Source: Sci News

The Kepler supernova remnant is the debris from a detonated star that is located about 20,000 light years away in the Milky Way Galaxy.

In 1604, early astronomers, including Johannes Kepler who became the object’s namesake, saw the supernova explosion that destroyed the star.

Astronomers now know that Kepler’s supernova remnant is the aftermath of a so-called Type Ia supernova, where a white dwarf exceeds a critical mass limit after interacting with a companion star and undergoes a thermonuclear explosion that shatters the white dwarf and launches stellar debris outward.

In the new study, a team of astronomers from the United States, Spain and Japan estimated the speeds of 15 small, metal-rich debris knots in the supernova remnant.

To do this, the researchers analyzed X-ray spectra obtained by NASA’s Chandra X-ray Observatory in 2016.

By comparing the wavelengths of features in the X-ray spectrum with lab values and using the Doppler effect, they measured the speed of each knot along the line of sight from Chandra to the remnant.

They also used Chandra images obtained in 2000, 2004, 2006 and 2014 to detect changes in position of the knots and measure their speed perpendicular to our line of sight.

These two measurements combined to give an estimate of each knot’s true speed in 3D space.

The fastest knot was measured to have a speed of 37 million km per hour (23 million mph), the highest speed ever detected of supernova remnant debris in X-rays.

The average speed of the knots is about 16 million km per hour (10 million mph), and the blast wave is expanding at about 24 million km per hour (15 million mph).

These results independently confirm the 2017 discovery of knots traveling at speeds more than 32 million km per hour (20 million mph) in the Kepler supernova remnant.

The high speeds in Kepler are similar to those scientists have seen in optical observations of supernova explosions in other galaxies only days or weeks after the explosion, well before a supernova remnant forms decades later.

This comparison implies that some knots in Kepler have hardly been slowed down by collisions with material surrounding the remnant in the approximately 400 years since the explosion.

Based on the Chandra spectra, eight of the 15 knots are definitely moving away from Earth, but only two are confirmed to be moving towards it.

This asymmetry in the motion of the knots implies that the debris may not be symmetric along our line of sight, but more knots need to be studied to confirm this result.

The four knots with the highest total speeds are all located along a horizontal band of bright X-ray emission. These knots are all moving in a similar direction and have similar amounts of heavier elements such as silicon, suggesting that the matter in all of these knots originated from the same layer of the exploded white dwarf.

One of the other fastest moving knots is located in the ‘ear’ of the right side of the remnant, supporting the intriguing idea that the 3D shape of the debris is more like a football than a uniform sphere.

The explanation for the high-speed material is unclear.

Some astronomers have suggested that the Kepler supernova remnant is from an unusually bright Type Ia, which might explain the fast-moving material.

It is also possible that the immediate environment around the remnant is itself clumpy, which could allow some of the debris to tunnel through regions of low density and avoid being decelerated very much.

The team’s paper was published in the Astrophysical Journal.

Source: Sci News