Explanation:
The Milky Way is an ordinary
12 billion year old spiral galaxy, and even our
middle-aged Sun is pushing 4.5 billion years.
But all the stars in dwarf
galaxy I Zwicky 18 are
much younger.
In fact, based on Hubble Space Telescope image data,
that galaxy's first stars formed only
about 500 million years ago, making it
the youngest known galaxy.
In this view, the bright knots
are the two major star forming
regions of I
Zwicky 18, embedded in expanding
filaments of glowing interstellar gas.
Scattered, much older background galaxies are seen as small
red blobs, and a companion galaxy lies just beyond the
upper right corner of the cropped picture.
Astronomers believe that
diminutive
I Zwicky 18 resembles the earliest galaxies formed, but also
want to understand how such a young galaxy can be
only 45 million light-years away - surrounded by
mature galaxies in an aging Universe.
The tiny galaxy itself is a mere 3,000 light-years
across.
