New York, Jan 8 (IANS): Welcome to the most-exhaustive, brightest and mysterious world of 'unseen' galaxies ever found.

NASA's Hubble Space Telescope has uncovered the long-suspected underlying population of galaxies that produced the bulk of new stars during the universe's early years, said a study.

The newly discovered galaxies are 100 times more numerous than their more massive cousins.

“But they are 100 times fainter than galaxies typically detected in previous deep-field surveys of the early universe,” said study leader Brian Siana of the University of California.

“The bright galaxies we generally see represent the tip of the iceberg. We believe most of the stars forming in the early universe are occurring in galaxies we normally can't see at all. Now we have found those 'unseen' galaxies,” added Siana.

The research team used Hubble's 'Wide Field Camera 3' to search for faint, star-forming galaxies in ultra-violet light - a reliable tracer of star birth.

The galaxies existed when the universe was undergoing a "baby boom" of star formation, estimated to have peaked between 9 billion and 12 billion years ago.

"Our goal with these observations was not to find a large number of galaxies, but to find much fainter galaxies," Alavi explained.

The researchers now believe that they have completed the census of galaxies at an epoch when the universe was roughly 3.4 billion years old.

“Though these galaxies are very faint, their increased numbers mean that they account for the majority of star formation during this epoch,” said team member Anahita Alavi from University of California.

These early galaxies would be the prime target for NASA's James Webb Space Telescope, an infrared observatory scheduled to be launched in 2018.