Sizing up the Milky Way’s first monster stars

290616 firststars 1
Supernova remnant G266.2-1.2, as seen in X-ray and optical wavelengths. Supernova remnants are made of dust that includes elements produced by the supernova that spawned it. Eventually, the matter in supernova remnants mixes with other gas and dust and forms a new generation of stars.
NASA / CXC / Morehead State Univ / T.Pannuti et al

Astronomers have found that at least one of the Milky Way’s first generation of stars was enormous – maybe 20 times more massive than the sun – despite it being long gone now.

The US team examined a second-generation star – which is made from remnants of the first generation – and found traces of sulfur and phosphorous. 

It was also the first time those elements have been spotted in such a star.

“Stars remember the nurseries where they were born, and we were able to glean some valuable pieces of that memory with these new observations,” explains lead researcher Ian Roederer from the University of Michigan.

The star in question, named BD+44⁰493, is the brightest known second-generation star – so bright it can be seen through high-powered binoculars, despite being around 600 light-years from Earth.

Because of its unique makeup, BD+44 493 is thought to have formed from one of the Milky Way’s first stars.

These were made primarily of helium and hydrogen and met their demise as supernova explosions, spraying heavier elements into space which helped form second-generation stars.

Understanding this first wave of stars holds particular importance, Roederer says, because “knowing more about the composition of the universe’s original stars can tell us where we came from”. 

“Stars are the factories where all the universe’s elements aside from hydrogen and helium were made, including the ones that make up our Earth and even our own bodies.”

To understand its chemistry, the team studied the ultraviolet spectrum of BD+44⁰493 using the Hubble Space Telescope. 

Along with sulfur and phosphorous, the researchers also found zinc, which has only been identified in one other second-generation star. 

Given the significant amounts of all three elements, it’s thought the first-generation star that exploded and contributed to BD+44⁰493 must have been enormous – perhaps more than 20 times the size of our sun. 

The team is keen to study the UV spectrum of more second-generation stars as technology improves. 

“We’ve put a new spin on a very old technique to measure the chemical fingerprints of this star,” says Roederer.

Their findings were published in Astrophysical Journal Letters.

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