Monday 5 June 2017


Spring is nearing its end and so we're saying goodbye to the galaxy season. In order to go out with a bang, I present you one of Spring's classics: the famous "Antennae" galaxies in the obscure constellation of Corvus, the crow. Frustration will be the share of observers in the more northern latitudes because this object appears not very high above the horizon to them. Even from my home in Northern Italy I had to point my binoscope fairly low, into the hazy glow above the mountains. Yet, I've never seen this pair of colliding galaxies like this before. Simply amazing! 

NGC4038 and NGC4039 are indeed two spiral galaxies that are crashing into each other right as we speak! Or make that 63 million year ago because that's how long it takes for their light to reach us. A billion years ago, they were still two separate galaxies, each minding its own business. But alas, gravity condemned them to a dramatic fate. 600 million years ago, they started to collide and NGC4039 (the somewhat smaller, upper half on my sketch) literally passed through its counterpart whereby both galaxies were severely disrupted. Both galaxies released long tails of stars in the process, which were invisible to me but which show well on long-exposure photographs - hence the nickname "Antennae". These star trails extend some 360,000 lightyears into space! 

Within another 400 million years the Antennae's nuclei will collide into a single, supermassive black hole. Simulations suggest that the galaxies will eventually melt into a big, elliptical galaxy, much like M87. For the time being, the collision's triggering an incredible burst of activity and star formation, as you can guess from the many complex and bright internal structures.

This is also the fate that awaits our own Milky Way in 5 billion years, when we'll crash into the Andromeda Galaxy. But don't worry, this doesn't mean the end. Even though galaxies contain hundreds of billions of stars, they're mostly void and it's not likely that the stars themselves crash into each other. Think of the enormous distance between our Solar System and the nearest stars! No, the Earth will die around approximately the same time - supposing that we, stupid human beings, haven't cocked up our planet before - but not because of the collision with Andromeda. In 5,4 billion years from now, our Sun will run out of hydrogen and will enter its red giant phase, fusing helium into heavier elements. This will cause our Sun to grow considerably; so much that Mercury and Venus will be swallowed up and the Sun's outer atmosphere might even reach the Earth. So we will get scorched or our planet may even evaporate altogether. Suddenly a collision with Andromeda seems somewhat less worrying, doesn't it?

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