Heavenly Palace

Yes, Bob's thread also. I just don't know how far we can use it to bamboozle readers into learning related subject matter.

Here's my shot for today. Imagine this galaxy scaled down such that light years are kilometers. A very aggressive shrink; ten orders of magnitude. Having done so, the whole thing is only 100,000 km across, about 8 earth diameters, which can be imagined. Yes?

In that shrunken galaxy, stars are sand-grain sized and with one-kilometer spacings. More or less.

That is our galaxy or probably any other. Grains of sand quite far apart. They appear much closer in night sky for shining brightly, and because many overcomes sparse.

 

Leisk likes. Bad decision because I could kill the joy by saying how fast light moves in than shrunken space. How fast (much slower) chemical-expulsion rockets could move. Making snails (our favorite slow things) look fast.

All that would be serve the notion that earth-like technologies cannot possibly explore this galaxy. Major buzzkill. I do apologize but numbers are as they are.

Meanwhile, earth humans are doing great at robotically exploring our star's planets etc. Doing great at detecting planets around other stars. Very few decades ago all that would have been beyond imagination and yet it has been done.

 

I don't believe that particular issue will be a problem. The Hawking radiation has an effective temperature, inversely proportional to the BH's mass. For usefully sized BHs, that is very cold, well below the current temperature of the cosmic microwave background radiation (CMB) of 2.7 Kelvin. So cold that stellar and larger BHs should not be evaporating at all yet, but still accreting even from sucking up some of that CMB. (I'm guessing here that they don't really start evaporating until the CMB becomes colder than their Hawking temperature.)

But it seems that other related problems could be severe. Tidal rips, extremely high energies of other infalling debris, etc.

 

Now that was sciency.

Yes, telescopes (across the range of wavelengths) are great and getting even better. They only fail as communication tools and it's not even their fault. It's the speed of light. Seems very fast to us, but galaxies etc. are gosh-darn BIG.

Chat with your ET friends and wait 10 to 100,000 years for reply?

 

I was thinking in different terms, but your words end up matching with my understanding. The gradient is connected to the curvature, in turn connected to the mass.

The Hawking radiation itself is damn cold, for any BH larger than a marble (?) or so. It would seem to stand out better as a cold spot on the cosmic background radiation.

But this is relevant only out in a really extreme vacuum with virtually no gas to feed upon. Even the interstellar gas medium within the galaxy should not be this sparse. Within the galactic zone, infalling gas particles should be bouncing off each other as they approach the horizon, interfering with each other as they get close, creating a very hot plasma cloud orbiting around the hole for a while before it can fall in. An accretion disk. This is the heat that you want to look for, vastly more detectable than the Hawking radiation.

And this extremely hot cloud will be highly destructive to any spacecraft trying to perform gravitational slingshot maneuvers through it.

Another approach to finding isolated BHs is to look for gravitational lensing and Einstein rings.

Under classical general relatively (GR), there is no issue with this. But GR and quantum mechanics, taken together, create a number of contradictions, and the BH event horizon is one of the places they conflict.

We just don't yet have a Grand Unified Theory. Lots of ideas are on the table. The neutron star merger observations last year helped clear a good block of ideas off the table, but plenty of other ideas remain.

 

"destructive to any spacecraft"@47. Completely agree. But the degree of space distortion that one would use for slingshot is simply found further out in that case.

Also planted a new thought about black holiness. Infalling matter that is itself gravitationally bound (stars, planets, rocky bits) would deliver all of matter&energy to the beast. But gases and little bits would lose some via heating and radiation described above. Is that correct?

 

I found some Hawking radiation calculators.

A BH of one solar mass has a Hawking temperature of a chilly 61.6 nK. That is nano-Kelvin.

At one earth mass, the temperature rises to 0.02 K, but the BH is only the size of a marble, radius just under 9mm. That is much too small for gravitational slingshots.

At one lunar mass, the temperature is a much warmer 1.67 K, but a radius of about 0.1 mm.

For the gases and little bits, I believe that is correct. They should collide and compress and get exceeding hot. Some fraction gets expelled as solar wind or polar jets, quite a bit of energy radiates away from the heat, but eventually most of the matter gets dragged in to the BH. But don't take me as an expert, I'm partly guessing here.

For shooting solid objects into a central body, such as the sun or a BH, remember that a trajectory must be aimed for impact, not a close-in perihelion. Miss by even a little bit, and the object orbits around and comes back. Orbital angular momentum is a conserved quantity, and even a little bit is enough to create an elliptical orbit around the primary. That is why it is very difficult and expensive to send things (e.g. hazardous nuclear waste) directly into the sun. Shooting them out on solar escape paths is much easier and cheaper, with significantly lower delta-Vs.

With the sun, we don't need to completely remove an object's angular momentum, just enough to drop perihelion below the surface. Aerodynamic drag will then finish the job. But while the sun has a radius of about 700,000 km, a similar mass BH has a radius under 3 km, meaning the object's angular momentum must be set almost perfectly to zero. Miss the event horizon somewhat, and the object gets shredded by tidal forces and ablation from plasma in the accretion disk, and added to that orbiting plasma.

For solid objects in natural orbit, decaying by radiation pressure or relativistic or any other similar mechanisms, they should mostly run into that very hot accretion disk plasma issue. Only those that have a particularly unlucky loss in a match of gravitational billiards with another orbiting object, should suffer a direct dunk in the central BH.

 

To those reading I wish to say that fuzzy1 is giving you the goods here. Best cow-farming astrophysicist who bothers with PriusChat. I think that's fair.

==
For slinging trash at Sun, I still don't get why it's a small target. Looks big to me and has a locally impressive gravity well just in case your aim is a bit off.

 

The earth orbits the sun at about 30 km/sec in an almost circular orbit.

To boost a payload completely out of the sun's domain, making it gravitationally unbound, one needs to kick it up to solar escape speed, which happens to be sqrt(2) times the circular orbit speed at any given point. That means a speed of 42 km/sec. The rockets need to add a delta-V of (42-30) = 12 km/sec to the speed the object already has by virtue of being with the earth. Because of the exponential rocket equation, with nozzle exhaust speeds on the order 4 km/sec, this is expensive.

To drop a payload directly into the sun, one needs to drop it back to an 'orbital speed' of essentially zero, then allowing it to fall inward. This means a rocket delta-V of nearly 30 km/sec, backwards compared to earth's motion. Because of the exponential nature of the rocket equation, 30 is not merely 2.4X more expensive than 12, it is vastly more expensive.

If the payload's forward speed around the sun is even a little bit above zero, the result is a very elliptical orbit, with a perihelion distance (nearest approach to the sun) quite a ways above the solar surface. The payload then loops around, and comes all the way back to us. Though since it gets back before we do, there will be no collision -- this time. Not bets on future returns.

I should refigure the maximum allowed speed that still drops something into the solar atmosphere, but my handy orbital equation cheat sheet (figured during my late teen years) is not within reach. There should be better stuff available online, when I get enough time to look for it.

 

Now that's what I'm talking about! Let's take this 8.5 tons of TG1 crash-thread and teach. We have seen a recent comet getting not quite sucked in. Solar gravity well looks deep to me but I defer.

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Going against satflare's April-2 central prediction for TG1 re-entry, I say March 30. Its big draggy solar panels hit weak atmosphere in each orbit bottom. First not getting blown off; just bent back. A few orbits later, bent back will fail and those solar panels will 'detach' we might actually get to see that!

Satflare stays with April 2 (+/-) even while their re-entry prediction graph points towards sooner. Tomorrow or day after, they may predict sooner.

 

There is a person, presumably in the business, predicting 31 March

Scientists Narrow Down When China's Falling Space Station Will Burn Up in the Atmosphere

 

Hey, I think I understood that bit.

 

Humanity Star is just to look at and perhaps the only thing intentionally launched as 'debris'. It's orbital info is here:


Humanity Star - Orbit


Deorbiting is predicted very soon and before TG1:

SATVIEW - Forecast for reentry of space junk HUMANITY STAR (43168U). Track it in Real time

I don't understand how 'they' can be sure of HS re-entry even while its perigee is higher than TG1.

 

I would have liked to have made a career in some field of astronomy or basic physics. Or better yet, the intersection of the two. But at the time it seemed that there weren't anywhere near enough well paying positions compared to the number of people interested. With too much competition, it seemed that I'd have difficulty floating or scrambling to the upper levels.

Electrical engineering seemed to be similar enough to make use of my skills, and interesting enough, with a much better chance of getting good compensation. In the end, I felt burned out in the changing corporate culture a decade and a half before my Social Security Normal Retirement Age. Fortunately, I no longer needed the compensation either.

If the right opportunity presented, I could still be enticed into astrophysics. There is no longer any chance of me making any mark in the theoretical or observational fields, but I'd love to dig into measurement and observing equipment testing, operation, and next-gen improvement. Reading some of the LIGO reports after last year's neutron star merger observation, really got my heart rate up. Especially the part about a DAC saturation blanking out a brief bit of data, every few hours. That looks very much like an ADC metastability issue I tracked down and remedied in one of our designs. Though LIGO has vastly more feedback loops, any one of which could be the culprit(s).

 

First guess: density.

HS is a meter wide sphere, with a mass of merely 8 kg. Its low cross sectional density means that air drag will pull it down much quicker. It is a feather, while others are bowling balls.

Second guess: sorry, no more ideas yet.

 

Humanity star has very low density. Thus when at perigee it has relatively little kinetic energy. So, the 'winds' at 228 km slow it faster than TG1 at 215 km. That's about what I read, makes sense to me, so I'm going with that.

As to why HS launchers thought such a thing could stay up for 9 months, I got nothin'

 

Well, ya see: obvious to fuzzy1 but missed by a little space tech company that actually launched two commsats on the same firestick.

Perhaps the world of astro is not closed to him after all

 

TG1 overall density ~0.53 says I, which is like mid-range wood. Not quite bowling ball (3.8). HS obviously is much less than either.

Sputnik-1 was more like a bowling-ball density. Had a perigee similar to our two next contestants, but stayed up for xx months.