Neutron stars, the remnants of massive stars that have run out of fuel and collapsed under their own gravity, shine on even though they're technically dead, scientists said.
Although the nuclear fusion fires that sustained its parent star are extinguished, a neutron star still shines with radiation generated by its magnetic field, a trillion times stronger than Earth's, made intensely concentrated as the core collapsed.
"A neutron star is right at the threshold of matter as it can exist -- if it gets any denser, it becomes a black hole," Zaven Arzoumanian of NASA's Goddard Space Flight Center in Greenbelt, Md., said in a NASA release Wednesday.
A proposed NASA mission called the Neutron Star Interior Composition Explorer would unveil the dark heart of a neutron star, he said.
"We have no way of creating neutron star interiors on Earth, so what happens to matter under such incredible pressure is a mystery -- there are many theories about how it behaves," he said.
In the proposed mission, an array of 56 telescopes attached to the International Space Station would collect X-rays generated both from hotspots on a neutron star's surface and from its powerful magnetic field.
Notable deaths of 2014 [PHOTOS]