Star that birthed Tycho's supernova wasn't hot and bright

By Brooks Hays  |  Sept. 26, 2017 at 4:22 PM
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Sept. 26 (UPI) -- An international team of scientists from the United States, Australia and Germany have offered new insights into the origins of Tycho's supernova.

Until now, many astronomers assumed Tycho's supernova was formed by the explosion of a white dwarf that had been slowly stealing material from its companion star. But the latest analysis, published this week in the journal Nature Astronomy, suggests otherwise.

First observed 445 years ago by the astronomer Tycho Brahe, Tycho's supernova is the most famous example of a Type Ia supernovae, the violent nuclear disruption of a white dwarf.

In addition to serving as standard candles for cosmologists, Type Ia supernovae also play an important role in the formation and evolution of galaxies. The exploded shell of gas and dust serves as seed material for the next generation of stars.

Despite their cosmological importance, scientists still don't entirely understand their origins.

What's clear is that Tycho's supernova was caused by the thermonuclear disruption of a white dwarf star that reaches the Chandrasekhar mass limit, roughly 1.4 times the sun's mass. Unable to support so much mass, the stellar core collapses and explodes.

There are two main theories on how a white dwarf might reach the Chandrasekhar limit. A white dwarf could slowly accrete material from its stellar companion in a binary system, or a pair of white dwarfs in a binary system could merge. Astronomers believe the two possibilities would result in very different electromagnetic emissions signatures.

In the accretion scenario, the white dwarf would be extremely hot and luminous -- an intense source of X-ray and extreme ultraviolet photons. An explosion of such a star would ionize any and all gas within some 300 light-years. Because ionized gas is slow to become neutral again, an ionized nebula would persist for at least 100,000 years after such an explosion.

Thus, the detection of neutral gas in the vicinity of a supernova remnant can allow researchers to place upper limits on the temperature and brightness of its progenitor.

The most recent observations of Tycho's supernova remnant have revealed significant amounts of neutral gas. The findings rule out the possibility of an exploded hot and luminous white dwarf.

According to the latest analysis, Tycho's supernova was likely born of the explosion triggered by the merger of two white dwarfs in a binary system. However, scientists say other more exotic scenarios are also possible.

Topics: Tycho Brahe
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