Damage from stellar explosion is not slower after 400 years

Astronomers have used NASA’s Chandra X-ray Observatory to store material that stays away from the side of an exploding star at speeds faster than 20 million miles per hour. This is about 25,000 times faster than the speed of sound on Earth.

Kepler’s supernova remnant is the pound of a detonated star that lies about 20,000 light-years away from Earth in our Milky Way. In 1604, early astronomers, including Johannes Kepler who named the object, saw the supernova explosion that destroyed the star.

We now know that Kepler’s supernova remnant is the aftermath of a so-called Type Ia supernova, in which a small dense star known as a white dwarf overcomes a critical mass limit after interacting with a companion star and a thermonuclear explosion. undergoes that the white dwarf and launches his remnants outward.

The latest study followed the velocity of 15 small “knots” of pun in Kepler’s supernova remnant, all glowing in X-rays, all glowing in X-rays. The fastest node was measured at a speed of 23 million miles per hour, the highest speed ever discovered from supernova remnants in X-rays. The average speed of the nodes is about 10 million miles per hour, and the explosion wave expands to about 15 million miles per hour. These results independently confirm the 2017 discovery of nodes traveling at speeds more than 20 million miles per hour in Kepler’s supernova remnant.

Researchers in the latest study estimated the velocity of the nodes by analyzing Chandra X-ray spectra, which give the intensity of X-rays at different wavelengths, obtained in 2016. By comparing the wavelengths of functions in the X-ray spectrum with laboratory values ​​and with using the Doppler effect, they measure the velocity of each node along the line of sight from Chandra to the rest. They also used Chandra images obtained in 2000, 2004, 2006 and 2014 to detect changes in the position of the nodes and to measure their velocity perpendicular to our line of sight. These two measurements combine to give an estimate of the actual velocity of each node in three-dimensional space. A graph provides a visual explanation of how motions of nodes in the images and the X-ray spectra were combined to estimate the total velocities.

The 2017 work uses the same general technique as the new study, but uses X-ray spectra of another instrument on Chandra. This meant that the new study had more accurately determined the velocity of the node along the line of sight and thus the total velocities in all directions.

In this new sequence of four Chandra images of Kepler’s supernova remnant, red, green, and blue reveal the low, medium, and high-energy X-rays, respectively. The film zooms in to see several of the fastest moving nodes.

The high velocities 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 formed decades later. This comparison implies that some nodes in Kepler have hardly been slowed down by collisions with material around the remnant run in the nearly 400 years since the explosion.

Based on the Chandra spectra, eight of the 15 nodes move away from the Earth, but only two are confirmed to be moving towards it. (The other five do not show a clear direction of movement along our line of sight.) This asymmetry in the motion of the nodes implies that the pun may not be symmetrical along our line of sight, but more knots need to be studied to confirm this result.

The four nodes with the highest total velocities all lie along a horizontal band of bright X-rays. Three of them are labeled in a close-up view. These four nodes all move in a similar direction and have similar amounts of elements such as silicon, suggesting that the matter in all these nodes originated from the same layer of the exploded white dwarf.

One of the other fastest moving knots lies in the “ear” of the right side of the remnant, and supports the intriguing idea that the three-dimensional shape of the pun is more like a football than a uniform atmosphere. This button and two others are labeled with arrows in a close-up view.

The explanation for the high-speed material is unclear. Some scientists have suggested that Kepler’s supernova remnant is of an unusually powerful Type Ia, which may explain the fast-moving material. It is also possible that the immediate environment around the remnant itself is lumpy, which could allow some of the debris to tunnel low-density regions and prevent them from decelerating completely.

The 2017 team also used their data to refine previous rumors about the location of the supernova explosion. This allowed them to search for a companion to the white dwarf left behind after the supernova, and to learn more about what caused the explosion. They found a lack of bright stars near the center of the remnant. This implied that a star like the sun did not give material to the white dwarf until it reached critical mass. A fusion between two white dwarfs is favored instead.

The new results are reported in a paper led by Matthew Millard, of the University of Texas at Arlington, and published in the April 20, 2020 issue of the Astrophysical Journal.

A paper by Toshiki Sato and Jack Hughes reported the discovery of fast-moving nodes in Kepler’s supernova remnant and was published in the August 20, 2017 issue of The Astrophysical Journal.