4.3 million solar masses: the weight of the black hole in the middle of our Milky Way
Black holes are the most powerful predators in the universe, lurking in the darkness of space for billions of years. Natural laws don’t apply to them. Anything that gets too close to a black hole disappears forever – be it an asteroid, planet or even a su
hen a star suddenlysudde seems in a hurry, it’s down to one of two reasons: first, it got too close to the explosion of a neighbouring star and was violently pushed away by the force of the impact. Barnard’s Star, a low-mass red dwarf, reached a record speed of over 500,000 kilometres per hour as a result of this process.
Second, it got too close to the greatest predator in the universe – a black hole. These gigantic star-eaters lurk unseen in the deepest darkness at the centre of the universe for billions of years and mercilessly swallow whatever gets too close to them. This leads to the dramatic end of a star’s life, with no chance of escape – even if it’s racing along at no less than 1.4 million kilometres per hour. But where do the monstrous top dogs of the universe find the strength to tear entire solar systems to pieces?
Black holes are true serial killers – they are always devouring something. Let’s take the monster black hole at the centre of the Milky Way as an example. Sagittarius A* is massive, weighing 4.3 million times the mass of our sun. And it has a huge appetite. It regularly gorges on a star – before indulging in planets, asteroids and gas clouds for dessert. With an age of at least 11.4 billion
years, Sagittarius A* has probably gulped down hundreds of thousands of stars in its lifetime.
In order to murder a star, a black hole simply has to stay still – and wait. As soon as something approaches it, the object will be attracted to its unimaginably large force of gravity – and swallowed in one gulp. An escape attempt is futile. The maximum speed in the universe is limited by the speed of light – 299,792,458 metres per second – and at a certain distance from the black hole, this is no longer fast enough to escape its jaws. This effect allows the galactic cannibals to appear black, even though they’re actually full of light.
However, there’s no need to panic – Earth doesn’t lie in the hunting grounds of a black hole. The nearest star-eater, A0620-00 in the constellation of Monoceros, lurks at a distance of around 3,500 light years – roughly 3,500 times 9.5 trillion kilometres – which is much too far for it to be a threat to us. But exactly how close would the Earth have to get to a black hole for it to be able to snap us up? The figure varies because it’s different for every black hole – and depends on the density of its mass and, therefore, its gravitational force.
The most dense – and, consequently, the smallest – known black hole is XTE J1650-500. Located in the Ara constellation, it is around 15,000 light years away from Earth, has a diameter of just 24 kilometres and a static 3.8 solar masses. The density of XTE J1650-500 is about one quintillion kilograms per cubic metre. As a comparison, the average human has a density of around 1.06 grams per cubic centimetre, while a teaspoon of matter from XTE J1650-500 weighs around 1,000 times as much as the Great Pyramid of Giza. Don’t get too close.
Hydrogen clouds condense into a compact ball of gas and a star is born. The star begins to fuse hydrogen with helium – and produces energy in the process. Stars, such as the sun, lose their outer layers at the end of their lives due to the force of a supernova explosion.
If the star exceeds the limit of 1.44 solar masses, its burning processes change. The growing giant begins to fuse helium and then carbon.
Sun Neutron star White dwarf Black hole
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In the end, a white dwarf is all that remains of our sun. The star expands and fuses heavy elements like neon and oxygen to meet its own energy needs. Iron is the last element to form during the nuclear fusion. The core then collapses and unleashes a supernova. Neutron stars form when the dying star has eight to 20 solar masses. Stars with more than 20 solar masses turn into a black hole.