A snapshot of the stellar slave has been taken by European astronomers, who say this is the first visual proof that a black hole of leviathan size lies at the heart of the Milky Way.

Astronomers have long suspected that most galaxies have at their core a vast black hole, one of the most powerful and enigmatic forces in the known Universe.

A few years ago, X-ray sensors detected potent bursts of radiation from a source about 26,000 light years from Earth that indicated our galaxy was no different.

But some experts remained unconvinced, arguing that other forces might be the cause.

The latest work, published in Thursday's issue of the British journal Nature, takes the voyage of discovery a stage further and, the authors say, is damning evidence that a "super-massive" black hole is at work.

European astronomers led by Rainer Schoedel of the Institute for Extraterrestrial Physics in Garching, Germany, sifted through 10 years of imaging of a curious star, S2, that races around the location of the suspected black hole, which is called Sagittarius A*.

Those pictures enabled the team to plot two-thirds of the star's orbit.

Then, in May this year, the team used a revolutionary imaging system at the world's largest optical telescope in order to finetune their calculations.

They conclude that S2 is on a highly elliptical orbit around Sagittarius A* that lasts only 15.2 Earth years. By comparison, our Sun takes 230 million years to circle the galaxy.

At its closest point, the gravitational pull of Sagittarius A* forces S2 to whizz within a hair's breadth of its rapacious jaws, at an excruciating velocity of 50,000 kms (30,000 miles) per second.

S2, at this point, is a mere 17 light hours (17 hours travelling at the speed of light) from potential oblivion before it makes its escape and goes around again.

The wealth of data has yielded a Photo-fit picture of Sagittarius A*: a force with a tiny body and a mass between 2.2 million and 3.7 million times more than that of the Sun.

Only a "super-massive" black hole could be this, the authors say. Other options ranging over a dense cluster of so-called dark particles can be "robustly" ruled out.

"These new data probe the Galactic Centre more closely than ever before," says Karl Gebhardt, a University of Texas astronomer, in a commentary.

"The only compelling explanation is that there is a supermassive black hole lurking there. These results are the best evidence yet that super-massive black holes are not just theory, but fact."

The study also highlights the benefits of a new tool, adaptive optics imaging, at the European Southern Observatory's very large telescope in Chile.

When stars are viewed from the Earth, their image is blurred by the light's passage through the atmosphere, an effect that also makes them twinkle.

The new system measures these distortions and sends them to a deformable mirror. The mirror is able to change its shape to correct the distortions and almost completely remove the blurring, making the image also as sharp as if it were viewed from a telescope in space.

The predominant theory about black holes is that they are created from massive stars that run out of fuel and collapse in on themselves, generating a body of extremely intense gravity. Not even light can escape their clutch, which is why they cannot be observed optically.

A growing body of opinion also holds that some black holes may be created by non-stellar means. The super-massive ones, at the centre of galaxies, may be born from large volumes of gas that suddenly collapse, becoming things of extraordinary mass but tiny volumes, according to this school of thought.

SPACE.WIRE