Ikigai Daily
Menu
WonderAstrophysics biography fact

At 19, Subrahmanyan Chandrasekhar calculated that a white dwarf, the dense core left when a star like the Sun dies, cannot be more than about 1.4 times the Sun's mass. Above this limit, now named after him, it can no longer hold itself up against its own gravity.

Subrahmanyan Chandrasekhar

BiographySpaceScience

The story behind the card

Chandrasekhar did the calculation in 1930 on the ship taking him from India to England to study at Cambridge, combining quantum mechanics with Einstein's special relativity. A white dwarf is held up by electron degeneracy pressure: when electrons are squeezed very tightly together, they resist being packed any closer, a purely quantum effect. He showed that this resistance has a ceiling. When he presented the result in 1935, the influential astronomer Arthur Eddington mocked it in public, and many colleagues sided with Eddington for years, although the mathematics was right. The limit is now central to understanding supernovae and neutron stars. Chandrasekhar shared the 1983 Nobel Prize in Physics for his work on the structure and evolution of stars.

Türkçe oku
Subrahmanyan Chandrasekhar 19 yaşındayken, Güneş gibi bir yıldız ölünce geride kalan yoğun çekirdeğin, yani beyaz cücenin, Güneş kütlesinin yaklaşık 1,4 katından ağır olamayacağını hesapladı. Bugün onun adıyla anılan bu sınırın üzerinde yıldız, kendi kütle çekimine karşı ayakta kalamaz.

Chandrasekhar bu hesabı 1930'da, Cambridge'de okumak için Hindistan'dan İngiltere'ye giden gemide, kuantum mekaniğini Einstein'ın özel görelilik kuramıyla birleştirerek yaptı. Beyaz cüceyi ayakta tutan şey elektron yozlaşma basıncıdır: birbirine çok sıkıştırılan elektronlar daha fazla yaklaşmaya direnir; bu tamamen kuantum mekaniğine özgü bir etkidir. Chandrasekhar bu direncin bir üst sınırı olduğunu gösterdi. Sonucu 1935'te sunduğunda dönemin etkili astronomu Arthur Eddington herkesin önünde onunla alay etti; matematiği doğru olduğu hâlde meslektaşlarının çoğu yıllarca Eddington'dan yana durdu. Bu sınır bugün süpernovaları ve nötron yıldızlarını anlamanın temel taşlarından biridir. Chandrasekhar, yıldızların yapısı ve evrimi üzerine çalışmalarıyla 1983 Nobel Fizik Ödülü'nü paylaştı.

Sources and further reading

Background reading: Chandrasekhar limit
Get the mobile appAbout our cards

Related cards

These cards share a subject or reading mode with the card above.

WonderSpace

In 1962 John Glenn asked for NASA mathematician Katherine Johnson to check the electronic computer's orbit calculations by hand before his flight. If she said the numbers were good, he said, he was ready to go. He became the first American to orbit Earth.

Johnson worked from 1953 at the Langley research centre in Virginia, first for NASA's predecessor, NACA, and then for NASA. She began among the 'human computers', mostly women who did calculations by hand, in the segregated West Area Computing unit for Black mathematicians. She calculated the trajectory for Alan Shepard's 1961 flight, checked Glenn's orbit and later worked on Apollo 11's path to the Moon. When Apollo 13 was crippled in 1970, her work on backup procedures and charts helped the crew return safely. She retired in 1986, received the Presidential Medal of Freedom in 2015 and became widely known through the 2016 book and film Hidden Figures. She died in 2020, aged 101.

NASARead card
WonderBiography

In her 1925 doctoral thesis, the British-American astronomer Cecilia Payne showed that stars are made mostly of hydrogen and helium, unlike the Earth. She read this from starlight split into its colours, using new physics that explained how heat strips electrons from atoms.

At the time, astronomers assumed stars had roughly the same make-up as the Earth. Working at Harvard College Observatory, Payne showed that the differences between star spectra, starlight spread out into its colours, came mainly from temperature rather than composition, and that hydrogen was vastly more abundant than anyone expected. Henry Norris Russell, the leading American astronomer, found this implausible, and in the published thesis she called her own hydrogen figure 'almost certainly not real'. Four years later Russell reached the same result by other means and acknowledged her work. The astronomers Otto Struve and Velta Zebergs later called hers the most brilliant PhD thesis ever written in astronomy. In 1956 she became the first woman promoted to full professor in Harvard's Faculty of Arts and Sciences.

Cecilia Payne-GaposchkinRead card
WonderBiography

In 1912 Henrietta Swan Leavitt found that certain pulsing stars, called Cepheids, take longer to brighten and dim the brighter they really are. That rule turned them into cosmic measuring sticks: by timing a Cepheid, astronomers can work out how far away it is.

Leavitt joined Harvard College Observatory in 1893, at first as a volunteer, as one of the women known as 'computers' who measured stars on photographic plates for low pay. Studying the Magellanic Clouds, two small galaxies whose stars all lie at roughly the same distance from us, she catalogued 1,777 variable stars. Because they were all about equally far away, a Cepheid that looked brighter really was brighter, which revealed the link between brightness and period. Once others had measured the distances to a few nearby Cepheids, the rule could be used anywhere. In the 1920s Edwin Hubble used it to show that the Andromeda nebula lies far outside the Milky Way. Leavitt died in 1921, before the importance of her work was widely recognised.

Henrietta Swan LeavittRead card
DriveSpace

Nancy Grace Roman, NASA's first Chief of Astronomy, built the agency's space astronomy programme in the 1960s and spent years winning support for the telescope later named Hubble.

Roman, an astronomer who had studied the motions of stars, joined NASA in 1959 and became the first woman in an executive post at the agency. She ran its early orbiting observatories and, once they worked, began arguing for a large telescope above the atmosphere, which blurs and blocks much of the light from space. In 1971 she set up a steering group of astronomers and engineers to define what the telescope had to do, then spent the 1970s building support and writing testimony for Congress. She also backed investment in electronic light detectors, and Hubble became the first major observatory to use CCDs, the kind of sensor later found in digital cameras. She retired in 1979; Hubble was launched in 1990, and she is often called the 'Mother of Hubble'. In 2020 NASA named a new space telescope after her.

Nancy RomanRead card
WonderSpace

Wang Zhenyi, an 18th-century Chinese scholar, explained lunar eclipses with a round table as the Earth, a hanging crystal lamp as the Sun and a round mirror as the Moon. Moving them showed how the three line up.

Wang lived from 1768 to 1797 in Qing-dynasty China, where women were rarely allowed to study astronomy. She learned from her grandfather's large library and from her family, and taught herself most of her mathematics and astronomy. She argued that the Earth is round, against the old idea of a flat Earth under a round sky, wrote on the slow shift of the equinoxes, and rewrote the mathematician Mei Wending's difficult Principles of Calculation in simpler language for beginners. Only about ten of her scientific papers survive, partly because much of her work was destroyed during her final illness; she died at 29. She also left 13 volumes of poetry and prose, and wrote that women and men have the same reason to study. A crater on Venus is named after her.

Wang Zhenyi (astronomer)Read card
Next card in the archiveUmm Kulthum, the Egyptian singer known as 'the Star of the East', was one of the most celebrated voices of the twentieth-century Arab world. Her monthly radio concerts of classical Arabic poetry, sung with long improvised passages, drew listeners across the region.Read next →