An X-ray Detection of Star Formation In a Highly Magnified Giant Arc
  In the past decade, our understanding of how stars and galaxies formed during
the first 5 billion years after the Big Bang has been revolutionized by
observations that leverage gravitational lensing by intervening masses, which
act as natural cosmic telescopes to magnify background sources. Previous
studies have harnessed this effect to probe the distant universe at
ultraviolet, optical, infrared and millimeter wavelengths. However, strong
lensing studies of young, star-forming galaxies have never extended into X-ray
wavelengths, which uniquely trace high-energy phenomena. Here we report an
X-ray detection of star formation in a highly magnified, strongly lensed
galaxy. This lensed galaxy, seen during the first third of the history of the
Universe, is a low--mass, low--metallicity starburst with elevated X-ray
emission, and is a likely analog to the first generation of galaxies. Our
measurements yield insight into the role that X-ray emission from stellar
populations in the first generation of galaxies may play in re-ionizing the
Universe. This observation paves the way for future strong lensing-assisted
X-ray studies of distant galaxies reaching orders of magnitude below the
detection limits of current deep fields, and previews the depths that will be
attainable with future X-ray observatories.
