Stellar Mass and size

[Blue Ghost]

MT went overboard on sensors in several directions. The MT version of densitometers are waaay too powerful for Traveller standards, being more in line with Star Trek. The MT Neutrino Sensor is also in that category. Later editions dialed it back a bit, which is why I see Densitometers with serious range as being BIG regardless of TL, while neutrino sensors are a survey tool, not a combat sensor.

Yeah, if you automatically know where everything is, the topography of all the worlds, abundancy of water, composition of all atmospheres and other details, the moment you jump in system, then there's little point in running the adventure.

I can't remember what I had planned for the story, but the tech described in the referee's book just truncated whatever it was I had planned.

Back on topic, rogue stars might be an interesting threat. That might fall outside your standard Imperial capability to deal with, but it would be entertaining to see how players dealt with it.

 

[Blue Ghost]

A very cold Brown Dwarf

Here's a link to "sun" (brown dwarf) whose temperature is said to be below freezing;

http://www.nasa.gov/press/2014/apri...find-close-cold-neighbor-of-sun/#.VLD4t9LF-o0

Extract;

Brown dwarfs start their lives like stars, as collapsing balls of gas, but they lack the mass to burn nuclear fuel and radiate starlight. The newfound coldest brown dwarf is named WISE J085510.83-071442.5. It has a chilly temperature between minus 54 and 9 degrees Fahrenheit (minus 48 to minus 13 degrees Celsius). Previous record holders for coldest brown dwarfs, also found by WISE and Spitzer, were about room temperature.

Image (artists concept);

 

[GypsyComet]

Between recent estimates of rogue body counts and stories like Karl Schroeder's Lockstep, you could run entire campaigns out in the Rogue Dark.

 

[Blue Ghost]

I heard a little blurb in one of the docs I saw recently that fired my imagination. As per your's and Aramis's figures, there are stars whizzing past other stars at trillions of miles per hour. Fast enough not to get locked by another stars pull.

Again, this is perhaps out of the scope of the Traveller rules set in terms of the players being able to deal with the threat, but imagine a star barreling through an in inhabited solar system at that speed.

 

[JimMarn]

I heard a little blurb in one of the docs I saw recently that fired my imagination. As per your's and Aramis's figures, there are stars whizzing past other stars at trillions of miles per hour. Fast enough not to get locked by another stars pull.

Again, this is perhaps out of the scope of the Traveller rules set in terms of the players being able to deal with the threat, but imagine a star barreling through an in inhabited solar system at that speed.

There are stars, and maybe solar systems, orbiting our galaxy's black hole at high speeds. Very unlikely there are inhabitants there, if there were, the radiation from gasses infalling into the black hole would have killed them off.

I think it is on Discovery science, on one of the universe documentaries, on what would happen to our solar system if a black hole moved into our stellar neighborhood and moved across our solar system.

 

[aramis]

There are stars, and maybe solar systems, orbiting our galaxy's black hole at high speeds. Very unlikely there are inhabitants there, if there were, the radiation from gasses infalling into the black hole would have killed them off.

I think it is on Discovery science, on one of the universe documentaries, on what would happen to our solar system if a black hole moved into our stellar neighborhood and moved across our solar system.

Both, actually, plus on hulu+ real science specials...

The radiation from a feeding black hole is likely to be lethal to well over a parsec.

 

[Blue Ghost]

I was thinking more of a sun that had been flung out into the outer spiral arms, and had "gone rogue" so to speak, like a planet or moon being flung out from its orbit after billions of years. At least that was the gist of the documentary I saw.

A black hole, baring exceptionally high Tech Levels, would be impossible to deal with. Would you even know it was coming? Even at high Imperial tech levels?

 

[GypsyComet]

Assuming a tradition of survey astronomy, a local and moving black hole will give itself away visually as it gravity lenses the star light behind it. It may also show up as a path of stars that have all shifted slightly as it passed.

A high tech society that no longer looks at the stars that way may not know something is coming until it eats a world or passes through a system and throws traffic and radiation all over the place. Densitometers might pick it up early even if there are no big survey sensors around. That sort of big and fast moving gravity field is probably (hand-waving imaginary tech, here) going to wreck the calibration of every densitometer in a system, and should raise alarms.

 

[tjoneslo]

A high tech society that no longer looks at the stars that way may not know something is coming until it eats a world or passes through a system and throws traffic and radiation all over the place. Densitometers might pick it up early even if there are no big survey sensors around. That sort of big and fast moving gravity field is probably (hand-waving imaginary tech, here) going to wreck the calibration of every densitometer in a system, and should raise alarms.

I have great difficulty imagining a 3+ solar mass black hole going through the Oort cloud of a typical star system without any kind of signal. Just one Oort cloud object intersecting with the black hole would produce a significant x-ray burst. Even through the interstellar medium at any relative rate of speed is going to produce an interesting, and unusual, signal.

In order to make a black hole's approach stealthy, you would need:

A cold black hole, meaning no accretion disk or other material around it. This implies a BH which has been away from anything that could feed an accretion disk for a long time (A billion years?). This in turn implies the BH is coming in from off the galactic plane.

To make that interesting have the BH orbiting the galaxy at 90 degrees from the galactic plane, but at the same distance from galactic center. Meaning that in about 120 Million years, it'll be back through the neighborhood again. That gives an incoming velocity of about 230 km/s or about 4300 years / parsec.

So for about a thousand years you will seeing signs: x-ray bursts, comets incoming, weird anomalies, jump space disruptions. And then the black hole tears the whole system apart. Not exactly a fast moving disaster. But one that no one can avoid.

Does anyone know how you calculate the safe jump distance from a black hole?

 

[Blue Ghost]

Someone relayed an adventure they had regarding being near a blackhole....just outside its event horizon, or just on the edge of its accretion disk. I can't remember much more than that.

Should I start a new thread, and call it "Astrophysical Disasters" or something like that? If you're an evil GM, and really like to screw with your players, then I'd imagine such a thread will be highly entertaining, and educational :smirk:

 

[JimMarn]

I was thinking more of a sun that had been flung out into the outer spiral arms, and had "gone rogue" so to speak, like a planet or moon being flung out from its orbit after billions of years. At least that was the gist of the documentary I saw.

A black hole, baring exceptionally high Tech Levels, would be impossible to deal with. Would you even know it was coming? Even at high Imperial tech levels?

One scenario I have seen mentioned on a science/astronomy program was as colliding galaxies merge, one of the black holes would orbit around the larger one at large distances.

If this was any sort of large astronomical distance, the smaller one could absorb solar systems.

While I felt at first this was nothing to worry about, Andromeda galaxy M-31 isn't likely to collide with our galaxy for billions of years from now, astronomers keep finding dim dwarf galaxies that are much closer to our galaxy.

 

[Blue Ghost]

Assuming a tradition of survey astronomy, a local and moving black hole will give itself away visually as it gravity lenses the star light behind it. It may also show up as a path of stars that have all shifted slightly as it passed.

A high tech society that no longer looks at the stars that way may not know something is coming until it eats a world or passes through a system and throws traffic and radiation all over the place. Densitometers might pick it up early even if there are no big survey sensors around. That sort of big and fast moving gravity field is probably (hand-waving imaginary tech, here) going to wreck the calibration of every densitometer in a system, and should raise alarms.

I guess the other reason I bring up these topics is because in years past I've read anecdotes here of adventures that involved destroying worlds, overthrowing governments, cruising the edge of black holes, and so forth. Scenarios that go beyond the scope of the rules without creating higher technologies or capabilities described by the TL chart.

I can't really wrap my ahead around that kind of stuff in terms of playing them out with the game's CT or even MT ruleset, but players and GMs here are pretty inventive in that regard (again based on the accounts put here). Which tells me that there was (or perhaps still is) a desire for stuff that goes beyond your typical political interventions. Either way it's interesting to discuss.

 

[Blue Ghost]

Hank Green gives the Reader's Digest explanation on Super Giants and Hyper Giants;

https://www.youtube.com/watch?v=L8_RnYjFvt0

 

[WistfulD]

So for about a thousand years you will seeing signs: x-ray bursts, comets incoming, weird anomalies, jump space disruptions. And then the black hole tears the whole system apart. Not exactly a fast moving disaster. But one that no one can avoid.

Does anyone know how you calculate the safe jump distance from a black hole?

I'm unconvinced. That thing is going to be closer and heavier than anything else in the neighborhood, and be either a long time coming, or a rapid changer of measurements. Even if the solar system's inhabitants aren't looking out at other stars with scopes and noticing the gravitational lensing, they are going to notice the influence on their planet's orbit. Besides, there are two options--either the inhabitants evolved there, or they are descended from colonists. If they evolved there, they went through a phase of telescopic astrocartography. If they didn't there was a stellar survey when they got there. Either way, the BH would have been discovered.

 

[tjoneslo]

I'm unconvinced. That thing is going to be closer and heavier than anything else in the neighborhood, and be either a long time coming, or a rapid changer of measurements.

I'm assuming both are true. It also depends upon the plane of ecliptic for the planets in the system and the mass of the central star.

Either way, the BH would have been discovered.

Probably. But we're constructing a worst case scenario here.

In addition to gravitational lensing (through various telescopes), there is the detailed analysis of stellar motion (much more likely for the IISS to keep their maps in order). And I'm quite sure the IISS keeps very close track of mis-jumps for the same reason. Finding unexpected hidden masses between stars the hard way is a disruption for trade (i.e. bad).

A 3 solar mass black hole has a diameter of 15km. At a distance of 1500km the tidal forces would tear a ship apart in milliseconds.

 

[Blue Ghost]

Nebula; slightly stellar related, Hang Green explains nebula;

https://www.youtube.com/watch?v=tkIdzyG0OJw&list=UUrMePiHCWG4Vwqv3t7W9EFg

 

[Hemdian]

Does anyone know how you calculate the safe jump distance from a black hole?

That depends on if you define safe jump distance as based on gravity or tidal force IYTU.

Using gravity, a typical stellar black hole of ten solar masses would have a safe distance of about 4.49 AU (if I've done my sums right). Using tidal force, the same black hole would be ... I make it 0.58 AU but that seems awful close. Anyone want to recheck my figures?

 

[Frankymole]

Probably, since a spinning black hole drags space around with it, allowing infalling matter to orbit closer than a non-spinning black hole.

 

[Blue Ghost]

Sci-show's Hank Green on Black Holes;

https://www.youtube.com/watch?v=L8GCR88T3fE

https://www.youtube.com/watch?v=kq4u7Sv7GT4

I can't recall much from my old University Astronomy classes. Can someone give me the lowdown or a link that explains the difference between spinning and non-spinning black holes?

p.s. loose tangent; there's a report that a white hole may have been observed in the last couple of years. A white whole ejecting organized matter as opposed to sucking in matter and crushing it.

ADDENDUM;

White holes explained; https://www.youtube.com/watch?v=Y1HqOEbq2L4

 

[whulorigan]

I can't recall much from my old University Astronomy classes. Can someone give me the lowdown or a link that explains the difference between spinning and non-spinning black holes?

If a star is rotating when it collapses (as probably all do), angular momentum is still conserved, even if the mass of the star collapses within its own Schwarzschild Radius (the distance from the center of mass, or singularity, at which the escape velocity equals the speed of light). Thus, as the star collapses, it will begin to rotate faster.

Since in General Relativity gravitation is expressed as a distortion in the geometry of flat space-time, a rotating mass drags the space-time frame around with it, effectively producing a “Coriolis” in the fabric of space-time. For low-intensity gravitation (the type were are familiar with on a day-to-day basis), this is reasonably insignificant (although it is significant enough to cause observable non-Newtonian effects resulting in the precession of the perihelion of the planet Mercury as it orbits around the Sun).

When gravitational fields become extremely intense for a rotating object (such as when you get very close to a neutron star or the event horizon of a black hole), the rotating mass effectively “drags” space-time around with it as it rotates. For a rotating black hole (i.e. a “Kerr" Black Hole), this means that directly above the event horizon (in an oblate spheroidal volume of space-time centered on the singularity that bulges above the equator and is tangent to the poles of rotation) there is a region of space-time in which it is still theoretically possible to escape from the black hole, but in which it is impossible to remain stationary due to the “motion” of the space-time in which your ship is imbedded being dragged around the rotating black hole (i.e. you would have to have a velocity vector opposite to the direction of rotation faster than lightspeed in order to remain stationary).

Link: Rotating Black Hole (Wikipedia)
Link: Kerr Metric (Wikipedia)

http://en.wikipedia.org/wiki/Kerr_metric

http://en.wikipedia.org/wiki/Kerr_metric