Hypothetical Astronomy
May 15, 2012 5:49 PM   Subscribe

If all non-solar-system stars ceased to exist, how would things look different to us on earth? Would anything change?

Imagine if all stars that did not have planets orbiting them suddenly blinked out. (That means our sun is safe.) How many stars would blink out? Would the sky be twice as dark at night? Almost completely dark? Would it effect anything on Earth as we know it?

A kid asked me this on the train today, as I was reading a book with the solar system on the cover. My mind was blown by a six year old.
posted by juniperesque to Science & Nature (16 answers total) 2 users marked this as a favorite
I think this really depends on what you define as a planet.
posted by RonButNotStupid at 5:52 PM on May 15, 2012

No one really knows yet. In about 50 years we'll have a lot better idea.

CPB's average (a mean) doesn't really tell you anything, because the range and deviation appears to be very wide. All that really says is that they are estimating that there are 1.6 times as many planets as stars -- but stars with planets likely have several. And as RBNS says, "what's a planet?"
posted by Chocolate Pickle at 6:07 PM on May 15, 2012

Well, leaving aside the planet issue, the closest star is over 4 light years away, so you'd see absolutely nothing different for 4 years. Then Alpha Centauri (Rigil Kentaurus) would disappear. Several years later, Sirius (α Canis Majoris) would follow. Most of the stars that you can see with the unaided eye in the sky are just mind-bogglingly far away and wouldn't disappear for centuries. For instance, all the stars in the Big Dipper are 78 light years away or further. It would take centuries for celestial navigation to be severely affected, during which time the positions of the stars would have changed (or rather, appeared to change) a fair amount anyway.

As far as any other affects on humans, the stars in the sky provide noticeable light only in the most remote of rural areas. Even if the stars themselves vanished from existance, there's no gravitational effects to speak of. The only thing I can think of that might have to change would be astrology. Really nothing at all would happen, which is probably why the completely pointless light pollution that is universal in suburban and urban areas is so prevalent.
posted by wnissen at 6:32 PM on May 15, 2012 [1 favorite]

Also, as far as "affecting anything on earth", that likely depends on the mechanism for sudden blinking out of these stars (assuming you define a planet such that at least some stars don't have a thing orbiting them which qualifies).

I have a hard time imagining that sudden removal of a source wouldn't at least produce some weird gravitational waves; if the stars did something more violent (all go nova all at once) then that would definitely affect us here.
posted by nat at 6:33 PM on May 15, 2012

You could use CPB's average in a way if you knew the average number of planets around stars with planets - notice this is different from the average number of planets per star.

If we assumed the average number of planets around stars with planets is 10 (for example) then one would find that CPB's average would lead to 93% of stars disappearing... (i.e. only 6% or so of stars would have planets...)
posted by NoDef at 6:39 PM on May 15, 2012

Even if all the individual stars you can see disappeared the nighttime wouldn't be all that much darker - on average we get 15x as much light from Venus as the very brightest star, for instance (and more than 10,000 times as much light from the moon - even when the moon is near new and close to the horizon it brightens the sky appreciably).

The Milky Way (basically, the combined light of billions of stars in our Galaxy) puts out enough light that it can cast visible shadows in a dark enough site, but it looks quite diffuse - you need to be at a dark, clear, fairly moonless site to see it in the first place. So eliminating all stars would have some effect on how dark it is at night, but not one you'd generally be able to notice.

nat: I really doubt that there'd be any macroscopically noticeable gravitational radiation even if you took all stars other than the Sun and (say) compressed them each to black holes. Gravity's an extremely weak force. Gravitational waves from the nearest stars would certainly reach a level where current instruments could detect them, at least.

Regular stars can't go nova (and the energies involved in a nova aren't that great anyway). Supernovae could have an impact on Earth, but only if they are really nearby (and again, there aren't any stars massive enough to produce a supernova close enough to us that this would be a worry): see http://en.wikipedia.org/wiki/Near-Earth_supernova .
posted by janewman at 6:46 PM on May 15, 2012 [1 favorite]

Yeah, I agree, not macroscopically noticeable, but I'd expect detectable. I don't really know though.

Also regular stars can't just all suddenly blink out either so I'm not sure exactly which usually rules we're applying (re the nova comments).
posted by nat at 9:44 PM on May 15, 2012

No one really knows yet [how many stars do and don't have planets]. In about 50 years we'll have a lot better idea.

I'd scale that estimate down by an order of magnitude. The whole point of the Kepler mission is to scrutinize one segment of the sky, essentially a random segment, and count how many planets we find. The mission has only been running a couple years and they're already into the thousands on the candidate planet counter. (and they can only see a small fraction of the planets due to the optical technique they are using) After another couple years, 5 tops, they will have enough data to make a decent estimate of how many stars have planets. And what kinds of planets, distance to host star, etc.

Which will give us very good values for two of the terms in the Drake Equation ...
posted by intermod at 9:51 PM on May 15, 2012

Kepler is looking for transits. It can measure slight brief reductions in brightness caused when a planet passes on front of a star.

Kepler thus can only detect planetary systems where we are on the planetary ecliptic. If we aren't, Kepler isn't going to see anything.
posted by Chocolate Pickle at 9:56 PM on May 15, 2012

nat: In the extreme case (shrinking to a black hole) gravitational waves should definitely be detectable - LIGO is expected to be sensitive enough to detect mergers of 10-solar-mass black holes up to a few Mpc away; Alpha Centauri A has about one-twentieth as much mass, but is a million times closer than that limit (and the strength of the gravitational waves that reach us should follow an inverse square law, so waves from the collapse would be ~10^12 times stronger). LIGO should definitely notice (though we'd see Alpha Centauri disappear at the same time, since gravity waves travel at the speed of light).

A nova is a very specific type of event: basically fusion that starts up when material is dumped onto the surface of a white dwarf (the extreme density of the white dwarf is required for a nova to occur). Nothing like that can happen in anything like a regular star.
posted by janewman at 10:02 PM on May 15, 2012

Chocolate Pickle: the fact that Kepler will only catch edge-on systems isn't really a limitation - correcting for that is pretty simple (just a matter of geometry and the assumption that the orientations of the systems will be distributed randomly).

A bigger problem is that you really need to see repeated transits to characterize a system (e.g., to determine the orbital period). For Jupiter, that would take 12 years... it'll take much more than 5 years before we can estimate the full distribution of planets from Kepler data (at least without making a lot of assumptions about how planets would be distributed in mass and distance that would allow you to extrapolate from the period/diameter/stellar mass ranges constrained so far).
posted by janewman at 10:06 PM on May 15, 2012

Best answer: I don't think we really need the rest of the galaxy for anything. It could all wink out and, assuming the sun didn't, we'd be fine for hundreds of millions of years.

That doesn't mean we never got anything from the galaxy. We did: all the beautiful elements our planet and ourselves are made of, which were all formed in long-ago novas and supernovas.
posted by zompist at 1:41 AM on May 16, 2012 [1 favorite]

I happen to keep a list of stars within 23 light years that are likely to have solid ground in some form. As such, the title for it is the Terra Firma List. The logic is basically:

1. Rocky planets, asteroids, comets, Kepler bodies, debris disk, etc. detected.
2. Gas giants detected. Ever notice how our gas giants act as mini solar systems? Moons count as Terra firma.
3. Brown Dwarfs: really big gas giants, see #2.

There are around 164 systems on the list (it changes often as measurements are made). Within that 164, there are 28 that fit the bill, including Sol. That's around 17%, meaning 83% of the stars in our part of the galaxy would disappear. I don't know what the distribution in other parts of our galaxy are, let alone other galaxies though.

For those that are curious, these are the terra firma stars by order of nearest to furthest away: Sol, Sirius A (largely included because the Dog Star is just awesome), Epsilon Eridani, Epsilon Indi Ba & Bb, Tau Ceti, SCR 1845-6357, UGPS J072227.51-054031.2, DEN 1048-3956, GJ674, Gliese 876, LHS 288, Groombridge 1618 (possible), DENIS J081730.0-61552, GJ832, LP944-020, DEN 0255-4700, 2MA 0939-2448, Stein 2051 A, 2MA 0415-0935, GJ229, GJ570, 2MA 0937+2931, GJ581, SIMP J013656.5+093347, Xi Bootis A and B, and GJ667.

Linked stars are the cool ones with known planets. Most of the rest are brown dwarfs. Many of the stars have things that'll kill us, like X-Ray producers and binary companions that'd make stable orbits difficult. Gliese 876 and GJ581 are the nice ones with tons of planets. Personally, I like Epsilon Eridani the most. The star is similar to our own, and it's nice and close.
posted by jwells at 5:27 AM on May 16, 2012 [1 favorite]

Cool, jwells!

Can you explain your logic again? I'm not following the 1-2-3.
posted by intermod at 7:14 PM on May 17, 2012

It relies on direct detection, and the nature of a parent object. The first is simpler. We infer the presence of a planet a few ways, like when a star's light dims as it passes in front. Astronomers are then able to work up the size of it from several observations. There's also infrared observation. When we look at Tau Ceti (paraphrasing here) we just see this huge blob around the star, which is the debris disk. That technique works on other stars too, like Epsilon Eridani, and maybe Sirius. The debris is those disks tends to clump together, via a process that isn't understood very well*, into solid ground (asteroids, comets, planets, etc.). And sometimes we just see big clumps in the disks, which is solid ground big enough for us to see.

The nature of the parent object is more difficult. As proposed on Kuro5hin, if we look at our own solar system, gas giants behave less like planets and more like stars. We can run a small thought experiment and say that if Sol's debris disk had been a bit bigger, with slightly different composition, Jupiter might have gathered enough matter to form a star. We'd have a binary star system and Earth would likely get roasted, but thats beyond the point. So, each gas giant 'star' has its moons ('planets'): Jupiter has 66; Saturn 62; Uranus 27; and Neptune 13. The clincher for this is the 'planets' discovered around brown dwarfs, which are closer to being a star than Jupiter. Are they moons or planets? Closer to home, are Jupiter's moons/planets natural moons, or captured asteroids? I don't care. They're either likely to have solid ground or not, and they are.

So using this line of thinking, we can create the short list of the 28 stars I gave above, out of the 164ish stars within 25 lightyears. It includes stars that have debris disks, planets, asteroids, etc. (basically the 12 I linked to), as well as objects that are likely to be orbited by such objects, but that are so small we can't detect them yet.

* The astronaut who did that, BTW, is on ISS now. He is the one that grabbed the Dragon capsule with the robotic arm a few days ago.
posted by jwells at 6:59 AM on May 31, 2012

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