Text on screen: What is a neutron star?
When a star bigger
and more massive than the sun
runs out of fuel at the end of its life,
its core collapses while the outer
layers are blown off in a
supernova explosion
What's left behind
depends on the star's original mass.
A star roughly 10 to
20 times our sun
leaves behind a neutron star.
A more massive star
becomes a black hole.
Unlike black holes, neutron stars
are directly observable, usually
as pulsars - the lighthouses of the
cosmos. Discovered
50 years ago, they are the
densest observable objects in the
universe.
Neutron stars compress up
to twice the sun's mass into a 
city-sized sphere. Matter is
packed so tightly that a teaspoon
of neutron star interior
would weigh more than a billion tons
on Earth.
Still, the nature of the ultra-dense matter
in the cores of neutron stars
is unknown.
Because neutron stars
pack so much mass into such a
tiny volume, they produce
gravity strong enough to bend the light they emit,
distorting their appearance in
a way that enables the mass
and size of the star to be measured.
Scientists cannot
reproduce the extreme conditions
in and around neutron stars on
Earth. They must look
into the galaxy to answer decades-old
questions about extreme matter and
gravity.
NASA's Neutron star Interior
Composition Explorer mission,
or NICER, will make X-ray
observations of neutron stars from its
perch on the International Space Station.
It will give astronomers more
insight into these mysterious
objects - helping determine
what is under their surface.
A multipurpose
mission, NICER includes a
technology demonstration called SEXTANT.
It will analyze NICER's
observations to validate the use of
rapidly rotating neutron stars
as navigation beacons, for travel
in deep space, throughout the solar
system and beyond.
Text on screen: nasa.gov/nicer
