Proof that Albert Einstein's black holes do exist, claim scientists

By Richard Alleyne, Science Correspondent

The team proved the existence of black holes by tracking the motions of 28 stars circling around the Milky Way Photo: PA

Ever since Albert Einstein came up with his general theory of relativity, black holes has been central to our knowledge of the Universe.

Now experts say they have shown that the theoretical phenomenon, whose gravitational pull is thought to hold galaxies together, exist "beyond any reasonable doubt".

The team of scientists spent 16 years studying the existence of a super massive black hole thought to be at the centre of our galaxy, the Milky Way.

While the black hole itself is invisible to the eye, the team proved its existence by tracking the motions of 28 stars circling around it.

Just as swirling leaves caught in a gust of wind can provide clues about air currents, so the stars' movements reveal information about forces at work at the galactic centre.

The observations show that the stars orbit a central concentration of mass four million times greater than that of the Sun, claim the team from the Max-Planck Institute for Extraterrestrial Physics in Garching, near Munich, Germany.

"Undoubtedly the most spectacular aspect of our long term study is that it has delivered what is now considered to be the best empirical evidence that super-massive black holes do really exist," said study leader Professor Reinhard Genzel.

"The stellar orbits in the galactic centre show that the central mass concentration of four million solar masses must be a black hole, beyond any reasonable doubt."

The astronomers were also able to measure with great accuracy how far the Earth is from the centre of the galaxy - a distance of 27,000 light years.

Usually the central region of the Milky Way is hard to see because the view from Earth is blocked by interstellar dust.

To overcome this problem, the astronomers, who published their findings in the Astrophysical Journal, focused on infrared light wavelengths that can penetrate the dust clouds.

The galaxy's central mass, long suspected of being a giant black hole, is known as "Sagittarius A star".

The European Southern Observatory study, which began in 1992, was made using the 3.5 metre (11ft) New Technology Telescope at the La Silla observatory and the Very Large Telescope - an array of four 8.2 metre (26ft) telescopes at the Paranal observatory. Both operate from the Atacama desert in Chile.

The team, who found that one particular star made a full orbit of the black hole in the 16 year study, now hope to use even more powerful telescopes to further test Einstein's theories.

A black hole is a theoretical region of space in which the gravitational field is so powerful that nothing, not even electromagnetic radiation (visible light), can escape its pull. They are believed to be the remnants of burnt out suns.

While the idea of a black hole dates back as far as 1783, it was only after Einstein published his general relativity theory in 1916 that the modern concept was introduced by the German physicist Karl Scharzchild. The actual phrase black hole was not, however, coined until 1968.

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