Look at Barnard's Star[1], which is actually a fusing red dwarf star: it is not much bigger than Jupiter.
it's just that one is farther away from the camera
That does not appear to be the case if we mean mass, not diameter.
> the Sun is 3.33e5 as massive as Earth.
That being said it is still a nice finding, way more difficult to discover than "normal" exopanets.
<div style="margin-left: 8px" title="Chile" class="sprites-flag_cl"></div>About ESO [1]
> We are an intergovernmental organisation established in 1962 supported by 16 Member States (Austria, Belgium, Czechia, Denmark, Finland, France, Germany, Ireland, Italy, the Netherlands, Poland, Portugal, Spain, Sweden, Switzerland and the United Kingdom), our host country Chile and strategic partners.
So Chile has a distinct status, hence the margin...?
You could basically have a bath in a brown dwarf, sure you might not last long, but still...
What will this substance look like? Will it ring like a bell if struck? What color will it be? Will it conduct electricity? If so, how? Are the atomic nuclei now the charge carriers because the electrons are stuck? It would likely be a super-thermal-conductor, does that have any analogous properties to a super-electrical-conductor? Which of these can we observe without the sensor collapsing to degenerate matter itself?
I hope there's life around to conduct these experiments when they become possible.
(tl;dw it's an exciting discovery but moon is the wrong terminology for what was found)
“A subsatellite, also known as a submoon, moonlet or informally a moonmoon, is a "moon of a moon" or a hypothetical natural satellite that orbits the moon of a planet”
Isn't the dividing line between the largest possible gas giants and the smallest brown dwarfs a bit fuzzy?
The exact model limit is unclear, but the physics modelling is relatively straightforward.
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but Nancy Grace Roman Space Telescope WILL find Earth-sized exoplanets and even REAL moons
I am stupid-excited to see it launched/first-light in my remaining lifetime (Musk better not screw it up)
For perspective on the technology, JWST "only" has 28mbps downlink
NGR has 500mbps downlink, that's right 1.5 TERABYTES PER DAY download speed
all from ONE MILLION MILES AWAY in L2 (11 seconds ping time!)
Technology is getting amazing!
1. Answering where humans come from is probably one of the the oldest question we have had. All religions try to answer this in one way or the other. I say, trying to come up with scientific answers is extremely valuable.
2. We feel awe at the wonders of nature, not much different from the awe that we feel when we see great human art. Tax dollars as well as charity are used to subsidize art often. This is similar, though there is more money involved here.
3. The problems one sees in different domains are always different. Funding agencies give money to the "directly economically useless domains" because the workforce that is trained and technology that is developed can then be applied to the "directly economically useful domains". The support money to the former is much smaller than the support money to the latter, but just enough to inject fresh ideas and creativity to the latter.
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I think the key idea is fixed minimum/maximum boundaries for a lot of astrophysical phenomena—stellar protium fusion, the Chandrasekhar limit, Tolman–Oppenheimer–Volkoff limit, etc.
> If a brown dwarf is right on the edge of stardom would it start protium fusion in only the part of itself that is the right pressure
The nuclear cross-section of protium fusion in astronomical bodies is determined by temperature, pressure, and density. These variables are in turn dictated by the total mass of the object in question. Brown dwarfs never have sufficient mass for protium fusion, so they never undergo any protium fusion whatsoever. This is a hard-and-fast boundary for stardom.
> or would that ignition precipitate a pressure wave through the entire body forcing fusion to begin everywhere
The three variables above are not uniformly distributed throughout the body; there is a maximum at the centre, and fusion only happens here. Even in the Sun, about 99% of the fusion happens within about a quarter of the radius from the centre. The temperature drops rapidly thereafter, reducing the nuclear cross-section of the proton-proton chain to essentially zero. At the photosphere (surface), the temperature is ~5777 K, which is a decidedly Earthly temperature (lightning bolts are ~ 30000 K). So no, fusion does not happen everywhere.
Now, we need to discuss star formation and why brown dwarfs have never experienced protium fusion at any time in their lives. Star formation is still a very active area of research, debate, and fitting models to empirical study, and this is especially true for the detailed interior and structure of protostars and pre-main-sequence stars; hence, this is going to be quite surface-level (pun not intended).
Collapsing molecular clouds form stars. The total mass of a given cloud (or a particular region of it) sets an upper bound on the resultant object, because the total mass dictates the gravitational potential energy and hence the terminal velocity of the matter, and hence the rate of matter infall at the centre before the cloud dissipates. If the mass is low enough, the central object will become a brown dwarf, or even a large gas giant and a 'rogue planet'.
As the gas cloud collapses, the central region increases in density, temperature, and pressure, but no fusion occurs yet. Conservation of angular momentum forms a circumstellar disc, and material continues to fall onto the central region. As long as this infall continues, the central region is called a protostar. At some point the mass of protostar crosses the boundary needed for deuterium fusion; if the infall stops here, the result is a brown dwarf. If this infall continues, the mass increases beyond the boundary (~80 Jupiter masses) needed for protium fusion, and protium fusion can begin. When the infall stops and the circumstellar disc largely dissipates, the result is a pre-main-sequence star.
Note that both these very young pre-stellar objects are not yet at hydrostatic equilibrium, and are still comparatively rarefied (or 'puffy') compared to main-sequence stars; they are still collapsing, and the temperature, density, and pressure at their cores continues to increase. Only when this equilibrium is achieved and gravitational collapse is halted do stars begin life on the main sequence.
Now, it should be evident why brown dwarfs never experience protium fusion: at no point in their lives have they ever had any region in their interior hot, dense, or hyperbaric enough to have a high enough nuclear cross-section for protium fusion. At their formations, they were simply not massive enough; they continue to collapse, which admittedly provides a considerable power output—surface temperatures are ~1000 K. The largest brown dwarfs experience deuterium/tritium/lithium fusion into helium, but this also stops over time.
(Side note: in my opinion the word 'brown dwarf' is a bit of a misnomer, because look at how bright molten iron (~ 1500 K) is even in broad daylight[1]; now imagine an object ten to twenty times the radius of Earth, emitting this much heat from every square millimetre. If you approached a 'new' brown dwarf it would cast a lot of light.)
[1]: https://commons.wikimedia.org/wiki/File:Scunthorpe_Molten_St...
https://en.wikipedia.org/wiki/HAT-P-1b
It also orbits its star in only under 5 days, so a few theoretical visualization/renderings of it would probably be quite spectacular.
'Planet' comes from the Greek word for 'wanderer' which was very useful for labeling the handful of bright stars that moved through the heavens in a pattern. Then we got to the Space Age and kept calling them (and similar new additions) 'planets' even as we learned far more about them. And immediately there's a problem. Setting aside Pluto (and the Sun), you've still got Mercury on one end (5% of Earth's mass, and smaller than several moons) and Jupiter on the other end (320% of Earth's mass - more than everything else in the solar system put together, and over 1000 times Earth's volume). "Planet" stops being a word you can use with any sort of detail. (Thus the IAU definition battle and Pluto's "demotion".) Astronomers have pretty good terminology for stars, but once you go sub-stellar, the labeling rapidly gets difficult, and for good reason.
not %
just 320 Earth masses
...do they though?
The "proper" terminology says all main sequence stars are dwarves, but nobody calls them all that in practice. Some astronomers insist on saying "yellow dwarf", but some don't really bother. In general having the only two kinds of star be "giant" or "dwarf" is contentious, but it's also contentious that there isn't a name for whatever is in the "middle". "Main-sequence star" is a broader category and doesn't apply. They're all "stars", obviously, so that isn't specific enough.
The only decent terminology is for the spectral classes, but those only work as long as you look at spectra. The moment you try to figure out what the theory says those stars would look like as proper 3D objects, things get very messy. You also immediately get the issue that star size and brightness goes O>B>A>F>G>K>M. So... it's alphabetic except it isn't. And C is something completely different and doesn't fit the brightness classification at all.
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Earthshine is brighter than moonshine, sure. Earthshine at its brightest, delivers about 0.15W/sq meter to the moon. Sunshine meanwhile delivers 1360W/sq meter to the moon. The near side of the moon is the only side which experiences eclipses. The amount of energy from the sun is SO large, compared to earthshine, that ~1.5 eclipses per year for a few hours each represents a loss of light that outweighs the additional light gained from earthshine by about 5x.
We're talking fractions of a percent here of course, but it's not ambiguous. The near side of the moon is also the darker side.
You're right that it's noisier in radio.
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see the Classification header of the page
The fuzziness is in the physical properties needed to achieve that. 13 Jupiter masses is generally the threshold where deuterium fusion starts, but that can vary: a brown dwarf composed of only primordial H and He would need a bit more, while one with some heavier elements from previous generations of stars will be denser and need slightly less. Rotation speed also matters: a faster rotator will experience centrifugal force and thus have less interior pressure.
And there is fuzziness in what we can observe, so sometimes we're not sure if an object is a brown dwarf. We may not know its exact mass and composition, and we might not be able to tell if it's radiating energy from deuterium fusion, or just from gravitational compression, or (in a binary system) if it's just reflecting light from its companion star.
> The star is being orbited by a brown dwarf, an object too massive to be a planet but too small to be a star.
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Before the late 70s satellites used film that was dropped back from orbit to the ground and developed to identify Cold War troop movements.
I'm sympathetic to space colonization, which seems like the most optimistic long term future for humanity, but the focus on exoplanets, -moons, even signs of exo-civilizations feels like making up theories about the bottom of the ocean centuries before the invention of submarines.
