What is the age of the oldest white dwarf star?
“The ages of the white dwarfs were determined from their temperatures. The observed white dwarfs are basically cooling embers. The nuclear fire of the stars burned out billions of years ago. The light emitted comes from the heat remaining from the earlier nuclear burning. By measuring the spectrum of the light, the brightness in various colors, the temperatures of the stars were determined. The two coolest of the white dwarfs studied, PSR J0034-0534 and PSR J1713+0747, are 3400 degrees Kelvin (5600 F), making them the coolest known white dwarfs. For comparison, the surface of the sun measures 5800 degrees Kelvin and the coolest previously known white dwarfs are 4000 degrees Kelvin. These cool white dwarfs will be important for calibrating the white dwarf temperature scale and the ages of the oldest stars in the Milky Way galaxy. Models for white dwarf cooling have been developed, which take into account the light emitting and absorbing properties of the surface and the atmosphere of th
Gyr: gigayear, or one billion years. A white dwarf star is an object that is about as heavy as the Sun but only the radius of the Earth. The average density of a white dwarf is a million times denser than water. White dwarf stars form in the centers of red giant stars, but are not visible until the envelope of the red giant is ejected into space. When this happens the ultraviolet radiation from the very hot stellar core ionizes the gas and produces a planetary nebula. The envelope of the star continues to move away from the central core, and eventually the planetary nebula fades to invisibility, leaving just the very hot core which is now a white dwarf. White dwarf stars glow just from residual heat. The oldest white dwarfs will be the coldest and thus the faintest. By searching for faint white dwarfs, one can estimate the length of time the oldest white dwarfs have been cooling. Oswalt, Smith, Wood and Hintzen (1996, Nature, 382, 692) have done this and get an age of 9.5+1.1-0.8 Gyr f
By searching for faint white dwarfs, one can estimate the length of time the oldest white dwarfs have been cooling. Oswalt, Smith, Wood and Hintzen (1996, Nature, 382, 692) have done this and get an age of 9.5+1.1-0.8 Gyr for the disk of the Milky Way. They estimate an age of the Universe which is at least 2 Gyr older than the disk, so to > 11.5 Gyr. Hansen et al. have used the HST to measure the ages of white dwarfs in the globular cluster M4, obtaining 12.7 +/- 0.7 Gyr. In 2004 Hansen et al. updated their analysis to give an age for M4 of 12.1 +/- 0.9 Gyr, which is very consistent with the age of globular clusters from the main sequence turnoff. Allowing allowing for the time between the Big Bang and the formation of globular clusters (and its uncertainty) implies an age for the Universe of 12.8 +/- 1.1 Gyr.
