Comments on: Exoplanets survive their star's fiery death. Or were they born from it…?

By: amphiox

amphiox — Fri, 01 Apr 2011 23:17:27 +0000

What exactly is the material that makes up the white dwarf. What elements are it composed of. How does the white dwarf shine if not through nuclear fusion?

A white dwarf’s composition will depend how big a star it was before (which determines how many rounds of fusion it will get done before fusion ceases). Small ones will be mostly helium, while larger ones will have a lot of carbon or oxygen.

White dwarf’s shine entirely from the heat of their final core collapse, I think, so they will gradually cool down and get dimmer as time passes.

By: amphiox

amphiox — Fri, 01 Apr 2011 05:22:34 +0000

re #4,5 and other replies to them;

The minimum mass for a red dwarf star is about 80J (it’s the minimum mass for hydrogen fusion in the core), while a hot Jupiter planet would have a mass between about 0.5 to 13J, and a brown dwarf would be anywhere from about 13J to 70-80J.

So for a planet to gain enough mass to become a red dwarf star would require quite a lot of mass gain. Not sure if there would even be enough material in the outer atmosphere of a red giant along the pertinent orbital paths to be sucked up for that to happen. It would be more likely with a big brown dwarf.

(Must say that the actual transition, when the formerly dark object finally ignites fusion and starts to produce it’s own visible light, would be hell of an interesting thing to observe in real time, assuming a method existed to do so against the glare of the red giant star!)

By: Dennis

Dennis — Fri, 29 Oct 2010 22:10:42 +0000

What program is used to build these models to test star formation over time? More to the point, is there a commercial version I can “play” with?

By: TripCyclone

TripCyclone — Tue, 26 Oct 2010 22:07:09 +0000

I know it doesn’t seem like much to some of you, but this little tidbit is exciting to me. In the main article BA linked to near the beginning of this post, it mentions “Many of these Texas observations were in large part facilitated by George Miller…” I thought I’d add a note of pride here as about seven years ago, George was a middle school student who was participating in Science Olympiad. As a member of the local astronomy club, a request came in asking for some help in teaching George and another student some basic astronomy for the “Reach for the Stars” event that year. While he got some assistance attending a star party, I went to the school to help them, using a Starlab portable planetarium. When a notice went out about this recent news from his father, I contacted the father and confirmed that it was the same kid. Seems the extra help both from myself when visiting the school and his visit to a star party helped spur his interest in astronomy as a career path.

I also told his father that this was the first time I had worked with Science Olympiad, and it was one of the reasons I became an assistant coach for Science Olympiad at the middle school I teach at now. As a teacher, it’s always great when you get to hear about how your efforts positively influenced a student. Especially when they get to be involved in exciting research such as this.

By: AJ in CA

AJ in CA — Tue, 26 Oct 2010 01:13:17 +0000

@Messier: IIRC, Larry Niven wrote a story about a tidally locked planet orbiting a red dwarf, and the life that lived in the “twilight zone” near the terminator between the light and dark sides of the planet. I think the story was called “Flare Time”. It addressed how different life forms had evolved the means to hide from the sun during flares.

IIRC, the book was a collection of short stories called N-Space. It also had a really fun one called “Night on Mispec Moor” about a planet with a local life form that essentially caused the recently dead to rise as zombies and attack the living

Eh, sorry to bring science fiction up in a blog about science fact, but IMHO, sci-fi is great fodder for thought experiments that may one day turn into real experiments.
Except the zombie one. Hopefully

By: andy

andy — Mon, 25 Oct 2010 21:20:05 +0000

@Glaisne: same reason every star shines: because they are hot. Heat something up enough and it will begin to glow red, heat it further and it glows yellow, then white, then blue. It doesn’t matter why the object is hot, it only matters that it is hot.

The reason the Sun is hot and the reason a white dwarf is hot are different though: the Sun’s temperature is a result of energy being produced by nuclear fusion reactions in its core. The white dwarf is hot because it was once the core of a giant star and hasn’t managed to cool down yet.

By: AJ in CA

AJ in CA — Mon, 25 Oct 2010 19:36:36 +0000

@Glaisne: In my understanding, a white dwarf is the final state of a star with roughly sun-like mass that has exhausted its fuel and gone through the red giant phase.
Ultimately it contracts until it can’t contract any further (at this point it has lost some of its original mass, and is not massive enough to overcome electron pressure and shrink down to a neutron star). This compression heats its surface again, and its surface area is so small that it takes billions and billions of years for it to cool off. Theoretically, white dwarfs will eventually cool down enough to become “black dwarfs” – essentially huge balls of gas, depleted of hydrogen (and helium, depending on the mass of the star) – it’s thought that the universe is not yet old enough for any white dwarfs to have reached this stage, yet. A white dwarf contains all the elements that were created through fusion, such as oxygen, neon, and carbon, as well as whatever metals existed in the cloud that it first coalesced from.
It’s a bit of confusing terminology, because “red dwarfs” and “white dwarfs” differ in more ways than just coloration. A white dwarf is the hot and slowly cooling “corpse” of a star, while a red dwarf is a very low-mass star that’s still “live” (fusing hydrogen). Red dwarfs burn their fuel so slowly that first-generation red dwarfs (some of the first stars to form in the universe) would still exist, and continue to do so for a very long time.

By: Glaisne

Glaisne — Mon, 25 Oct 2010 17:40:56 +0000

What exactly is the material that makes up the white dwarf. What elements are it composed of. How does the white dwarf shine if not through nuclear fusion?

By: Messier Tidy Upper

Messier Tidy Upper — Mon, 25 Oct 2010 14:35:32 +0000

“Imagine M-dwarf [red dwarf] bathing on a beach and having your star suddenly – with no warning at all – become ten times brighter.”

Source : Pages 30-31 “The Faintest Stars” article by James B. Kaler in ‘Astronomy’ magazine, August 1991.

Wonder what the presence of the white dwarf so near this red dwarf does to its magnetic fields and consequent starspots and flare activity?

By: réalta fuar

réalta fuar — Mon, 25 Oct 2010 12:48:54 +0000

The odds of these planets being “second-generation” are just about zero (all kinds of things wrong with that scenario, we’re not talking about a pulsar here). They almost certainly evolved normally in the disc around the close binary, then migrated in during the red giant phase of the primary. Gas drag can easily win out over mass loss so planets can migrate OUT or in during a star’s evolution off the main sequence. So, they didn’t have to have been in resonance orbits before the primary became a red giant (and planetary nebula) as they could have evolved into resonance afterwards.