A NASA space telescope has discovered that our galaxy is blowing bubbles – and each one is 25,000 light-years wide! The two vast structures, stretching to the north and to the south of the centre of the Milky Way, have space scientists guessing as to their origin.

They are so big that a beam of light, travelling at 186,282 miles per second, would take 50,000 YEARS to get from the edge of one to the edge of the other.

The previously unseen bubbles were spotted by astronomer Doug Finkbeiner, of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts, using NASA’s Fermi Gamma-Ray Telescope. He admitted: “We don’t fully understand their nature or origin.”

They span more than half the visible sky, from the constellation of Virgo to the constellation of Grus, and are thought to be millions of years old. They were not noticed before because they were lost in a fog of gamma radiation across the sky.

Astronomers’ best guess is that the bubbles were created by an eruption from a supersized black hole at the centre of our galaxy.

Finkbeiner and his team discovered the bubbles by processing publicly available data from Fermi’s Large Area Telescope – a kind of advanced “Photoshopping”. The space telescope, launched in 2008, is the most powerful detector of gamma rays, which are the most energetic form of light. Its previous major finds have included a neutron star exploding like a cosmic firecracker.

Scientists now are conducting more analyses to better understand how the structure was formed. The bubble emissions, which are much more energetic than the gamma-ray fog seen elsewhere in the Milky Way, appear to have well-defined edges. Their shape and emissions suggest it was formed as a result of a large and relatively rapid energy release – but what from remains a riddle.

As well as the possibility of a particle jet from the supermassive black hole at our galaxy’s centre, astronomers are also considering that they might have been produced by gas outflows from a burst of star formation, several million years ago.

Scientist David Spergel, of Princeton University, New Jersey, said: “In other galaxies, we see that starbursts can drive enormous gas outflows. Whatever the energy source behind these huge bubbles may be, it is connected to many deep questions in astrophysics.”