Scientists discover ancient star in Milky Way's halo

Iron deficient and carbon rich star formed 13.5 billion years ago.
By Laurel Kornfeld | Feb 12, 2018
A metal-poor star Spanish scientists discovered in the Milky Way's halo may be one of the first stars to have formed in the galaxy.

Found in the galactic halo, which is home to the galaxy's oldest and most metal-poor stars, J0815+4729 was uncovered in data collected by the Sloan Digital Sky Survey (SDSS), a project that imaged roughly one-third of the sky in deep color an took spectra of over three million astronomical objects.

In astronomy, the term "metals" applies to all elements beyond hydrogen and helium. Most ancient stars were metal-poor. Their deaths in supernova explosions produced larger metals that were incorporated into the next generation of stars.

A galaxy's halo is a spherical-shaped extension surrounding its main, visible component.

J0815+4729 is approximately 70 percent the mass of our Sun. Located 7,500 light years away, it is believed to have formed a mere 300 million years after the Big Bang.

"We know of only a few stars of this type of halo, where the oldest and most metal-poor stars in our galaxy are found," commented David Aguado of the Instituto de Astrofisica (IAC), an international research center in Spain.

Once they recognized the star as metal-poor, the researchers analyzed the star's physical and chemical properties using spectroscopy, collecting spectra with the ISIS spectrograph on the William Herschel Telescope and the OSIRIS spectrograph on the Gran Telescopio Canarias (GTC). Both telescopes are located in La Palma, Spain.

The analysis revealed J0815+4729 to have one million times less the amounts of calcium and iron our Sun has, a characteristic of the universe's oldest stars.

To their surprise, the researchers discovered the star has about 15 percent more carbon than the Sun. Some theorize this high carbon content is the result of the star having accumulated carbon produced when other ancient stars died in supernova explosions.

"Theory predicts that these stars could form just after--and using material from--the first supernovae, whose progenitors were the first massive stars in the galaxy, about 300 million years after the Big Bang," noted Jonay Gonzalez-Hernandez, also of IAC.

As a next step, the research team plans to obtain even higher resolution spectra of the star to learn whether it has high levels of any other elements.

Findings of the study have been published in The Astrophysical Journal Letters.



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