Previously undetected exploding star in the Milky Way spotted by XMM-Newton

Paris, July 19 : The XMM-Newton, which is the ESA's (European Space Agency's) orbiting X-ray observatory has discovered an exploding star in the Milky Way, which was missed by the legions of star watchers around the planet.

On 9 October 2007, ESA's orbiting X-ray observatory XMM-Newton was turning from one target to another. As it did so, it passed across a bright source of X-rays that no one was expecting.

The source was not listed in any previous X-ray catalogue, yet XMM-Newton was receiving some 50 X-rays every second from this mysterious object.

The only celestial object the XMM-Newton team could find at this location was a faint star, known only by its catalogue number USNO-A2.0 0450-03360039.

Acting quickly, Andy Read of the University of Leicester and Richard Saxton of ESA's European Space Astronomy Centre (ESAC), Spain, arranged for an astronomical telegram to be circulated across the Internet, informing other astronomers of the newly-discovered X-ray source.

Astronomers using the 6.5-m Magellan-Clay telescope at Las Campanas Observatory in Chile, found that USNO-A2.0 0450-03360039 had dramatically brightened by more than 600 times.

Analyzing the light from the source meant that they could classify the object as a nova.

Novae occur when a compact star, called a white dwarf, feeds off the gas of a nearby companion star.

When sufficient gas builds up on the white dwarf, a nuclear reaction begins releasing large quantities of energy, prompting the white dwarf to shoot up in brightness.

But there was a puzzle.

The incandescent explosion does not immediately release X-rays; the expanding cloud of debris created in the detonation temporarily masks them.

As this clears, the X-rays shine through. So, for XMM-Newton to see this nova, the explosion must have taken place many days before. Yet, no one had reported seeing it.

Usually, dedicated amateur and professional astronomers find novae by regularly sweeping the night sky for stars that suddenly brighten. This one, it seemed, had slipped the net.

Saxton contacted the robotic survey project ASAS and asked them to check their data.

They found the nova. It had taken place on 5 June 2007 and had been clearly visible, even to the unaided eye.

"Anyone who went outside that night and looked towards the constellation of Puppis would have seen it," said Saxton.

The nova is now officially designated V598 Puppis and is one of the brightest for almost a decade, doubling the irony that it was not spotted during its brilliant peak.

ANI