Hubble snaps dying stars

Planetary nebula SMP 93: A so-called 'bi-polar'

By BBC News Online science editor Dr David Whitehouse

Scientists using the Hubble Space Telescope (HST) have made detailed observations of 27 dying stars in a companion galaxy to ours called the Large Magellanic Cloud (LMC).

The observations will help them understand the cosmic "carbon cycle" which has been essential for life on Earth.

SMP 27 is called a "quadrupolar" nebula

The observations represent highly detailed study of different types of so-called planetary nebulae, which are large discs of gas thrown off by stars late in their evolution.

In the HST pictures, colour corresponds to temperature. Blue represents hotter regions of the nebulae and red the cooler parts.

Object SMP 93 is an example of a so-called bipolar nebula, in which twin lobes of gas project away from a dying star. SMP 10 has a pinwheel shape and is known as a 'point-symmetric' nebula.

SMP 4 has an elliptical appearance, and SMP 27, consisting of four lobes of gas, is called a "quadrupolar" nebula.

SMP10 is called the "pinwheel"

Scientists are interested in these stellar relics because they are all at roughly the same distance - about 168,000 light-years - from Earth.

Knowing the distance to these objects allows astronomers to compare their shapes and sizes, and to contrast the brightness of their central stars.

By sampling this population, scientists have noticed that the bipolar nebulae are richer in some heavier elements, such as neon, than those with a more spherical shape.

Neon is produced only when massive stars die in supernova explosions. A higher abundance of neon in 'bipolar' planetary nebulae indicates that their mother stars were born more recently than those that created the more symmetrically shaped clouds of gas.

SMP4 is an elliptical nebula

Astronomers know that stars that form planetary nebulae produce a lot of carbon which is essential for life on Earth.

The question of how life-forming atoms were made is at the heart of understanding how and why life evolved in our own Solar System shortly after our Sun had formed from clouds of carbon-enriched gas and dust 4.6 billion years ago.

Astronomers using these planetary nebulae images, together with spectroscopic information from ground-based observatories, hope to gain insights into the carbon cycle in the LMC.

The mother stars of these planetary nebulae produce carbon deep in their interiors. In the last few thousand years of their active lives, just before ejecting planetary nebulae, these stars are able to dredge up the carbon locked deep in their cores.

They go through a 'carbon star' phase and then fling the carbon-rich gas into space as they form planetary nebulae, material for new generations of stars and planets.