Published in The Astrophysical Journal, the team was led by the University of Texas at Austin (UT Austin) and included scientists from the University of Chicago. In 2014, astronomers spotted a sudden bright spot in the sky, a sign of a star exploding in space.
When an exploding star was first spotted, astronomers around the world scrambled to track it with telescopes because the light it emitted changed rapidly over time. By watching its evolution, using telescopes that can see visible light as well as X-rays, radio waves and infrared, scientists can deduce the physical characteristics of the system.
By doing this multiple times, astronomers have identified signatures and grouped these exploding stars into one category. 2014C, as this particular event was named, looked like a so-called Type Ib supernova. They are what happens when the largest known star in the universe dies.
In fact, scientists believe that 2014C may have initially been not one but two stars orbiting each other, one larger than the other. More massive stars evolve faster, expand, and the hydrogen gas in their outer layers is sucked away. When it finally ran out of fuel, its core collapsed, causing a massive explosion.
However, observations in the first 500 days after the explosion showed that it emitted more X-rays over time, which is unusual and seen only in a few supernovae. “It shows that the shock wave is interacting with dense matter,” said Vikram Dwarkadas, a research professor of astronomy and astrophysics at the University of Chicago.
The team set out to gather all the data on 2014C, including new data they obtained as well as data from studies over the past eight years, and put it into a coherent picture of what happened to the star.
X-ray emissions, infrared light, and radio waves all show unique patterns of increasing and then decreasing. Meanwhile, the optical light — as measured by UT Austin’s Hobby-Eberly telescope — appears to remain stable. The radio signal showed that the shock wave was expanding at a very high speed, while the optical light showed a slower speed.
The researchers believe that the strange behavior is related to the dense clouds of hydrogen gas around the two stars that were left over from their early lives. When the star exploded, it created a shock wave that traveled in all directions at 67 million miles per hour. When the shock wave reaches this cloud, its behavior will be affected by the shape of the cloud.
In the simplest model, this cloud layer will be assumed to be spherical and symmetrical. However, if the cloud forms a “doughnut” around the two stars (that is, thicker around the middle), the thicker part of the ring will slow down the shock wave, appearing to move slower in optical light substance. Meanwhile, in thinner areas, the shock wave rushes forward, as seen in radio waves. “The scene is like water hitting a stone in the middle of the river,” Dwarkadas said.
The problem remains, the scientists say, but the inhomogeneity could explain the different velocities of the shock waves displayed by different wavelengths. Scientists say the study provides valuable clues about the evolution of these stars and the loss of mass in these systems, and in a larger sense, the life and death of these relatively mysterious stars.
