Kepler’s Supernova Remnant

A Historical View

Kepler’s Supernova was first observed on October 9, 1604 from northern Italy.  Johannes Kepler, best known for discovering the laws of planetary motion, began observing the supernova on October 17th from Prague and continued to track the object for an entire year.  In the end, he published an entire book on his observations in 1606: “On the new star in Ophiuchus’s foot.”  Kepler’s original drawing marking the location of the supernova is shown below.  This supernova was remarkable, because it was easily visible to the naked eye and occurred within our own Milky Way galaxy.

395px-Kepler_Drawing_of_SN_1604

Adding Modern Telescopes

Today, astronomers can use modern telescopes to get a better look at the remains of this supernova.  In 2004, a team of astronomers undertook a project to image the remnant of Kepler’s Supernova at optical, infrared, and X-ray wavelengths using the Hubble Space Telescope, Spitzer Space Telescope, and Chandra X-ray Observatory as part of NASA’s Great Observatories program.  The image created by combining these observations (shown below) reveals a bubble of gas and dust that is 14 lightyears in diameter and expanding at a rate of about 4 million miles per hour.  A shell of iron-rich material is expanding outwards and is surrounded by a spherical shock wave that is sweeping up interstellar gas and dust.  Each wavelength of radiation probes a different part of this structure.  At optical wavelengths, we can see where the shock wave is slamming into the surrounding interstellar material.  The bright knots seen in the image are due to dense clumps that form behind the shock.  At infrared wavelengths, we see the small dust particles that are swept up and heated by the shock wave.  Observations at these longer wavelengths, allow astronomers to probe the chemical composition and physical environment of the ejecta and surrounding material.  X-ray observations are sensitive to regions of very hot gas.  Lower energy X-rays are found in an interior shell and mark the location of the ejecta from the exploding star.  Higher energy X-rays are concentrated in the regions directly behind the shock and are coincident with optical and infrared emission.

kepler_multiwavelength

Astronomers had previously concluded that Kepler’s  Supernova was a Type Ia supernova, a thermonuclear explosion of a white dwarf. However, there is still debate within the astronomical community about what circumstances are required to produce a Type Ia supernova.  There are two possible origins:

  1. A white dwarf accretes material from a red giant companion until it becomes unstable and explodes (animation)
  2. Two white dwarfs spiral into each other and merge (animation)

New Chandra observations (Burkey et al. 2012) of this remnant revealed a disk structure near the center of the remnant.  One reasonable explanation of this emission structure is that it is produced by supernova ejecta colliding with disk-shaped material expelled by a companion star prior to the explosion.  If this theory is correct, it would favor the first possible origin for Type Ia supernovae.  Of course, it is also possible that the observed emission is simply due to debris left over from the initial explosion.  Interestingly, the disk structure seen in the Chandra observations matches closely with a similar structure seen in previous Spitzer observations.  The image below shows X-ray emission (from Chandra) in blue and infrared emission (from Spitzer) in pink.  The location of the disk structure is outlined and labeled in white.

kepler_disk

This composite image also indicates that iron-rich material is concentrated on one side of the center of the remnant.  Following the logic from above, this could be explained by ‘shadowing’ from the companion star, which may have blocked the ejection of material in some portion of the remnant.  A fun animation of how the supernova explosion might have interacted with material expelled by the evolved companion star is available here.

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