ESA's Herschel space observatory has discovered an extremely distant galaxy making stars more than 2000 times faster than our own Milky Way. Seen at a time when the Universe was less than a billion years old, its mere existence challenges our theories of galaxy evolution.
The galaxy, known as HFLS3, appears as little more than a faint, red smudge in images from the Herschel Multi-tiered Extragalactic Survey (HerMES). Yet appearances can be deceiving: this small smudge is actually a star-building factory, furiously transforming gas and dust into new stars.
The galaxy HFLS3 was found initially as a small red dot in Herschel submillimetre images (main image, and panels on right). Subsequent observations with ground-based telescopes, ranging from optical to millimetre-wave (insets) showed that there are two galaxies appearing very close together. They are at very different distances, however, with one of them, seen in millimetre-wave (inset, blue) being so distant that we are seeing it as it was when the Universe was just 880 million years old. HFLS3 is a 'maximum starburst' galaxy, the most distant of its type ever found.
The extreme distance to HFLS3 means that its light has travelled for almost 13 billion years across space before reaching us. We therefore see it as it existed in the infant Universe, just 880 million years after the Big Bang or at 6.5% of the Universe's current age.
Even at that young age, HFLS3 was already close to the mass of the Milky Way, with roughly 140 billion times the mass of the Sun in the form of stars and star-forming material. After another 13 billion years, it should have grown to be as big as the most massive galaxies known in the local Universe.
This makes the object an enigma. According to current theories of galaxy evolution, galaxies as massive as HFLS3 should not be present so soon after the Big Bang.
HFLS3 is making so many stars that it is called a 'maximum starburst'. The whole galaxy is wreathed in star formation, to the point where the intense radiation of the young stars almost blows away the star-forming material in the galaxy. Environments like this do not exist on galaxy-wide scales in the Universe today.
Even in the early Universe, they are expected to be extremely rare. The mere existence of a single such object so early in the Universe poses a challenge to current theories of early galaxy formation, which predict that they should reach such large masses only much later.
Read the complete news on ESA's website
"A Dust Obscured Massive Hyper Starburst Galaxy at Redshift 6.34", by D. A. Riechers et al. is published in Nature, 18 April 2013.