Copyright: ESA/Herschel/HerMES/IRAM/GTC/W.M. Keck Observatory
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.
Our own Milky Way makes stars at a rate equivalent to one solar mass per
year, but HFLS3 is seen to be churning out new stars at more than two
thousand times more rapidly. This is one of the highest star formation
rates ever seen in any galaxy.
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.
The first galaxies to form are expected to be relatively small and
lightweight, containing only a few billion times the mass of our Sun.
They form their first stars at rates of a few times that experienced by
the Milky Way today.
The small galaxies then grow by feeding off cold gas from intergalactic
space and by merging with other small galaxies. So, finding the age at
which the first massive galaxies appeared can constrain galaxy evolution
theories. But this is not easy.
“Looking for the first examples of these massive star factories is like
searching for a needle in a haystack; the Herschel dataset is extremely
rich,” says Dominik Riechers of Cornell University, who led the
investigation.
Tens of thousands of massive, star-forming galaxies have been detected
by Herschel as part of HerMES and sifting through them to find the most
interesting ones is a challenge
“This particular galaxy got our attention because it was bright, and yet
very red compared to others like it,” says co-investigator Dave
Clements of Imperial College London.
Red in this case means brightest at longer infrared wavelengths and,
owing to the effect of redshift in our expanding Universe, this can
indicate extreme distance. Follow-up observations with a suite of
ground-based telescopes confirmed that HFLS3 was the most distant galaxy
of its kind ever found, seen just 880 million years after the Big Bang,
at redshift 6.34.
With this in hand, the astronomers were able to confidently translate
the galaxy’s infrared brightness into a star formation rate, discovering
its extraordinary nature.
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.
“Early starbursts like HFLS3 produced the heavy elements that made up
later generations of stars and galaxies, and much of the matter we know
today,” says Dr Riechers.
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.
The team are continuing to comb the enormous dataset from Herschel looking for more examples of such extreme, early galaxies.
“With these observations, Herschel has found a rare example of a galaxy
bursting with stars at a time in cosmic history when there were very few
such galaxies,” says Göran Pilbratt, ESA’s Herschel Project Scientist.
“This underlines the pioneering nature of Herschel and its ability to
reveal a previously hidden Universe, improving our understanding of how
galaxies form.”
Notes for Editors:
“A Dust‐Obscured Massive Hyper‐Starburst Galaxy at Redshift 6.34” by D. A. Riechers et al. is published in Nature, 18 April 2013.
The survey was conducted as part of the Herschel Multi-tiered
Extragalactic Survey (HerMES), led by S. Oliver of the University of
Sussex, UK and J. Block of JPL/Caltech, USA.
Herschel is an ESA space observatory with science instruments provided
by European-led Principal Investigator consortia and with important
participation from NASA.
Markus Bauer
ESA Science and Robotic Exploration Communication Officer
Tel: +31 71 565 6799
Mob: +31 61 594 3 954
Email: markus.bauer@esa.int
Dominik A. Riechers
Cornell University, New York, USA
Tel: +1 626 395 4670
Email: riechers@astro.cornell.edu
Dave Clements
Imperial College London, UK
Tel: +44 20 75947693
Email: d.clements@imperial.ac.uk
Göran Pilbratt
ESA Herschel Project Scientist
Tel: +31 71 565 3621
Email: gpilbratt@rssd.esa.int
