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View Full Version : A Star Is About To Go 2.5% The Speed Of Light Past A Black Hole



Fraser
2016-Jun-25, 04:40 PM
http://www.universetoday.com/wp-content/uploads/2016/06/eso1622a-700x432.jpg
Since it was first discovered in 1974, astronomers have been dying to get a better look at the Supermassive Black Hole (SBH) at the center of our galaxy. Known as Sagittarius A*, scientists have only been able to gauge the position and mass of this SBH by measuring the effect it has on the stars that orbit it. But so far, more detailed observations have eluded them, thanks in part to all the gas and dust that obscures it.
Luckily, the European Southern Observatory (ESO) recently began work with the GRAVITY (http://www.eso.org/public/teles-instr/vlt/vlt-instr/gravity/) interferometer, the latest component in their Very Large Telescope (http://www.eso.org/public/teles-instr/paranal/) (VLT). Using this instrument, which combines near-infrared imaging, adaptive-optics, and vastly improved resolution and accuracy, they have managed to capture images of the stars orbiting Sagittarius A*. And what they have observed was quite fascinating.
One of the primary purposes of GRAVITY is to study the gravitational field around Sagittarius A* in order to make precise measurements of the stars that orbit it. In so doing, the GRAVITY team - which consists of astronomers from the ESO, the Max Planck Institute, and multiple European research institutes - will be able to test Einstein's theory of General Relativity (http://www.universetoday.com/45484/einsteins-theory-of-relativity/) like never before.
In what was the first observation conducted using the new instrument, the GRAVITY team used its powerful interferometric imaging capabilities to study S2, a faint star which orbits*Sagittarius A* with a period of only 16 years. This test demonstrated the effectiveness of the GRAVITY instrument - which is 15 times more sensitive than the individual 8.2-metre Unit Telescopes the VLT currently relies on.
As GRAVITY’s lead scientist, Frank Eisenhauer - from the Max Planck Institute for Extraterrestrial Physics in Garching, Germany - explained in a recent ESO press release (https://www.eso.org/public/news/eso1622/):

"It was a fantastic moment for the whole team when the light from the star interfered for the first time — after eight years of hard work. First we actively stabilised the interference on a bright nearby star, and then only a few minutes later we could really see the interference from the faint star — to a lot of high-fives.”
But more than that, the observation of S2 was very well timed. In 2018, the star will be at the closest point in its orbit to the Sagittarius A** - just 17 light-hours from it. As you can see from the video below, it is at this point that S2 will be moving much faster than at any other point in its orbit (the orbit of S2 is highlighted in red and the position of the central black hole is marked with a red cross).
https://youtu.be/-aKVw2Ol-Ek
When it makes its closest approach, S2 will accelerate to speeds of almost 30 million km per hour, which is 2.5% the speed of light. Another opportunity to view this star reach such high speeds will not come again for another 16 years - in 2034. And having shown just how sensitive the instrument is already, the GRAVITY team expects to be able make very precise measurements of the star's position.
In fact, they anticipate that the level of accuracy will be comparable to that of measuring the positions of objects on the surface of the Moon, right down to the centimeter-scale. As such, they will be able to determine whether the motion of the star as it orbits the black hole are consistent with Einstein's theories of general relativity.
As recent simulations (http://www.universetoday.com/128856/japanese-3d-galaxy-map-confirms-einstein-one-smart-dude/) of the expansion of galaxies in the Universe have shown, Einstein's theories are still holding up after many decades. However, these tests will offer hard evidence, obtained through direct observation. A star traveling at a portion of the speed of light around a supermassive black hole at the center of our galaxy. One can hardly ask for a better test of relativity than that!
Further Reading: eso.org (https://www.eso.org/public/news/eso1622/)
The post A Star Is About To Go 2.5% The Speed Of Light Past A Black Hole (http://www.universetoday.com/129563/star-go-2-5-speed-light-past-black-hole/) appeared first on Universe Today (http://www.universetoday.com).


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