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A neutron star packs more mass than the Sun into a ball only about 20 to 25 kilometres across, roughly the size of a city. Its matter is so dense that a single teaspoonful would weigh billions of tonnes on Earth.

Astrophysics

Science

The story behind the card

A neutron star is what remains when a star of more than about eight times the Sun's mass runs out of fuel. Its core collapses, and the outer layers are blown away in a supernova, a vast stellar explosion. The collapse forces electrons into protons to make neutrons, the particles that give these stars their name, packed as tightly as in the nucleus of an atom. Walter Baade and Fritz Zwicky predicted such stars in 1934. The first evidence came in 1967, when Jocelyn Bell, a PhD student at Cambridge, and Antony Hewish picked up regular radio pulses that proved to come from spinning neutron stars, now called pulsars. The fastest known spins 716 times a second. In 2017, detectors recorded for the first time the gravitational waves, ripples in space and time, from two neutron stars colliding.

Türkçe oku
Nötron yıldızının kütlesi Güneş'inkinden fazladır, ama çapı yalnızca 20–25 kilometredir; yani bir kent büyüklüğündedir. Maddesi o kadar yoğundur ki bir çay kaşığı dolusu, Dünya'da milyarlarca ton gelirdi.

Nötron yıldızı, kütlesi Güneş'in yaklaşık sekiz katından büyük bir yıldızın yakıtı tükendiğinde geriye kalan çekirdektir. Çekirdek kendi üzerine çöker, dış katmanlar ise süpernova denen dev bir patlamayla uzaya savrulur. Çöküş elektronları protonların içine bastırarak nötronlara dönüştürür; yıldız adını bu parçacıklardan alır ve maddesi bir atom çekirdeği kadar sıkı paketlenir. Walter Baade ile Fritz Zwicky böyle yıldızların varlığını 1934'te öngördü. İlk kanıt 1967'de geldi: Cambridge'de doktora öğrencisi olan Jocelyn Bell ile Antony Hewish, düzenli aralıklarla gelen radyo sinyalleri yakaladı. Bu sinyallerin, bugün pulsar denen dönen nötron yıldızlarından geldiği anlaşıldı. Bilinen en hızlı pulsar saniyede 716 kez döner. 2017'de ise iki nötron yıldızının çarpışmasından doğan kütleçekimsel dalgalar, yani uzay-zamandaki dalgalanmalar ilk kez ölçüldü.

Sources and further reading

Background reading: Neutron star
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