astronomy

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lemming, w Dark Matter Black Holes Could Fly through the Solar System Once a Decade

I thought these were disproved by lack of gravitational microlensing?

InvertedParallax,

The main way you’d see that kind of microlensing is if they aggregated.

But given the way gravity works, they should aggregate, otherwise why call them black holes?

Classy,

If they were relatively evenly distributed would that counteract lensing?

InvertedParallax,

Yes, it would just be surprising because, gravity should make them not be evenly distributed.

The whole thing with dark matter is that it’s this magic stuff that causes gravity but isn’t affected by it, which… is not how gravity normally works.

Though there is still room for it, we just need a better framework other than “I added 3 and 5 and got 12, so obviously I must mean to add 3 and 5 and 4 too”.

MartianSands,

You’re mistaken. Dark matter, whatever it is, isn’t affected by anything except gravity. It interacts with gravity just like “normal” matter.

The evidence is also significantly better than you’re describing

InvertedParallax,

Then it should also coelescce, particularly since it doesn’t have the em force to keep it repelled, the universe should be dominated by massive dark matter black holes.

Yes, there’s math that explains part of the distribution, but also there is 0 force opposing any collapse we’d have a lot more neutron stars and other degenerate matter catalyzed by dark matter.

We have hypotheses like this when our observations don’t make sense and we need to explain them, it’s definitely a possibility but we still have room to understand the large scale physics at play.

MartianSands,

You don’t need a force to prevent collapse if there’s no drag force to slow things down. It would actually be almost impossible for a cloud of dark matter to collapse since any individual particle has momentum and no way to slow down, so they’ll all be in some sort of mutual orbit

InvertedParallax,

I’m guessing you’ve seen as many lorentz attractor simulations as I have, what always happens is something like tidal effects or angular momentum means 90% slow down while a few particles get shot out of hell at ludicrous speed.

The effect is similar to drag, and is basically how we get entropy even without em effects.

Gork, w Dark Matter Black Holes Could Fly through the Solar System Once a Decade

What would happen if one of these tiny black holes hit Earth? The article doesn’t really talk about it.

Donjuanme,

Absolutely nothing.

Also not sure why they wouldn’t evaporate nearly instantaneously. Sounds to me like more dark matter bunk.

deegeese,

Passing near the earth, we’d get some strange tides. Passing through the earth, it would eat earth.

Rhaedas,

Nonsense. The event horizon on such things is incredibly small, as is the mass vs. that of Earth.

deegeese,

You don’t need the event horizon, you just need local gravity around 1G. For the masses described in the article, that radius is from hundreds of meters to 10s of kilometers.

Rhaedas,

Which still wouldn't do what you suggest. The mass is the same, so it has the same effect from a distance. Unless by "eat earth" you meant it would take in dirt until it suck to the core, still about the same mass.

Bluetreefrog, w Dark Matter Black Holes Could Fly through the Solar System Once a Decade

The book, Seven Eves is about one of these hitting the moon.

Davel23,

The cause of the incident is never specified in the book.

thebardingreen,
@thebardingreen@lemmy.starlightkel.xyz avatar

The book Earth by David Brin is about one of these hitting the Earth

Lemming6969, w Dark Matter Black Holes Could Fly through the Solar System Once a Decade

What if dark matter is some form of black hole or exotic ultra dense material made entirely out of the missing antimatter, which for whatever reason doesn’t otherwise interact with electromagnetism? 2 birds, 1 stone.

Zachariah, w Betelgeuse has a tiny companion star hidden in plain sight
@Zachariah@lemmy.world avatar

After more than a century of speculation, data seem to confirm that Betelgeuse (the brightest star in the Orion constellation, shown here) has a much smaller star as an orbital companion.

Two independent studies found evidence of a star about the same mass as the sun, orbiting Betelgeuse about once every 2,100 days.

daisyKutter, w Betelgeuse has a tiny companion star hidden in plain sight
@daisyKutter@lemmy.ml avatar

Named Lydia?

ekZepp, w ESO telescope captures the most detailed infrared map ever of our Milky Way
@ekZepp@lemmy.world avatar
1stTime4MeInMCU, w ESO VLT discovers new exoplanet around the nearby Barnard star, only 6 light years away.

Aww that’s cute. Barnard’s star has kind of an interesting history of exoplanet claims that were sadly ruled out after further examination. Great to hear we finally have good evidence.

lunarul, w ESO VLT discovers new exoplanet around the nearby Barnard star, only 6 light years away.

Barnard b [2], as the newly discovered exoplanet is called, is twenty times closer to Barnard’s star than Mercury is to the Sun. It orbits its star in 3.15 Earth days and has a surface temperature around 125 °C. “Barnard b is one of the lowest-mass exoplanets known and one of the few known with a mass less than that of Earth. But the planet is too close to the host star, closer than the habitable zone,” explains González Hernández. “Even if the star is about 2500 degrees cooler than our Sun, it is too hot there to maintain liquid water on the surface.

LazerFX, w Brightness of first Chinese broadband constellation satellites alarms astronomers

And that’s because SpaceX at least try to minimise pollution (both light and radio). Not successfully, but it’s minimised.

The Chinese don’t give a fuck, just like they don’t give a fuck who their toxic rockets land on when launched over their own people.

TC_209, (edited ) w Brightness of first Chinese broadband constellation satellites alarms astronomers
@TC_209@hexbear.net avatar

The primary source of the linked article: https://arxiv.org/abs/2409.20432

Observed magnitudes of Qianfan spacecraft range from 4 when they are near zenith to 8 when low in the sky.

Since this is the first run of the Qianfan satellite constellation, the most appropriate comparison would be to Starlink’s original satellites. As you can see below, the notion that China’s satellites are “significantly brighter than those of Western systems” is a inaccurate.

A 2022 paper on Starlink Original, VisorSat and Post-VisorSat models: https://arxiv.org/pdf/2210.17268

The Original spacecrafts have a relatively flat phase function, so they are comparatively bright over a wide range of phase angle. […] the characteristic magnitudes are: 4.7 (Original) […]

A 2024 paper on Starlink newer Direct-to-Cell satellites: https://arxiv.org/abs/2407.03092

The mean apparent magnitude of Starlink Mini Direct-To-Cell (DTC) satellites is 4.62 while the mean of magnitudes adjusted to a uniform distance of 1000 km is 5.50.

Clearly, even the newest Starlink satellites are well above the magnitude 7 limit astronomers recommend for satellite brightness.

4oreman, w Tiny Black Holes Could Lurk Inside Asteroids, Moons, or Even Planets Like Ours

?at theu where

abcdqfr, w Tiny Black Holes Could Lurk Inside Asteroids, Moons, or Even Planets Like Ours

How tiny? Inside earth tiny?

zout,

As small as event horizon of 1 micron tiny to 1/10 the earth's diameter tiny for this paper.

Sterile_Technique, w Tiny Black Holes Could Lurk Inside Asteroids, Moons, or Even Planets Like Ours
@Sterile_Technique@lemmy.world avatar

Isn’t an event horizon just a question of being dense enough to bend light past the point of no escape?

A hollow planet supporting a detached core with enough density to have an event horizon seems kinda ridiculous… If even light can’t escape it, I don’t see some rocky ‘shell’ withstanding that much gravity. Any hollow section would have collapsed well before reaching the point of the planet’s densest point forming an event horizon.

lolcatnip,

What matters is the total mass of the black hole, not its density. If you replaced Earth’s core with a black hole of the same mass, the gravity you’d feel at the surface (or beneath the surface) would be the same. You’d only notice a difference if you were in the hollow region formed by removing the core.

The way I see it, the real problem with a planet like Earth is that because the inside is so hot, the inner parts are too soft to support their own weight, and the crust is probably too fragile to support its own weight. That’s not a problem, though, in an asteroid or a planet that’s solid all the way through.

Sasha,

Depending on the mass of the black hole, the “shell” doesn’t need to be a shell it could be effectively completely solid with an atom sized black hole at the centre.

PBH’s as discussed in this article have pretty wild mass ranges, so anything is possible. It’s entirely possible to have black holes so small they can’t easily absorb new matter as they’re smaller than protons. Tiny black holes only have large surface gravity, nothing noteworthy at a distance.

threelonmusketeers, w Hurricane Milton from Dragon Endeavor photo taken by Astronaut Matthew Dominick

Super cool photo, but does this technically count as astronomy? Isn’t astronomy “a camera on (usually) on earth, pointed up into space”, not the other way around?

acockworkorange,
astronomy
/ə-strŏn′ə-mē/
noun
  1. (obsolete) Astrology.
  2. The science which treats of the celestial bodies, of their magnitudes, motions, distances, periods of revolution, eclipses, constitution, physical condition, and of the causes of their various phenomena.
  3. A treatise on, or text-book of, the science.

From the GNU version of the Collaborative International Dictionary of English.

threelonmusketeers,

Are you saying that observing the Earth should count as astronomy?

acockworkorange,

Technically correct. The best kind of correct.

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