MONSTER black holes sometimes play a cosmic game of hide and seek, shrouding themselves from view behind giant clouds of gas and dust, say North-East scientists.

But they are still millions of light years away and much too distant to pose any threat to Earth.

Scientists believe the supermassive black holes lurk at the centres of most big galaxies, but many are hidden from the view of most telescopes.

Astronomers have discovered evidence of the monster black holes at the centre of two of our galactic neighbours.

One, the galaxy NGC 1448, is "just" 38 million light years from our own body of stars, the Milky Way. The other, IC 3639, is 170 million light years away. Both are classified as "active" galaxies that emit intense levels of radiation.

In each case the powerful black hole is hidden behind clouds of gas and dust.

Black holes are places where gravity is so powerful it traps light and distorts time and space. They can only be detected from the last gasp emissions of radiation from objects falling into them.

The hidden black holes were spotted by the American space agency's Nasa's NuSTAR ((Nuclear Spectroscopic Telescope Array) orbiting observatory which is designed to see X-rays.

Astronomers from the universities of Durham and Southampton conducted analysis of the NuSTAR data.

Ady Annuar, from the University of Durham's Centre for Extragalactic Astronomy, which led a study looking at the black hole at the centre of the NGC 1448 spiral galaxy, said: "These black holes are relatively close to the Milky Way, but they have remained hidden from us until now.

"They're like monsters hiding under your bed.

"Their recent discoveries certainly call out the question of how many other supermassive black holes we are still missing, even in our nearby universe."

Research co-author Professor David Alexander, in the Department of Physics at Durham University, added: "These hidden monsters have been predicted to be fairly abundant in our Universe.

"It is only after the advent of NuSTAR that we actually began to find each of them one by one."

Daniel Stern, project scientist for NuSTAR at Nasa's Jet Propulsion Laboratory, said: "It is exciting to use the power of NuSTAR to get important, unique information on these beasts, even in our cosmic backyard where they can be studied in detail."

The findings of the study were presented at the American Astronomical Society in Grapevine, Texas, on Saturday.