BellaOnline Forums Education Astronomy White Dwarfs *new*

White dwarfs are the corpses of medium-sized stars that have run out of fuel. They typically have the mass of the Sun, while being around the size of the Earth. It's no wonder that early twentieth century astronomers were dumbfounded by them.

White Dwarfs

Astrophysicists calculate that two white dwarf stars in a close binary system might end up in a type Ia supernova, but one not as bright as the usual ones. They would need to be of equal mass and close enough for the emission of gravity waves to make them spiral together and merge.

Here is an artist's conception of such a merger. No one has ever seen such an event.

Reactions varied to the apparent density of what we now call white dwarfs.

Ernst Öpik (1893-1985) was an Estonian astronomer who spent the second half of his career at Armagh Observatory in Northern Ireland. In 1916 he estimated the density of a number of binary stars and found that 40 Eridani B seemed to have a density of more than 25,000 times that of the Sun. He proclaimed it "impossible", and you can see why he'd have thought so!

Henry Norris Russell first realized that something was amiss when he got a spectrum for 40 Eridani B at Harvard Observatory. His reaction was that of dismay. However the director of the observatory, Edward Pickering had a different reaction. He smiled and said to Russell, "It is just these exceptions that lead to an advance in our knowledge."

Last week Japanese amateur astronomer Koichi Itagaki discovered a nova in Sagittarius. This is the third nova that has been discovered this year in Sagittarius.

A nova is a powerful explosion that results in a sudden brightening of a star. It can stay bright for a few weeks or even a few months before it fades away again. Novae happen in close binary systems where one member of the pair is a white dwarf. It pulls hydrogen gas away from its companion until there is enough to burn explosively – spectacular enough for us to see over millions of light years.

The Hubble Space Telescope has found for the first time a population of white dwarfs embedded in the hub of our Milky Way, looking towards the constellation Sagittarius.

[Left] - A view of the Milky Way's central bulge. Giant dust clouds along this line block most of the starlight coming from the galactic center. Hubble, however, peered through a region (marked by the arrow) called the Sagittarius Window, which offers a keyhole view into the galaxy's hub.

[Upper right] - A small section of the dense collection of stars crammed together in the galactic bulge. The region surveyed is located 26,000 light-years away.

[Lower right] - Hubble uncovered extremely faint and hot white dwarfs. This is a sample of 4 out of the 70 brightest white dwarfs spied by Hubble in the Milky Way's bulge.

(Images and text credit: NASA, ESA, A. Calamida and K. Sahu (STScI), and the SWEEPS Science; A. Fujii; NASA press release)