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

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

[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: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: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.