Behold a star from the second generation of generation of stars after the Big Bang, something scientists have been seeking for a while. Its unique make-up may prove that our galaxy developed by cannibalizing dwarf galaxies.
In the dwarf galaxy Sculptor, this star is made out of the same material as the oldest stars in the Milky Way. The Harvard Center for Astrophysics found this beauty, and a press release explains:
"This star likely is almost as old as the universe itself," said astronomer Anna Frebel of the Harvard-Smithsonian Center for Astrophysics, lead author of the Nature paper reporting the finding.
Dwarf galaxies are small galaxies with just a few billion stars, compared to hundreds of billions in the Milky Way. In the "bottom-up model" of galaxy formation, large galaxies attained their size over billions of years by absorbing their smaller neighbors.
"If you watched a time-lapse movie of our galaxy, you would see a swarm of dwarf galaxies buzzing around it like bees around a beehive," explained Frebel. "Over time, those galaxies smashed together and mingled their stars to make one large galaxy - the Milky Way."
If dwarf galaxies are indeed the building blocks of larger galaxies, then the same kinds of stars should be found in both kinds of galaxies, especially in the case of old, "metal-poor" stars. To astronomers, "metals" are chemical elements heavier than hydrogen or helium. Because they are products of stellar evolution, metals were rare in the early Universe, and so old stars tend to be metal-poor.
Old stars in the Milky Way's halo can be extremely metal-poor, with metal abundances 100,000 times poorer than in the Sun, which is a typical younger, metal-rich star. Surveys over the past decade have failed to turn up any such extremely metal-poor stars in dwarf galaxies, however.
"The Milky Way seemed to have stars that were much more primitive than any of the stars in any of the dwarf galaxies," says co-author Josh Simon of the Observatories of the Carnegie Institution. "If dwarf galaxies were the original components of the Milky Way, then it's hard to understand why they wouldn't have similar stars."
The team suspected that the methods used to find metal-poor stars in dwarf galaxies were biased in a way that caused the surveys to miss the most metal-poor stars. Team member Evan Kirby, a Caltech astronomer, developed a method to estimate the metal abundances of large numbers of stars at a time, making it possible to efficiently search for the most metal-poor stars in dwarf galaxies.
"This was harder than finding a needle in a haystack. We needed to find a needle in a stack of needles," said Kirby. "We sorted through hundreds of candidates to find our target."
Among stars he found in the Sculptor dwarf galaxy was one faint, 18th-magnitude speck designated S1020549. Spectroscopic measurements of the star's light with Carnegie's Magellan-Clay telescope in Las Campanas, Chile, determined it to have a metal abundance 6,000 times lower than that of the Sun; this is five times lower than any other star found so far in a dwarf galaxy.
The researchers measured S1020549's total metal abundance from elements such as magnesium, calcium, titanium, and iron. The overall abundance pattern resembles those of old Milky Way stars, lending the first observational support to the idea that these galactic stars originally formed in dwarf galaxies.
You can download a supermassive version of the image over at the link. [Harvard Center for Astrophysics]