Reasons to Believe

Better Candles

We don’t usually think of huge explosions as being of much value except to destroy things.

However, some of the biggest explosions in the universe are providing us with the most accurate tools for measuring distances out to the edge of our observable universe. And they just got better.

I am referring to Type Ia supernovae. These events in the life of some stars give off light equivalent to the brightness of a whole galaxy of several hundred billions stars. Consequently, they can be seen from enormous distances. Besides their extreme brightness, the most important feature of Type Ia supernovae is that the light-intensity of the explosion as a function of time follows a curve that is the same for all events. As a result, they can be used as a standard candle. If its absolute brightness curve is the same for every event, then the dimming of its brightness is due to its distance from us and, therefore, can be used to determine this distance.

In what way have these standard candles gotten better? As a result of recent observations, by two astronomers, Rasmus Voss and Gijs Nelemans, we have greater confidence that the absolute brightness of a Type Ia supernova is, in fact, the same each time we see one explode.

Astronomers propose two different models to explain what brings about these incredible events. The first, called the accretion model, involves a binary star system where a white dwarf star accretes matter from its companion star, slowly growing in mass until it nears about 1.38 solar masses. The temperature of its core then rises to the point of initiating a runaway fusion reaction, resulting in the supernova event. White dwarf stars undergoing this kind of mass accretion have also been known to give off soft X-ray emission. The second, called the merger model, also involves a binary star system, but the explosion is triggered by a rapid direct merger of the two stars. Astronomers do not expect this model to give off X-ray emission, unless other unusual factors cause the merger to be slowed down to occur over thousands of years.

What Voss and Nelemans have discovered is soft X-ray emission coming from a binary star system prior to its going supernova. They did this by noting the location of a particular event (2007on in the elliptical galaxy NGC 1404) and looking for the X-ray emission images archived from some time earlier. This result, combined with other information they had about the object, led them to conclude that the better model for Type Ia supernovae is the accretion model. Establishing this provides greater confidence in our understanding of the processes leading up to this kind of supernova, and the assumption that its absolute brightness is, indeed, constant, or can be corrected for.

One of the most important discoveries made using Type Ia supernova is the accelerating expansion of our universe, adding to the growing body of evidence for the greatest level of fine-tuning yet. Gaining confidence in these measurements yields more support for the RTB creation model, which depends on this fine tuning to demonstrate the Creator’s design.

Subjects: Universe Design

Dr. David Rogstad

Dr. Dave Rogstad received his PhD in physics from Caltech and worked over 30 years for NASA’s Jet Propulsion Laboratory. Though now retired, Dave continues to serve as an RTB board member and participates regularly in several RTB podcasts.