A star is about to go 2.5% the speed of light past a black hole

June 27, 2016 by Matt Williams, Universe Today
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.

A star is about to go 2.5% the speed of light past a black hole
Spitzer image of the core of the Milky Way Galaxy. Credit: NASA/JPL-Caltech/S. Stolovy (SSC/Caltech)

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 1990s 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).

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.

A star is about to go 2.5% the speed of light past a black hole
Artist’s impression of the influence gravity has on space-time. Credit: space.com

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.

"It 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.

Explore further: Successful first observations of galactic center with GRAVITY

More information: www.eso.org/public/news/eso1622/

Related Stories

First light for future black hole probe

January 13, 2016

Zooming in on black holes is the main mission for the newly installed instrument GRAVITY at ESO's Very Large Telescope in Chile. During its first observations, GRAVITY successfully combined starlight using all four Auxiliary ...

Journey to the center of our galaxy

March 31, 2016

Peering deep into the heart of our home galaxy, the Milky Way, the NASA/ESA Hubble Space Telescope reveals a rich tapestry of more than half a million stars. Apart from a few, blue, foreground stars, almost all of the stars ...

Image: Computer simulation of a supermassive black hole

April 7, 2016

This computer-simulated image shows a supermassive black hole at the core of a galaxy. The black region in the center represents the black hole's event horizon, where no light can escape the massive object's gravitational ...

Hubble sees a supermassive and super-hungry galaxy

January 11, 2016

This NASA/ESA Hubble Space Telescope image shows the spiral galaxy NGC 4845, located over 65 million light-years away in the constellation of Virgo (The Virgin). The galaxy's orientation clearly reveals the galaxy's striking ...

Recommended for you

Can China keep it's climate promises?

March 26, 2019

China can easily meet its Paris climate pledge to peak its greenhouse gas emissions by 2030, but sourcing 20 percent of its energy needs from renewables and nuclear power by that date may be considerably harder, researchers ...

What happened before the Big Bang?

March 26, 2019

A team of scientists has proposed a powerful new test for inflation, the theory that the universe dramatically expanded in size in a fleeting fraction of a second right after the Big Bang. Their goal is to give insight into ...

Cellular microRNA detection with miRacles

March 26, 2019

MicroRNAs (miRNAs) are short noncoding regulatory RNAs that can repress gene expression post-transcriptionally and are therefore increasingly used as biomarkers of disease. Detecting miRNAs can be arduous and expensive as ...

In the Tree of Life, youth has its advantages

March 26, 2019

It's a question that has captivated naturalists for centuries: Why have some groups of organisms enjoyed incredibly diversity—like fish, birds, insects—while others have contained only a few species—like humans.

6 comments

Adjust slider to filter visible comments by rank

Display comments: newest first

Benni
4 / 5 (4) Jun 27, 2016
Hey Schneibo, maybe you can get us a picture of this with your special telescope by which you claim we can see the surface of BHs?
antialias_physorg
3.9 / 5 (7) Jun 27, 2016
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.

Woha...at 2.5% speed of light and "just" 17 light hours out that isn't enough speed to break orbit? And have an orbital period of 16 years? (For comparions: Pluto is less than 5 light hours away and has an orbital period of 248 years)

The gravity of that sucker just boggles the mind.
Da Schneib
3.3 / 5 (7) Jun 27, 2016
Heh, somebody didn't close their italics attribute in the article...

Meanwhile, isn't this pretty much the same article as the previous one with GRAVITY mentioned in the title?

Last, @antialias, keep in mind that Sgr A* is at one focus of R2's elliptical orbit. The laws of orbital mechanics and the mass of Sgr A* prevent R2 from breaking orbit. "In takes you East, East takes you out, out takes you West, West takes you in."
Protoplasmix
3.9 / 5 (7) Jun 27, 2016
Hey Schneibo, maybe you can get us a picture of this with your special telescope by which you claim we can see the surface of BHs?
You mean the Event Horizon Telescope? – "The most compelling evidence for this is the recent observation by 1.3 mm VLBI of Schwarzschild radius scale structure in Sgr A* … This new 1.3 mm VLBI detection confirms that short-wavelength VLBI of Sgr A* can and will be used to directly probe the event horizon of this black hole candidate: in short, Sgr A* is the right object, VLBI is the right technique, and this decade is the right time."

Hey Beeni, how are those Different Equations are coming along?
TheGhostofOtto1923
2.3 / 5 (3) Jun 27, 2016
Niven and Benford collaborated on a hard scifi novel, Shipstar, which uses a star as its engine to obtain somewhat relativistic speeds.

"Our Bowl is a shell more than a hundred million miles across, held to a star by gravity and some electrodynamic forces. The star produces a long jet of hot gas, which is magnetically confined so well it spears through a hole at the crown of the cup-shaped shell. This jet propels the entire system forward – literally, a star turned into the engine of a "ship" that is the shell, the Bowl. On the shell's inner face, a sprawling civilization dwells.
http://www.centau...?p=30948

-Anyone familiar with these authors knows the amount of work they put into their concepts, and its interesting to read about the process in benfords article.
Whydening Gyre
3 / 5 (2) Jun 27, 2016
Meanwhile, isn't this pretty much the same article as the previous one with GRAVITY mentioned in the title?

I call it the "sister" article...

Last, @antialias, keep in mind that Sgr A* is at one focus of R2's elliptical orbit. The laws of orbital mechanics and the mass of Sgr A* prevent R2 from breaking orbit. "In takes you East, East takes you out, out takes you West, West takes you in."

The article DID say it likely will change the star's orbital parameters, so wouldn't it remain a possibility...?
(never say never...) :-)

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.