Supernova hunters discover comet

Observation by amateur astronomer helps confirm the discovery.
By Laurel Kornfeld | Jul 31, 2017
An international group of scientists conducting a survey to search for supernovae, the remnants of massive stars that exploded as they died, was surprised when they unexpectedly discovered a comet instead.

The All Sky Automated Survey for Supernovae (ASAS-SN), based at Ohio State University, uses a group of eight 14-centimeter telescopes placed around the world to search the visible sky for supernovae every two to three nights.

When scanning images obtained on July 19, Jose Prieto of Universidad Diego Portales in Chile immediately noticed a bright object moving in relation to background stars.

He checked a catalog of moving objects for any known asteroids or comets in that position but did not find any.

"While I was scanning the images obtained the night of July 19, I noticed this light source was different from the typical transient sources we discover--slightly extended with respect to normal stars and moving between consecutive images that were obtained within minutes of each other."

With help from amateur astronomer Joseph Brimacombe, an Australian team member who took his own images of the object from that country, ASAS-SN scientists quickly realized they had discovered something new.

They then turned their worldwide network of telescopes on the object and followed it for three days, during which time it grew significantly brighter.

But when they continued the observations for a second three-day period, the object's brightness faded.

This sudden increase in brightness, called an outburst, is a characteristic of comets. It occurs when ejected dust and gas cause the material surrounding the comet's nucleus to temporarily expand.

"Comets move so fast that even being able to see it in Chile and Argentina on the same night was a real challenge," said team member Benjamin Shappee of the Carnegie Observatories in Pasadena, California.

"Without Joseph's observation, the next night would have been much more difficult, since we would only have had a rough idea of where to look."

Designated ASASSN1, the comet, which is approaching the Sun, should be visible for several months.

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