less out of phase and thus allowing some of the laser light to arrives at the final photodiode, thus creating a signal.

Light that does not contain a signal is returned to the interferometer using a power recycling mirror, thus increasing the power of the light in the arms. In actual operation, noise sources can cause movement in the optics that produces similar effects to real gravitational wave signals. A great deal of the art and skill in the design of the observatories, and in the complexity of their construction, is associated with the reduction of spurious motions of the mirrors. Observers also compare signals from both sites to reduce the effects of noise.

The observatories are so sensitive that they can detect a change in the length of their arms equivalent to ten-thousandth the charge diameter of a proton. This is equivalent to measuring the distance to Proxima Centauri with an error smaller than the width of a human hair.

Although the official description of LIGO talks about gravitational waves shortening and lengthening the arms of the interferometers by almost infinitesimal amounts, I think it might also be reasonable to describe what is going on as very slight changes in the speed of the photons being reflected back and forth 280 times in the 4 km long arms, as compared to the reference photons in the resonant cavities.

Some Comments on the Interpretation Commentators continually refer to gravitational waves as being “ripples in the fabric of spacetime”. There seems to be some deep-seated human desire to regard spacetime as being real and tangible, more or less like some sort of four dimensional fluid in in which the Universe is immersed. Computer based animations invariably depict empty space as some sort of rubberized sheet being dimpled by massive ball bearings and this promotes the same sort of mental images, attitudes and beliefs. Which is a pity.

It may be a lost cause but I point out once again that spacetime is a human construct for measuring, modeling and discussing what is going on in the Universe. It has no more reality that the Cartesian coordinate grid of latitude and longitude lines here on Earth.

It was not Einstein who promoted the idea that curved spacetime is an actual physical reality. This only happened after his death and was promoted by authors such as MTW and Stephen Hawking. For example, John Wheeler often made the comment that “mass/energy tells spacetime how to curve, and spacetime curvature tells matter how to move”. The cover of MTW classic textbook shows a little ant wandering around on the surface of an apple and dutifully following its curvature.

I would say to John Wheeler that he has started to confuse mathematical models with reality and that the analogy with the ant is a false one. The ant can feel the curvature of the apple with its little feet. The surface and its curvature is real and tangible. But spacetime is a manmade imagination created for our own convenience. A better analogy is the lines of latitude and longitude we have invented for talking about movement on the surface of our home planet. These lines do not actually exist. They cannot be observed. They are not tangible. I would say to John Wheeler that spacetime does not tell matter how to move any more than the latitude and longitude grid on Earth tells ducks how to migrate.

Which is not to say that I think that spacetime does not correspond to something that it observable. In fact I do. But this is a heretical idea that I will explore in other essays.

I also agree that applying a spacetime metric to this “something” is a good idea. But spacetime is not that something, and that something is not spacetime. In other words, do not get a reference system invented by mankind for convenience of describing physics mentally confused with reality itself.

Another crime in my book is commentators who compare gravitational waves with electromagnetic waves. Unless such commentators can explain how two stars orbiting each other can produce quantized packets of energy and then how these packets can be reflected, polarized, refracted etc. I suggest that they refrain from such analogies. If they must use analogies I suggest that they try acoustic comparisons instead.

Note that Doppler effects are a familiar phenomenon in sound waves and they should also occur for other moving disturbances such as gravitational waves. But where gravitational waves are concerned the effects should not be called red-shifting. The Doppler effect is not called red-shifting when it applies to acoustic waves and I think it should not be called red-shifting for gravitational waves either. It is just a plain old Doppler effect.

Discussion I do not find it surprising that a pair of massive pair of stars rotating about each other might have tiny push-pull effects a long way away. I think this is what you would expect to find even with a basics inverse-square law based on classical physics. For example, if a large asteroid suddenly knocked the moon out of its orbit, I think it reasonable to expect that observers on Earth would notice changes in gravity very soon afterwards.

Nor am I surprised that gravitational disturbances travel at the speed of light. In fact I am surprised that this has not been measured experimentally years ago. For example, the passage of the Moon overhead produces a noticeable gravitational tidal effect on the surface of the Earth. Since the centre of the pattern of this disturbance coincides exactly with where the Moon appears to be then that is evidence for the gravitational effect to be arriving hand in hand with the visible light from the Moon.

I would be surprised if gravitational waves are ever found to consist of discrete quantized packets, analogous to photons. In my currently preferred conceptual model of the Universe, photons are disturbances in something that can be modelled by spacetime constructs, and gravitational waves are disturbances of that something itself.

This is more than a semantic difference. Consider a laser beam that is pointed at the sky and turned on and off again. This sends bunches of well-collimated photons off on a journey into deep space which, in principle, can continue travelling indefinitely. Barring absorption by dust or blocking by some solid barrier, the beam of photons stands a chance of being able to be detected on some distant galaxy at some time in the future. Not so a gravitational wave. The energy from a gravitational wave spreads outwards in all directions and becomes increasingly weak with distance from its source. I think there is almost no chance of being able to detect gravitational waves coming from binary star events and suchlike outside of their local galaxy. Colliding galaxies might be a different story.

Conclusion After initial doubts, Einstein eventually decided that gravitational waves were a necessary feature of his Theory of General Relativity. The recent detection of gravitational waves, apart from being a remarkable achievement, is further confirmation that General Relativity works well as a model. However I think it is not proof that General Relativity is the only viable and useful way of looking at physics in our Universe.

#physics #gravitational waves #Einstein #General Relativity #hereticalphysics

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babyheroeclipseweasel · 3 months

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cnbnews · 4 years

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围绕超大质量黑洞运行的恒星轨迹首次成功证明爱因斯坦广义相对论的正确性。图为科学家模拟出的恒星非常接近银河系中心超大质量黑洞的轨道。（截屏）

【希望之声2020年4月17日】（希望之声记者张玉文综合编译）欧洲南方天文台天文学家对人马座A*黑洞附近的S2恒星进行历时27年的300多次观测，确认S2恒星绕银河系中心超大质量黑洞旋转的轨道不是椭圆形的，而是（莲）花环状的，“史瓦西旋进”理论首次在围绕黑洞运行的恒星轨迹中得到证实，再次证明爱因斯坦广义相对论的正确性。

《天文学与天体物理学》（Astronomy & Astrophysics）杂志周四（16日）发表一项新的研究成果，天文学家首次观测到一颗恒星围绕银河系中心的超大质量黑洞并非沿椭圆形轨道运行，证实爱因斯坦广义相对论“史瓦西旋进”（Schwarzschild precession）学说是正确的。

人马座A*（SgrA*）是银河系中心的超大质量黑洞，周围有稠密的恒星，这次观测的是被称为S2的恒星。天文学家在他们的研究报告中写道，使用位于智利的欧洲南方天文台超大望远镜上的几台仪器对S2恒星进行了300多次观测后，研究小组确认S2的的轨道是（莲）花环形的轨道，史瓦西旋进理论首次在围绕黑洞运行的恒星轨迹中得到证实。

这份研究报告的合着者德国普朗克地外物理研究院（Max Planck Institute for Extraterrestrial Physics）院长莱因哈德·根泽尔（Reinhard Genzel）在一份声明中表示：“爱因斯坦的广义相对论预测，一个物体围绕另一个物体的绑定轨道（boundorbits）并非如牛顿万有引力描述的椭圆形，这个绑定轨道不是封闭的，而是运动平面上向前进的。” 他还表示：“水星绕行太阳的轨道首先证实了这个着名的效应，一百年后的今天，我们又在围绕银河系中心黑洞运行的恒星运动轨迹中探测到这一效应。”

研究人员表示，在为爱因斯坦理论找到证据的同时，这项新发现还可以帮助研究人员对位于银河系中心的物质的类型和数量进行更精确的计算。

这项研究的另外两名合着者——巴黎天文台的盖·佩林（GuyPerrin）和法国格勒诺布尔大学（University of Grenoble）的卡琳·佩劳特（Karine Perraut）在声明中说：“因为遵循广义相对论观测S2是如此的成功，可使我们确定有多少诸如分布的暗物质或可能存在的小黑洞等看不见的物质，这对理解超大质量黑洞的形成和演化具有重大意义。”

史瓦西旋进即恒星最接近黑洞绕行时，随着每条轨迹的微妙移动都能巧妙绕过黑洞的轨道。

伟大的物理学家阿尔伯特·爱因斯坦（Albert Einstein）系犹太裔理论物理学家，他创立了现代物理学的两大支柱之一的相对论，他还发现了能量守恒定律。爱因斯坦在科学哲学领域颇具影响力，由于他对理论物理的贡献，特别是发现了光电效应原理，他赢得了1921年度的诺贝尔物理学奖。爱因斯坦的光电效应原理为建立量子理论奠定了基础。爱因斯坦曾经说：“空间、时间和物质，是人类认识的错觉。”

爱因斯坦对佛学也有很深的理解，他曾表示：“如果世界上有一个宗教不但不与科学相违，而且每一次的科学新发现都能够验证其观点，这就是佛教（Buddhism）。”他还断言：“未来的宗教将是一种宇宙宗教……它超越个人的上帝，避免教条和神学;它涵盖了自然和精神两方面，作为一个有意义的统一，它基于一种来自于自然的和精神体验的宗教意识。”

本文章或节目经希望之声编辑制作，转载请注明希望之声并包含原文标题及链接。

爱因斯坦吐舌照片是怎么来的？

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一切都是安排好的爱因斯坦给我们留下了太多的疑惑

10岁印度裔小女孩智商162 超爱因斯坦和霍金

爱因斯坦再世？14岁男孩家中自制核反应堆攻破多年技术难题

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原文链接：爱因斯坦100多年前创立的广义相对论得到科学新发现证实

原文链接：爱因斯坦100多年前创立的广义相对论得到科学新发现证实 - 新闻评论

本文标签：天文, 广义相对论, 恒星, 爱因斯坦, 物理, 相对论, 科学, 轨道, 黑洞

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spacetimewithstuartgary · 4 years

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ESO Telescope Sees Star Dance Around Supermassive Black Hole, Proves Einstein Right 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. TOP IMAGE....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 theory of general relativity. Its orbit is shaped like a rosette and not like an ellipse as predicted by Newton's theory of gravity. This effect, known as Schwarzschild precession, had never before been measured for a star around a supermassive black hole. This artist’s impression illustrates the precession of the star’s orbit, with the effect exaggerated for easier visualisation. Credit: ESO/L. Calçada CENTRE IMAGE....This simulation shows the orbits of stars very close to the supermassive black hole at the heart of the Milky Way. One of these stars, named S2, orbits every 16 years and is passing very close to the black hole in May 2018. This is a perfect laboratory to test gravitational physics and specifically Einstein's general theory of relativity. Research into S2's orbit was presented in a paper entitled “Detection of the Gravitational Redshift in the Orbit of the Star S2 near the Galactic Centre Massive Black Hole“, by the GRAVITY Collaboration, which appeared in the journal Astronomy & Astrophysics on 26 July 2018. Credit: ESO/L. Calçada/spaceengine.org LOWER IMAGE....This visible light wide-field view shows the rich star clouds in the constellation of Sagittarius (the Archer) in the direction of the centre of our Milky Way galaxy. The entire image is filled with vast numbers of stars — but far more remain hidden behind clouds of dust and are only revealed in infrared images. This view was created from photographs in red and blue light and forming part of the Digitized Sky Survey 2. The field of view is approximately 3.5 degrees x 3.6 degrees. Credit: ESO and Digitized Sky Survey 2. Acknowledgment: Davide De Martin and S. Guisard (www.eso.org/~sguisard) BOTTOM IMAGE....This chart shows the location of the field of view within which Sagittarius A* resides — the black hole is marked with a red circle within the constellation of Sagittarius (The Archer). This map shows most of the stars visible to the unaided eye under good conditions. Credit: ESO, IAU and Sky & Telescope

#space #science #Astronomy #physics #black holes #Einstein #relativity

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shirlleycoyle · 4 years

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A Star Is Orbiting our Galaxy’s Black Hole in a Stunning Pattern

A star that is pirouetting around the supermassive black hole at the center of the Milky Way, our galaxy, has validated a key part of Albert Einstein’s theory of general relativity. The star, called S2, is like “a precision probe of the gravitational field around the closest massive black hole," according to a study published on Thursday in Astronomy & Astrophysics.

For decades, scientists have gazed across 26,000 light years to watch S2 orbiting Sagittarius A*, our galactic center, which is occupied by a black hole with an estimated mass of four million Suns.

S2 is a perfect natural laboratory to test out some of Einstein’s predictions about the environment near extremely massive objects, including a phenomenon called Schwarzschild precession. This precession occurs when an object is locked in a very close orbit with a much more massive object. Instead of tracing out the same elliptical orbit, as modeled in Newtonian physics, general relativity predicts that the smaller object will have an orbit shaped like a stenciled rosette, due to the curvature of spacetime around the massive object.

The precession of Mercury around the Sun. Image: Rainer Zenz

A century ago, Einstein figured out that Mercury’s orbit was precessing in this rosette pattern due to the Sun’s effect on space and time. Now, a team of scientists known as the GRAVITY collaboration has found the same pattern on a much more massive scale.

“We are repeating the same experiments from back then,” said study lead Frank Eisenhauer, a senior staff scientist at the Max-Planck Institute for Extraterrestrial Physics, in a call. “But now, we do it with a black hole.”

The team is named after the GRAVITY instrument on the European Southern Observatory's Very Large Telescope (VLT) in Chile. Since it first became operational in 2017, GRAVITY has combined light from VLT’s four telescopes to become a “super-telescope” that can sharply resolve S2’s orbit around Sagittarius A*.

Observations with GRAVITY and other advanced instruments have now produced the “first direct detection” of Schwarzschild precession around Sagittarius A*, according to the study. S2 orbits in the same rosette pattern around the galactic center as Mercury does around the Sun, corroborating Einstein’s theories yet again.

This is the GRAVITY collaboration’s second major confirmation of general relativity on the scale of black holes. The instrument came online just in time to watch S2 make its closest approach to the black hole in May 2018. The star passed within 20 billion kilometers of Sagittarius A*, a distance only four times larger than Neptune’s orbit around the Sun. As a result of the intense gravitational forces near the black hole, S2 accelerated to three percent the speed of light during the pass.

Observations from the event revealed that the black hole’s gravitational field stretched light from S2 into longer wavelengths, causing it to redden from our perspective. This effect, known as gravitational redshift, was another prediction of relativistic effects on time and space.

“The gravitational redshift probes the time part, and this orbit, how a star moves in space, probes the space part,” said Eisenhauer. “So far, it clearly holds well. Einstein is right.”

Despite how well it has passed tests so far, general relativity may eventually be pushed to its limits by future observations of stars near the galactic center. If there are fainter stars even closer to Sagittarius A* than S2, perhaps with orbits measured in months rather than years, a new generation of extremely large telescopes coming online this decade may be able to spot them.

These stars could be close enough to the black hole to display signs of the rotation of spacetime itself. “The star will not only make a rosette, but since the whole space is rotating, the star will rotate with the space,” Eisenhauer explained.

“We might then come into a situation where we actually see deviations from Einstein’s theory because conceptually we know that Einstein’s theory cannot correctly describe everything,” he added. “We know when scales get very small, it does not fit together with quantum physics.”

In the coming years and decades, scientists may well be able to find one of these daredevil stars with an orbit so close to Sagittarius A* that it exposes some of the most mysterious secrets of black holes—and the underlying rules of the universe that makes them.

A Star Is Orbiting our Galaxy’s Black Hole in a Stunning Pattern syndicated from https://triviaqaweb.wordpress.com/feed/

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