Half Star - Half Planet

A star cool enough to toast marshmallows.

When you sit at a campfire and look up at the stars, even the tiniest pinpricks of light that you see are massive furnaces, producing intense heat. But hidden among them are celestial bodies so dim that they are invisible to the naked eye.

One such star, a brown dwarf smaller than Jupiter recently became the coldest star ever detected with a radio telescope. At a paltry 797 degrees Fahrenheit [ 425 Celsius ], it's cooler than the average campfire. That's an ideal temperature for roasting marshmallows.

A big star like our sun, said Kovi Rose, a doctoral candidate in astronomy at the University of Sydney, is a '' nuclear fusion machine that's working perfectly in space and compressing hydrogen gas and fusing that into helium.''

That produces energy that radiates from the star as heat and light.

Brown dwarfs are too small to generate the powerful gravity required to compress hydrogen to the point of nuclear fusion. Instead, '' a brown dwarf is partway, in mass and temperature, between a star and a planet,'' said Tara Murphy, an astronomy professor at the University of Sydney and a co-author with Mr. Rose of a new paper.

It's not the coolest star ever found, but it's the coolest to emit radio waves - unusual in itself, because most brown dwarfs don't do that. [ Kate Golembiewski ]


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