Binary Star EF Eridanus Baffles Astronomers

baldinux writes "Reuters is reporting the finding of a new stellar object in the Eridanus constellation that may require the astronomical community to create a new category of stellar entities -- that is, dead ones. In the binary system, one of the stars 'gave too much' (Reuters) of its own resources to its partner white dwarf star, resulting in a breakdown of nuclear fusion, thus producing this 'dead' entity. Researchers at Gemini North (click here for images) and Keck II observatories at Mauna Kea, Hawaii, have been analyzing this unique system."

Comments

I'd make a Dark Star reference...

[Anonymous Coward]

but no one would get it....

Re:I'd make a Dark Star reference...

[Anonymous Coward]

Hahahahaha!!!!

I don't get it.

Re:I'd make a Dark Star reference...

[DeanAsh]

The Babylon 5 kind of Dark Star reference?

Us getting it is pretty much dependant on you giving it.

Re:I'd make a Dark Star reference...

[Pogue Mahone]

I would!

</hand up>

Re:I'd make a Dark Star reference...

[Anonymous Coward]

Are you trying to make me cry?

Re:I'd make a Dark Star reference...

[Billy the Mountain]

My first Linux computer, by default, was named darkstar.

BTM

Re:I'd make a Dark Star reference...

[sstamps]

"I went up to Doolittle in the hall today..." *snickers* *guffaws* *points and laughs*
"..and I said ', Doolittle?'"
"He said, ''" *laughs*
"..and I said 'Well, ', and he didn't get it!" *more guffaws* *BOOP*

Re:I'd make a Dark Star reference...

[sstamps]

Once more, with feeling. :P

"I went up to Doolittle in the hall today..." *snickers* *guffaws* *points and laughs*
"..and I said '[expletive deleted], Doolittle?'"
"He said, '[expletive deleted]'" *laughs*
"..and I said 'Well, [expletive deleted] [gesture deleted]', and he didn't get it!" *more guffaws* *BOOP*

Re:I'd make a Dark Star reference...

[dpilot]

You mean the Dark Star with the smart bombs?
I'd get it.
People in the University theater thought I looked like Doolittle.

But there's some sort of joke going begging here, and the punch line is, "where the Sun don't shine."

Re:I'd make a Dark Star reference...

[Anonymous Coward]

He didn't ask "Who's a dork?"

Oh wait, I guess he did.

In human terms...

[Anonymous Coward]

In human terms this is known as marriage.

Re:In human terms...

[Anonymous Coward]

Or perhaps its the divorce?

They should name binary pair...

[bobdotorg]

They meet, they accrete, and then dance for years as they happily twirl about. But as time goes by her ass grows more massive as she sucks out his soul and he becomes a shadow of his former self.

So I propose the name: Succubus and the Bitter Old Man.

Re:They should name binary pair...

[Associate]

Does the radiation spike around 350Hz?

Damn Loc Ness Monster.

Quit the pickle

[Breakfast Pants]

And the dwarf finds itself in quite the pickle without a new host to feed on (look out earth).

Probly Classified as an L or a T dwarf

[aws4y]

Though it may have lost its hydrogen and helium burning capeability I would hypothesise that the thing is now an L or T dwarf that is to say it might be Duterium or Lithium burning, or its spectral profile might be very dusty or contain methane. In otherwords we might have just seen an L or T dwarf being made but I highly doubt this is a new class of star.

Re:Probly Classified as an L or a T dwarf

[Anonymous Coward]

From the article;

the burned-out star has lost so much mass that it can no longer sustain nuclear fusion at its core

I think they are talking about a "star" that doesn't really shine (any more than Jupiter does). I don't understand what the big deal is. We know what it is. It is a star that has lost mass. So when we find more like it, we can say "Whoa. This must have been a star. And it has lost mass somewhere. Time to more on to the next thing."

Re:Probly Classified as an L or a T dwarf

[DLWormwood]

In otherwords we might have just seen an L or T dwarf being made but I highly doubt this is a new class of star.

From the article...

"Now the donor star has reached a dead end -- it is far too massive to be considered a super-planet, its composition does not match known brown dwarfs, and it is far too low in mass to be a star... There's no true category for an object in such limbo"

The unstar appears to fall between the cracks of current astronomical classification...

Re:Probly Classified as an L or a T dwarf

[barawn]

If there's no nuclear fusion in its core, it's not a star.

Actually, this object is incredibly interesting. Composition-wise, it's a star frozen in time, and without all the nasty chemical-changing properties of nuclear fusion going on. There's a lot that could be learned from objects like that.

Re:Probly Classified as an L or a T dwarf

[Christopher Thomas]

Though it may have lost its hydrogen and helium burning capeability I would hypothesise that the thing is now an L or T dwarf that is to say it might be Duterium or Lithium burning,

This seems unlikely, as both D and Li burn a lot more readily than p, if I understand correctly. Thus, the star should have used these up very early in its life. If it started life as something larger than a red dwarf, you could argue that there would be deuterium and lithium in its outer layers that wouldn't have mixed with the core material, but a) the outer layers were mostly what was stripped off by the companion star, and b) the star would have passed through a red dwarf stage as it lost mass, resulting in more thorough mixing during that time period.

So, I'm not sure it's a good bet to say that there would still be D or Li left. What do the spectrographs say, for this object?

or its spectral profile might be very dusty or contain methane. In otherwords we might have just seen an L or T dwarf being made but I highly doubt this is a new class of star.

I'm not sure "star" is the correct term any more, as there's no fusion happening (in all likelihood). A few classifications I can think of:

• Stellar remnant.
  Pretty broad category, so probably not specific enough. Also tends to refer to things like planetary nebula and not stars (we haven't seen anything star-like that's been around long enough to cool down past "white dwarf" levels).
  
  
• Black dwarf.
  It's a stellar core that can no longer sustain fusion. But this term usually refers to the (as yet unobserved) cooled ashes of a burned-out stellar core (cold white dwarf).
  
  
• Brown dwarf.
  It's a sub-stellar mass that's still massive enough that it probably could sustain deuterium fusion, if it had any deuterium to fuse. That probably makes it a brown dwarf on a technicality, even though it's of a bizzare spectral type compared to other brown dwarfs (as you point out).
  
  
• MACHO.
  This is another category that's probably too broad to be useful. If it's stripped to below the point where deuterium fusion can occur, but is not a planet (i.e. condensed from a nebula directly as opposed to from another star's protoplanetary disk), it probably counts as a MAssive Compact Halo Object, on a technicality.
  

I'm voting for "brown dwarf" or "black dwarf", but those are still on technicalities.

Re:Probly Classified as an L or a T dwarf

[Maxite]

"From the article...

"Now the donor star has reached a dead end -- it is far too massive to be considered a super-planet, its composition does not match known brown dwarfs, and it is far too low in mass to be a star... There's no true category for an object in such limbo"

The unstar appears to fall between the cracks of current astronomical classification..."

Hmmm... how about having part of the name being the type of star that it used to be before it's binary partner gobbled up too much of it's matter, and then adding something along the lines to explain why it no longer is that type of star.

So, for example, if that star was like the sun, we could say "Ex-Regular sized Yellow Star; nova fatality".

Hmmm.. Nova fatality.. Fatalova star.. Fits kind of well in many situations.. Fatal Lover, victim of a femme fatale; only this femme fatale was a white dwarf.

Re:Probly Classified as an L or a T dwarf

[barawn]

Thus, the star should have used these up very early in its life.

Deuterium and tritium are byproducts of the pp chain - the star constantly regenerates them.

Once the pp chain stops, deuterium burning will continue for a while (stars are *big*, after all) but would, eventually, stop.

Spectrography might be able to detect the relative ratios of deuterium, etc. in the object, but not likely - its core is still quite dense, and there's little light being generated from there.

Pretty broad category, so probably not specific enough. Also tends to refer to things like planetary nebula and not stars (we haven't seen anything star-like that's been around long enough to cool down past "white dwarf" levels).

Stellar remnants are a broad class which encompasses anything left after a star has left the main sequence (planetary nebula, black hole, white dwarf, neutron star, etc.). This *is* a stellar remnant, though it doesn't have any classification within the stellar remnant class. Planetary nebulae are actually former stars. The former star is sitting at the center of the nebula.

This kind of object really does need a new classification - it's a new way for a star to die. I vote for "starved star", though it's not like my vote means anything. :) "Bulemic star" would probably be too non-politically correct.

The problem in naming is that mass doesn't define everything - composition is the other issue. A brown dwarf has the composition of the protoplanetary disk, slightly modified by fusion (lower concentration of D, higher concentrations of products of D fusion). A black dwarf is an almost entirely pure carbon diamond.

This object certainly is not a black dwarf - it's not a degenerate object, for one. It's also certainly not a brown dwarf - compositionally, it's totally different.

Keep in mind that this star was probably burning on the main sequence - burning, probably quite actively, for billions of years alongside its "partner" star. Virtually all of its internal composition probably bears little resemblance to the protoplanetary disk - it's been heavily changed by fusion and by virtue of having been *plasma* for that long.

What amazes me is that it's 300 light years away. 300 ly! That's virtually in our backyard! Jeez, if someone ever develops faster-than-light travel, this would be one of my first stops for astrophysics. In all seriousness, though, it'd be on my top list for observations when the next class of optical telescopes develop. A white dwarf, and a star frozen in development. And only 300 ly away.

Makes me wonder how many more of these they'll find.

MACHO.

MACHO, as you noted, means "massive compact halo object". This object isn't in the galactic halo. Therefore it's not a MACHO.

Re:Probly Classified as an L or a T dwarf

[Christopher Thomas]

Deuterium and tritium are byproducts of the pp chain - the star constantly regenerates them.

Fair enough. However, these should have been burned very quickly, as when pp fusion stopped, the star would have been *well* within the envelope for rapid DD fusion, and probably a lot of lithium fusion paths as well. This would have occurred while the star was still in pp fusion mode, too; the p + p reaction is the rate limiting step (requires a Weak transformation, which is extremely unlikely compared to Strong interactions). So little, if any, D and Li should have been available at the time pp fusion ceased.

Spectrography might be able to detect the relative ratios of deuterium, etc. in the object, but not likely - its core is still quite dense, and there's little light being generated from there.

It will be able to pick up absorption lines, as this thing does have an atmosphere. The material that's presently the atmosphere should mostly be material from what was the core of the original star, though the core's original fine structure would have vanished when the object became a red dwarf with deep convective mixing.

This object certainly is not a black dwarf - it's not a degenerate object, for one. It's also certainly not a brown dwarf - compositionally, it's totally different.

This depends on which definitions for the objects you accept. If a black dwarf is defined as an object composed mostly of electron-degenerate matter that's below a certain temperature, it's certainly true. Ditto if it's defined as a non-fusing star depleted of hydrogen that's below a certain temperature. If it's defined as a "star that is no longer burning", though, this would qualify. Depends on what we want the category to include (right now, it's "white dwarf husks" by default because that's the only sample in the category that exists).

As for brown dwarfs, while there are classes within them, the definitions that I've heard have ranged from "sub-stellar object large enough to have sustained deuterium fusion" to "any sub-stellar object that condensed directly from a nebula, as opposed to a protoplanetary disk", with no clear dividing line between brown dwarfs and gas giant planets that formed in isolation. I'd argue that the definition is certainly flexible enough to include a stripped stellar core in the category, albeit in its own spectral class.

What amazes me is that it's 300 light years away. 300 ly! That's virtually in our backyard! Jeez, if someone ever develops faster-than-light travel, this would be one of my first stops for astrophysics. In all seriousness, though, it'd be on my top list for observations when the next class of optical telescopes develop.

I'm still waiting for us to launch clusters of radio telescopes for multi-AU baseline radio interferometry. That would let us image stellar atmospheres and planetary magnetospheres, and tell us one heck of a lot about stars and planets in our local neighbourhood.

As for interstellar probes, launching a very small sailcraft for flybys to every star within 10 LY should be do-able. Communications back is the bottleneck, and that can be done by waving the mirror if necessary (extremely slow data transmission, but we'll have years to listen to it). I even seem to recall that there was a white dwarf at around 11 LY that we could study.

I'm not optimistic about faster than light drives being available any time soon.

Re:Probly Classified as an L or a T dwarf

[barawn]

So little, if any, D and Li should have been available at the time pp fusion ceased.

You're right that the D and Li phases wouldn't last much longer afterward pp stopped, though it depends on the mass loss rate. But there would've been a fair amount of D and Li available.

Actually, the D burning would continue probably for quite some time due to hydrodynamics, now that I think about it. While fusion was occurring, the turbulence inside the star would dominate the hydrodynamics, so D would remain mixed throughout the star. Once the fusion stopped, deuterium, being denser than hydrogen, would naturally sink slowly to the core. So you probably would have "fits" of deuterium burning (which remixed the deuterium) as the star slowly burned up its deuterium.


It will be able to pick up absorption lines, as this thing does have an atmosphere.

That's what I meant, though again it depends on the density profile of the object. The core of the object is likely too dense to let anything pass through it. We don't know what the core of Jupiter is made of - this object is something like 50 times denser.

The core composition is the interesting part, unfortunately. For that we'd need to be there.

If it's defined as a "star that is no longer burning", though, this would qualify.

That's what a stellar remnant is, not a black dwarf. A white dwarf is also a star that's no longer burning - it's white because it's still hot. Black dwarves are white dwarves that have crystallized. There's a specific definition because there's a phase transition (crystallization) that they have to go through, so there's a clear dividing line between white dwarves and black dwarves.

I even seem to recall that there was a white dwarf at around 11 LY that we could study.

Sirius B. First white dwarf ever discovered. Problem is it's sitting right by Sirius A, which is *not* a white dwarf - it's a blue-white supergiant. That must've been a hell of a system when it was active... The nice thing about this system is the fact that it's a bare white dwarf. Plus it has an interesting companion. Bonus.

That would let us image stellar atmospheres

We actually already can image stellar atmospheres. Only big stars, but stellar atmospheres nonetheless.

Here's an example. I used Betelgeuse because I think it was the first and only star for a while. I think there've been more by now...

Re:Probly Classified as an L or a T dwarf

[Christopher Thomas]

You're right that the D and Li phases wouldn't last much longer afterward pp stopped, though it depends on the mass loss rate. But there would've been a fair amount of D and Li available.

I'm not convinced of this, for reasons mentioned in my previous post - as pp -> D e+ ve is the rate limiting step, the amount of D present at any given time would be miniscule (it's burned far more quickly than it's produced, so remaining D represents the tail end of the survival time distribution). Any that is left when pp fusion ceases would still be fusing at a rate far, far greater than pp fusion takes place. If the D stuck around for years after pp fusion stopped, I'd be surprised. I'd have to run numbers, but "days" seems more plausible.

I doubt there'd be much D outside the active part of the core, as a) it's only produced in the active part of the core, and b) as the active region shrank as the star lost mass, it would be surrounded by a region in which D could still burn - so the D left in the areas that were once core would be burned up almost immediately.

That's what I meant, though again it depends on the density profile of the object. The core of the object is likely too dense to let anything pass through it. We don't know what the core of Jupiter is made of - this object is something like 50 times denser.

We know what Jupiter's outer atmosphere is made of, and that's all we'd need to know for this thing, as after it hit the "red dwarf" stage, it would lose most of its internal structure. As far as I can see, all of the remaining material should be from the core of the original, larger star, so the atmosphere should represent a reasonable sample of what that original stellar core contained. If I'm overlooking something, by all means let me know.

Black dwarves are white dwarves that have crystallized.

Ok, that clears up the definition a bit. I'd argue that "brown dwarf in a new spectral class category" is the most reasonable classification, then.

I even seem to recall that there was a white dwarf at around 11 LY that we could study.

Sirius B. First white dwarf ever discovered.

I'm pretty sure that there was an _isolated_ white dwarf found somewhere around that distance, as well. Apparently they're common as dirt (much like the yellow dwarf stars they come from). Sirius A probably makes a more interesting neighbour, but it'll give us quite a bit of light pollution if we're trying to watch for sail reflectivity changes for the communications link.

That would let us image stellar atmospheres

We actually already can image stellar atmospheres. Only big stars, but stellar atmospheres nonetheless.

An intereferometric array on that scale would give us detailed images of anything magnetically active within a hundred light years. So, far _sharper_ pictures of the outer layers of stellar atmospheres :).

Arguably we can also get some idea of what's going on by looking at brightness variations and mapping them to resonance modes of the star, but a radio intereferometer with that kind of baseline can resolve features the size of the Moon at 100 light-years, and features the size of Lake Ontario at 10 light-years. We could pick out every flare and prominence and sunspot on each star in range.

Re:Probly Classified as an L or a T dwarf

[barawn]

I doubt there'd be much D outside the active part of the core, as a) it's only produced in the active part of the core, and b) as the active region shrank as the star lost mass, it would be surrounded by a region in which D could still burn - so the D left in the areas that were once core would be burned up almost immediately.

I was actually thinking about the unburned D in the outer stellar envelope. I'm not sure how much there would be, though - I can't find measurements of the Sun's deuterium abundance in the outer region of the star. The reason I was saying so is that with hydrogen burning, the star actually stops burning hydrogen far before it runs out of hydrogen in the star - it's just that the outer shell hydrogen has no chance to reach the core so long as the star burns at all. Likewise, the primordial deuterium in the stellar envelope for this star would've been unable to reach the core so long as the star was burning, but after fusion ceased, it should've sunk down to the core, only to reinitiate fusion briefly.

It should be noted that as the star collapsed, before it started burning, D would've sunk to the core as well, so you could be right.

We know what Jupiter's outer atmosphere is made of, and that's all we'd need to know for this thing, as after it hit the "red dwarf" stage, it would lose most of its internal structure. As far as I can see, all of the remaining material should be from the core of the original, larger star, so the atmosphere should represent a reasonable sample of what that original stellar core contained. If I'm overlooking something, by all means let me know.

I doubt the outer atmosphere would bear much resemblance to the "old" inner core of the star: the core would contain the heaviest elements, and the outer atmosphere would be primarily hydrogen. It would depend a lot on the exact mass loss mechanism and the density profile of the dying star, actually! The sun's 'burning region' is quite large - fusion is occurring in almost 1/3 the radius of the Sun. For a dying star that was losing mass very slowly, the core would shrink slowly over time, and in the end, the outer region of the star would be quite different than the interior (because it was the star's 'core' long ago). But if was losing mass quickly, then the star would be more uniform.

As I said before, though, it's an amazingly interesting object. I think 'brown dwarf of a new spectral class' is actually appropriate for a name, though.

Re:Probly Classified as an L or a T dwarf

[Christopher Thomas]

I was actually thinking about the unburned D in the outer stellar envelope. I'm not sure how much there would be, though - I can't find measurements of the Sun's deuterium abundance in the outer region of the star. The reason I was saying so is that with hydrogen burning, the star actually stops burning hydrogen far before it runs out of hydrogen in the star - it's just that the outer shell hydrogen has no chance to reach the core so long as the star burns at all.

This is only true for stars about the size of the sun. Stars that are red dwarf sized have deep convective layers throughout, mixing the star's material pretty thoroughly. It's only heavier stars that have non-convective cores (and stars much heavier than the sun have cores dominated by convection and outer layers that are dominated by radiative heat dissipation; I was very surprised to learn that - it stems from the CNO reaction rate going up as a ludicrous power of temperature).

The original star would have been segregated. The outer layers would have been stripped off by the companion star. While some mixing between what used to be mantle and what used to be outer core would have occurred when "outer core" was reassigned as "mantle", over time the net effect of the companion's stripping of material would be to remove most of the material that was originally non-core, leaving an object the mass of a red dwarf that contained mostly material that was from the original star's core (rich in metals, depleted in primordial deuterium and lithium). As the star's mass dropped to the point where it became a red dwarf, it would lose internal structure due to deep convection, burning any deuterium left from previous hydrogen-fusing phases.

I hope that this clarifies why I don't think any of the original star's primordial deuterium would be left in this object. (Non-primordial deuterium has already been addressed.)

I doubt the outer atmosphere would bear much resemblance to the "old" inner core of the star: the core would contain the heaviest elements, and the outer atmosphere would be primarily hydrogen. It would depend a lot on the exact mass loss mechanism and the density profile of the dying star, actually! The sun's 'burning region' is quite large - fusion is occurring in almost 1/3 the radius of the Sun. For a dying star that was losing mass very slowly, the core would shrink slowly over time, and in the end, the outer region of the star would be quite different than the interior (because it was the star's 'core' long ago). But if was losing mass quickly, then the star would be more uniform.

I'd be more concerned with convective mixing polluting old-core material with convectively down-swept material from the old mantle. I wouldn't expect fusion in the shrinking star to substantially taint composition, as fusion rate drops so quickly with decreasing stellar mass (projected lifetime goes from billions of years as a yellow dwarf to hundreds of billions or longer for a red dwarf). That, combined with convective mixing, suggests that we should have an object with reasonably uniform composition, that more or less reflects the composition of the original core.

Gravitational fractioning after fusion stops is another matter. You've indicated that you believe this would occur relatively quickly; I'm not so sure (you'd have convection from residual heat for a long time, and there's a lot of really dense material that you'd need to segregate to get significant fractioning). However, you almost certainly know more about those mechanisms than I do.

As I said before, though, it's an amazingly interesting object. I think 'brown dwarf of a new spectral class' is actually appropriate for a name, though.

Now, what do we call it when it's below the mass threshold for hypothetical deuterium burning? ;)

See: altruism is evil.

[Chemisor]

> In the binary system, one of the stars 'gave too
> much' (Reuters) of its own resources to its
> partner white dwarf star, resulting in a breakdown
> of nuclear fusion, thus producing this 'dead' entity.

A good example to illustrate the evil of altruism.

Re:See: altruism is evil.

[iggymanz]

No, it shows how the evil objectivist capitalist white dwarf exploited the poor downtrodden proletariat worker-class star

Re:See: altruism is evil.

[Anonymous Coward]

one could just as easily argue that the lack of altruism on behalf of both parties was the problem.

Obviously...

[Jesrad]

... the locals found that they had enough light with one star already and did not need to run their backup fusion powerplant. *switch*

Dead star

[mknewman]

I think this sort of star has been postulated for quite a while, especially with black holes and neutron stars sucking material out of companion stars, but this is the first observation of the result of that process, a star that is no longer fusing. It's a dead husk. I think that makes it a supergiant planet or an ex-star, but I doubt it's fusing anything anymore. It's been sucked dry.

Could this "re-ignite" the dwarf star?

[MobyDisk]

IANAC (I am not a cosmologist)
AINAA (I am not an astrophysicist)
IAAAJ (I am an average joe)

Could the dwarf star absorb enough mass that fusion could start again? That would be awesome!

Re:Could this "re-ignite" the dwarf star?

[barawn]

Could the dwarf star absorb enough mass that fusion could start again? That would be awesome!

This is what novae are (not supernovae, which are different). When a white dwarf star accretes matter, it builds up on its outer shell. Since the white dwarf is incredibly dense, its gravity is incredibly strong, so the layer of matter (hydrogen) is incredibly hot. Eventually the density of hydrogen grows enough that fusion can occur again, and it does - and the star burns off (very quickly - ~few days) what took it several years to build up.

This causes a white dwarf to go from barely visible to extremely bright. In the night sky, it looks like a new star comes out of nowhere, then disappears - hence the word "nova", meaning 'new'.

Re:Could this "re-ignite" the dwarf star?

[Anonymous Coward]

Dwarf Fusion.. sounds like a great Red Dwarf spinoff

Re:Could this "re-ignite" the dwarf star?

[Thuktun]

hence the word "nova", meaning 'new'

Except in Chevrolet-importing, Spanish-speaking nations, of course.

Bad headline, not baffling

[Alsee]

It is an oddball arrangement they have never seen before, but the only baffling thing is what to call it. It's way too big to be a supergiant planet, but it has been drained down and "switched off" the shining process so it doesn't qualify as a star anymore.

An interesting addition to the stellar zoo, but probably of little scientific signifigance.

-

Re:Bad headline, not baffling

[trentblase]

It's not too big to be a supergiant planet. It's the same size as jupiter.

Re:Bad headline, not baffling

[Xilman]

It's not too big to be a supergiant planet. It's the same size as jupiter.

Same diameter, near enough, but much more massive. The article says it has a mass about a twentieth of that of the Sun. Jupiter has a mass about 1/1047 that of the Sun. From which we can conclude that the object has about fifty times the mass of Jupiter and is about fifty times as dense.

Paul

That sucks...

[Cragen]

"Like the classic line about the aggrieved partner in a romantic relationship, the smaller donor star gave, and gave, and gave some more until it had nothing left to give," said astronomer Steve Howell

Gave? Methinks it was TOOK! (All the telltale signs are there -- oh, sorry, I'm trying wean myself from CSI.)

That's About "Three-Fitty" Hz...

[KnarfO]

...for those South Park deprived /.'ers out there...

OMG we ran out of categories!

[js7a]

Someone put an order in to Edmund Scientific! We need a new category and we're all out! What WILL we do?

Re:OMG we ran out of categories!

[Anonymous Coward]

I propose the category of "Anomalous Eridanus -like objects"...

New category not possible

[rts008]

Naming a new category is not possible anymore...I foresaw this and patented the process of developing AND implementing new categories. This new career RULES!!! since I've been too STUPID in the past to develop a REAL business plan! Mod this: -16 for OFFTOPIC -10 for FUNNY -pi for INFORMATIVE

What I'd like to know is

[$RANDOMLUSER]

OK, the donor "star" no longer has enough mass to maintain fusion, but it's still a big compressed ball of (mostly) hydrogen and helium, held together by gravity. The white dwarf "vampire" star is still sitting right there.

So what caused the process to stop? Why isn't the vampire still sucking on the donor?

Maybe it is, and we can't see it, (even though I suspect we'd see something as the matter was gravitationally accelerated into the vamp star.

Or maybe the two are farther apart than they used to be, even though this doesn't make much sense for a binary star.

Either way, I'm puzzled.

Re:What I'd like to know is

[cjameshuff]

It's not fusing internally any more, so it's cooling down and shrinking. Its "surface" is deeper in its gravity well and colder, so it's not getting stripped away as quickly. The vampirism probably hasn't stopped, just become too small to detect.

Also, the thing probably has much higher concentrations of "metals" than typical brown dwarfs or gas giants...for a while, it was fusing, and it probably lost lighter elements to the white dwarf more easily.

Re:What I'd like to know is

[$RANDOMLUSER]

I'm not sure about that.

Since it's a binary system, we'll assume that the two are cosmologically the same age, meaning that whatever generation they are, we're looking at roughly the same elemental mixture at birth (ignition), which we should be able to get from the dwarf's (vampire's) stellar spectra.

I'll further posit that as the vamp star went through the nova phase, between 30 and 50 percent of the expelled mass would have been absorbed by the donor star (they're that close), but this would have been mostly composed of the lighter elements.

However, remember that as the vamp absorbs matter (mass), it's gravitational attraction increases. I'm thinking of a running siphon where the end points are moving downward synchronously.

I'm still wondering what made the process stop. Why does an avalanche not continue until all the snow on the mountainside is gone? Sand/sand dunes? What was the bubble that broke the siphon? What's the lowest energy point? Why?

So, anyways, I'm still puzzeled and fascinated by this discovery. I hope we find out more about it.

Re:What I'd like to know is

[$RANDOMLUSER]

OMG! OMG! OMFG! I left an open paren on this! I'm __SO__ embarressed! Bad spelling is forgivable, but a syntax error! gulp.

Re:What I'd like to know is

[barawn]

Since it's a binary system, we'll assume that the two are cosmologically the same age, meaning that whatever generation they are, we're looking at roughly the same elemental mixture at birth (ignition), which we should be able to get from the dwarf's (vampire's) stellar spectra.

They're not the same mass, though. And since the white dwarf companion is - well - a white dwarf, it obviously was far more massive. It burned out first, for one.

A white dwarf's elemental composition, moreover, is not a good indicator of its original composition - just of its mass. It's a stellar core, after all - it's almost all carbon, with heavier elements inside in shells that again, depend on the mass of the star, and very little on its elemental origin.

I'll further posit that as the vamp star went through the nova phase, between 30 and 50 percent of the expelled mass would have been absorbed by the donor star (they're that close), but this would have been mostly composed of the lighter elements.

Yah - but the mass came *from* the donor star originally! It basically gets back a fraction of what it gave (although much less than 30%, I imagine - the shell is ejected with extremely high velocities. Fusion's powerful, after all).

However, remember that as the vamp absorbs matter (mass), it's gravitational attraction increases.

Not significantly. The amount of matter accreted that actually *stays* on a white dwarf is quite low. You need heavier elements (not H, He) to do that, and that's a tiny fraction of what it accretes (since it primarily accretes H). That's why it takes so long for Type Ia supernovae to occur, which is good - it allows the planetary nebula to be far from the star, so we can observe the supernova directly.

I'm still wondering what made the process stop.

So are astronomers. Most likely it's simply the fact that the other star is too dense - without fusion, the star would contract, and become more dense, though the lighter layers would separate, and continue to be accreted by the white dwarf.

Eventually, however, the starved star will fall into the white dwarf. Which will produce a *big* nova (but just a nova - not enough mass for a Type I supernova) and a slightly larger white dwarf.

Re:What I'd like to know is

[cjameshuff]

When it goes nova, the white dwarf casts off most of the matter it gains, so it stays at nearly the same mass. However, the donor star is no longer fusing, so it cools and shrinks. As it becomes cooler and more compact, its "surface gravity" increases and the average molecular velocity goes down, both effects slowing the mass loss. It'll lose lighter elements preferentially, especially as it cools and heavier elements combine into even heavier molecules, while helium stays as single atoms and hydrogen mostly forms slightly lighter H2 molecules. (H2: 2 amu. He: 4 amu. CO: 28 amu. Higher molecular weight == lower molecular velocities at a given temperature, and lower rates of loss.) As a result, it ends up denser and with a higher surface gravity than typical objects of its size and temperature.

Also, only a tiny portion of the nova-expelled mass would be reabsorbed by the donor star, and most of that would again be lost to the dwarf. Actually, it seems likely that the energy of the extremely nearby nova would blast even more mass away from the donor star.

Suprising?

[Jozer99]

How is this suprising? There are no rules saying how big a body of gas in space can be, so scientists are to blame for the fact that their classification system does not have enough room in it for bodies of a certain size. I can't see how this is a revalation, more of just finally finding something of the right size.

Re:Suprising?

[barawn]

I can't see how this is a revalation, more of just finally finding something of the right size.

It's the same size as a brown dwarf. The problem was that no one had found anything that's the same size as a brown dwarf, but not a brown dwarf (i.e., an object condensed from a nebula/disk but not large enough to complete the pp-chain at its core).

Things are classified typically by mass and composition. Almost everything falls into certain classes by those rules (stars, brown dwarves, white dwarves, planets, neutron stars, black holes, etc.). This falls well outside of any previous category of object. It's way interesting, too - its composition might reveal a lot about plasma physics and the interior structure of stars.

naming

[Anonymous Coward]

How about "red subdwarf" or "brown superdwarf"?
But would you rather be a subdwarf or a superdwarf oh anorexic star?

Re:Obligatory Gay Niggers from Outer Space quote..

[Anonymous Coward]

FEMALE CREATURES?!