The heaviest star in the universe is "almost too massive" to exist

The heaviest star in the universe has been discovered – it's only 15 miles wide.

That's more than twice the mass of the sun, which means that a piece of sugar would weigh 100 million tons. It's the same weight as the entire human population.

Known as the neutron star, it is the remnants of a supernova, a star that explodes, and is 700,000 times heavier than the Earth.

It's also a pulsar, emitting radio waves as a beacon when it's spinning.

Neutron stars are formed when the outer part of a giant sun explodes and the nucleus implodes. Its protons and electrons merge into each other to form neutrons.

Named J0740 + 6620, it represents 2.17 times the mass of the sun, 333 000 times that of the Earth. The results were published in Nature Astronomy.

It's "the most massive neutron star ever detected – almost too massive to exist," the team said.

The measurement approaches the limits of the compactness of a single object without crashing into a black hole.

It was detected about 4,600 light years from Earth by the Green Bank telescope in West Virginia. A light year is about six billion kilometers.

Scientist acknowledging Cromartie, of the University of Virginia, said, "Neutron stars are as mysterious as they are fascinating. These city-sized objects are ginormous atomic nuclei.

Colleague Maura McLaughlin, who studied the star with Duncan Lorimer, said: "These stars are very exotic."

Neutron stars have temperatures of one million degrees, are highly radioactive and possess intense magnetic fields.

Mass is the amount of material in a material, while weight is a measure of the degree of gravity that acts on that mass.