Brightest Star In The
Galaxy Has New Competition
(15 July 2008) A contender for the
title of brightest star in our Milky Way galaxy has been unearthed in the dusty
metropolis of the galaxy's centre.
Nicknamed the "Peony nebula
star," the bright stellar bulb was revealed by NASA's Spitzer Space Telescope
and other ground-based telescopes. It blazes with the light of an estimated 3.2
million suns.
The reigning "brightest star" champion is Eta Carina, with
a whopping solar wattage of 4.7 million suns. But according to astronomers,
it's hard to pin down an exact brightness, or luminosity, for these scorching
stars, so they could potentially shine with a similar amount of
light.
"The Peony nebula star is a fascinating creature. It appears to
be the second-brightest star that we now know of in the galaxy, and it's
located deep into the galaxy's centre," said 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." Oskinova is principal
investigator for the research and second author of a paper appearing in a
future issue of the journal Astronomy and Astrophysics.
Scientists
already knew about the Peony nebula star, but because of its sheltered location
in the dusty central hub of our galaxy, its extreme luminosity was not revealed
until now. Spitzer's dust-piercing infrared eyes can see straight into the
heart of our galaxy, into regions impenetrable by visible light. Likewise,
infrared data from the European Southern Observatory's New Technology Telescope
in Chile were integral in calculating the Peony nebula star's
luminosity.
"Infrared astronomy opens extraordinary views into the
environment of the central region of our galaxy," said Oskinova.
The
brightest stars in the universe are also the biggest. Astronomers estimate the
Peony nebula star kicked off its life with a hefty mass of roughly 150 to 200
times that of our sun. Stars this massive are rare and puzzle astronomers
because they push the limits required for stars to form. Theory predicts that
if a star starts out too massive, it can't hold itself together and must break
into a double or multiple stars instead.
Not only is the Peony nebula
star hefty, it also has a wide girth. It is a type of giant blue star called a
Wolf-Rayet star, with a diameter roughly 100 times that of our sun. That means
this star, if placed where our sun is, would extend out to about the orbit of
Mercury.
With so much mass, the star barely keeps itself together. It
sheds an enormous amount of stellar matter in the form of strong winds over its
relatively short lifetime of a few million years. This matter is pushed so hard
by strong radiation from the star that the winds speed up to about 1.6 million
kilometres per hour (one million miles per hour) in only a few
hours.
Ultimately, the Peony nebula star will blow up in a fantastic
explosion of cosmic proportions called a supernova. In fact, Oskinova and her
colleagues say that the star is ripe for exploding soon, which in astronomical
terms mean anytime from now to millions of years from now.
"When this
star blows up, it will evaporate any planets orbiting stars in the vicinity,"
said Oskinova. "Farther out from the star, the explosion could actually trigger
the birth of new stars."
In addition to the star itself, the astronomers
noted a cloud of dust and gas, called a nebula, surrounding the star. The team
nicknamed this cloud the Peony nebula because it resembles the ornate
flower.
"The nebula was probably created from the spray of dust leaking
off the massive Peony nebula star," said Andreas Barniske of Potsdam
University, lead author of the study.
Wolf-Rainer Hamann, also of
Potsdam University, is another co-author of the paper and the principal
investigator of a Spitzer program enabling this research.
NASA's Jet
Propulsion Laboratory, Pasadena, Calif., manages the Spitzer Space Telescope
mission for NASA's Science Mission Directorate, Washington. Science operations
are conducted at the Spitzer Science Center at the California Institute of
Technology, also in Pasadena. Caltech manages JPL for NASA. Spitzer's infrared
spectrograph, which was used to determine the luminosity of the Peony nebula
star, was built by Cornell University, Ithaca, N.Y. Its development was led by
Jim Houck of Cornell.
(source: NASA Jet Propulsion
Laboratory)
