Several hundred million light years away from Earth in the heart of a pair of galaxies are two super massive black holes that can swallow planets, stars and gases.

"They are monstrous," Berkeley astrophysicist Chung-Pei Ma told reporters. "We did not expect to find such massive black holes because they are more massive than indicated by their galaxy properties. They're kind of extraordinary."

Each black hole is estimated to have a mass of about 10 billion times greater than the sun. The previous record-holder was located in the galaxy M87 part of the Virgo cluster of galaxies. The galaxy is about 54 million light years from the sun and the black hole in its center only had a mass of 6.3 billion suns.

In the study published on Monday in the scientific journal Nature, the researchers from the University of California led by Nicholas McConnell and Chung-Pei Ma said that the gigantic black holes could be the leftovers of quasars from the early galaxy.

The scientists used the Gemini and Keck observatories in Hawaii and the McDonald Observatory in Texas to monitor the cluster of galaxies where the two black holes were found. One black hole is located in a galaxy called NGC 3842 found the Leo cluster of galaxies which is about 320 million light years from Earth. The second black hole is located in NGC 4889, the brightest cluster in the Coma cluster about 335 million light years away.

Black holes are dense objects formed from the collapse of a super-size star. Black holes have strong gravitational pulls that not even light can escape from. Scientists believe that most galaxies have black holes at their center. The recently discovered giants are dormant now but in their youth they powered the bright quasars from the early universe.

"For an astronomer, finding these insatiable black holes is like finally encountering people nine feet tall whose great height had only been inferred from fossilized bones. How did they grow so large?" Ma said in a news release. "This rare find will help us understand whether these black holes had very tall parents or ate a lot of spinach."

As large as these newly discovered black holes there could still be other giants lurking in the darkness of space. The researchers are already setting their sights on finding these massive monsters.

"If there is any bigger black hole," Ma said, "we should be able to find them in the next year or two. Personally, I think we are probably reaching the high end now. Maybe another factor of two to go at best."