Spaceflight Now: Breaking News

10 billion billion billion megaton bomb waits in space
Posted: July 24, 2000

Supernova 1987A as seen by the Hubble Space Telescope in July 1997. Photo: P. Garnavich (CfA), SINS
Astronomers at the University of Southampton have found a star that will produce one of the biggest explosions in our Universe. The star, known as KPD1930+2752, will explode within the next 200 million years. It is the first star of its kind to be found and may hold the clues to where the stuff that makes up our bodies comes from and perhaps to the future of the Universe itself.

KPD1930+2752 is actually two stars, one hot bright star and a faint, dense star known as a white dwarf. The hot star whirls around the white dwarf, just like the Earth revolves around the Sun, but travelling at over one million kilometers per hour, it takes only 137 minutes to complete one trip around its companion.

But KPD1930+2752 is doomed. Energy is being sucked away by 'gravitational waves' -- a type of energy predicted by Einstein's Theory of General Relativity -- so the stars will collide within the next 200 million years. What makes KPD1930+2752 special is that the star will then be too massive and dense to survive. The star will be ripped apart in a vast thermonuclear explosion bright enough to be seen from the other side of the Universe.

These explosions, known as Type Ia Supernovae, hurl their metallic debris into space, particularly iron, nickel and cobalt. Almost all the iron on the Earth comes from Type Ia Supernovae which exploded billions of years ago, including the iron in our blood.

Type Ia Supernovae seen in nearby galaxies all reach the same brightness when they explode, so astronomers can look for Type Ia Supernovae in very distant galaxies and use them to measure the distance-the fainter the supernova looks, the further away the galaxy is. By using this method, astronomers have found that the Universe is not only expanding, but that the expansion appears to be speeding up and will prevent the Universe collapsing in a 'Big Crunch'.

But this method only works if Type Ia Supernovae in distant galaxies are the same as the ones nearby. Astronomers have worried about this problem for several years because they have not been sure what causes Type Ia Supernovae.

Now that KPD1930+2752 has been found it can be studied in detail so that astronomers can work out how Type Ia Supernovae in distant galaxies might behave and so, perhaps, determine the fate of the Universe itself.

The discovery of KPD1930+2752 will be published in 'Monthly Notices of The Royal Astronomical Society'.

This Hubble Space Telescope image, taken in February 1994 with the Wide Field and Planetary Camera 2, shows the full system of three rings of glowing gas surrounding supernova 1987A. Located in a small galaxy called the Large Magellanic Cloud, the supernova is a massive star that exploded in about 165,000 BC, but its light didn't arrive here until February 1987. Photo: P. Challis (CfA)

The key observations of KPD1930+2752 were obtained in April using the Isaac Newton Telescope. The Isaac Newton Telescope is operated on the island of La Palma by the Isaac Newton Group in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias.

This research was supported by the Particle Physics and Astronomy Research Council.

KPD1930+2752 will be very distant from the Earth when it explodes so it poses no threat to us.

KPD1930+2752 is a subdwarf B star. It is about one fifth the size of the Sun and is about half as massive. Unlike normal stars, which are composed almost entirely of hydrogen, KPD1930+2752 is made of helium. It is not entirely clear how stars like KPD1930+2752 are made, but recent work suggests they are the remains of stars like the Sun which lose half their mass just before they complete the end of the red giant phase of their evolution. Only some small fraction of stars evolve this way and this is thought to be related to the fact that most subdwarf B stars are binary stars.

KPD1930+2752 will merge within 200 million years. The white dwarf will then gain extra mass from the subdwarf B star and will exceed a critical mass, called the Chandresekhar limit. This is thought to lead to a Type Ia supernova explosion.

There has been some debate among astronomers over the cause of Type Ia supernova explosions. Most agree that they are caused by the explosion of a white dwarf star which gains too much mass but what is not clear is how it gains this mass. There are many white dwarfs which are known to be gaining mass from a normal star, but these are made of hydrogen which causes a series of small explosions before the Chandresekhar limit is reached. This is what causes a nova explosion. To make a supernova, the white dwarf has to be supplied with helium, which explodes less easily but releases much more energy. KPD1930+2752 is the first star found where helium will be dumped onto a white dwarf star which will then exceed the Chandresekhar limit.