13.5 billion year old star discovered

The first stars to form after the Big Bang would have been made entirely of elements made in the Big Bang itself which are the lightest and simplest like hydrogen, helium and lithium. The heavier and more complex elements which astronomers call "metals" were made in subsequent stars thermonuclear furnaces. The first stars seeded the universe with the heavier elements when they exploded as supernovae.

So when we find a star with mostly light elements we conclude it’s one of the universe’s very early stars. That’s the case with a star announced by Johns Hopkins University on November 5, 2018. This 13.5 billion year old star appears to be one of the oldest stars known and it’s also the new record holder for stars with the fewest heavy elements known so far.

The star is unusual because unlike other stars with very low metal content, it is part of the Milky Way’s ‘thin disk’ the part of the galaxy in which the sun resides. And because this star is so old, we can say it’s possible that our galactic neighborhood is at least 3 billion years older than previously thought. The star is a part of a system of two stars that revolve around a common point, also known as a binary star system. The star has low mass and low metal content. In fact it now also holds the record for the lowest complement of heavy metals. It has metallicity similar to that of Mercury while the Sun has as much as 14 times that of Jupiter.

In general we think the universe’s first stars were extremely massive, and lived quite short lives. In fact, until the late 1990s, many researchers thought that the early universe could only form massive stars. But that view has slowly evolved over the years as simulations have become increasingly sophisticated. The finding of this star means that there is a possibility that more such stars with low mass and low metal content are present across the galaxy and the Universe some of them even older than the discovered star.

Phedias Hadjicharalambous

Cyprus Astronomy Organisation