One stellar explosion is not enough for attention. After appearing five times in pictures taken by the Hubble Space Telescope, a bizarre “reappearing supernova” is now helping scientists solve one of astronomy’s biggest mysteries: how fast the universe is expanding.
About 13.8 billion years ago, the universe as we know it was just a tiny dot in space containing all of the existing matter. Then there was an explosion: big Bang. This matter rushed out – and continues to do so today, all the time picking up speed.
Scientists have known about the expansion of the universe for almost a century. But how fast it expands is more of a mystery. The two methods of measuring this speed, called the Hubble constant, disagree. One of these methods is based on “standard candles” – using bright objects at a known distance to calculate the speed at which stars and galaxies are moving away from us. Supernovae, exploding stars that emit abundant and steady light, are one such important distance marker. Another method uses the “cosmic microwave background”, the leftover radiation from the Big Bang. The problem is that these two methods give different answers.
There are many explanations for the different meanings. Scientists may not have taken into account repulsive dark energy, a mysterious phenomenon that appears to be causing the universe to expand at an even faster rate. The universe may contain particles that we have not yet identified. Or one of the current calculations may simply be wrong.
“It’s a riddle” Patrick Kelly (will open in a new tab)assistant professor of physics and astronomy at the University of Minnesota and lead author of a new study of the Hubble constant, told Live Science.
Supernova Refsdal enters. Kelly first discovered this exploding star in 2014, when it exploded four times at different locations around the same cluster of galaxies. The supernova appeared in several places because the cluster’s extreme gravity warped and reflected the supernova’s light, creating what is called gravitational lens. Based on Refsdal’s “Hit the Mole” act, astronomers predicted that a supernova would reappear in 2015. came true (will open in a new tab).
In their new study, Kelly and colleagues triangulated measurements of the supernova’s location to calculate a new value for the Hubble constant. Results published May 11 in the journal The science (will open in a new tab), find a value for the Hubble constant that is much closer to the value obtained from the cosmic microwave background than from the standard candle method. The universe is expanding at about 41.4 miles per second (66.6 kilometers per second) per megaparsec (or for every 3.2 million light years).
But the findings did not end the debate; it is just another of many methods for studying the expanding universe. “They do not rule out [standard candle] supernova value,” Kelly said.
Supernova Refsdal is the first star of its kind to reappear in multiple images, but Kelly expects more in the future. According to Kelly, this should bring scientists closer to understanding the true meaning of the Hubble constant. “Once we have a few of these, it will be interesting what they all have to say together.”