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AbandonedPlanet t1_j9ud3sv wrote

I mean, aren't gas giants just "failed" stars that never got big enough? Why is this so rare if binary star systems aren't?

Edit: notice how my comment is in the form of 2 questions and not statements? It's because I don't know what I'm talking about. I didn't think the words "failed star" would rile everyone up so much. I'm sorry to have upset everyone and I hope I can be forgiven.

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Apprehensive_Note248 t1_j9ume7w wrote

Rare in that we haven't processed that many exoplanets relative to the number of stars we've been able to chart, and haven't seen this kind of pair yet with the exoplanets we have found.

Honestly, I roll my eyes at these kinds of descriptions as sensationalized garbage.

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noonemustknowmysecre t1_j9uqq8n wrote

Part of me is happy that there's space news. Part of me is disgusted at the current state of quality in news in general. We're right next to the rack of tabloids declaring batboy was found on Gliese 581c.

I should start paying for a newspaper again or something.

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snuggl3ninja t1_j9v96my wrote

Space and astrophysics are way more interesting than these headlines (for those who study and understand more of it). If these headlines grab one kids attention and makes them turn to study it as a career path or hobby then it's done its job. We don't want dense scientific papers to have to also attract the next wave of scientists, that's what these bait headlines are for. For example in these posts the headline brings you in. To either learn more or educate people on the actual science. It's a win/win.

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lordnacho666 t1_j9ulv5b wrote

So judgemental. Aspiring star is fair enough. We're all working on getting somewhere.

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Brickleberried t1_j9uvfrb wrote

I don't like calling gas giant "failed stars". There are two ways to define a planet (at the high mass end; edit: 3 ways, see lower comment):

  1. If it formed from core accretion in a disk, it's a planet. (Conversely, if it formed from disk instability and gravitational collapse, it's not a planet.)
  2. If it's under the mass required to fuse deuterium (~13 Jupiter masses), it's a planet.

Both definitions have pros and cons. Since we typically think of gas giants as planets that formed via core accretion, I wouldn't call any of them "failed stars" since they form completely differently than actual stars.

However, if a nominal gas giant formed via disk instability/gravitational collapse, but doesn't burn regular hydrogen, then "failed star" is appropriate.

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khinzaw t1_j9uzn4w wrote

It's brown dwarfs specifically that are failed stars.

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Chaotickane t1_j9v6c48 wrote

Brown Dwarfs are essentially high mass gas giants though. That's the issue, we don't have enough knowledge about them and the limit to which they transition to stars to properly classify them better. They are difficult to find and observe because they don't shine bright comparatively and we only have hypothetical limits to what mass is necessary to ignite.

But yes, lower end mass gas giants like what is in our solar system are definitely not close enough to be considered failed stars in any regard.

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Brickleberried t1_j9v7r5t wrote

But even so, the definition of brown dwarf isn't necessarily set in stone. It definitely can't fuse normal hydrogen, but do you define the lower limit by the physical process, by formation mechanism, or by observational feasibility?

  • Physical process: must be fusing deuterium? It's a nice physical process to define by. However, it's basically impossible to tell observationally whether a (potential) brown dwarf is burning deuterium. There are no outward signs. You can often measure mass, and the deuterium burning mass is approximately 13 Jupiter masses, but it depends on metallicity and age. Therefore, if you find an object that's around the limit, you're not sure what to call it without knowing metallicity or age, which is harder to do. Additionally, an older 13 M_J brown dwarf won't be fusing deuterium anymore, so does that mean it started as a brown dwarf and then became a planet when it burned all the deuterium in its core? That's not very satisfying.

  • Formation mechanism: formed via disk instability/gravitational collapse (as opposed to core accretion)? There is very likely overlap in masses between high-mass core accretion objects and low-mass gravitational collapse objects. You could therefore have like a 10 M_J brown dwarf via gravitational collapse that has never fused deuterium, but a 15 M_J planet formed via core accretion that fuses deuterium. That's not very satisfying either to have an overlap in mass ranges.

  • Observational: use 13 M_J as your cutoff? It's reasonable since that is generally the most observational characteristic that can somewhat distinguish the above scenarios. However, that means some your brown dwarfs formed via core accretion, while some planets formed via gravitational collapse. Similarly, it means that some of your brown dwarfs never fused deuterium, and some of your planets do fuse deuterium. Physically, it doesn't make sense to have either, but observationally, it's a very nice cutoff. Still, this isn't very satisfying either.

As far as I'm aware as a PhD in astronomy in exoplanets, there's not really an agreed-upon consensus among these three choices of definition.

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saanity t1_j9v2rhp wrote

Every astronomy enthusiast gets mad when you call gas giants a failed star. That's like saying an asteroid is a failed planet. It is what it is and has an important place in our universe.

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atomfullerene t1_j9w9sac wrote

It's also thought that stars and planets form in fundamentally different ways, so an actual failed star like a brown dwarf should be different from a planet, even one of about the same size.

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kompootor t1_j9wbnrm wrote

As I found out not too long ago, that debate was already mostly settled when I learned it and is long-settled now -- gas giants have a icy-rocky planetary core formed in the accretion disk along with the other rocky planets, and the much larger mass that they build up allows them to hold an enormous atmosphere during accretion while the rocky planets will bleed or evaporate most or all of theirs away. (See perhaps NASA's brief on planet formation -- I feel like Wikipedia's article is skirting the gas giant issue so probably has some conflict between editors.)

A failed star is a brown dwarf, which can form as part of a binary just like any stellar binary. The reason this particular system isn't that is that they say it's specifically a Jupiter-like gas giant. Further, they obviously got the mass since afaik methods of finding exoplanets will always get the orbit (by wobble at least), and the article says recorded the light during transit, so they would have calculated the radius; thus they'd be able to calculate the planet's density. Now, the density of Jupiter is 1.33 g/cm^3. Compare a brown dwarf, which as a failed star has no (or very little) core fusion to provide pressure that counteracts the enormous compression that's from the gravity of its enormous mass (about .07 solar masses, which is still huge) -- it is thus degenerate matter (in the core at least), as in a white dwarf, and at least in one case the average density was calculated at 108 g/cm^3. There would be plenty of other evidence to line up too -- I'm sure they weighed the possibility that it could be a brown dwarf, or at the very least a very unusual type of planet that must be tested for everything.

(And just for fun, the densities of main-sequence and off-sequence stars are all "known" (more or less -- it's not pure hydrogen or pure clean fusion), because math. I can't find a simple list, but you can find masses and radii -- anyway, as a type-M star, it is about 5 g/cm^3; compare the Sun at about 1.4 g/cm^3 -- more mass means more pressure inward, but also more fusion so more pressure outward,(See Thompson, Astr 1144 Lect.10, OSU)

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airplane001 t1_j9xc8wr wrote

I think the difference between gas giants and the smallest brown dwarfs is their origin. Planets are formed in the proto-planetary disk while stars are formed in a nebula as the center of a system

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JustAPerspective t1_j9zepko wrote

>I mean, aren't gas giants just "failed" stars that never got big enough?

No one knows.

See, the article talks about how previous theories are no longer necessarily applicable - which means everything we've been assuming about this stuff now gets rechecked, because right there in front of us is proof that what we believed before... ain't so.

It disrupts the presumed accuracy of every model that has relied on the previous interpretation. All speculation that relied on the previous theories for validity is now suspect, and how much of a rewrite will need to happen is yet to be determined.

Which is a constant in all facets of science, just btw. Every discovery, from the coronal loop optical illusion theory to the actual diameter of Terra's atmosphere, to the true electromagnetic strength of Sol, even the existence of tectonic plates... are updates to what humans believed was completely true.

"Imagine what you'll 'know' tomorrow." - K, MIB

Some minds refuse to accept new data if it contradicts what they believed before. Other minds are eager to accept and integrate new concepts. Reckon we're all finding the happy balance between both guidances?

Unsolicited Advice: Don't worry about the emotional stability of internet randos - if they're adults, they know it's their job to regulate their own feelings. If they're children, they'll blame you whenever they're unhappy anyway.

Your zen should be far more precious than internet rando opinions. 🖖

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