A small galaxy in the constellation Lynx that only recently started making stars has the lowest level of oxygen ever seen in a star-forming galaxy. That makes it the best place yet to probe the chemical elements cooked up by the big bang.
The big bang produced just three main elements: hydrogen, helium and a little lithium.聽Thus, the first galaxies presumably had little oxygen, but are so small and remote that we can鈥檛 see them.
So Yuri Izotov at the Main Astronomical Observatory in Kiev, Ukraine, and his colleagues hunted for star-forming galaxies closer to home that resemble the primordial ones by having little oxygen.
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鈥淭hey are very rare,鈥� says Trinh Thuan at the University of Virginia in Charlottesville. That鈥檚 because star-forming galaxies have massive stars that explode soon after birth, raising the oxygen level.
Hunting for helium
The astronomers used the Sloan Digital Sky Survey in New Mexico to look for galaxies with little oxygen.聽Up came a smudge 620 million light years away that they named J0811+4730.
Data from the Large Binocular Telescope in Arizona revealed this galaxy to be a record-breaker, bearing 9 per cent less oxygen than the previous champ.聽Its oxygen-to-hydrogen ratio is only 1.7 per cent that of the sun, which has 1 oxygen nucleus for every 1740 hydrogen nuclei.
Some dwarf galaxies have even less oxygen, but the new galaxy is special because it鈥檚 doing something that they are not:聽creating new stars from its gas. The hottest of these stars strip electrons from helium gas, so observers can measure that element鈥檚 abundance.
鈥淚f we want to know the primordial helium abundance, we鈥檝e got to look at these galaxies,鈥� says Grant Mathews at the University of Notre Dame in Indiana. Finding this out helps reveal the conditions that prevailed during the first three minutes of the universe鈥檚 life, because helium was one of the few elements created by the nuclear reactions right after the big bang.
Small but mighty
The new galaxy is important for another reason:聽it gives us a close-up look at the type of vigorous dwarf galaxies that probably reionised the early universe. Reionisation marked the transition from the time when neutral gas pervaded the universe to the state it has today, when the gas between galaxies is ionised.
The new galaxy is both a pipsqueak and a powerhouse. Its stellar mass is only one-thirty-thousandth that of the Milky Way.聽Yet it鈥檚 churning out new stars at a quarter the rate of the Milky Way 鈥� an impressive feat for such a tiny galaxy.
In fact, says Thuan, the newly found galaxy spawned 80 per cent of its stars in just the past few million years. The hottest of these stars emit the same kind of blistering radiation that reionised the universe shortly after the big bang. The galaxy serves as a surrogate for the galaxies we can鈥檛 yet see that transformed the entire cosmos some 13 billion years ago.
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Read more: Spiralling galaxy arms spread oxygen around for future planets
