Witnessing a Supernova

Five objects at various distances that have been observed by Chandra

Some of the most spectacular celestial events in the Universe are the unimaginably explosive deaths of its biggest stars.

When a truly massive star reaches the end of its life, it will explode in an event that is known as a supernova.

A supernova is exponentially brighter than the star from which it originated from.

A supernova detected in a far-away galaxy in 1994 was so bright that it outshone the brightness of its entire host galaxy – the combined brightness of billions of stars was not enough to outshine the brightness of this supernova.

Supernova 1994D
The supernova SN 1994D as seen in galaxy NGC 4526.

A supernova from the Milky Way has not been directly witnessed since 1604. So what would it be like to witness a supernova?

An exceedingly bright star would suddenly appear, which would last for a few weeks or months before slowly fading away.

Depending on how close the supernova was, it may be brighter than the full moon, and may even be visible in the day.

The ninth-brightest star in the sky, Betelgeuse, is a supernova-candidate. Located in the constellation Orion, the star is about 640 light years away, which would make it perhaps the closest supernova to Earth in recorded history.

It is a red giant that is in the final stages of its life and will one day erupt in a supernova.

Below is a video showing what the Betelgeuse supernova may look like from Earth.

It would be an incredible site to see. Unfortunately it is not possible to predict exactly when this star will become a supernova, and so while it may happen within our lifetimes, it may still be tens of thousands away.

There have been possibly eight historically witnessed supernovae in the Milky Way in recorded history. The last has not been witnessed by the naked eye since 1604, any supernovae witnessed since then have been from other galaxies.

Historical descriptions of supernovae show that they were very significant events. The brightest supernova that has been witnessed was seen in the year 1006, and was said to have a visual magnitude of -7.5, which would make it sixteen times the brightness of Venus. The supernova was bright enough to cast shadows and was visible in the daytime.

A supernova remnant about 7,000 light years from Earth.
The remnant of supernova SN 1006 as seen from Earth today.

The development of technology has allowed the discovery of supernovae outside the Milky Way galaxy. In 2015, a celestial event known as ASASSN-15lh was witnessed which, if it were a supernova, would make it the most luminous supernova yet discovered.  At its brightest, the object was 50 times more luminous than the entire Milky Way galaxy, and was 570 billion times more energetic than the sun.

These numbers are impossible to comprehend in human terms – the numbers are so big that they essentially become meaningless. If an object like that was closer to Earth I would have no doubt it would be one of the most talked about events in all of human history.

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