Brightest star in the Galaxy has new competition
BY DR EMILY BALDWIN
ASTRONOMY NOW

Posted: July 16, 2008

Eta Carinae has a new rival for its long-held title of brightest star in the Milky Way, in the shape of the Peony nebula star that resides in the dusty metropolis of the Galaxy’s centre and blazes with the light of 3.2 million Suns.

Although the reigning ‘brightest star’ champion Eta Carinae has a luminosity equivalent to 4.7 million Suns, because it is hard to pin down an exact brightness for such scorching stars, the Peony nebula star could potentially shine with a similar amount of light. It was thanks to the Spitzer Space Telescope’s dust-piercing infrared eyes and data from the European Southern Observatory’s New Technology Telescope in Chile, that the luminosity of the new contender could finally be revealed.

“Infrared astronomy opens extraordinary views into the environment of the central region of our Galaxy,” says Lidia Oskinova of Potsdam University in Germany. "There are probably other stars just as bright if not brighter in our Galaxy that remain hidden from view."

The Peony nebula star was so-called because of the shape of the cloud of dust – the nebula – that surrounds the massive star, which is thought to have ‘leaked’ off the star during its lifetime. The nebula is revealed as the reddish cloud of dust seen in and around the white circle in the Spitzer image shown here. Image: NASA/JPL-Caltech /Potsdam Univ.

Brightness is a key indicator of size, and astronomers reckon that the Peony nebula star started off life with a hefty mass of roughly 150 to 200 times that of our Sun, pushing the limits of stellar stability. Theory predicts that if a star starts out too massive, it becomes unstable and must break into a double or multiple stars instead.

The Peony nebula star also has a diameter of roughly 100 times that of our Sun, placing it into the category of Wolf-Rayet stars, which rapidly shed their mass via frighteningly strong winds that can exceed over a million kilometres per hour. This rapid mass loss will ultimately lead to the star’s demise, and the Peony nebula star will explode in a cosmic firework display – a supernova. Oskinova and her colleagues say that the star is ripe for exploding anytime between now and in a few millions of years, but that it may not all be about destruction.

"When this star blows up, it will evaporate any planets orbiting stars in the vicinity," says Oskinova. "Farther out from the star, the explosion could actually trigger the birth of new stars."

Thanks to the ever-improving limits of multi-wavelength observations that can penetrate the dusty corners of the Milky Way, it may not be long before Eta Carinae is knocked off the brightest star top-spot for good.