The immense wave of energy, the most powerful ever recorded from beyond the sun, caused at least two satellites to shut down briefly. But it reached the earth's surface at a strength equal only to a typical, single dental X-ray.

``We've been monitoring things like this for 30 years and we've never seen anything like this before,'' Kevin Hurley, a research physicist at the University of California, Berkeley, said yesterday at a NASA news conference.

The burst of gamma and X-ray radiation struck the earth over the Pacific Ocean at night on August 27 and was so powerful that it temporarily ionised the upper atmosphere just as the sun does in the daytime, said Hurley.

Seven scientific satellites, five in orbit of the Earth, one approaching an asteroid far beyond, and one near the orbit of Jupiter, alldetected the massive eruption. Hurley said the burst was so intense that two of the satellites were forced to shut down to protect their electronics.

However, the energy was largely absorbed by the upper atmosphere and only a minuscule amount of radiation reached the earth's surface. It posed no hazard to life, Hurley said.

The eruption came from a neutron star, called `SGR190014', in the constellation Aquila some 20,000 light years away. A neutron star is the collapsed core left after a massive star explodes. A light year is about 9.5 trillion km.

Astronomers said it is extremely rare for such a distant stellar explosion to have any effect on Earth, attesting to the immensity of the energy release.

They estimated that the energy, if captured and put to use, could power all of the earth's energy needs for a billion billion years -- that is one billion periods of one billion years.

``In this five-minute-long flash we saw as much energy as there will be coming from the sun for the next 300 years,''said Hurley.

``If we could harness this energy we would have enough power for every city, every village, every light bulb until the end of the universe and far beyond.''

The source star already was being studied because it is one of the four known members of a class of stellar objects called `soft gamma ray repeaters'. These are neutron stars that put out steady flashes of gamma rays.

But the extreme energy burst last month also suggests that the object is a magnetar -- a weird type of star first suggested by astrophysicists Robert Duncan of the University of Texas, Austin, and Christopher Thompson of the University of North Carolina, Chapel Hill.