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The anemic star bears the mark of its ancient ancestor



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The newly discovered ancient star, which has a record low in iron, bears evidence of a class of even older stars, long hypothesized, but is thought to have disappeared.


In an article published in the magazine Monthly News of the Royal Astronomical Society: letters, researchers led by Dr. Thomas Norlander of the ARC Center of Excellence for All-Sky Astrophysics in 3 Dimensions (ASTRO 3-D) confirm the existence of an ultra-metallic poor red giant star located in the Milky Way halos on the other side of A galaxy about 35,000 light-years from Earth.

Dr Nordlander, of the Australian National University (ANU) ASTRO 3-D junction, along with colleagues from Australia, the US and Europe, deployed the star using the University's SkyMapper telescope at the Siding Springs Observatory in NSW.

Spectroscopic analysis showed that the star had an iron content of only a fraction of 50 billion.

"It's like a drop of water in an Olympic pool," explains Dr. Nordlander.

"This incredibly anemic star, which probably formed just a few hundred million years after the Big Bang, has iron levels 1.5 million times lower than those of the Sun."

Its reduced iron content is enough to put the star – officially called SMSS J160540.18-144323.1 – in the record books, but it's what this low level suggests about its origin that astronomers really care about.

The first stars in the universe are thought to consist only of hydrogen and helium, along with traces of lithium. These elements were created immediately after the Big Bang, while all the heavier elements emerged from the heat and pressure of cataclysmic super-titanic explosions of stars. Stars like the Sun, which are rich in heavy elements, therefore contain material from many generations of stars exploding as supernovae.

As none of the first stars has yet been found, their properties remain hypothetical. They have long been expected to be incredibly massive, perhaps hundreds of times more massive than the sun and explode into incredibly energetic supernovae known as hypernovae.

Confirmation of the anemic SMSS J160540.18–144323.1, though not itself one of the first stars, adds powerful evidence.

Dr. Norlander and his colleagues suggest that the star formed after one of the first stars exploded. This exploding star was quite impressive, only ten times more massive than the Sun, and exploded only slightly (astronomically), so that most of the heavy elements created in the supernova fell back into the residual neutron star left behind.

Only a small amount of just wrought iron escaped the gravitational pull of the residue and continued, in agreement with far greater amounts of lighter elements, to form a new star – one of the first second-generation stars now to be discovered.

Co-researcher Professor Martin Aspund, Principal Investigator at ASTRO 3-D at ANU, said it is unlikely that any true first stars will ever survive to this day.

"The good news is that we can study the first stars through their children – the stars that came after them, like the one we found," he says.

The study was conducted in collaboration with researchers at Monash University and the University of New South Wales in Australia, the Massachusetts Institute of Technology and the Joint Institute for Nuclear Astrophysics, as well as in the US, Max Planck Institute of Astronomy in Germany, Uppsala University in Sweden in Padua in Italy.


A new ultra-metal-poor star has been discovered


More information:
T Nordlander et al. The lowest open stellar abundance of Fe: the halogen star SMSS J160540.18−144323.1, Monthly News of the Royal Astronomical Society: Letters (2019). Doi: 10.1093 / mnrasl / slz109

provided by
ARC's Center of Excellence for All Sky Astrophysics in 3 Dimensions

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Anemic star bears the mark of its ancient ancestor (2019, August 1)
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