Proxima Centauri Might Not Be the Closest Star To Earth 98
StartsWithABang writes The Alpha Centauri system consists of three stars, including Proxima Centauri, the closest star to Earth. But while main-sequence, hydrogen-burning stars are easy to find due to their visible light output, brown dwarfs — which only fuse the small amounts of deuterium they're born with — often emit no visible light at all, and can only be seen in the infrared. In 2013, WISE discovered a binary pair of brown dwarfs just 6.5 light years away, making them the third-closest star system to Earth, and leaving open the possibility that there may yet be brown dwarfs closer to us than any star, a question that it will take the James Webb Space Telescope to answer.
Are Brown Dwarfs Stars? (Score:5, Interesting)
Re: (Score:3)
Is the quality "star" one of mass, or energy output? Where between white and brown do you draw the line?
Re:Are Brown Dwarfs Stars? (Score:5, Informative)
Is the quality "star" one of mass, or energy output? Where between white and brown do you draw the line?
The no-man's land between planet and star is a question of interior nuclear fusion: planets don't do it, stars do. But a brown dwarf is an object that does it - a little bit, early in life. Fusion of (normal) hydrogen into helium is pretty hard to do, but fusion of deuterium - hydrogen's heavier cousin - is easier. Brown dwarfs have enough central heat/pressure from gravitational contraction that they fuse all their deuterium away, quickly, and then fade into the night. It's thought that this no-man's land mass range is from about 13 to 80 Jupiter masses.
Re: (Score:3)
Re:Are Brown Dwarfs Stars? (Score:5, Informative)
Your question about white dwarfs is spot-on though because those stars are pretty much what #49246567 describes. A star fuses enough hydrogen that the mass of its outer layers drops off, inner reactions then push that layer outward to form a red giant, the red giant sheds those outer layers, and a white dwarf is that hot, deuterium-rich star left behind. That star then cools and dims over time.
Re:Are Brown Dwarfs Stars? (Score:5, Informative)
Not all stars that were large enough to do core hydrogen fusion become red giants. Most red dwarf stars won't because they are fully convective, meaning that they will fuse almost all of their hydrogen in the "core" and not have hydrogen fusion in the shell (and no red dwarf has enough mass to do helium fusion). When low mass red dwarf stars run out of gas they simply pass directly to the white dwarf stage (burnt out core)
Re: (Score:2)
White Dwarfs are exactly what the post above you describes. Hydrogen is fused into heavier deuterium that sinks to lower layers in a star until the outer layer is light enough that it gets pushed outward to form a red giant. Then, that outer layer is shed, leaving behind a bright, hot, deuterium
Re:Are Brown Dwarfs Stars? (Score:5, Informative)
Hydrogen is fused into heavier deuterium that sinks to lower layers in a star
Stars do not produce deuterium. Any environment that can fuse normal hydrogen can easily burn up any deuterium that is present. Nearly all the deuterium in the universe is believed to be left over from the Big Bang. More info here [wikipedia.org].
Re: (Score:2)
Re: (Score:2)
Re:Are Brown Dwarfs Stars? (Score:5, Interesting)
Okay, so it must be helium fusion going on in dwarfs then?
In stars like our sun, the main process is the proton-proton chain [wikipedia.org]. Deuterium is produced, but it is then almost immediately fused with an additional proton into He3, which then undergoes additional fusion to form He4.
Stars bigger than 1.3 solar masses use the Carbon-Nitrogen-Oxygen Cycle [wikipedia.org] to fuse hydrogen into helium in a reaction catalyzed by carbon.
White dwarfs have little material left to fuse. They are mostly carbon and oxygen, but they are not big enough or hot enough to fuse the carbon or oxygen into heavier elements. So they slowly cool off and die.
Re: (Score:1)
Re:Are Brown Dwarfs Stars? (Score:4, Interesting)
The decay from white dwarf to black dwarf is slow. In fact it's so incredibly slow that the universe isn't old enough to have them in it yet.
Estimates for the time it takes are 10^15 to 10^37 years, depending on factors like pronton decay and WIMP existence. The universe is "only" 13.8*10^9 years old.
This makes their indetectability practically moot.
Theoretically it's still fun to think about. The only ways to detect them with current physics would be occlusion (low detection chance) and gravitational influence (low detection range).
Re: (Score:3)
White dwarf and neutron stars are the remnants of stars that had core fusion during the main sequence.
Brown Dwarf stars never had core hydrogen fusion and thus are failed stars. The smallest thing you can truly call a star is a Red Dwarf because they at least have core hydrogen fusion.
Re: (Score:3)
Jupiter is producing more heat due to convection bringing core heat to the surface, it's not doing fusion. Like on Earth, core heat is due to the extreme pressures and radioactive materials heating the core to high temperatures. None of that pressure is enough to fuse nuclei together, however.
Brown dwarfs will actually do fusion, but only a little of it, and only for a relatively short time since they only have enough mass to fuse heavy hydrogen nuclei, which is the easiest thing that you can fuse. The p
Re: (Score:2)
hmm, i think that's about 3/5 of a question sir. ...... what?
Re:Are Brown Dwarfs Stars? (Score:5, Informative)
There's a continuum of sorts between gas giant planets and dwarf stars, with a few notable points where you could draw the distinction. They all come from the same general start - a cloud of interstellar gas collapses into a spherical object. Depending on how big it is, you can get different objects.
First you have gas giants, no fusion at all. This would be your Jupiter and Saturn type planets. Jupiter is actually about as big, volume-wise, as a gas giant can get. Add more mass, and it starts getting denser rather than bigger.
At 13 Jupiter masses, you have enough gravitational pressure to fuse deuterium. This is what most astronomers define as a brown dwarf star, but others, and apparently you, consider it to still be a planet. Previous terminology included "substar", which I would not be opposed to. Deuterium isn't particularly common, so these objects glow very dimly, as far as stars go.
At 65 Jupiter masses, you can start fusing lithium as well. This is one way to distinguish brown dwarfs from other stars - red dwarfs and yellow dwarfs, like our sun, consume their starting lithium very quickly, and so the presence of lithium spectra indicates a brown dwarf.
At around 80 Jupiter masses, it starts fusing hydrogen, becoming a red dwarf, like Proxima Centauri. Still very dim, but at this point it's undeniably a star.
At around 750 Jupiter masses, the star develops a more complex internal structure, and becomes a yellow dwarf, such as Sol.
So where do you draw the line? Anywhere you want, but most astronomers settled on the simplest one: if it's undergoing fusion, it's a star, if it isn't, it's a planet.
Re: (Score:2)
There is at least one type of mud in that clear definition. Formation heat. During formation a lot of heat is generated, and that heat helps fusion. So young 12 Jupiter masses can fuse deuterium for a while, slowing the cooldown with the fusion energy.
Re:Dark Matter? (Score:2)
If the population of hard-to-spot brown dwarf stars turns out to be higher than previously thought, would the increased mass be enough to account for dark matter?
Re: (Score:3, Informative)
No, or to be precise, not significantly. That calculation was done the other way around: what if all that dark matter was in the form of brown dwarfs, rogue planets, asteroids etc. Then it turns out you need such a huge number of such objects that they would definately be very very prominent in observations. So going back to the observational side of the question, given how hard it is to detect those things we get a very rough upper limit on their mass contribution. How close to that limit we actually are
Re: (Score:3)
herve villechaize was a star
Re: (Score:2)
I don't think brown dwarfs count as stars.
Grumpy is not gonna like this...
Re: (Score:2)
I was going to say much the same thing. If it doesn't do (or didn't do in the past in the case of white dwarfs) hydrogen fusion in the core is it really a star?
I don't think that it is. Just being massive enough to emit some energy isn't enough. Jupiter, for example, gives off some heat but no one would argue that it's a star.
Re: (Score:2)
Indeed. While technically stars beyond any doubt, they aren't exactly the kind of stars we are looking for at the moment. (IMHO).
Intriguing headline.. (Score:5, Funny)
Surely the Sun is the closest star to Earth, right?
Re:Intriguing headline.. (Score:5, Funny)
No, Linsey Lohan is, so drugged up she's rarely vertical
Re: (Score:2)
I wouldn't call her a star at this point. Train wreck, maybe.
Re: (Score:3)
As long as Uranus doesn't get any closer to me, I'm OK with it.
yes, brown dwarfs can be stars (Score:2)
Re: (Score:2)
Which they are unable to, since they're lifeless objects.
Oh, I'm sorry, was that meant as a dig against some people who's existence bugs you for whatever reason? Have you considered getting professional help for your weird obsession?
Place your bets... (Score:5, Funny)
Proxima Centauri Might Not Be the Closest Star To Earth
Put another way, Sol Might Be the Closest Star To Earth
Re:Place your bets... (Score:5, Informative)
Proxima Centauri Might Not Be the Closest Star To Earth
Put another way, Sol Might Be the Closest Star To Earth
Jupiter is not a brown dwarf. It is not massive enough to even burn deuterium. No fusion == no star
Re: (Score:3, Funny)
Ok, deuterium, fine - no need to get heavy.
Re: (Score:2)
Re: (Score:2)
Not the guy you were talking to, but I'll answer.
Nothing. You've got fuel but no oxidizer.
Jupiter has thunderstorms larger than our planet. If the atmosphere could burn, it would have done so long ago.
Re: (Score:2)
How long does the fusion need to last to constitute a star? Arguably, the US and Russia have produced a number of stars quite close to Earth indeed, if only briefly.
Re: (Score:2)
Re: (Score:2)
It needs to be self sustaining by burning its own mass using certain fusion reasons. When stars "start up" there's probably a spark like a fusion explosion somewhere in there that starts the reaction in the first place, but after that, it keeps going.
Theoretically, you could say that if you put together a certain critical mass of fuel and maybe you compressed/nuked it to start it up, you might get a "star" for some period of time like a month or a year or 10,000 years or something, which is why we also hav
Re: (Score:2)
Even if it was, Earth is still closer to Sol than it is to Jupiter.
Re:Place your bets... (Score:5, Informative)
Nope -- regardless of star status, Jupiter is farther away from the Earth than Sol.
Re: (Score:1)
I would think excluding the sun would be a given. Also not one mention of Schulz's star, which (supposedly) 70,000 years ago came within 1 light year [space.com]
Re: (Score:2)
Proxima Centauri Might Not Be the Closest Star To Earth
Put another way, Sol Might Be the Closest Star To Earth
Depending on when the last periodical mass extinction was, Nemesis [wikipedia.org] is.
Re: (Score:2)
Proxima Centauri Might Not Be the Closest Star To Earth
Put another way, Sol Might Be the Closest Star To Earth
The Earth is closer to the Sun than it is to Jupiter, so the point is moot no matter what you define Jupiter as.
Them are no stars... (Score:5, Funny)
Re:Them are no stars... (Score:5, Informative)
Sheesh, it's just semantics. Definitions are for communication, if they call them brown dwarfs then you know what they're talking about. The IAU's considered an object with a mass capable of fusing deuterium a brown dwarf, which is 13 Jupiter masses. Don't like it? Too bad, as long as it's qualified with "brown dwarf" then you know what they're referring to. So, the term "closest start to Earth" is another issue of semantics. In the context of this article, it means, "closest object outside of our own solar system with a mass over 13 Jupiters." Now, if they start handing out medals and big prize money to stars for being the closest to Earth, then go ahead and debate it, otherwise who cares?
Re: (Score:3)
I don't think that word [wikipedia.org] means what you think it does.
Re: (Score:2)
As we get most of their light in the infrared, they could very well be an actual brown color to our eyes depending on how it was illuminated. If you shined the light of an actual star on it from a short distance, it would probably be a very angry looking Jupiter. If there was no other illumination anywhere nearby, it would probably have a reddish glow like the color of a dying ember while it was fusing. After that, it would be indistinguishable from a gas giant planet.
childish language (Score:2)
lol (Score:1)
No one has said this yet... (Score:2)
Forgetting the obvious? (Score:1)
The Sun, that big yellow fireball which appears in the sky during daylight hours when the weather is good, is in fact the closest star to the Earth.
So this article is really about which star is the second closest to the Earth.
Semantics (Score:5, Funny)
Re:Semantics (Score:5, Funny)
If it's not the closest, are we going to rename it?
Proximish Centauri??
Re: (Score:1)
Approximish Centauri.
Re: (Score:3)
If it's not the closest, are we going to rename it?
No, because it will presumably still be the nearest in the constellation of Centaurus. It's 'Proxima Centauri' not 'Proxima'
Re: (Score:2)
If it's not the closest, are we going to rename it?
No, because it will presumably still be the nearest in the constellation of Centaurus. It's 'Proxima Centauri' not 'Proxima'
Constellations are not defined by a collection of stars at roughly the same distance. They are a collection of stars roughly close together, in a pattern _as viewed from Earth_. Apparently adjacent stars in the same constellation can vary in distance from earth by thousands of light years.
So any newly discovered star closer to Earth is most likely to be in the scope of some other constellation.
Re: (Score:2)
They can vary by a whole fuckload more than a few measly thousand light years.
Stars that are part of a constellation are generally visible with the naked eye, which means that they are typically less than 1000 light years away. The furthest star that's visible with the naked eye (with good eyesight/conditions) is V762 Cas in the constellation of Cassiopeia at 16000 light years.
Wrong name for that telescope (Score:2)
If the telescope is meant to detect brown dwarfs, why is it not called the Spud Webb [wikipedia.org] Space Telescope?
Well, ... (Score:2)
of course not - the Sun is ;-)
Not very surprising (Score:1)
Since the discovery that Alpha Centauri was the closest neighboring star, and then the discovery of White Dwarfs and Red Dwarfs, there has been much speculation that there were closer stars than Alpha Centauri, and there was, it was discovered that Proxima Centauri was closer. If another star is discovered closer, it will be no different from last time it happened.
Indeed the Nemesis proposal is a white, red, or brown dwarf companion to the Sun, responsible for extinction events