In 1604, a white dwarf star went supernova. This is very normal behavior for a white dwarf star; but this one, at a distance of just 20,000 light-years from Earth, was visible to the naked eye, and documented by astronomers around the world, including the German astronomer Johannes Kepler.
Kepler’s Supernova, as it became known, is still expanding to this day, blowing the star’s gut into space. And according to new research, it is not slowing down. Knots of material in the ejecta move at speeds of up to 8,700 kilometers per second (4,970 miles per hour) – more than 25,000 times faster than the speed of sound in the Earth’s atmosphere.
You might think “Duh, space is a frictionless vacuum, things will just keep moving forever”, but a cloud of puns could slow material down by slowing it down. And it was thought that this might be the case for Kepler’s Supernova.
That’s because, as we now know, Kepler’s Supernova was something known as a Type Ia supernova. This takes place when a white dwarf star in a binary system cannibalizes its companion, and gathers so much mass that it is no longer stable – resulting in a cosmic boom.
But not all of the material thrown off the companion star makes its way to the white dwarf. Instead, it collects in a cloud around the binary system, what we call the circumstellar medium. As the white dwarf goes supernova, it explodes out into this medium.
Because of its proximity and relative shortness, Kepler’s Supernova is now one of the most important objects in the Milky Way for studying the evolution of Type Ia supernovae. And a wealth of data dating back decades has helped reveal how fast the supernova ejecta travels.
A team of astronomers led by Matthew Millard University of Texas at Arlington used images of the supernova obtained by the Chandra X-ray Observatory of 2000, 2004, 2006, 2014 and 2016 to track 15 nodes of material in the supernova ejecta, and observe their changes in position to calculate their velocity in three-dimensional space.
Some of the nodes appear to be slower, as expected from interaction with the circumstellar medium.
To the team’s surprise, their measurements show that other nodes expand almost freely, 400 years after the event – and that their velocities, averaging 4,600 kilometers per second (2,860 mps), are comparable to those seen in optical observations of supernovae. in other galaxies only days or weeks after the actual explosion.
This suggests that at least some of the supernova material can blow directly through the circumstellar medium without slowing it down.
Interestingly, the indications of these nodes are not uniformly distributed. Eight of the 15 knots move away from Earth; but two move in it (the direction of the remaining five could not be determined).
This asymmetry in direction suggests that the explosion itself may have been asymmetric; or, there is an asymmetry in the circumstantial medium along our line of sight. However, it is not known at this point – further study is needed.
However, the asymmetry may reveal information about the supernova explosion itself. Four of the faster nodes are close together, moving in the same direction, and have similar elemental abundance. This, the researchers note, suggests that they originated from the same region on the surface of the proponent of the white dwarf.
In all, their findings suggest that the supernova itself may have been unusually energetic for a Type Ia. Measuring the velocities of more ejecta nodes in the coming years could help confirm their measurements and calculations, build a more complete three-dimensional map of the distribution of the material, and place constraints on just how energetic that explosion is. could have been.
The study was published in The Astrophysical Journal.
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