Supernovae are some of the brightest objects in the night sky. They are the self-destruction of the largest stars, and on occasion can outshine entire galaxies. One particular type of supernova, involving the catastrophic dance of two stars, has mystified astronomers since it was first discovered in 1941; to date, it’s not clear what causes a supernova in a binary star system.
After observing the nuclear ashes of the youngest supernova in the Milky Way, a team of astronomers led by Harvard University has come up with a potential answer. At just 110 years old, they have concluded that this violent flash of light was produced by the spectacular collision of two white dwarfs. Publishing their results in the Astrophysical Journal, this finding implies that there are at least three broad ways to destroy a star via a supernova.
In single star systems with at least eight solar masses, the star explodes when it runs out of nuclear fuel to burn. The star’s immense gravitational field overcomes the increasingly weak heat emerging from its core, causing it to collapse before undergoing a titanic explosion. Type 1a supernovae, like the one observed in this study, require at least two stars to occur – that much, astronomers agree on.
One of the prevailing theories of how they happen is that a white dwarf, a stellar remnant that is unable to undergo fusion in order to produce heat, steals the atmosphere from a companion star. At a critical point, the white dwarf becomes massive enough to exert gargantuan pressures on its core; this initiates a runaway fusion reaction, which immediately leads to its obliteration.
This animation shows two white dwarfs merging. astropage.eu via YouTube
Most astronomers have thought that this companion star was an ageing red giant. However, a recent study revealed that a type 1a supernova was observed burning its nearby companion star, which turned out to be a main sequence star. Either way, the supernova was caused by the theft of another star’s atmosphere.
This new study, after observing supernova G1.9+0.3, gives credence to another theory of how type 1a supernovae occur. Using NASA’s Chandra X-ray Observatory and the National Science Foundation’s Jansky Very Large Array, they analyzed the high-energy bursts jettisoning from this young cataclysm. When an object is heated up, it gives off electromagnetic energy, and certain wavelengths apply to certain types of ignition.
The team concludes that the energy regime they’ve observed from this particular supernova could only have come about through one event: the collision of two white dwarfs. “We observed that the X-ray and radio brightness increased with time, so the data point strongly to a collision between two white dwarfs as being the trigger for the supernova explosion in G1.9+0.3,” said co-author Francesca Childs, an astrophysicist at Harvard University, in a statement.
This happens when two closely orbiting white dwarfs lose energy through the emission of gravitational waves, causing them to spiral inwards and merge. During this particular merger, they reached a critical mass that initiates a destructive, runaway fusion reaction, creating a supernova. In light of recent research, this new finding means that there are two ways to create a type 1a supernova, and at least three ways to kill a star overall.
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