S5-HVS1 by Bill Kirton

Courtesy NASA/JPL-Caltech

This is a deliberately different blog, but it’s not very long, so please bear with me. I know it's that season, but I didn't want to do any Star of Bethlehem stuff, so I found a substitute and decided to tell you about a star called S5-HVS1. I know, I know... it's not a very romantic name. But that's fine, because it’s not a star you’ll gaze at with your loved one as you quote Byron at her/him and swear eternal devotion. Why? Because it’s heading out of the Milky Way at 1,700 kilometres A SECOND.

But it wasn’t always so hell-bent on leaving us.

Oh no. Once it was part of a binary star system, but the two of them got a bit too close to Sagittarius A*, the black hole at the middle of the Milky Way, which is bigger than 4 million suns. (Actually, 'bigger than' is probably wrong there because, apparently, when something has 'greater mass' than something else, that doesn't necessarily mean it's bigger.)

Anyway, it turned out be not a good idea, because the two stars spiralled inwards, and the one which wasn’t S5-HVS1 switched into a binary partnership with Sagittarius A*.

Well, we’ve all heard what black holes are like and, sure enough,  the star which wasn’t S5-HVS1 got sucked into its new partner and just vanished into… well, nowhere. But…

another result of this break-up of the relationship was that poor old S5-HVS1 was not only ditched by its partner, but got hurled away at a ridiculous speed and, in about 100 million years, it’ll leave our galaxy and carry on drifting through intergalactic space, all on its own, FOREVER.

But my point in writing of this event in such a seemingly flippant way is not really to highlight the phenomenon itself. It’s to register my awe at the fact that a handful of human beings (at the Siding Spring Observatory of the Australian National University, as it happens) have actually measured and speculated confidently about it and have brains huge enough to comprehend things such as enormous speeding stars, galaxies, black holes, event horizons and even conceive of eternity itself.

In fact the whole process I’ve described (thanks to a report in The Guardian newspaper) is known as the Hills mechanism, because the astronomer Jack Hills proposed the likelihood of it happening more than 30 years ago.

A member of the team, Emeritus Professor Gary Da Costa said that S5-HVS1 will just ‘keep going and eventually end up as a white dwarf like our sun; it just won’t have any neighbours’. (
I love the casual use of ‘eventually’ there.)

When Hamlet told Horatio: ‘There are more things in heaven and earth than are dreamt of in thy philosophy’, he didn’t know the half of it.


Sandra Horn said…
My brain cannot comprehend all this cosmic mallarky, but thank you for trying...have a wonderful Winter Solstice, Bill!
Umberto Tosi said…
I'm with S5-HVS1! I left this galaxy more than 30 years ago myself - about when your star transitioned from binary to metaphor! Happy holidays and thanks for another most engaging post, Bill!
julia jones said…
I only have a little brain but yes -- I'll register my awe at the people who research and understand these things. Maybe we'll discover that the Magi were really travellers from the Siding Spring Observatory doing a bit of intercontinental time lapse...
Bill Kirton said…
Thanks, all. I re-read it myself today and was yet again filled with wonder. I just can't cope with such extreme velocities, distances, time scales. God must be even more powerful than the vicar said he was.

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