I was looking at this picture from NASA, and reading the description, and I got to thinking:
How do we know there isn’t an extremely faint star, closer than Proxima Centauri? According to the NASA site:
(I wonder what they thought the closest star to the Sun was before 1915.)
I realize with Hubble and our much improved telescopes nowadays, that it’d be harder to miss something, but isn’t there still a gap on the distance vs brightness scale where we might have missed a really close star?
Another thing that makes me wonder this is the recent discovery of the Sagittarius Dwarf Galaxy in 1994 - which was suddenly realized to be the nearest known neighbor to our Milky Way.
My point is, we (as in, the scientific community and by extension us lay-people) are so confident about Proxima Centauri being the closest star - probably as confident as the pre-1915 people were about whatever they thought was the closest - yet history shows that surprises do happen.
How can we be so sure? What are the chances that there is a closer, fainter star than Proxima? If there were such a star significantly closer than 4 light years, would it have a measurable gravitational effect on our solar system?
(please, no facetious remarks about “the closest star is the Sun” - that’s why I carefully tried to mention “the closest star to the Sun”)
Proxima Centauri and our sun used to be close back in their college days, but they kind of drifted apart after the Big Bang. I understand that Proxima Centauri has been dating another sun for some time now.
The thing is a star can only be so dim before it fails to be a star. It’s not likely that an actual star (as opposed to a brown dwarf) is undiscovered in our near vicinity.
Before 1915 I believe that they thought Alpha Centauri was the closest star. They did not know that A.C. was a multiple star system, of which Proxima Centauri is the member that gets closest to the Sun. Or does my memory fail me? Anyone?
According to this, Proxima Centauri is about a million times fainter in absolute magnitude than the Sun. I don’t think a star can get much dimmer than that.
I vaguely remember that Alpha and Proxima being a double system, sometimes Alpha is the closest star, sometimes Proxima is, depending on their position on their orbits (though it seems to me it’s rather long). No dount someone else will know better…
I recall from astronomy class two years ago that it is believed that we have discovered all stars out to 20 light-years. However, I don’t know how certain this statement is, or if it’s been improved on since then.
Here’s another way of putting it: could there possibly be another small, extremely faint star (not brown dwarf) much closer, say 1 light year away, half a light year? Or is it that for an object to be so close but remain undetectable, it physically couldn’t be a star?
I guess we need someone like Bad Astronomer or Chronos to help out with the orders of magnitude involved - I’m not sure what sort of numbers we’re playing with.
I remember there used to be a theory, I think called the ‘Nemesis’ theory that there was a star closer to the sun. It had an orbit of, I think, 23 million years around the sun and every 23 million years or so would disturb the Oort cloud and disturb debris into the solar system some of which struck the Earth causing extinction events. The star would have been very, very faint.
I haven’t heard of this theory lately so I assume it’s dead
This doesn’t answer the OP, but the OP brings up something important. Something that is often missing from news, that is the confidence in the information provided.
Good science reporting will tell the reader/viewer/listener the confidence that the sciences have in a given piece of information. News coverage of science is usually very poor, often being factually wrong (bungling the figures and/or concepts) and rarely indicating the degree of certainty.
[going out on limb]
As this info the cited page is one of Nasa’s done in conjunction with university scientists, the confidence of the statement is probably pretty high since it didn’t use the wording “closest known star”.
[/going out on limb]
All the time I hear CNN stories where they say, “Scientist now say that such and such is true.” Frequently, the truth is that what they were discussing is nothing more than a new but promissing theory that is in the initial stages of being checked out.
An example from a couple of days ago:
CNN was discussing the possible asteroid impact in 2019. They said that if the collision did happen it would be equivilant to a large nuclear weapon.
A large nuclear weapon? Estimates center at about the 1.15 Million Megaton range. 58 Megatons is about the size of the largest device ever detonated. That is a far cry from 1.15 Million, about a factor of 20,000 difference.
That’s the nomen ludi. The lowest luminosity a star can have is 10[sup]-4[/sup] L[sub]SUN[/sub]. I don’t know if you know anything about magnitudes, but that corresponds to M = 14.83. At a distance of 4 light-years, that’s m = 10.27. At 1 light-year, m = 7.26. At 0.5 light-years, m = 5.76. If you’re good, you can see m = 5.76 with your naked eye. I find it extremely unlikely that something that bright could go without being detected. But, as scotth rightly points out, a numerical uncertainty would be helpful, and I don’t have one. Sorry.
Frequently hard science fiction portrays real science very accurately. They are often just fictional stories set against or including very real and accurate science principals.
A few authors that are notable examples:
Larry Niven
Jerry Pournell
Isaac Asimov
John Cramer
John Cramer has even put sections in the back of his books that spell exactly what elements in his story where current true science, what was extrapolation, and what was completely invented for his story line.
A good example of a book that in the course of a fictional story really demonstrates real science effects is the “Integral Trees” by Larry Niven. The way tidal effects line long objects up in a radial spoke pattern is completely accurate. The ability to use tidal forces at the ends of very long objects in a large gravitational gradient as a source of gravity to live in is quite accurate as well. The explanation of how applying force 90 degrees from the directions you want to go will get you there in an orbital situation is very good as well. This is just taken from the top of my head, I am sure there are many more.
If you have seen the recent Popular Mechanics with the article about a bridge to space in it? There is at least one science fiction story based on that idea. The story revolves around advances in material science that hadn’t happened at the time, but the application of idea and engineering details are very good.
One more, if you want a really accurate portrayal of what would happen in a real earth impact (by a space object) event, read Lucifer’s Hammer by Niven and Pournell. The story is fiction, but the situation is plausible and the details of the results are correct.
The comment about the newly discovered dwarf galaxy is misleading.
Nearby dwarf galaxies are hard to detect because they are diffuse and dim. Since stars are basically point-like, you don’t have that problem as far as detection is concerned. It’s much harder to find near-by galaxies as opposed to nearby stars.
That said, there may be some brown dwarf lurking around just below detection limits (at something higher than 20th magnitude, say), but it would have to be pretty small and prety dim and really isn’t a star. Any sustainable star that has nuclear fusion in its core and a significant paralax would have been discovered long ago.