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The lives of stars
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| The Ring Nebula, M57. A planetary nebula. |
Most of the light and radiation we can observe in the Universe originates in stars – individual stars, clusters of stars, nebulae lit by stars and galaxies composed of billions of stars. Stars are spheres of glowing hydrogen and other chemical elements which produce their prodigious energy output by converting lighter elements to heavier ones through nuclear processes similar to those in hydrogen bombs. Like human beings they are born, mature and eventually die but their lifetimes are vastly longer than our own. Hubble has gone beyond what can be achieved by other observatories by linking together studies of the births, lives and deaths of individual stars with theories of stellar evolution. In particular Hubble’s ability to probe stars in other galaxies enables scientists to investigate the influence of different environments on the lives of stars. This is crucial in order to be able to complement our understanding of the Milky Way galaxy with that of other galaxies.
Uncovering the Galaxy’s stellar nurseries
Another area where Hubble’s work has been widely acknowledged is the linking of star formation with stellar evolution. Hubble’s infrared instrument, NICMOS, is capable of looking through the dust surrounding newly born stars. Some of the most surprising discoveries so far have come about by peering through the clouds of dust surrounding the centre of our Milky Way. Astronomers found that this centre, which was thought to be a calm and almost ‘dead’ region, is in fact populated with massive infant stars gathered into clusters.
The Cone Nebula
Stellar skeletons
The last phases of solar-like stars have been investigated through observations of planetary nebulae and proto-planetary nebulae. These are colourful shells of gas expelled into space by dying stars. The varying shapes and colours of these intricate structures with different colours tracing different, often newly created, chemical elements, have shown that the final stages of the lives of stars are more complex than once thoughtHubble was the first telescope to directly observe white dwarfs in globular star clusters. White dwarfs are stellar remnants and provide a ‘fossil’ record of their progenitor stars which shone so brightly that they long ago exhausted their nuclear fuel. Through these measurements it is possible to determine the ages of these ancient clusters which is an important cosmological tool.
Supernovae
Most scientists today believe that the expansion of the Universe is accelerating. This result came from combined measurements of remote supernovæ with most of the world’s top-class telescopes, including Hubble, and it was a very surprising one. Hubble has given these supernovae measurements an added precision, mostly due to its high resolution.
Gamma Ray Bursts
Gamma Ray Bursts emit very intense gamma-ray radiation for short periods and are observed a few times per day by special gamma-ray detectors on observatories in space. Today, partly due to Hubble, we know that these bursts originate in other galaxies - often at very large distances. Their origin has eluded scientists for a long time, but, after Hubble observations of the atypical supernova SN1998bw and the Gamma Ray Burst GRB 980425 a physical connection of these became probable.
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| Newly born massive stars in the Papillon Nebula |
The Eskimo Nebula. A planetary nebula. |
The rings surrounding supernova 1987A. |
Old star cluster Hodge 301 surrounded by supernova remnants |
Gerard Gilmore
Astronomer, University of Cambridge |
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"Hubble has in my view revolutionised the study of globular clusters – especially those
in other galaxies. These objects are so dense and the stars so tightly packed together
that it is almost impossible to separate the stars from each other with ground-based
telescopes. We have been able to measure what kind of stars they are composed of, how
they evolve and how gravity works in these complex systems." |
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The death of a giant - Supernova 1987A
When the first nearby supernova for centuries (Supernova 1987A) exploded in the Large Magellanic Cloud in 1987 it was scrutinised with every available telescope on Earth. On many occasions since its launch in 1990 Hubble has turned its gaze to the site of this unique event 150,000 light years away, and thanks to its very high resolution, it has been possible to monitor in detail the progress of the cataclysmic explosion. Hubble has seen two rings (and one central one) of gas on each side of the exploding star which were expelled by the dying star in its last death throes several thousand years before the final explosion. In recent years astronomers have watched as different parts of these rings are hit by the blast wave from the explosion as it expands through space.
SELECTED PRESS RELEASES
Extreme star birth in the Carina Nebula
New stars shed light on the past
Hubble's panoramic view of Orion Nebula reveals thousands of stars
oung stars sculpt gas with powerful outflows
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