Ia Supernovae can help us understand dark energy?
A study of one hundred galaxies has allowed a group of researchers to select a list of the best type Ia supernovae that can be used to better define the cosmic distances with an accuracy better than twice that previously obtained, and then to determine the rate of the accelerated expansion of the Universe.
A group of researchers have published in Science a list of Ia supernovae type (SN-Ia) that can be used to better measure cosmic distances and, therefore, to determine the rate of expanding of the space. Through analysis of satellite data GALEX (Galaxy Evolution Explorer) of NASA, the authors argue in their paper that this set of supernovae, which occur in the vicinity of young stars, however, provides their distance with a precision twice as good compared to that previously obtained.
“We found a population of SN-Ia whose brightness depends very precisely by the pace at which reduces the intensity of the radiation, which allows measuring their distance with high accuracy,” says Patrick Kelly of the University of California at Berkeley, author of the study. “Furthermore, we found that these supernovae are close to a population of hot young stars.”
These results are very important because they can be used to derive additional insight into dark energy, one of the greatest mysteries of modern cosmology. Dark energy is the main suspect responsible for the acceleration of the cosmic expansion, a phenomenon that was discovered in 1998. The key to measure this acceleration is given precisely by Type Ia supernovae, which account for astronomers a kind of “cosmic light bulb”. Imagine, for example, aligning a number of bulbs 60 Watt along a football field and stand at one end. It is obvious that the farthest light bulb does not appear as bright as the one closest to us, because of its distance. But since we know its brightness we can use the variation of its brightness according to a mathematical law to derive its distance.
The Ia supernovae type are called “standard candles” because they emit substantially the same amount of light. The physical mechanism that causes the explosion of the star is not yet clear and explosions, lighting the host galaxy, do not always occur evenly. They may differ considerably depending on several factors that appear to be related to the environment in which we find the star and its evolutionary history. It’s a bit like if our 60-watt bulb emits a light of 55 watts, thus it is obstructing the measure.
Kelly and his team have studied the reliability of this method by analyzing the environment in which they are a hundred Ia supernovae using data from GALEX that operates in the ultraviolet (UV) band. Populations of hot, young stars emit more UV radiation so GALEX can distinguish the galactic components that are younger from the older ones. The results of this study suggest that Ia supernovae type associated with hot young stars are the most reliable indicators of cosmic distances than their counterparts. “Most likely, these explosions are the result of young white dwarfs,” says Kelly.
“GALEX has explored the whole sky, allowing it to more easily identify these ‘standard candles’ and identify the next stellar explosions,” adds Don Neill, a member of the GALEX team at the California Institute of Technology in Pasadena who was not involved in the study. “Any optimization that will be performed on this method will have a direct impact on the theories that attempt to describe dark energy, allowing us, hopefully, to understand the secrets of this mysterious force responsible for the accelerated expansion of the Universe.”
Therefore, astronomers will be able to make even more precise measurements of the cosmological distance ladder focusing on this particular class of exploding stars. Finally, according to the authors, this method will allow us to explore the space up to 6 billion light years away, or maybe longer.