Anne’s Picture of the Day: Kepler’s Supernova

January 6, 2012

Kepler’s Supernova, a supernova remnant in Ophiuchus

SN 1604

Image Credit: NASA/CXC/NCSU/S. Reynolds et al.

Kepler’s Supernova (SN 1604) is the remnant of a Type Ia supernova explosion that occurred in the Milky Way, some 16,000 – 23,000 light-years away in the constellation of Ophiuchus. This asymmetric bubble-shaped shroud of gas and dust, that is considered to be one of the prototypical objects of its kind, is about 19 – 33 light-years across, and is expanding at roughly 2,000 kilometers per second (4 million miles per hour).

A Type Ia supernova is a result from the violent explosion of a white dwarf star (a compact star that has ceased fusion in its core). The white dwarf increases its mass beyond a critical limit (the Chandrasekhar limit) by gobbling up matter from a companion star. A runaway nuclear explosion then makes the star suddenly as bright as a whole galaxy, before gradually fading from view.

Kepler’s Supernova Remnant is a fast-moving shell of iron-rich material from an exploded white dwarf star, that blasted the stellar remains into space, causing an expanding shock wave that is sweeping up interstellar gas and dust, while heating the gases to millions of degrees and generating highly energized particles. New analysis suggests that the supernova explosion was more powerful, and occurred at a greater distance, than previously thought (13,000 light-years).

It appears to be expanding into dense material that is rich in nitrogen, what means that this supernova could be the nearest example of a relatively rare “prompt” Type Ia explosion, which occur in more massive progenitors only about 100 million years after the star formed rather than several billion years.

If that is the case, Kepler could teach astronomers more about all Type Ia supernovas and the ways in which prompt explosions from massive stars differ from their more common cousins associated with lower mass stars. This information is essential to improve the reliability of the use of Type Ia stars as “standard candles” for cosmological studies of dark energy as well as to understand their role as the source of most of the iron in the universe.

The supernova was first observed in northern Italy on October 9, 1604. Johannes Kepler began observing it in Prague on October 17, without the benefit of a telescope. It was subsequently named after him because his observations tracked the object for an entire year and because he wrote a book on the subject.

Visible to the naked eye, this supernova was brighter at its peak than any other star in the night sky, and all the planets other than Venus. It was visible during the day for over three weeks.

SN 1604 is the most recent supernova to have been observed with certainty by the naked eye in our own Milky Way, even though there is astronomical evidence for a Milky Way supernova whose signal would have reached Earth around the years 1680 (Cassiopeia A), and another object whose light should have arrived around 1870. However there is no historical record of either having been detected at the time, by the unaided eye.

This image is created by X-rays from Chandra X-ray Observatory with Optical data from the Digitized Sky Survey. Red represents low-energy X-rays and shows material around the star — dominated by oxygen — that has been heated up by a blast wave from the star’s explosion. The yellow color shows slightly higher energy X-rays, mostly iron formed in the supernova, while green (medium-energy X-rays) shows other elements from the exploded star. The blue color represents the highest energy X-rays and shows a shock front generated by the explosion.

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