A newly deployed Nasa-funded scientific instrument has helped to provide the best ever views of a powerful interstellar explosion known as a nova.

The Keck Interferometer at the W M Keck Observatory in Hawaii helped to produce the first unified model for a nearby nova called RS Ophiuchi.

"We were getting ready for a routine engineering run when all of a sudden the nova went off," said team member Marc Kuchner of Nasa's Goddard Space Flight Center.

"It was very bright and easy to observe, so we took this opportunity and turned it into gold."

Kuchner and his colleagues used the 'nulling' mode of the Keck Interferometer, which combines starlight using two 10-metre telescopes.

In the nulling mode, the interferometer suppresses the blinding light of a star allowing researchers to study the surrounding environment.

The instrument can observe very faint objects near bright sources and produces 10 times more resolving power than a single Keck telescope working alone. It is the only instrument of its kind in operation.

The Keck Nuller was undergoing tests on 12 February 2006, when a nova flared up in the Ophiuchus constellation.

The system consists of a white dwarf and a red giant. The red giant is gradually shedding its massive gaseous outer layers, and the white dwarf is sweeping up much of this wind, growing in mass over time.

As the matter builds up on the white dwarf's surface it eventually reaches a critical temperature that ignites a thermonuclear explosion causing the system to brighten 600-fold.

RS Ophiuchi was previously seen to blow in 1898, 1933, 1958, 1967 and 1985, so astronomers were eagerly anticipating the 2006 eruption.

Just 3.8 days after the nova was detected, the group observed the explosion with the Keck Nuller.

The team set the instrument to cancel out the nova's light, allowing the group to see the much fainter surrounding material. The group next adjusted the nuller to observe the extremely bright blast zone.

The instrument, surprisingly, saw no dust in the bright zone, presumably because the nova's blast wave vaporised the dust particles.

But at distances starting at around 20 times the Earth-Sun distance, the nuller recorded the spectral signature of silicate dust. The blast wave had not yet reached this zone, so the dust must have pre-dated the explosion.

"This flies in the face of what we expected. Astronomers had previously thought that nova explosions actually create dust," said Richard Barry at Goddard, lead author of a paper on the Keck observations that will be published in The Astrophysical Journal.