The oldest known stars of the time when the universe was just 300 million years old have been discovered by astronomers near the centre of the Milky Way galaxy. These stars formed before the Milky Way and the galaxy formed around them.
- The stars are pure but contain material from an even earlier star, which died in an enormous explosion called hypernova*.
- The oldest of these stars is a red giant named SMSS J181609.62 -333218.7 which was discovered in the galactic bulge, about 25,000 light-years away.
The study was published in the journal Nature and challenges current theories about the environment of the early universe from which these stars formed.
Composition of oldest discovered stars
As per Big Bang, universe filled only with hydrogen, helium, and trace levels of lithium but these stars have surprisingly low levels of carbon, iron and other heavy elements.
- The unique chemical composition of these first stars indicates that they were all giants, with masses over 40 times of the Sun.
How was discovery done?
The team focused on the dense central parts of the galaxy, where stars formed even earlier. The team observed about five million stars with SkyMapper to select the most pure and therefore oldest specimens
- These were then studied in more detail using the Anglo-Australian Telescope in New South Wales and the Magellan telescope in Chile to determine their chemical make-up.
- The team also demonstrated that the stars spend their entire lives near the Milky Way centre.
* A hypernova is a type of star explosion which generates energy higher than that created during a supernovae explosion.