Archive for the ‘White Dwarves’ Category

Astronomers Pin Down Origins Of “Mile Markers” For Expansion Of Universe

November 28, 2012 Leave a comment

A study using a unique new instrument on the world’s largest optical telescope has revealed the likely origins of especially bright supernovae that astronomers use as easy-to-spot “mile markers” to measure the expansion and acceleration of the universe.

In a paper to appear in the Astrophysical Journal, researchers describe observations of recent supernova 2011fe that they captured with the Large Binocular Telescope (LBT) using a tool created at Ohio State University: the Multi-Object Double Spectrograph (MODS). MODS measures the frequencies and intensities of light shining from a star.

Based on the frequencies of light emanating from supernova 2011fe, this type of supernova – known as Type Ia – is most likely caused by the interaction between a pair of dead stars known as white dwarfs, the astronomers concluded. One white dwarf orbits the other and sheds material onto it, until the other white dwarf becomes unstable and explodes, shining billions of times brighter than the sun.

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Rapidly Rotating White Dwarf Stars Can Solve The Missing Companion Problem For Type IA Supernovae

September 5, 2012 Leave a comment

The research group of Izumi Hachisu (The University of Tokyo), Mariko Kato (Keio University) and Ken’ichi Nomoto (Kavli IPMU, The Univiersity of Tokyo) discovered that a Type Ia supernova occurs after its companion star evolves into a faint helium white dwarf in many cases, given the fact that the white dwarf is spinning in the progenitor system.

Supernovae are brilliant explosions of stars. Among them, Type Ia supernovae have been used as “standard candles”, which has led to the discovery of the accelerating expansion of the Universe. Type Ia supernovae are also important to study as they are the main producer of iron group elements in the Universe.

Some recent observations have provided indications of the progenitor binary star systems just before the explosions.

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Stellar Archaeology Traces Milky Way’s History

Unfortunately, stars don’t have birth certificates. So, astronomers have a tough time figuring out their ages. Knowing a star’s age is critical for understanding how our Milky Way galaxy built itself up over billions of years from smaller galaxies.

Jason Kalirai of the Space Telescope Science Institute and The Johns Hopkins University’s Center for Astrophysical Sciences, both in Baltimore, Md., has found the next best thing to a star’s birth certificate. Using a new technique, Kalirai probed the burned-out relics of Sun-like stars, called white dwarfs, in the inner region of our Milky Way galaxy’s halo. The halo is a spherical cloud of stars surrounding our galaxy’s disk.

Those stars, his study reveals, are 11.5 billion years old, younger than the first generation of Milky Way stars. They formed more than 2 billion years after the birth of the universe 13.7 billion years ago. Previous age estimates, based on analyzing normal stars in the inner halo, ranged from 10 billion to 14 billion years.

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12-Billion-Year-Old White Dwarf Only 100 Light-Years Away

April 16, 2012 Leave a comment

A University of Oklahoma assistant professor and colleagues have identified two white dwarf stars considered the oldest and closest known to man.  Astronomers identified these 11- to 12-billion-year-old white dwarf stars only 100 light years away from Earth.  These stars are the closest known examples of the oldest stars in the Universe forming soon after the Big Bang, according to the OU researcher.

Mukremin Kilic, assistant professor of physics and astronomy in the OU College of Arts and Sciences and lead author on a recently published paper, announced the discovery. Kilic says, “A white dwarf is like a hot stove; once the stove is off, it cools slowly over time.  By measuring how cool the stove is, we can tell how long it has been off. The two stars we identified have been cooling for billions of years.”

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