A massive star exploded in the Small Magellanic Cloud between 2,000 and 1,000 years ago and left behind an expanding, gaseous remnant called 1E 0102.2-7219. By using the NASA/ESA Hubble Space Telescope, astronomers retraced the speedy shrapnel from the stellar explosion to calculate a more accurate estimate of the location and time of the event.
This Hubble image shows the supernova remnant 1E 0102.2-7219. Image credit: NASA / ESA / J. Banovetz & D. Milisavljevic, Purdue University.
1E 0102.2-7219 is located approximately 202,000 light-years away in the constellation of Tucana.
The object was discovered in 1981 by NASA’s Einstein Observatory during a survey of the Small Magellanic Cloud.
Like detectives, Purdue University astronomers John Banovetz and Danny Milisavljevic and their colleagues sifted through archival images taken by Hubble, analyzing visible-light observations spanning 19 years.
The researchers measured the velocities of 45 tadpole-shaped, oxygen-rich clumps of ejecta flung by the supernova blast.
“A prior study compared images taken years apart with two different cameras on Hubble: the Wide Field Planetary Camera 2 (WFC2) and the Advanced Camera for Surveys (ACS),” Dr. Milisavljevic said.
“But our study compares data taken with the same camera, the ACS, making the comparison much more robust; the knots were much easier to track using the same instrument.”
To calculate an accurate explosion age, the scientists picked the 22 fastest moving ejecta clumps, or knots.
They determined that these targets were the least likely to have been slowed down by passage through interstellar material.
They then traced the knots’ motion backward until the ejecta coalesced at one point, identifying the explosion site.
Once that was known, they could calculate how long it took the speedy knots to travel from the explosion center to their current location.
According to their estimate, light from the blast arrived at Earth 1,738 years ago, during the decline of the Roman Empire.
However, the supernova would only have been visible to inhabitants of Earth’s southern hemisphere. Unfortunately, there are no known records of this titanic event.
The authors also measured the speed of a suspected neutron star that was ejected from the blast.
Based on their estimates, it must be moving at more than 3 million kmh (1.86 million mph) from the center of the explosion to have arrived at its current position.
The suspected neutron star was identified in observations with ESA’s Very Large Telescope in Chile, in combination with data from NASA’s Chandra X-ray Observatory.
“That is pretty fast and at the extreme end of how fast we think a neutron star can be moving, even if it got a kick from the supernova explosion,” Dr. Banovetz said.
“More recent investigations call into question whether the object is actually the surviving neutron star of the supernova explosion.”
“It is potentially just a compact clump of supernova ejecta that has been lit up, and our results generally support this conclusion.”
“Our study doesn’t solve the mystery, but it gives an estimate of the velocity for the candidate neutron star.”
“A new epoch of Hubble images would expand our understanding of 1E 0102.2-7219,” the astronomers said.
“Such images would enable multi-epoch analysis that would tighten uncertainties on proper motion, estimate potential deceleration, and further constrain the center of expansion and explosion age.”
“This, in turn, would test our conclusion that non-homologous expansion of 1E 0102.2-7219’s optical knots is caused by interaction of the original supernova blast wave with inhomogeneous circumstellar material.”
The results will be published in the Astrophysical Journal.
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John Banovetz et al. 2021. The Center of Expansion and Age of the Oxygen-rich Supernova Remnant 1E 0102.2-7219. ApJ, in press; arXiv: 2101.05288
