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October 27, 2004 02:00 PM (EDT)

News Release Number: STScI-2004-34

Stellar Survivor from 1572 A.D. Explosion Supports Supernova Theory

October 27, 2004: An international team of astronomers is announcing today that they have identified the probable surviving companion star to a titanic supernova explosion witnessed in the year 1572 by the great Danish astronomer Tycho Brahe and other astronomers of that era.

This discovery provides the first direct evidence supporting the long-held belief that Type Ia supernovae come from binary star systems containing a normal star and a burned-out white dwarf star. The normal star spills material onto the dwarf, which eventually triggers an explosion.

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Q & A: Understanding the Discovery

  1. 1. What is the difference between a nova and a type Ia supernova?

  2. Both nova and Type Ia supernova explosions are believed to occur on white dwarf stars, but the causes of the two outbursts are different. White dwarfs are the extremely small and dense remnants of the evolution of ordinary stars like our Sun after they have exhausted their nuclear fuel. Novae arise from close pairs of stars in which one is a white dwarf and the other is still an ordinary star similar to the Sun. Hydrogen gas is transferred from the solar-type star onto the surface of the white dwarf, where it slowly accumulates. Eventually, enough hydrogen builds up to the point that a new episode of nuclear fusion begins, and the resulting explosion blasts the outer layers of the white dwarf into space.

    Type Ia supernovae are also believed to originate in binary systems in which one (or possibly both) stars is a white dwarf. Again, the other star transfers matter to the white dwarf, gradually increasing its mass. When the mass of the white dwarfs approaches the Chandrasekhar limit (around 1.4 times the mass of the Sun), the white dwarf starts to collapse and heat up, and fusion of carbon nuclei starts throughout the dwarf. This leads to a titanic explosion, which consumes and destroys the entire star. Imagine a gigantic thermonuclear bomb about the size of the Earth but containing more mass than our Sun.

  3. 2. Why wasn’t the companion star destroyed by the explosion?

  4. The energy of the supernova certainly would have blasted away some of the companion's photosphere. But with the white dwarf destroyed, the companion's orbital momentum was converted into linear motion, and it flew away from the system on a tangent.

  5. 3. What will happen to the runaway star?

  6. The companion had enough velocity to leave the disk of our galaxy, depending on its trajectory. It will eventually bloat into a read giant star and then collapse down to a white dwarf. It probably will never pass close enough to another star to interact with it, but will remain a sole survivor of the ancient supernova blast.

  7. 4. Why is this supernova remnant so special?

  8. The supernova is believed to be the nearest Type Ia supernova to be recorded in human history. It appeared near the beginning of the astronomy revolution that was about to dawn with the theories of Nicholas Copernicus, observations of Galileo Galilei, and calculations of Johannes Kepler.

    Kepler's mentor, Tycho Brahe was awestruck by the supernova: "I suddenly and unexpectedly beheld near the zenith an unaccustomed star with a bright radiant light. Astounded, as though thunderstruck by this astonishing sight, I stood still and for some time gazed with my eyes fixed intently upon this star. It was near the stars, which have been assigned since antiquity to the asterism of Cassiopeia. I was convinced that no star like this had ever before shone forth in this location."

    Tycho's supernova may have even been alluded to in Shakespeare's "Hamlet." In the opening scene, two castle sentries refer to a particular star in the northern sky (the approximate location of the supernova) — and then discuss how celestial sightings often portend "fierce events." In this case, the apparition of a ghost:


    Last night of all, When yond same star that's westward from the pole Had made his course to illume that part of heaven Where now it burns, Marcellus and myself, The bell then beating one,—

    /Enter Ghost/


    Peace, break thee off; look, where it comes again!

    Shakespeare was only 8 years old when the supernova appeared, but it was the talk of the time, and he may have even viewed it!

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Credit: NASA, ESA, CXO and P. Ruiz-Lapuente (University of Barcelona)