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Cosmos shines light on missing matter

Helix nebula

Hundreds of planetary nebulae with intriguing shapes like this helix nebula have been found by an Australian-led team (Image: NASA, NOAO, ESA, Hubble Helix Nebula Team, M Meixner/STScI and TA Rector/NRAO)

The discovery of over 1000 glowing planetary nebulae could help balance cosmic accounts, says an international team of astronomers.

The researchers say that their discovery could help them calculate what happens to stars' missing matter, mass that seems to be 'lost' when they die.

Dr Quentin Parker, of Australia's Macquarie University in Sydney, and colleagues, say they have found 900 new planetary nebulae in the Milky Way and 500 in the neighbouring Large Magellanic Cloud.

"Planetary nebulae are the death throes of stars," says Parker, who is also with the Anglo-Australian Observatory.

They are glowing regions of ionised gas that average-sized stars like our Sun throw off when they get old.

The gas the dying star ejects interacts with the environment around it, such as the interstellar medium, to form weird and wonderful shapes.

These have been given names like the cat's eye, hourglass, helix, ant and red spider.

Missing matter

Studying planetary nebulae helps tell us about how stars' matter is recycled from old to new stars.

Nebulae last for tens and thousands of years so it's important for astronomers to study both young and old ones.

In general, it has been a lot easier for astronomers to find younger nebulae because they glow brighter.

But Parker and colleagues have been able to find the fainter older ones and are now confident that they have representative sample of different ages, especially of nebulae close to our Sun.

The mystery about dying stars is that they seem to lose much more mass than what appears to be thrown off in their nebulae. Some 85% of the mass appears to be unaccounted for.

Parker hope that analysing the hundreds of new nebulae discovered will help explains where the extra mass goes.

In the team's more detailed study of the Large Magellanic Cloud the team has found numerous extremely faint haloes around 60% of the planetary nebulae there.

Parker says one theory is that these represent pulses of mass shed from the star before the nebula itself is ejected.

"We suspect this is where much of the missing mass resides," he says.

A boost in numbers

While it took over 100 years to discover 1500 planetary nebulae in our galaxy, Parker and colleagues' recent discovery boosted the number by 60% in just a few years.

The 500 found in the Large Magellanic Cloud adds to 300 already known in that galaxy.

The researchers made the discovery using the UK Schmidt Telescope at Siding Spring Observatory in western New South Wales.

They used a special filter on the telescope to highlight a hallmark wavelength of hydrogen gas in planetary nebulae.

Parker hopes to take images of some of the new planetary nebulae using the high-resolution capability of the Hubble Space Telescope.

The research was published recently in the Monthly Notices of the Royal Astronomical Society.
