A full-sky survey by NASA's wide-field infrared WISE telescope turned up about 1,000 hot, dust-obscured galaxies, or hot DOGs, each of which pump out as much light as 100 trillion sun-like stars.

The objects are rare, accounting for about one in 100,000 light sources, and difficult to find since most of their energy is masked by dust.

Astronomers believe hot DOGs, which are twice as warm as similar galaxies, may be a transitional state between disk-shaped galaxies, like the Milky Way, and elliptical galaxies.

Most of the hot DOGs found by WISE are about 10 billion light years away, meaning they formed when the universe was a fraction of its present age.

Scientists suspect conditions in the early universe were more conducive for seeding and growing these hot galaxies, but they are not ruling out that the phenomenon could occur today.

"There is either just a weird set of circumstances that rarely comes up, or a common set of circumstances that comes up for only a very short period of time," that allows hot DOGs to form, said WISE project scientist Peter Eisenhardt of NASA's Jet Propulsion Laboratory in Pasadena, California.

Because the galaxies do not have enough stars to account for all their heat, scientists suspect they may contain unusually active super-massive black holes, which are regions of space so dense with matter that not even light can escape the grip of gravity.

At times, black holes feed on surrounding material, providing telltale signs of their existence.

All galaxies are believed to host a black hole, though some, such as Sagittarius A, located at the center of the Milky Way, are relatively dormant, at least at the present time.

Scientists estimate Sagittarius A contains 4 million times the mass of the sun. Other black holes are substantially larger, approaching 10 billion times the sun's mass.

Among the 563 million infrared objects detected by WISE during its two-year mission are millions of super-massive black holes.

The findings, which were unveiled during a conference call with reporters on Wednesday, are being published in the Astrophysical Journal.

(Editing by Jane Sutton and Stacey Joyce)

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