Astronomers discover the remains of a 2,000-year-old nova

For the first time, a European research team from the University of Göttingen discovered the remains of a nova in a galactic globular cluster. The rest is located near the center of the Messier 22 globular group and has recently been observed with modern instruments. The results will be published in the journal Astronomy and astrophysics.

A nova is a hydrogen explosion on the surface of a star that makes it much brighter. The remains form a glowing nebula. "The position and brightness of the remains correspond to an entry of 48 BC into an ancient collection of Chinese astronomers' observations," says the first author, Fabian Göttgens, of the Institute of Art. Astrophysics of the University of Göttingen. He did this PhD research in the Stellar Astrophysics Research Group headed by Professor Dreizler. "They probably saw the original nova in the same place," he adds. This means that modern measurements confirm one of the oldest observations of an event outside the solar system.

Globular clusters are large spherical clusters of several hundred thousand very old stars that revolve around their galaxy of origin. There are 150 known globular clusters in orbit around the Milky Way. Messier 22 is one of those star clusters. It is located in the constellation Sagittarius towards the center of the Milky Way. It has been observed with two dozen other globular groups with the MUSE instrument at the ESO Very Large Telescope in Chile. The MUSE instrument was developed with the participation of the Institute of Astrophysics, funded by the BMBF. It not only produces images, it also divides the light of the stars into colors, by measuring the brightness of the stars according to the color. This makes it particularly suitable for looking for nebulae that often shine only in a certain color, usually red.

The newly discovered remains of the nova form a bright red nebula of hydrogen and other gases, whose diameter is about 8,000 times the distance between the Earth and the sun. Despite its size, the nebula is relatively light, with a mass about 30 times that of the Earth, because the gas was dispersed by the explosion.