The Milky Way galaxy is "embedded" in a giant halo of hot gas which extends for hundreds of thousands of light years, Nasa studies suggest.
If the size and mass of the cloud - said to equal the total mass of the stars and planets in the galaxy - is confirmed, it could explain a strange imbalance in the make up of the galaxy which has confounded scientists for years.
Theories of the formation of the universe suggest that about twice as many baryons - subatomic particles made up of three quarks - should be present in the galaxy than are currently known about.
But according to the research, they may be present after all, in the cloud surrounding our galaxy.
FIve astronomers worked with the Chandra Observatory, the European Space Agency's XMM-Newton satellite, and the Japan Aerospace Exploration Agency's Suzaku satellite, to uncover the new research.
The scientists found that the temperature of the 'halo' is between one million and 2.5 million kelvins, "or a few hundred times hotter than the surface of the sun".
"Our work shows that, for reasonable values of parameters and with reasonable assumptions, the Chandra observations imply a huge reservoir of hot gas around the Milky Way," said co-author Smita Mathur of Ohio State University in Columbus.
"It may extend for a few hundred thousand light-years around the Milky Way or it may extend farther into the surrounding local group of galaxies. Either way, its mass appears to be very large."