One ring to rule them all

In the 1980’s, astronomers observing at radio wavelengths discovered a ring of gas in the constellation of Leo. It lies more than 30 million light years from us, spans 650,000 light years across and is associated with the galaxies NGC 3384 and 3368 (aka M96). As with other massive inert structures, the origin of the thing wasn’t immediately apparent.

Last year, astronomers using the GALEX ultraviolet space telescope recorded ‘metals’ (which in astronomical terms are any atoms apart from hydrogen and helium) in the ring. This suggested to them that the ring was the outer shell of a load of gas that collapsed to form a galaxy. As stars grew old and died in the galaxy inside the ring, they leaked out the metals they created through nuclear fusion, blown away on stellar winds and the force of a star’s dying breath in the form of supernovae and novae. However, this year, things have changed again. Something else lurks in the ring.

Stars. Stars can only be formed in the dense areas of gas and dust inside galaxies, wisps of primordial gas just don’t cut it. So if there are stars in the gas in the ring, as the Canada-France-Hawaii telescope says there are, then the gas in the ring must have come from a galaxy. How does this happen? Well a simulation of a collision between the two galaxies the ring is in orbit of shown in Astronomy Now suggests a billion years ago, the two came together in an incredibly violent encounter that threw out massive amounts of gas, tearing stars from the outer edges into the darkest regions of cold space to wander alone.

This things are not entirely unknown. Just below the right hand ‘V’ in the ‘W’ of Cassiopeia lies the Andromeda galaxy. Year on year, it grows imperceptibly brighter as the massive galaxy, possibly the largest in our local group (we’re not one hundred percent sure of our own Milky Way’s size, but it is similar), edges on its inevitable way towards us. It won’t hit in our lifetime, but will arrive in around four and a half billion years, when the Sun is preparing to swell into a red giant star, creating a very violent time for the Earth. Either Andromeda will strike the Milky Way and the two will forge a new giant elliptical galaxy in which the Sun will sit as a red giant with a crisp of an Earth around it, or the Andromeda galaxy will pass by, interacting with the Milky Way in such a way as to strip it of the outer stars – including our own Sun. So as the solar system watches the Sun bloat out into something big, red and deadly, swallowing Mercury and Venus whole, it may be that our home galaxy will be seen to recede slowly from view, with another galaxy eventually achieving equal brightness in a deadened night sky in which the stars are sparse and slowly fading out.

Hopefully that’ll cheer you up during this summer rain.

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