Explanation:
In this
artist's
illustration, two distant galaxies formed about
2 billion years after the big bang are
caught in the
afterglow of GRB090323,
a gamma-ray burst seen across the Universe.
Shining through its own host galaxy
and another nearby galaxy,
the alignment of gamma-ray burst and galaxies
was inferred from the afterglow spectrum following the burst's
initial detection by the
Fermi Gamma Ray Space
Telescope in March of 2009.
As seen by one of the European Southern Observatory's
very large telescope units, the spectrum
of the burst's fading afterglow also offered a surprising result -
the distant galaxies are richer in heavy elements
than the Sun, with the
highest abundances
ever seen in the early Universe.
Heavy elements that enrich mature galaxies in the local Universe
were made in past generations
of stars.
So these young galaxies have experienced a
prodigious rate of star
formation and chemical evolution compared to our own Milky Way.
In the illustration, the light from the burst site
at the left passes successively through the galaxies to the right.
Spectra illustrating dark
absorption lines of the galaxies' elements
imprinted on the afterglow light are shown as insets.
Of course, astronomers on planet Earth
would be about
12 billion light-years off the right edge of the frame.
