A group of Japanese researchers said Sunday it has succeeded in creating super-dense conditions comparable to that inside a neutron star, or a density several quadrillion times that of water.

It is the first achievement of its kind and is expected to contribute to research on neutron stars, which consist primarily of closely packed neutrons and result from the collapse of a much larger stellar body.

The result, if reproduced, is also expected to help scientists understand the structure of the mass of protons and neutrons.

Such density is similar to compacting an object 1.5 times larger than the sun into a sphere with a 20-km diameter and is believed to have the same density of a neutron star of that size.

"If details of high-density conditions become clear, I think research to understand the mass of protons and neutrons, as well as in neutron stars and even higher-density quark stars, will progress significantly," said Masahiko Iwasaki, chief researcher of the government-affiliated Institute of Physical and Chemical Research and a member of the group.

In the experiment of exposing particles known as kaon into liquid helium brought to a temperature close to absolute zero, or minus 273.15 C, the researchers succeeded in capturing nine elementary particles called quarks compacted into a space equal to 10-trillionth of a centimeter.