4.6 billion years ago, in an obscure region in the outer limits of the Milky Way galaxy, a new star was born from a cloud of gas and dust, predominantly composed of hydrogen gas. Around this new star, among a plethora of miniscule asteroids, a very particular assembly of planets eventually formed – four small inner rocky planets, and four, considerably larger gaseous counterparts in the farther reaches of the system. The third of these rocky planets fell into orbit around the new star at a distance which allowed liquid water to be present on the surface, with its size, mass and composition enough to sustain a rather thick atmosphere. 4.6 billion years later, this star and its planets are still here, and a species of intelligent beings call their habitable third planet ‘earth’.
The sun itself sustains most of the life that proliferates on our home planet. Only chemosynthetic organisms, mostly thriving deep in the earth’s oceans, do not derive the source of their energy from our parent star. All other ecosystems on our planet derive their energy from photosynthetic organisms as the basis of food chains – mostly, plants. And yet, even though our sun has been around for almost five billion years, sustaining life on our planet for at least around four billion of those years, the sun will not last forever.
The sun is currently stable due to two main opposing forces
In around five billion years time, the sun will eventually burn its entire supply of hydrogen present at its core. The sun is currently stable due to two main opposing forces; energy generated from its fusing core opposed by its own gravity. When the sun burns its entire hydrogen supply in the core, the core will contract slightly until the temperature becomes high enough to start burning hydrogen just outside the core as well. Since the fusing material is present closer to the surface, the sun’s outer regions will expand slightly as a result. Eventually, when this hydrogen is also extinguished, the core will contract again until the temperature in the core is high enough to start fusing helium. At this point, the core would be much hotter, and as a result, the sun’s outer layers will expand even further – a red giant is formed. At this point, the sun’s outer layers will reach out to approximately where the earth is right now. The surface temperature, with the surface now being much further from the core itself, drops by a couple thousand degrees, and thus the sun becomes red.
Eventually, however, the sun will also extinguish all of its helium, converting it mostly to carbon and oxygen via fusion. At this point, the sun will never be able to reach high enough temperature at the core to burn any further elements, and eventually the sun loses its outer layers, revealing the exposed, contracted and very hot core at the centre. Such exposed stellar cores are referred to as white dwarfs. This is the ultimate fate of the sun, a white dwarf corpse surrounded by the former outer region components of the sun, moving outwards and becoming more dispersed. This structure is referred to as a planetary nebula.
How do we know this? We have observed a number of planetary nebulae, which were previously sun-like stars, which have already run their course! Such examples include the famous Ring Nebula and the Dumbbell nebula, both currently visible with a telescope under dark skies from Malta.
Josef Borg is currently a PhD student within the Institute of Space Sciences and Astronomy, University of Malta, and also the president of the Astronomical Society of Malta.
Did you know?
• The sun contains around 99.8 per cent of the entire mass in our solar system. Our parent star truly dwarfs the rest of the objects in our solar system combined. All the planets and their moons, together with all the countless asteroids and icy bodies in the Kuiper belt and beyond, make up about 0.2 per cent of the mass of the entire solar system. The rest of the solar system’s combined mass is the sun itself.
• Stars form from huge molecular clouds of gas and dust in space, termed nebulae. Material from such nebulae starts to accumulate, resulting in the formation of a huge cloud of predominantly hydrogen gas in the centre. This huge cloud gets denser and denser, forming a rotating ball of gas at its centre. At its core, under its own gravitational pressure, this ball of gas reaches extremely high temperatures – millions of degrees – until the temperature becomes high enough to start fusing hydrogen into helium. At this point, a star is born.
• The sun is found around eight light minutes away from earth. The sun might seem close, but it’s actually rather far away. Light travels at a speed of 300,000km every second – thus, we say that a distance of 300,000km is equal to one light second. The Sun is a full eight light minutes away – around 150 million km away from earth.
For more trivia see: www.um.edu.mt/think
Sound Bites
• As Galaxy clusters collide, 10 million light-years of radio waves link them
Astronomers have spotted a ridge of radio emissions 10 million light-years long joining two galaxy clusters that are slowly colliding with each other. The researchers studied two galaxy clusters dubbed Abell 0399 and Abell 0401 using the low-frequency array, or LOFAR, based in the Netherlands. That observatory is perfectly tuned to spot very long low-frequency radio waves in space. The scientists used the array to study this pair of galaxy clusters because other observations had spotted a filament joining them, part of the massive web that fills much of space.
https://www.space.com/radio-ridge-between-galaxy-clusters.html
• Telescope spots double-asteroid system during close flyby of earth
A recent close encounter with a large asteroid and its little moon was captured by a telescope as the pair zipped past earth at 43,500 miles per hour (70,000 kilometers per hour) on May 25.
The image, captured by the European Southern Observatory’s (ESO) Very Large Telescope on May 25 and released on June 3, shows asteroid 1999 KW4 and its accompanying satellite whizzing past earth at a safe distance of about 3.2 million miles (5.2 million km). Asteroid 1999 KW4 is about 0.8 miles (1.3 km) wide, and its little companion orbits at a distance of around 1.7 miles (2.6 km).
Even though this asteroid was not at risk of colliding with our planet, its image could provide useful data on asteroid deflection, should one be headed towards earth in the future.
https://www.space.com/double-asteroid-earth-flyby-vlt-photo.html
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