Credits: NASA’s Goddard Space Flight Center
Most known neutron stars are observed as pulsars,
emitting narrow, sweeping beams of radiation. They squeeze up to two
solar masses into a city-size volume, crushing matter to the highest
possible stable densities. To explore these exotic states of matter,
NICER measures X-ray emissions across the surfaces of neutron stars as
they spin, ultimately confronting the predictions of nuclear physics
theory. Credits: NASA’s Goddard Space Flight Center. Animation
Technology advances in the past half-century allowed scientists to
study these compact stellar objects from space using different
wavelengths of light, especially those much more energetic than the
radio waves received by the Cambridge telescope. Several current NASA
missions continue to study these natural beacons.
The Neutron star Interior Composition Explorer, or NICER, is the
first NASA mission dedicated to studying pulsars. In a nod to the
anniversary of Bell’s discovery, NICER observed the famous first pulsar,
known today as PSR B1919+21.
NICER launched to the International Space Station in early June and
started science operations last month. Its X-ray observations – the part
of the electromagnetic spectrum in which these stars radiate both from
their million-degree solid surfaces and from their strong magnetic
fields – will reveal how nature’s fundamental forces behave within the
cores of these objects, an environment that doesn’t exist and can’t be
reproduced anywhere else. "What's inside a pulsar?" is one of many
long-standing astrophysics questions about these ultra-dense,
fast-spinning, powerfully magnetic objects.
The “stuff” of pulsars is a collection of particles familiar to
scientists from over a century of laboratory studies on Earth –
neutrons, protons, electrons, and perhaps even their own constituents,
called quarks. However, under such extreme conditions of pressure and
density, their behavior and interactions aren’t well understood. New,
precise measurements, especially of the sizes and masses of pulsars are
needed to pin down theories.
“Many nuclear-physics models have been developed to explain how the
make-up of neutron stars, based on available data and the constraints
they provide,” said Goddard’s Keith Gendreau, the principal investigator
for NICER. “NICER’s sensitivity, X-ray energy resolution and time
resolution will improve these by more precisely measuring their radii,
to an order of magnitude improvement over the state of the art today.”
NICER is currently installed on the International
Space Station. This turntable animation of the payload calls out the
locations of NICER’s star tracker camera, electronics, space station
attachment mechanism, 56 sunshields, pointing actuators and stow/deploy
actuator. Credits: NASA’s Goddard Space Flight Center. Animation
The mission will also pave the way for future space exploration by
helping to develop a Global Positioning System-like capability for the
galaxy. The embedded Station Explorer for X-ray Timing and Navigation
Technology, or SEXTANT, demonstration will use NICER’s X-ray
observations of pulsar signals to determine NICER's exact position in
orbit.
“You can time the pulsations of pulsars distributed in many
directions around a spacecraft to figure out where the vehicle is and
navigate it anywhere,” said Arzoumanian, who is also the NICER science
lead. “That’s exactly how the GPS system on Earth works, with precise
clocks flown on satellites in orbit.”
Scientists have tested this method using computer and lab
simulations. SEXTANT will demonstrate pulsar-based navigation for the
first time in space.
NICER-SEXTANT is the first astrophysics mission dedicated to studying
pulsars, 50 years after their discovery. “I think it is going to yield
many more scientific discoveries than we can anticipate now,” said
Gendreau.
NICER-SEXTANT is a two-in-one mission. NICER is an Astrophysics
Mission of Opportunity within NASA's Explorer program, which provides
frequent flight opportunities for world-class scientific investigations
from space utilizing innovative, streamlined, and efficient management
approaches within the heliophysics and astrophysics science areas.
NASA's Space Technology Mission Directorate supports the SEXTANT
component of the mission, demonstrating pulsar-based spacecraft
navigation.
More about NICER: https://www.nasa.gov/nicer/
Read about five famous pulsars from the past 50 years: https://nasa.tumblr.com/post/163637443034/five-famous-pulsars-from-the-past-50-years
NASA’s Goddard Space Flight Center in Greenbelt, Md.
Editor: Karl Hille
