Astronomers capture early fireball stage of nova for 1st time

Astronomers observed the images of a nova during its early fireball stage for the first time, which provided a deeper insight into the complicated process where it ejects material, gases expand and cool.

The research collaboration led by Georgia State University Astronomer Gail Schaefer observed that the expanding thermonuclear fireball from a nova that erupted last year in the constellation Delphinus.

A nova occurs after a thin layer of hydrogen builds up on the surface of a white dwarf-a highly evolved star with the mass of the sun packed into the volume of the Earth. A normal star accompanies the white dwarf in a binary star system, providing that hydrogen as the two stars orbit each other.

Because these objects are generally very far from the sun and faint until the explosion occurs, they do not appear on classical star maps. Instead, a "new" star suddenly appears where none was before.

On Aug. 14, 2013 the Japanese amateur astronomer Koichi Itagaki discovered a "new" star, promptly named Nova Delphinus 2013. Within 15 hours of discovery and within 24 hours of actual explosion, the NSF-funded Center for High Angular Resolution Astronomy (CHARA) and its Georgia State University astronomers pointed array telescopes, located at historic Mount Wilson Observatory in the San Gabriel Mountains of Southern California, toward Nova Del 2013 to image the fireball and measure it.

They measured the nova on a total of 27 nights over two months; the first measurement represents the earliest size yet obtained for a nova event.

It has been almost 350 years since Carthusian monk Pere Dom Anthelme discovered the first true nova in the constellation of Vulpecula in 1670. Since then thousands of novae have been discovered, but it is only in the last decade or so that it has become possible to image the earliest stages of the explosion due to interferometry's high resolution.

The new CHARA measurements follow the expansion of Nova Del 2013 from its very early relatively compact stages until the fireball was nearly the size of our solar system.

Studying how the structure of the nova changed at the earliest stages brings new insights to theoretical models of novae eruptions.

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The study is published in the Nature.