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Astronomers observe exploding fireball stage of nova

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A group of astronomers from Georgia State University recently observed and imaged the thermonuclear explosion of a nova into a fireball with unprecedented clarity.

The images are some of the earliest we've seen of a star's nova stage and depict how material explodes from the star, as well as how it eventually cools and dissipates.

An amateur astronomer first discovered the white dwarf star last year. A white dwarf is a very dense star, usually about the size of Earth, but with a mass comparable to the Sun's. White dwarf stars happen with stars whose masses aren't enough to make them neutron stars, those stars that make up about 97 percent of the Milky Way.

The star, named Nova Delphinus 2013, was undergoing the first stages of nova. Nova happens in a binary star system when hydrogen builds up on the surface of a white dwarf star. This hydrogen comes from the second star in the system when it gets too close. Eventually, this triggers a nuclear fusion reaction, creating a fireball explosion within the white dwarf.

Telescopes pick up this explosion as an exceedingly bright light in an area where no such light has previously been seen. Over time, that light fades as the explosion expands and cools, eventually disappearing into nothing.

The CHARA Array facility in Southern California picked up the explosion. This is actually a group of six telescopes that work together to create high-resolution images, making details of such events even more clear than images from space-based telescopes.

"Within 15 hours of the discovery of Nova Del 2013 and within 24 hours of the actual explosion, astronomers pointed the telescopes of the CHARA Array toward the nova to image the fireball and measure its size and shape," says the university. "The size of Nova Del 2013 was measured on 27 nights over the course of two months. The first measurement represents the earliest size yet obtained for a nova event."

After analyzing the data, astronomers estimate that Nova Del 2013 is over 14,000 light-years from the sun. This means that the nova actually occurred about 15,000 years ago, so we're now looking into a part of the Universe's history. Those images also showed that this star's nova was different than expected.

"The observations reveal the explosion was not precisely spherical and the fireball had a slightly elliptical shape" says the university. "This provides clues to understanding how material is ejected from the surface of the white dwarf during the explosion."

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