A Star Is About To Go 2.5% The Speed Of Light Past A Black Hole

Artist’s impression of the star S2 passing very close to the supermassive black hole at the centre of the Milky Way. Credit: ESO

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 interferometer, the latest component in their Very Large Telescope (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 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.

This was an historic accomplishment, as a clear view of the center of our galaxy is something that has eluded astronomers in the past. As GRAVITY’s lead scientist, Frank Eisenhauer – from the Max Planck Institute for Extraterrestrial Physics in Garching, Germany – explained to Universe Today via email:

“First, the Galactic Center is hidden behind a huge amount of interstellar dust, and it is practically invisible at optical wavelengths. The stars are only observable in the infrared, so we first had to develop the necessary technology and instruments for that. Second, there are so many stars concentrated in the Galactic Center that a normal telescope is not sharp enough to resolve them. It was only in the late 1990′ and in the beginning of this century when we learned to sharpen the images with the help of speckle interferometry and adaptive optics to see the stars and observe their dance around the central black hole.”

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.

“[I]t is not the speed itself to cause the general relativistic effects,” explained Eisenhauer, “but the strong gravitation around the black hole. But the very  high orbital speed is a direct consequence and measure of the gravitation, so we refer to it in the press release because the comparison with the speed of light and the ISS illustrates so nicely the extreme conditions.

As recent simulations 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 will certainly prove to be a fitting test.

And Eisenhauer and his colleagues expect to see some very interesting things. “We hope to see a “kick” in the orbit.” he said. “The general relativistic effects increase very strongly when you approach the black hole, and when the star swings by, these effects will slightly change the direction of the
orbit.”

While those of us here at Earth will not be able to “star gaze” on this occasion and see R2 whipping past Sagittarius A*, we will still be privy to all the results. And then, we just might see if Einstein really was correct when he proposed what is still the predominant theory of gravitation in physics, over a century later.

Further Reading: eso.org

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Japanese 3D Galaxy Map Confirms Einstein Was One Smart Dude

An international team of researchers have produced the largest  3-D map of the universe to date, which validates Einstein's theory of General Relativity. Credit: NAOJ/CFHT/ SDSS

On June 30th, 1905, Albert Einstein started a revolution with the publication of theory of Special Relativity. This theory, among other things, stated that the speed of light in a vacuum is the same for all observers, regardless of the source. In 1915, he followed this up with the publication of his theory of General Relativity, which asserted that gravity has a warping effect on space-time. For over a century, these theories have been an essential tool in astrophysics, explaining the behavior of the Universe on the large scale.

However, since the 1990s, astronomers have been aware of the fact that the Universe is expanding at an accelerated rate. In an effort to explain the mechanics behind this, suggestions have ranged from the possible existence of an invisible energy (i.e. Dark Energy) to the possibility that Einstein’s field equations of General Relativity could be breaking down. But thanks to the recent work of an international research team, it is now known that Einstein had it right all along.

Using the Fiber Multi-Object Spectrograph (FMOS) on the Subaru Telescope, the team – which was led by researchers from Japan’s Institute for the Physics and Mathematics of the Universe (Kavli IMPU) and the University of Tokyo – created the deepest 3-D map of the Universe to date. All told, this map contains some 3,000 galaxies and encompasses a volume of space measuring 13 billion light-years.

To test Einstein’s theory, the team  – which was led by Dr. Teppei Okumura, a Kavli IPMU Project Researcher – used information obtained by the FastSound Project over the past few years. As part of their effort to ascertain the origins of cosmic acceleration, this project relies on data collected by the Subaru telescope to create a survey that monitors the redshift of galaxies.

From what was observed over the course of 40 nights (between 2012 and 2014), the FastSound Survey was able to determine the on velocities and clustering of more than 3,000 distant galaxies. Measuring their redshift space distortions to see how fast they were moving, Okumura and his team were able to track the expansion of these galaxies out to a distance of 13 billion light-years.

This was an historic feat, seeing as how previous 3-D models of the Universe have not been able to reach beyond 10 billion light years. But thanks to the FMOS on the Subaru Telescope, which can analyze galaxies 12.4 to 14.7 billion light-years away, the team was able to break this record. They then compared the results to the kind of expansion predicted by Einstein’s theory, particularly the inclusion of his cosmological constant.

Originally introduced by Einstein in 1917 as an addition to his theory of General Relativity, the cosmological constant was basically a way to hold back gravity and achieve a static Universe. And while Einstein abandoned this theory when Edwin Hubble discovered that the Universe was expanding, it has since come to be an accepted part of the standard model of modern cosmology (known as the Lambda-CDM model).

https://youtu.be/RAiPZ_oUPI4

What the research team found was that even at a distance of 13 billion light-years into the Universe, the rules of General Relativity are still valid. “We tested the theory of general relativity further than anyone else ever has,” said Dr. Okumura. “It’s a privilege to be able to publish our results 100 years after Einstein proposed his theory.”

These results have helped resolve something that astronomers have been puzzling over for decades, which was whether or not Einstein’s cosmological constant could be shown to be consistent with an expanding Universe. And while various experiments have confirmed that General Relativity did match observational data, they have been somewhat limited in the past.

For example, the Pound-Rebka experiment, which took place in 1960, was the first confirmation of Einstein’s theory. However, this experiment, and the many that followed in the ensuing decades, were either indirect or confined to the Solar System. A 2010 experiment conducted by researchers from Princeton University confirmed General Relativity to a distance of 7 billion light years.

But with this experiment, General Relativity has been confirmed to a distance of 13 billion light years, which accounts for the vast majority of the Universe that we can see (which is 13.8 billion light-years). It seems that even a century later, Einstein’s theories are still holding up. And considering that he once claimed that the cosmological constant was the “biggest blunder” of his scientific career!

Further Reading: Publications of the Astronomical Society of Japan

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Faster-Than-Light Lasers Could “Illuminate” the Universe

It’s a cornerstone of modern physics that nothing in the Universe is faster than the speed of light (c). However, Einstein’s theory of special relativity does allow for instances where certain influences appear to travel faster than light without violating causality. These are what is known as “photonic booms,” a concept similar to a sonic […]