In 48 BC, Chinese astronomers noticed something strange occurring in the heavens – a star in the sky burning brighter than usual. And these observations, noted down and preserved for millennia, have puzzled space scientists ever since. But the 2,000 year-old mystery has finally been solved after scientists spotted the remains of a nova in a distant globular galaxy.
The finding, using instruments on the cutting-edge Very Large Telescope (VLT), confirms one of the oldest observations of an event occurring outside the solar system.
The position and brightness of the remains match an entry from 48 BC
Dr Fabian Göttgens
The University of Göttingen research team has discovered the remains of a nova in a galactic globular cluster.
A nova is an explosion of hydrogen on the surface of a star making it much brighter to see in the sky.
And it is the bringing remains of a star that forms a glowing nebula.
Dr Fabian Göttgens of the University of Göttingen’s Institute for Astrophysics said: “The position and brightness of the remains match an entry from 48 BC in an ancient collection of observations by Chinese astronomers.
“They probably saw the original nova in the same place.”
This means modern measurements confirm one of the oldest observations of an event outside the solar system.
Globular clusters are large, spherical clusters of several hundreds of thousands of very old stars that orbit together around their home galaxy.
There are 150 known globular clusters orbiting the Milky Way.
Messier 22 is one of these star clusters, lying in the Sagittarius constellation near the Milky Way’s centre.
It was observed together with two dozen other globular clusters with the instrument MUSE at the VLT in Chile.
The instrument not only produces images, it also simultaneously splits starlight by colour, measuring the brightness of stars as a function of colour.
This makes it particularly suitable for finding nebulae that often only glow in a certain colour—usually red.
The newly discovered remains of the nova form a red shining nebula of hydrogen gas and other gases, which has a diameter of about 8,000 times the distance between Earth and sun.
Despite its size, the nebula is relatively light, with a mass about 30 times that of Earth, because the gas was dispersed by the explosion.
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