A cosmic explosion that does not stop for 400 years

Astronomers were surprised to say that the streams of matter erupting from the Keplerian supernova have not lost their speed for several centuries – and this is not normal.

In 1604, the white dwarf went supernova. This is normal behavior for a white dwarf; only 20,000 light-years from Earth, it was visible to the naked eye and documented by astronomers around the world, including the German astronomer Johannes Kepler.

Supernova Kepler, as it came to be called, is still expanding to this day – the innards of the star burst into space. And, according to new research, this process is not slowing down. The material nodes in the ejection travel at speeds up to 8,700 kilometers per second – more than 25,000 times faster than the speed of sound in the Earth’s atmosphere!

You might think, “Yes, space is a vacuum without friction, matter will continue to move forever, what’s the big deal?” That’s right, but a cloud of space debris often slows down the movement of material within itself. Scientists believed that this process could have taken place in the case of Kepler’s supernova.

As we now know, Kepler’s supernova was a so-called Type Ia supernova. It forms when a white dwarf in a binary system devours its companion and accumulates so much mass that it is no longer stable, leading to a cosmic explosion.

But not all of the material separated from the companion star ends up on the white dwarf. Instead, it collects in a cloud surrounding the binary system – what we call the circumstellar medium. When a white dwarf goes supernova, it just explodes in this environment.

Because of its proximity and relative freshness of discovery, Kepler’s supernova is currently one of the most important objects in the Milky Way to study the evolution of Type Ia supernovae. And a wealth of data collected over the decades has helped to understand how fast a supernova ejection is moving.

A team of astronomers led by Matthew Millard University of Texas at Arlington used images of the supernova taken by the Chandra X-ray Observatory in 2000, 2004, 2006, 2014 and 2016 to track 15 knots of material in the supernova eruption and calculate their velocity in three-dimensional space.

To the team’s surprise, measurements show that while some nodes are slowing down, others expanded almost freely as much as 400 years after the explosion – and that their average speeds are 4,600 kilometers per second. In other galaxies, such numbers can be observed only for a few days or weeks after the actual explosion, after which the material begins to slow down.

But why is this happening? Interestingly, the directions of these nodes are unevenly distributed. Eight of the 15 nodes move away from Earth; and only two are moving towards our planet (the direction of the other five could not be established).

Scientists speculate that the supernova itself may have been unusually energetic for Type Ia. Measuring the velocities of more ejection nodes in the coming years could help validate their measurements and calculations, build a more complete 3D map of material distribution, and impose limits on how energetic this explosion could be.