Astronomers may have found the first exomoon
eso.org159 points by MarcoDewey 6 hours ago
159 points by MarcoDewey 6 hours ago
Worth noting that the artist's impression is... not accurate. Both CD-35 2722 b (the brown dwarf orbiting the primary star) and CD-35 2722 b I (the exomoon orbiting the secondary) should be much closer in size. It is estimated that Jupiter is essentially the largest any gas giant can get; adding more mass will simply increase density and interior temperature until deuterium and lithium fusion and brown dwarfdom, and then at around 80 Jupiter masses, protium fusion and stardom.
Look at Barnard's Star[1], which is actually a fusing red dwarf star: it is not much bigger than Jupiter.
One thing this implies is that the escape velocity of such objects increases linearly with mass, so the surface temperature they can sustain without losing mass increases quadratically with their mass. Massive super-jovian planets can orbit close to their star, limited only by tidal disruption. Some could even orbit within the outer envelope of the star for quite some time.
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 and then slowly burn out or would that ignition precipitate a pressure wave through the entire body forcing fusion to begin everywhere?
I kind of assumed the artist’s impression was working with perspective? The images shown in the sidebar seem to picture them at different relative sizes.
> It is estimated that Jupiter is essentially the largest any gas giant can get
That does not appear to be the case if we mean mass, not diameter.
Yes; I was under the impression that from context it was clear what I was talking about. In astrophysics, to avoid precisely this confusion, the convention is to use the adjective 'massive' when comparing, well, masses, and 'largest'/'smallest' for the dimension of length and its higher powers (radius/diameter/area/volume). For instance:
> the Sun is 3.33e5 as massive as Earth.
But... he literally said in the following sentence that adding more mass does not change size, implying that he is talking about diameter, not mass.
Correct, but the link for "super jupiter" also goes to something that astronomers are fairly sure is 1.38x the diameter of Jupiter. Much less massive of course. Meaning Jupiter's diameter is not an absolute hard limit nothing can be larger than.
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.
Nobody said it was, he said it was "pretty much". Y'all can't read anymore.
A small dense planet, which orbits a star, is orbited by a larger gaseous moon. It's interesting the discovery is in Chile which has some of the best night skies, a Class 1 on the Bortle scale specifically in the Atacama Desert. Hoping to make it out there one day.
At some point I did some research and the Atacama was suggested to me as the best vantage point on earth for simple skygazing. Definitely on my bucket list.
An important phrase from the article to consider before commenting: "This system is somewhat hard to define using Solar-System-based words like ‘planet’ and ‘moon’"
We don't really have that nomenclature. We just recently decided what a planet it for the solar system, and even that is contentious.
I know this is besides the article and all, but why would the Chilean flag be the only one to have 8px left margin? This is killing me...
<div style="margin-left: 8px" title="Chile" class="sprites-flag_cl"></div>I believe such organisations tend to do such things very intentionally :-)
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...?
Obviously, how else would you do it rather than the standard left-margin notation for the host country :)
The flags have also all (except for Finland, which appears slightly wider?) been squeezed into a uniform 3:2 aspect ratio; some of them (e.g. Belgium, Switzerland, United Kingdom) properly ought to have different proportions. I understand they can look more aesthetically pleasing when they’re all the same size, but it’s another little detail to notice. :-)
I guess it is more of a derivative of the question: "in which bucket should we put the brown dwarf? Is it a star or a planet?". The answer is neither of course; but since it is more closely related to stars than to planets, I'm more inclined to call this satellite an exoplanet (instead of exomoon).
That being said it is still a nice finding, way more difficult to discover than "normal" exopanets.
I thought we’re supposed to call them dwarf planets now. Dwarf star, dwarf planet.
It's a problem of useful/meaningful labeling.
'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.
Even within stars the layman labels are a bit iffy; it is better to use the stellar classification. 'Dwarf' is badly overused, as is 'giant'.
> Astronomers have pretty good terminology for stars,
...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.
Brown dwarfs fascinate me, they can be at room temperature (range from about 2,800 K down to 250 K (roughly 2,500 °C to -23 °C / 4,500 °F to -10 °F)
You could basically have a bath in a brown dwarf, sure you might not last long, but still...
The idea of a black dwarf is also pretty wild. The universe isn't old enough for any black dwarves to exist yet, but eventually the brown ones will radiate enough heat away that they're no longer held up by the vibrational energy of the atoms they contain. They'll stop being fluffy and settle into a mode where they're held up only by electron degeneracy pressure (a.k.a the Pauli exclusion principle)... it's a bit like how neutron stars are stable because they're not so massive that they collapse to a black hole. Black dwarves will be stable because they're not so massive that they collapse to a neutron star.
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.
About time!, I cant wait till we start putting large hardware on the dark side of the moon. That will make JST look like a toy.
The far side of the moon is no more or less dark than the side we see.
It is from the Moon's perspective. On the visual spectrum the Earth is much larger and more reflective than the Moon. You're looking at something like 40x greater illumination during a 'full Earth' than you get during a full Moon on Earth. Earth is also extremely noisy in the radio spectrum for radio telescopes, while the Moon itself blocks most of all of that out on the far side.
It's not. The nearside is also darker.
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.
Details for why ~40x: The Earth is 3.67 times larger in diameter in the lunar sky than the Moon appears in ours. Earth covers 13.5 times more visual sky area and is also about 3 times more reflective per unit area
As I mentioned in a sibling comment, the brightness of the Earth does not outweigh the lost sunlight during lunar eclipses. The near side of the Earth is darker.
I wonder if this thing in turn has something in orbit around it? At the size I wouldn't surprise me if it had satellites of its own in orbit, leaving open the question of what to call them. (I'm no astrophysicist, is this really possible I don't know, but it wouldn't surprise me. What would surprise me is if we could detect them)
https://en.wikipedia.org/wiki/Subsatellite:
“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”
It might be helpful to describe gravitational relationships with human generational terms of parent-child, grandparent-grandchild, sibling, cousin, etc. So the Sun is the Moon's gravitational grandparent and Jupyter is its parent-sibling (Aunt/Uncle, maybe pibling upwards and nibling downwards).
I had to look it up and it is theoretically possible, they could be called sub moons or moonmoon. I'm partial to the name moonmoon personally.
> Instead, it circles a brown dwarf, an object larger than a planet, that orbits the CD-35 2722 star.
Isn't the dividing line between the largest possible gas giants and the smallest brown dwarfs a bit fuzzy?
The definition of a brown dwarf is that there is enough heat and compression for deuterium and/or lithium fusion, but not protium fusion.
The exact model limit is unclear, but the physics modelling is relatively straightforward.
I had only the vaguest notion up until 15 minutes ago of how these are being categorized, this one is described as either a brown dwarf or giant planet? https://en.wikipedia.org/wiki/CoRoT-3b
see the Classification header of the page
I really wanna call it a planet. It doesn't orbit a proper star, but if we call similar objects that don't orbit a star at all rogue planets I don't see why not call it just a planet.
Nice result, but I find they are selling it a bit too much. I'd rather call it an exoplanet (orbiting a brown dwarf orbiting a star).
this would actually be a planet, based on my understanding of celestial bodies? moons are natural satellites orbiting planets. this "moon" is orbiting a brown dwarf.
First paragraph:
> The star is being orbited by a brown dwarf, an object too massive to be a planet but too small to be a star.
>According to the IAU working definition (from August 2018) an exoplanet can orbit a brown dwarf. It requires a mass below 13 MJ and a mass ratio of M/Mcentral<2/(25+√{621}), or roughly 1/25. This means that an object with a mass up to 3.2 MJ around a brown dwarf with a mass of 80 MJ is considered a planet. It also means that an object with a mass up to 0.52 MJ around a brown dwarf with a mass of 13 MJ is considered a planet
Outside of the small probability that this may assist us in the future, has looking beyond our moon ever benefitted or even affected humanity in any way?
There are three clear benefits.
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.
Digital cameras for humanity as a whole, and satellite based telescopes for maintaining US dominance for the last 50 years and the long peace. Knowledge is power.
Before the late 70s satellites used film that was dropped back from orbit to the ground and developed to identify Cold War troop movements.
No, but let's keep pouring billions into confirming that the laws of physics apply outside of our solar system - smaller objects orbiting larger ones? Who could have guessed?
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.
Literally not a moon, that headline is ridiculous (not posters fault)
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!
I nominate Moon 2: Electric Boogaloo.
nice work
lol
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