50 Fun Facts About White Dwarfs

A white dwarf packs a mass comparable to the Sun's into a volume roughly the size of what?

That gives an average density of about a tonne per cubic centimetre.

What is the source of a white dwarf's light?

Once formed, its material no longer undergoes fusion, so it slowly cools and reddens.

How far away is Sirius B, the nearest known white dwarf?

It is the smaller partner of the brightest star in the night sky.

In which year was 40 Eridani B recognised as the first white dwarf?

Russell, Pickering and Fleming found the dim star had a puzzling white A-type spectrum.

Who coined the name 'white dwarf' in 1922?

Eddington then popularised the term.

What holds a white dwarf up against gravitational collapse?

It is a quantum effect: the Pauli exclusion principle stops electrons crowding into the same state.

What is the approximate maximum mass of a non-rotating white dwarf, the Chandrasekhar limit?

Above it, the star can no longer hold itself up and collapses.

Who published the presently known value of the white dwarf mass limit in 1931?

He worked out the degenerate Fermi gas statistics on the ship from India to England in 1930.

In which year did Chandrasekhar share the Nobel Prize in Physics for his work on stellar structure?

He shared it with William Alfred Fowler.

Where was Chandrasekhar born?

He was born into a Tamil Brahmin family in what is now Pakistan.

Which physicist resolved the puzzle of white dwarf density in 1926 by applying the new quantum mechanics?

He showed that electrons obeying the Pauli principle would keep the star from collapsing even at zero temperature.

Which astronomer predicted in 1844 that Sirius and Procyon had unseen companions?

He guessed the period of Sirius's companion at about half a century.

Who first observed Sirius B, on 31 January 1862?

He was testing a telescope lens when the faint companion appeared.

Which Dutch-American astronomer discovered the first isolated white dwarf, now named after him, in 1917?

With 40 Eridani B and Sirius B it makes up the three 'classical' white dwarfs.

A 1917 photographic plate of van Maanen's Star gives the earliest known evidence of what?

Calcium absorption lines showed rocky debris polluting the star's atmosphere.

How many white dwarfs had been discovered by 1939?

By 1999 over 2,000 were known, and a major sky survey has since found over 9,000.

Who in 1916 calculated 40 Eridani B's density at 25,000 times the Sun's and called it 'impossible'?

Eddington later joked that astronomers' 1914 reply to such densities was 'Shut up. Don't talk nonsense.'

In Eddington's famous 1927 image, a ton of Sirius B's material would be a nugget that fits in what?

He imagined the star's light carrying the message 'I am composed of material 3000 times denser than anything you have ever come across'.

Around what mass is the distribution of observed white dwarfs strongly peaked?

Most lie between 0.5 and 0.7 solar masses, though extremes from 0.17 to 1.33 are known.

Roughly how many white dwarfs are thought to exist in the Milky Way?

Eight sit among the hundred nearest star systems to the Sun.

What fraction of the Milky Way's stars are expected to end up as white dwarfs?

Everything from about 0.07 to 10 solar masses takes that path.

A typical white dwarf's radius is what percentage of the Sun's?

That is comparable to our own planet, whose radius is about 0.9 per cent of the Sun's.

What is the approximate average density of a white dwarf?

Only neutron stars and hypothetical quark stars are denser.

A white dwarf accreting matter past the Chandrasekhar limit is the leading model for which event?

Their uniform brightness makes them standard candles for measuring galaxy distances.

What is a cooled-down stellar remnant of this kind, no longer radiating, eventually called?

None are thought to exist yet, since the cooling time exceeds the age of the universe.

What is the nickname of BPM 37093, a white dwarf whose core is thought to be largely crystallised carbon?

The Beatles song 'Lucy in the Sky with Diamonds' inspired it; observations in 2004 suggested about 90 per cent of its mass had crystallised.

What is the ejected shell of gas that surrounds a newly formed white dwarf called?

The name is a misnomer; early telescopes made them look like the disc of Uranus.

What was the first variable (pulsating) white dwarf found, in 1965–66?

It varied with a period of about 12.5 minutes.

Which white dwarf, identified in 1970, was the first found to have a magnetic field?

James Kemp and colleagues detected it from circularly polarised light.

Roughly what surface temperature has one of the coolest known white dwarfs, WD J2147–4035?

Few white dwarfs are seen below 4,000 K.

What did the Hubble Space Telescope determine about Sirius B in 2005?

Sirius B was once the more massive of the two stars.

How luminous is Sirius B compared with Sirius A in visible light?

The white dwarf's faintness next to the sky's brightest star is why it took until 1862 to see it.

Which white dwarf hosts a Jupiter-sized planet found transiting by TESS in 2019?

The star is about half the Sun's mass but only 40 per cent larger than our planet.

Which white dwarf, roughly Ganymede-sized, rotates once every 6.9 minutes?

It is one of the most massive white dwarfs known and among the smallest in size.

Which fictional planet orbits 40 Eridani A, the primary of the system with the first known white dwarf?

The real star, formally named Keid, is visible to the naked eye at magnitude 4.43.

Which two nuclei predominantly make up a typical white dwarf?

Stars near the 10-solar-mass ceiling instead form oxygen–neon white dwarfs.

Metal-rich white dwarf atmospheres are best explained by what?

Ton 345's metals matched a differentiated rocky planet stripped of its mantle.

What fraction of white dwarfs show infrared excess from a debris disc?

The discs are flat, optically thick and inherited from the progenitor's planetary system.

Which pair discovered 40 Eridani B and C as a visual pair on 31 January 1783?

It took another 127 years to realise B was something new.

Which astronomer confirmed 40 Eridani B's spectral type in 1914 and found Sirius B's in 1915?

Russell had publicly doubted the original spectral type.

Which Soviet physicist computed the limiting mass in 1932 but did not apply it to white dwarfs?

He concluded that quantum laws might be invalid for stars heavier than 1.5 solar masses.

Which famous astronomer clashed with Chandrasekhar over the mass limit at a 1935 conference?

Chandrasekhar had used Eddington's own polytrope models to reach his result.

What spectral type is Procyon B, the faint white dwarf companion of Procyon?

At magnitude 10.7 it is far outshone by Procyon A.

Which glowing shell in Aquarius, sometimes called the 'Eye of God', lies about 655 light-years away?

Gaia measured its distance; a white dwarf sits at its centre.

Barrow and Tipler estimated it would take how long for a white dwarf to cool to 5 K?

WIMP interactions, if they exist, might keep some white dwarfs warmer for 10^25 years.

The separation between two nuclei in a white dwarf is much smaller than what atomic yardstick?

White dwarf matter is pressure-ionised: there is no room for bound electron orbitals.

Which project has found over 9,000 white dwarfs, most of them new?

Only about a hundred were known in 1950.

Which physicist popularised the term 'white dwarf'?

Luyten's 1922 papers concerned faint white stars with high proper motion.

White dwarfs of spectral class DA, about 80% of those observed, have atmospheres dominated by which element?

The thin atmosphere is the only part of the star we can see, a leftover of its envelope from the asymptotic giant branch phase.

The binary AR Scorpii was identified in 2016 as the first pulsar whose compact object is what?

A second such pulsar was discovered in 2023, showing the highly magnetised remnant was not a one-off.