Research box title
Astronomers turn the clock back on the expanding remains of a nearby, exploding star. Using NASA’s Hubble Space Telescope, they retracted the fast shrapnel from the explosion to calculate a more accurate estimate of the location and time of the stars’ explosion.
The victim is a star that exploded long ago in the Small Magellanic Cloud, a satellite system to our Milky Way. The doomed star left behind an expanding, gaseous corpse, a supernova remnant named 1E 0102.2-7219, which NASA’s Einstein Observatory first discovered in X-rays. Like detectives, researchers sifted archive images taken by Hubble and analyzed observations of visible light ten years apart.
The research team, led by John Banovetz and Danny Milisavljevic of Purdue University in West Lafayette, Indiana, measured the velocities of 45 frog-footed, oxygen-rich clods of ejection thrown by the supernova explosion. Ionized oxygen is an excellent tracer because it glows most brightly in visible light.
To calculate an accurate blast age, the astronomers selected the 22 fastest moving ejections or nodes. The researchers determined that these targets would be least delayed by passage through interstellar material. They then tracked the knots’ movement backwards until the excrement collapsed at some point to identify the explosion site. Once known, they were able to calculate how long it took the fast knots to travel from the blast center to their current location.
According to their estimate, light from the explosion came to earth 1700 years ago during the decline of the Roman Empire. However, the supernova would have been visible only to inhabitants of Earth’s southern hemisphere. Unfortunately, no records of this titanic event are known.
The researchers’ results differ from previous observations of the supernova’s explosion site and age. Earlier studies, for example, exploded up to 2,000 and 1,000 years ago. However, Banovetz and Milisavljevic say their analysis is more robust.
“In a previous study, images taken years apart were compared to two different cameras on Hubble, the Wide Field Planetary Camera 2 and the Advanced Camera for Surveys (ACS),” Milisavljevic said. “But our study compares data taken with the same camera, the ACS, which makes the comparison much more robust; the nodes were much easier to detect with the same tool. This is proof of Hubble’s longevity that we could make such a clean comparison of images taken ten years apart. ‘
The astronomers also used the sharp ACS images to choose which feces to analyze. In previous studies, researchers averaged the speed of all the gas debris to calculate an explosion age. However, the ACS data revealed areas where the ejection slowed down as it struck in denser material thrown by the star before exploding like a supernova. Researchers did not include the nodes in the sample. They need the ejection that best reflects the original velocities of the explosion, and use it to determine an accurate age estimate of the supernova explosion.
Hubble also clocked the velocity of a suspected neutron star – the crushed core of the doomed star – that was ejected from the explosion. Based on their estimates, the neutron star must move more than 2 million miles per hour from the center of the explosion to reach its current position. The suspected neutron star has been identified in observations with the Very Large Telescope of the European Southern Observatory in Chile, in combination with data from NASA’s Chandra X-ray Observatory.
“It’s pretty fast and at the extreme point of how fast we think a neutron star can move, even if it got a kick out of the supernova explosion,” Banovetz said. “More recent investigations question whether the object is actually the surviving neutron star of the supernova explosion. It may just be a compact bunch of supernova ejection that is illuminated, and our results support this conclusion overall.”
The hunt can therefore still go to the neutron star. “Our study does not solve the mystery, but it does give an estimate of the velocity for the candidate neutron star,” Banovetz said.
Banovetz will present the findings of the team on January 14 during the winter meeting of the American Astronomical Society.
The Hubble Space Telescope is a project of international collaboration between NASA and ESA (European Space Agency). NASA’s Goddard Space Flight Center in Greenbelt, Maryland, controls the telescope. The Space Telescope Science Institute (STScI) in Baltimore, Maryland, conducts scientific operations of Hubble. STScI is operated for NASA by the Association of Universities for Research in Astronomy in Washington, DC