The recent discovery and subsequent observations of the supernova SN 2014J have led researchers to realize that the primary ‘yardstick’ used by astronomers to measure cosmic distances may not be such a constant after all.
Six weeks ago (on January 21), a super-bright supernova was discovered in the nearby galaxy of M82, by researchers in the UK. Located ‘only’ around 11.4 million light years from the Earth, the supernova was the brightest seen since SN1987A, over 27 years ago.
The real reason that the supernova is of such interest to researchers, though, isn’t the impressive brightness, it’s that it may be the closest Type Ia supernova in over 77 years — Type Ia supernovas are the primary ‘measuring sticks’ used by astronomers to measure the distances between objects in the cosmos.
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When University of California, Berkeley, astronomer Alex Filippenko’s research team looked for the supernova in data collected by the Katzman Automatic Imaging Telescope (KAIT) at Lick Observatory near San Jose, Calif., they discovered that the robotic telescope had actually taken a photo of it 37 hours after it appeared, unnoticed, on Jan. 14.
Combining this observation with another chance observation by a Japanese amateur astronomer, Filippenko’s team was able to calculate that SN 2014J had unusual characteristics — it brightened faster than expected for a Type Ia supernova and, even more intriguing, it exhibited the same unexpected, rapid brightening as another supernova that KAIT discovered and imaged last year — SN 2013dy.
“Now, two of the three most recent and best-observed Type Ia supernovae are weird, giving us new clues to how stars explode,” stated Filippenko, in reference to a third, apparently ‘normal,’ Type Ia supernova, SN 2011fe, that was discovered 3 years ago. “This may be teaching us something general about Type Ia supernovae that theorists need to understand. Maybe what we think of as ‘normal’ behavior for these supernovae is actually unusual, and this weird behavior is the new normal.”
It was observed several decades ago that Type Ia supernovae seem to “explode with about the same brightness, no matter where they are in the universe.” A trait which would make them good “standard candles” to judge distance with.
Subsequent research using this ‘fact’ then utilized “Type Ia supernovae to determine the distances to galaxies, compared distance with velocity and discovered that the universe is expanding faster and faster, rather than slowing down as expected.”
But if the brightness of Type Ia supernovae isn’t as constant as previously thought, then exactly how accurate is the previous research?
According to Filippenko: “While the latest discoveries do not contradict these results, refinements in understanding Type Ia explosions could help improve distance measurements and lead to more precise calculations of the expansion rate of the universe, thereby setting constraints on the nature of ‘dark energy’, a still mysterious energy comprising 70% of the universe and thought to be responsible for its acceleration.”
In addition to the findings related to measuring cosmic distances, the recent observations should lead to a better understanding of the types of stars involved in such explosions.
The explosion is categorized as a Type Ia supernova, which is theorized to be triggered in binary systems consisting of a white dwarf and another star — which could be a second white dwarf, a star like our sun, or a giant star.
In addition, the observations could yield insights into what kind of stars were involved in the explosion. Hubble’s ultraviolet-light sensitivity will allow astronomers to probe the environment around the site of the supernova explosion and in the interstellar medium of the host galaxy.
Because of their consistent peak brightness, Type Ia supernovae are among the best tools to measure distances in the universe. They were fundamental to the 1998 discovery of the mysterious acceleration of the expanding universe. A hypothesized repulsive force, called dark energy, is thought to cause the acceleration.
“Very, very early observations give us the most stringent constraints on what the star’s behavior really is in the first stages of the explosion, rather than just relying on theoretical speculation or extrapolating back from observations at later times, which is like observing adolescents to understand early childhood,” Filippenko stated.
The new findings were published in The Astrophysical Journal Letters.
Image Credit: W. Zheng and A. Filippenko, UC Berkeley; NASA/Goddard Space Flight Center