In a vacuum, light travels at a speed of nearly 300,000 km/s (186,282 mi/s) and it's generally believed that matter cannot exceed this speed. Recently, astronomers discovered matter traveling at more than 99.999% the speed of light.

It's the fastest speed ever recorded in the case of matter in the universe, and it has been achieved by jets of material shooting out of dying stars. Massive stars eventually run of hydrogen, the fuel for the nuclear fusion reactions taking place at their core, and then the gravity causes the core to collapse, forming a black hole of a neutron star.

When they do that, some of the matter from the star also explodes outwards at blistering speeds, producing an intense burst of gamma rays and other radiation. For some time now, astronomers theorized that the jets of matter expanding in these explosions would be propelled to very nearly the speed of light, but it has previously not been possible to clock them precisely.

Now, a team of scientists, led by Emilio Molinari of the Osservatorio Astronomico di Brera in Merate, Italy, successfully measured the speeds of the jets of matter, by tracking two gamma-ray bursts, that are produced by the expanding matter.

After the initial explosion, this matter starts colliding with surrounding gas, creating afterglows in both visible and infrared light. The amount of time it takes for this afterglow to reach its peak brightness can be used to calculate how fast material in the jets is moving.

So, by following two gamma-ray bursts, called GRB 060418 and GRB 060607 A, the team came up with a final speed of the expanding matter of about 99.9997% the speed of light.

"There's no other organized flows of matter that go this speed," agrees Neil Gehrels, chief scientist for the Swift mission at NASA's Goddard Space Flight Center in Greenbelt, Maryland, US, and not a member of Molinari's team.