This could help improve measurements of the universe’s expansion.
Supernovae are exploding stars. In fact, they are the largest explosions that occur in the known universe and are one of the most extreme environments. Imagine a star dozens of times the size and mass of our own sun that violently dies and explodes faster than you can say the word ‘supernova.’
But not all supernovae are the same. They come in many different flavors, one of them being “extraordinary.” These are brighter than normal supernovae, and according to astronomers from Japan, new information about the origin of these extraordinary explosions could help improve measurements of the universe’s expansion and advance our understanding of dark energy — the mysterious anti-gravity energy that is driving the expansion.
To study the expansion of the universe, astronomers look to Type 1a (“One-A”) supernovae. These supernovae — which include extraordinary — are known as “standard candles” as they emit the exact same level of brightness at all times. This is because of their physics: Type 1a supernovae change from stable to explosive at almost the exact same point in time in their evolution. This means that their brightness is consistent star to star. By using this brightness, astronomers can estimate the expansion rate of the universe.
But it turns out there is a problem with this method, and it is the fault of these extraordinary supernovae. Since they are much brighter than they should be, they may be contaminating the samples used for cosmological research, distorting the results and leading to inaccurate measurements of the universe’s expansion.
To account for this, astronomers need to figure out the origins of both normal and extraordinary supernovae to determine if the extra bright stars can be excluded from the samples.
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Even though astronomers have known about the existence of extraordinary stars for over 30 years, their origin is still highly debated. There are two popular scenarios for their evolution, both of which involve a binary system — two stars orbiting around each other. In the first scenario, accretion, the binary system is composed of one white dwarf and one normal star. The second scenario is known as a merger, where the binary system is formed by two white dwarfs.
To determine the origin, Masayuki Yamanaka, a Taro Hirao Foundation Researcher at Konan University, and his colleagues, observed an extraordinary supernova candidate, SN 2012dn, using 11 telescopes in Japan through OISTER (Optical and Infrared Synergetic Telescopes for Education and Research) for 150 days. Interestingly, the team discovered a strong infrared emission that has not been seen in typical supernovae. After performing detailed analysis of the infrared emission, the team concluded that the ejected material supports the “accretion” scenario.
In this scenario, gas is transferred onto the surface of the white dwarf from the companion star. During the transfer, some of the material escapes from the system, forming a dense gas surrounding the pre-supernova-explosion star system. The team’s observations indicate the SN 2012dn actually exploded while surrounded by this dense gas.
Next, the team will observe a normal Type 1a supernova to hopefully determine its origin.
The study can be found in the Publications of the Astronomical Society of Japan.
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