The twisted shockwaves of an exploded star
Copyright: NASA/ESA/Hubble Heritage (STScI/AURA) - ESA/Hubble Collaboration.
Acknowledgment: J. Hester (Arizona State Univ.).
Discovered on 5 September 1784 by astronomer William Herschel, the
Veil Nebula was once a star. Now it is a twisted mass of shock waves
that appears six times larger than the full Moon in the sky.
This
Hubble Space Telescope image shows just a small part of the nebula, a
region known as the ‘south-eastern knot’. The entire nebula is about 50
light years in radius, and is located almost 1500 light years away.
Ten
thousand years ago, the Veil Nebula did not exist. Back then, it was a
star, much brighter and larger than our own Sun, burning furiously
thanks to the nuclear furnace in its centre. As those reactions faltered
when its fuel was exhausted, the star collapsed and exploded.
This
is estimated to have happened some 5000–10 000 years ago. Sky watchers
would have seen the star brighten enormously over the course of a day or
two. It would have become brighter than a crescent moon.
Such a
titanically destructive event is called a supernova. Modern measurements
show that a supernova can outshine the combined light of 100 billion
normal stars. Over the course of a week or so, our ancestors would have
watched the fireball fade back into obscurity, only to be rediscovered
millennia later by William Herschel as an expanding ball of gases in
space.
During the star’s final detonation, it flung its outer
layers into space at more than 600 000 km/h. What we see now is these
layers colliding with the surrounding gases of interstellar space.
The
energy imparted in the collision heated the gas to millions of degrees,
causing it to emit light. The wavelength of this light depends upon the
atoms present in the excited gas. In this image, blue shows oxygen,
green shows sulphur, and red shows hydrogen.
Supernova explosions
are important because they seed the Universe with heavy chemicals,
building all the elements heavier than iron. They are rare in our
galaxy, with only one or two stars exploding over the course of a
century.
The Hubble Space Telescope is a project of international
cooperation between ESA and NASA. This image was taken with the Wide
Field and Planetary Camera 2, and was first published in July 2007.
Source: ESA/Images
