STOCKHOLM — Three researchers, one Japanese and two Americans, have won the Nobel prize in physics.

They're honored for "pioneering contributions to astrophysics," including the detection of cosmic neutrinos and the discovery of cosmic X-ray sources.

The laureates used the "very smallest components of the universe to increase our understanding of the very largest," including the sun, stars, galaxies and supernovae, the Royal Swedish Academy of Sciences said in its citation.

This year's Nobel winners have "opened new windows to space," Mats Jonsson, chairman of the Nobel committee of physics, said.

This year's Nobel awards started Monday with the naming of Britons Sydney Brenner, 75, and Sir John E. Sulston, 60, and American H. Robert Horvitz, 55, as winners of the medicine prize, selected by a committee at the Karolinska Institute.

The researchers shared it for discoveries about how genes regulate organ growth and a process of programmed cell deaths that shed light on how viruses and bacteria invade human cells, including in conditions such as AIDS, strokes, cancer and heart attacks.

The winner of the Nobel Prize in chemistry will be named on Wednesday morning and the Bank of Sweden Prize in Economic Sciences in Memory of Alfred Nobel later the same day.

The literature prize winner will be announced on Thursday, the Swedish Academy said on Tuesday.

The winner of the coveted peace prize -- the only one not awarded in Sweden -- will be announced Friday in Oslo, Norway.

The award committees make their decisions in deep secrecy and candidates are not publicly revealed for 50 years.

Alfred Nobel, the wealthy Swedish industrialist and inventor of dynamite who endowed the prizes left only vague guidelines for the selection committees.

In his will he said the prize being revealed on Tuesday should be given to those who "shall have conferred the greatest benefit on mankind" and "shall have made the most important discovery or invention within the field of physics."

The Royal Swedish Academy of Sciences, which also chooses the chemistry and economics winners, invited nominations from previous recipients and experts in the fields before cutting down its choices. Deliberations are conducted in strict secrecy.