New Delhi: Nearly 50 years after they were discovered, spinning neutron stars – the densest objects in the universe – are about to be studied by NASA starting tomorrow.

On Saturday, June 3, NASA is all set to launch the world's first mission to examine the rapidly spinning neutron stars, along with carrying out the world's first demonstration of X-ray navigation in space.

SpaceX's CRS-11, a cargo resupply mission to the International Space Station (ISS), will be the vehicle aboard which the mission will be launched.

The launch of the two-in-one Neutron Star Interior Composition Explorer (NICER) was earlier planned for June 1, but was delayed due to poor weather.

About a week after its installation, this one-of-a-kind investigation will begin observing neutron stars, the densest objects in the universe.

The mission will focus especially on pulsars – those neutron stars that appear to wink on and off because their spin sweeps beams of radiation past us, like a cosmic lighthouse.

Due to their extreme nature, neutron stars and pulsars have engendered a great deal of interest since their existence was proposed in 1939 and then discovered in 1967.

These objects are the remnants of massive stars that, after exhausting their nuclear fuel, exploded and collapsed into super-dense spheres.

Their intense gravity crushes an astonishing amount of matter – often more than 1.4 times the content of the Sun or at least 460,000 Earths – into city-sized orbs, creating stable, yet incredibly dense matter not seen anywhere else in the universe.

Just one teaspoonful of neutron star matter would weigh a billion tonnes on Earth.

"The nature of matter under these conditions is a decades-old unsolved problem," said Keith Gendreau, a scientist at NASA's Goddard Space Flight Centre in the US.

"Theory has advanced a host of models to describe the physics governing the interiors of neutron stars. With NICER, we can finally test these theories with precise observations," said Gendreau.

Although neutron stars emit radiation across the spectrum, observing them in the energetic X-ray band offers the greatest insights into their structure and the high-energy phenomena that they host, including starquakes, thermonuclear explosions and the most powerful magnetic fields known in the cosmos.

During its 18-month mission, NICER will collect X-rays generated from the stars' tremendously strong magnetic fields and from hotspots located at their two magnetic poles.

At these locations, the objects' intense magnetic fields emerge from their surfaces and particles trapped within these fields rain down and generate X-rays when they strike the stars' surfaces.

In pulsars, these flowing particles emit powerful beams of radiation from the vicinity of the magnetic poles.

On Earth these beams of radiation are observed as flashes of radiation ranging from seconds to milliseconds depending on how fast the pulsar rotates.

Since these pulsations are predictable, they can be used as celestial clocks, providing high-precision timing, like the atomic-clock signals supplied through the Global Positioning System (GPS).

Although ubiquitous on Earth, GPS signals weaken the farther one travels out beyond Earth orbit. Pulsars, however, are accessible virtually everywhere in space, making them a valuable navigational solution for deep-space exploration.

(With PTI inputs)