Astronomers have peered into one of the most mysterious phenomena in the solar system – the super-heated streams of electrically charged gases that form the inner core of a sunspot.

Astronomers have peered into one of the most mysterious phenomena in the solar system – the super-heated streams of electrically charged gases that form the inner core of a sunspot.

Scientists have speculated on the nature of sunspots ever since Galileo first observed them in the early 1600s but until now their origins have largely been a mystery.

Using the Solar and Heliospheric Observatory (Soho), a satellite loaded with instruments for monitoring the Sun, the astronomers were able to produce a detailed image of the hot plasma of a sunspot before it bubbles up to the surface of the Sun as a giant vortex.

Seen from Earth, sunspots appear as black dots but their physical appearance belies the extraordinary energy of their creation, often accompanied by violent solar storms that can disrupt radio communications and power supplies on Earth.

Thomas Duvall, an astrophysicist from Nasa's Goddard Space Flight Centre, in Maryland, said: "Until now, we've looked down at the top of the sunspots like we might look down at the leaves in treetops.

"For the first time we're able to observe the branches and trunk of the tree that gives it structure, but the roots are still a mystery."

Alexander Kosovichev, a senior scientist from Stanford University working on the Soho project, said it is the first time scientists have been able to look below the surface of a sunspot. "What we found is that sunspots aren't static but consist of very strong, downward flows of plasma travelling toward the interior of the Sun at speeds of about 3,000 mph," Dr Kosovichev said.

The research team used helioseismology – the measurement of sound waves passing through the Sun – to analyse the inner workings of a sunspot. The technique is similar to the way doctors monitor a foetus using ultrasound.