supernova 1604

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The Milky Way’s most recent supernova was hidden… until now!

“Close to the galactic center, the supernova remnant G1.9+0.3 was first discovered in the radio thanks to the Very Large Array (VLA), with its origin unknown. The fact that it was so small on the sky, despite being at a distance of 25,000 light years, brought up the possibility that this was a very young supernova: perhaps the youngest of all supernovae in the Milky Way. Follow-up observations took place in the 2000s with the Two-Micron All-Sky Survey in the infrared and with the Chandra X-ray observatory, where a wonderful surprise came to light: this supernova remnant was expanding at an incredible pace!

In 1604, Kepler’s supernova went off, the last Milky Way supernova visible to naked-eye skywatchers here on Earth. Yet since the development of radio and X-ray astronomy, other, more recent supernova remnants in our galaxy have been found. They’ve only been invisible to the naked eye because of the galactic gas and dust that blocks their visible light. In 1984/5, the VLA discovered the most recent known remnant near the galactic center, and follow-up observations showed a rapid expansion. The most recent data not only dates this remnant to be only 110 years old, but it teaches us that it’s a Type Ia supernova that formed from the merger of two white dwarfs. The standard model — of one white dwarf accruing matter from a binary companion — may not only be a minority of Type Ia events, perhaps it doesn’t occur at all.

Cosmic Detective Work

Supernovae are thought to be massive explosions signaling the end of a star’s life; however, stellar demise is not always the cause of these explosions. Supernovae explosions are not created equal and are divided into categories - the most common of which is a Type Ia. This class of supernova involves the detonation of small, dense, already dead stars called white dwarfs. 

New observations from NASA’s Spitzer Space Telescope have shed light on a new rare type of Type Ia supernova, involving a zombie star of sorts. The dead star (white dwarf) feeds off a neighboring aging star just like a zombie, until it has “eaten” so much material, it triggers an explosion. This new data shows just how exceptional these events are. Astronomers at NASA’s Goddard Space Flight Center in Greenbelt, Maryland get to play detective and search through the stellar remains for any clue that will explain exactly what causes these powerful explosions. 

Supernovae provide cosmic fuel, spewing out all the elements necessary to the Universe - including heavy metals like the iron found in our blood. Typically Type Ia explosions are very consistent and astronomers use these explosions as distance markers and use them to study how the universe is expanding. 

Over the past ten years, researchers have been mounting evidence that Type Ia explosions occur when two white dwarfs collide - with only one exception - Kepler’s supernova. Named for the famous astronomer who witnessed it back in 1604, Kepler’s supernova is thought to be caused by one white dwarf and its elderly red giant companion. Scientists know the companion was a red giant based on the white dwarf remnant sitting among the gas pool and dust shed by the aging star.

These new observations show that Spitzer has now observed a second explosion just like Kepler’s supernova, dubbed N103B. Located approximately 160,000 light-years away in our galactic neighbor, the Large Magellanic Cloud, lies Kepler’s older cousin - N103B. However, unlike Kelper’s supernova, there are no recorded historical sightings of the explosion. 

Both N103B and Kepler’s supernova are thought to have formed from an aging red giant orbiting and already “dead” white dwarf. Typically older stars molt (meaning they shed their outer layers) and this material falls onto the companion white dwarf. Once the white dwarf has accumulated enough mass, it will become unstable and ultimately explode. 

Just a decade ago, scientists thought the white dwarf red giant scenario was the common cause of Type Ia explosions, scientists now suggest that a pair of white dwarf stars are the more likely (and common) culprit. The new Spitzer data shows how complex these explosions are and how there are many different triggers. However, the exact reason as to why these “dead” stars explode is still to be determined. 

-ALT

Image & Source Credit: NASA/JPL-CalTech

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The greatest supernovae that no one ever saw

“For a long time, we thought this event, estimated to have occurred in 1680, was the Milky Way’s most recent supernova. But remember the following:

-We’re some 25,000 light-years from the galactic center,

-Supernovae occur about once-per-century in galaxies,

-We haven’t seen a supernova since 1604, and

-We were able to find one only 11,000 light-years away that occurred since that 1604 event.

Are there others that occurred since 1680? Up until relatively recently, we would have said “quite possibly,” but we wouldn’t have been sure.”

Did you know the Milky Way had a supernova go off in it as recently as the 1860s?!