Imagine a supernova exploding in our galaxy. In fact, a number have. One of the most recent occurred in 1054 AD in the constellation Taurus. Known today as the Crab Nebula, the object was so bright it could be seen even with the Sun overhead. Even one thousand years later the Crab ranks as the brightest steady source of very high-energy gamma rays in the sky. Although it may take a hundred thousand years to explode, astronomers recently found another soon-to-be supernova.
This newly found object has piqued cosmologist’s interest because it will explode as a Type Ia supernova. Most single stars end their life in a fairly mundane fashion. For example, as the Sun exhausts its hydrogen fuel, it will collapse, start fusing helium, and expand into an asymptotic giant branch star. Its radius will grow larger than Earth’s orbit. After blowing off much of its outer layers and exhausting its helium fuel, the Sun will collapse again into an object called a white dwarf. Although it will still retain a large fraction of its current mass, its radius will be the size of the Earth.
Some white dwarfs have a companion star. If the companion is close enough, the white dwarf will grow in mass by stealing from the companion. When the mass of the white dwarf exceeds 1.4 times the mass of the Sun, it explodes as a Type Ia supernova. Because all Type Ia supernova occur under the same conditions, they all exhibit a uniform brightness. And since they are so bright, Type Ia can be seen from across most of the observable universe.
For the past decade, researchers have been using these supernovae to measure the expansion history of the universe. In fact, the mysterious dark energy causing the universe to expand faster and faster was discovered using these objects. Consequently, a recently discovered white dwarf has caught cosmologists’ interest.
A team of Italian astronomers found a white dwarf accreting matter from a nearby companion and, thus, emitting x-rays. Because we view the system on edge, the companion eclipses the white dwarf. Detailed measurements during the eclipse allowed the team to determine that the mass of the white dwarf was nearly 1.3 times the mass of the Sun. If theoretical accretion rates are correct, the white dwarf will gain enough mass to detonate as a Type Ia supernova somewhere between 10,000 to 200,000 years from now.
Why is this significant? First, this system resides less than a kiloparsec away. With a distance this close, the amount of energy released during the supernova could significantly reduce Earth’s capacity to support life. (For an assessment of the risk from a galactic Type Ia supernova, see this article, paying particular attention to section 4 regarding gamma rays.) Second, the proximity of this binary system may provide an opportunity for astronomers to better understand the characteristics of Type Ia supernovae.
The rarity of Type Ia supernovae within the Milky Way enables our galaxy to contain a habitable planet like Earth. Yet enough of these objects exist throughout the universe to assist scientists in their quest to understand the nature of the universe. Such a balance comports well with a Creator who wants to make a place for humans to reside and ensure that humanity can properly study the creation also.
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