Exeter, Devon UK • Jul 15, 2024 • VOL XII

Exeter, Devon UK • [date-today] • VOL XII
Home ScienceLite Science When Stars Collide

When Stars Collide

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This story really has it all. Really it does; astronomy, physics, chemistry, two dying stars spiralling into one another (resulting in a cataclysmic explosion) and a whole lot of gold, the earth’s mass in gold to be precise!

It all started in a galaxy not too far away – about 130 million light years away in fact, in the earth’s ‘cosmic backyard’. Two neutron stars, due to mutual gravitational attraction, spiralled into one another releasing large bursts of energy reverberating across the universe.

So, what is a neutron star? In good old KS3 physics you may have been taught a bit about stellar evolution, and you might recall that a neutron star is formed when the core of a large star (20-30 time more massive than our Sun) collapses in on itself. Like black holes, they are classified as ‘extreme gravity objects’ and are in fact the smallest and densest stars known to exist within our universe. With a radius the size of 15km they are the equivalent to squashing the mass of the sun into a volume the size of London!

Stars Collide. Source: Pixabay

The energy released by a star has information embedded in it concerning the properties of the source. It’s mass, location and composition can all be decoded once detected. For the last half a century scientists have developed increasingly advanced technology to help us probe the universe using a range of radiation, the latest being gravitational waves.

Many readers may be familiar with LIGO (Laser Interferometer Gravitational-wave Observatory); this year’s Physics Nobel Prize was awarded to three of its contributors. There are actually two LIGOs, both in the USA one at Hanford and the other at Livingston. They are both 4km in length and were constructed with the aim of detecting gravitational waves or ‘ripples in space time’ emanating from cosmic explosions. Since they came on line gravitational waves from five black-holes mergers have been detected but not from other cosmic characters, until recently.

This event marks the beginning of a new frontier in astronomy

On 17 August high energy bursts of gamma radiation were detected by both LIGOs and VIRGO (the European gravitational wave detector). Using all three detectors allowed for the triangulation of the signal, pin pointing the direction for astronomers to place their telescopes in order to study the light emitted.

With over 70 collaborating telescopes and the gravitational wave detectors working together across the globe, it meant that for the first time ever the signals could be studied using both gravitational waves and the entire electromagnetic spectrum, from high energy gamma radiation to low frequency radio waves. The use of all types of signal is called multi messenger astronomy.

So why was this event so ground-breaking? For a long time scientists have been wondering over the mystery of how heavier elements such as platinum and gold were forged, as fusion in red giants can only form elements up to iron, which is only the 26th element in the periodic table. Leading theories claimed that energetic merges, such as this, are responsible for the production of the heavier elements such as gold, silver and uranium, elements that play a crucial role in modern life.

Cosmic Explosion. Source: NASA

Now, by studying the infra-red spectrum of the radiation emitted, this theory appears to be correct. The spectra contain the distinctive fingerprint of these heavier elements that have been forged.  It has actually been estimated that the collision of these two neutron stars would have created the mass of earth in gold. The collision has also provided information concerning how quickly our universe is expanding. The typical method of this determination is carried by measuring the speed at which a ‘standard candle’, which is an astronomical body with known luminosity, is moving relative to the earth.

It’s already been hailed as the most significant astronomic event of the last decade and there is still plenty more data to be deciphered.  The merging of these dying stars has brought a global community of astronomers and physicists together to explore the universe using completely different signals. This event marks the beginning of a new frontier in astronomy where we can make use of electromagnetic and gravitational waves to explore our vast and chaotic universe.


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