The Spica system

[Malenfant]

After much digging around, it seems that the Spica system may be able to hold onto some planets after all.

From what I've uncovered, Spica (Alpha Virginis, arabic name "Azimech") is a rather complex system. It consists of:

- A B1 V/B4 V Close Binary pair with a separation of 0.12 AU.

- a B5 V star orbiting the pair at 4 AU

- a B7 V star orbiting others at 40 AU

- a distant K V star presumably orbiting (?) all of the above at about 10,000 AU.

The B V quadruple system is ridiculously off-limits

, but the K V system may well have planets - it's likely that it would be a captured star, which means it's probably much older than the B V stars (which are only a few million years old, tops). It's also out of range of the nasty X-ray radiation that the B V stars emit.

So there's a definite possibility that the K V star (we'll say it's a K5 V) can have a planetary system with a habitable world around it!

It's a bit of a twist, since the planet wouldn't actually be orbiting any of the stars that we're familiar with as "Spica", but hey, if it works it works

.

The view would be rathre pretty from such a world - the close binary pair would appear as single very bright star at magnitude -15 nearly 10 times brighter than the full moon and easily visible in daylight, the middle B5 V companion would poke out from the inner pair about once a year as a separate star at magnitude -13, and the outer B7 V companion would be a separate star that would get as far as about half the diameter of the full moon from the others at magnitude -12.

(thanks to Grant Hutchison on the Celestia boards for that info

)

 

[mike wightman]

Thanks for that Mal, I'd found this link , and I was wondering if you could add any more to this

the brighter nearing the end of its stable lifetime

 

[Malenfant]

Yeah, that's the site I first looked at to get the info

.

I've seen the first star occasionally classed as a V-IV star, which means it's about to become a subgiant. These massive stars only spend a few million years as Main Sequence stars.

The B stars will probably rapidly evolve into supergiants and start puffing out their outer layers, which means the skies around the K V companion are going to get prettier

. And very soon after that (about a million years or two at most) they'll all start blowing up as supernovae, which means that the K V system is going to get fried. The planets around them would probably survive though at 10k AU from the other stars, but they'll be toasted.

 

[mike wightman]

So are there any changes between now and 3504 years in the future that could be included?

How long does it actually take for a star to change, i.e. expand etc.???

 

[Malenfant]

We can probably assume that there are no significant changes on that timescale. Any change would be apparent over the order of 100,000 years, probably.

 

[mike wightman]

There must come a day when everything changes. Is this a gradual shift over tens of thousands of years, or something that occurs in a matter of months?
Do we know exactly how old Spica's primary star is and how long its got left, or is it more of a best guess thing?

 

[Malenfant]

No, it's a gradual shift. If it was a red supergiant (like Antares...) then the final stages before the supernova would occur over a timescale of years and things would change more noticeably. But these are B V stars, and even for them things take longer to change.

The primary star at Spica probably has at least a few hundred thousand years before anything changes noticeably - it might have edged a little bit closer to subgianthood over three and a half thousand years, but not enough to be really noticeable. The other B stars probably have more like a million or two million years - the K V of course is going to be pretty static throughout.

 

[Gruffty]

Mal, the stellar data for Spica system is brilliant - that's a really excellent piece of work on your part. I had no idea Spica was such a complex system (it doesn't come up the way you've described it in my copy of Celestia!).

Now we have a description of the "title system" of the sector, plus a realistic chance of a planetary system and possibly a habitable world as well .

 

[Gruffty]

One of Mal's fantastic POVray pictures, showing the multiple stars, would go down a treat.....

 

[Malenfant]

I think you'd have to add some stc files in Celestia to show all the companions. I'll try to make one when I get home. (I sure didn't know Spica was multiple before I checked

). A Celestian rendering of the system would probably look better than a POV one

.

 

[Malenfant]

Actually, having just made the system in Celestia, it's positively underwhelming

.

From a habitable world around the K5 V star, the entire 4 B-star Spica system is just one very bright star. It's not spread out around the whole sky - in fact, even when the whole system is about as widely separated as it can get, it takes up less room in the sky than the full moon does from Earth.

 

[Gruffty]

Oh.

POVray pic then? (Cos the ones on your site are soooooo kewl)......

 

[Malenfant]

The renderer wouldn't make much difference to the layout of the system . Though POVray can at least cope with multiple light sources, which Celestia can't. (and thanks ).

 

[Gruffty]

Bah

 

[Malenfant]

Here's a couple of pictures of Spica, as viewed in Celestia. Note the field of view (the number given there is the vertical field of view of the window, not the horizontal):

View from a world orbiting the K5 V star (Spica E)

Zoom in of Spica A/B/C/D in the previous view

Celestia thinks that Spica A is the sun, unfortunately, so the illumination is somewhat wrong (it thinks its sunset because Spica is near the horizon, which is why the sky in the zoom-in is brown). In reality of course most of the illumination is coming from Spica E, the planet's actual primary.

For comparison, the full moon from Earth is about 31' in size. The angular diameter of Spica E would be about 48'.

Each of the B stars is about 1000 times less bright than the full moon on Earth. So four of them packed into the same spot in the sky is going to provide a fair bit of illumination (but not heat). The world has to be tidelocked as it's close enough to the K star to be habitable, so the 'night time illumination' would light up the dark side when it's facing the B stars as it orbits its primary.

 

[Gruffty]

What about a view of the whole stellar system from space? Would we be able to see the arrangement of the stars a little more clearly from space?

 

[Malenfant]

If you were a hell of a lot closer to Spica A-D, you'd just see the zoomed-in image. (don't forget, the K star is about 10,000 AU from the others)

But otherwise, why would the view magically change if you're not on the planet?

 

[Gruffty]

Just thought it might look pretty, that's all..........

 

[Malenfant]

Well, arguably it is. I mean, there's this bloody great bright star illuminating the darkside's sky (as viewed from some parts of the planet anyway) while the primary isn't there

.

But the real universe isn't like what you see in the 70s and 80s scifi pictures - it's not seven huge moons and blazing stellar disks filling the sky

(at least, not if you want to live there ).