New Planets!

[Uncwilly]

Originally Posted by xilman

Think about what you just wrote.

So, my typing and my thinking are out of sync. Such is the burden of my life.
I meant to either say that it is not a planet, or is still a 'star', as that is a phase of stellar evolution (ooh.).

Originally Posted by xilman

What if the BH was a technological construct? For instance, the inhabitants of an honest-to-$Deity planet may have had an unfortunate accident when developing their gravitational engineering technology.

I think that IAU members understood that they were not refering to artifical objects. I thought that one of the drafts (maybe from the previous round) specifically excluded artificial objects. Would you classify SOHO as a planet? small solar system body?

Originally Posted by xilman

The orbit is not clear, in at least two important respects. For a start, there are substantial numbers of very significant sized rocks crossing the Earth's orbit. If you are going to object to my (admittedly tongue in cheek) claim, do as Ernst did and point out that those rocks are (very likely) perturbed into their present orbits by other bodies such as Jupiter or Neptune.

http://en.wikipedia.org/wiki/Clearing_the_neighbourhood
Look at the data in the details section. I would take anything with a µ value (µ= M/m, where M is the mass of the body, and m is the aggregate mass of all the other bodies that share its orbital zone) above 10 as having cleared it's zone.
http://en.wikipedia.org/wiki/List_of...y_discriminant

Fun debate.

[mfgoode]

An extrasolar planet TrES-2 orbiting a star 500 light years away has been found thru home fabricated telescopes 4" dia. (10cms).
Its unique property is that it crosses the parent Star further up than its equator and will be interesting to study as it may reveal yet unknown properties. It is of the class 'Hot Jupiter's'.
NASA is planning its Kepler Mission slated to launch in 2008 for an investigation of this and other similar planets.

http://news.yahoo.com/s/space/200609...trasolarplanet

Mally

[xilman]

Originally Posted by Uncwilly

I think that IAU members understood that they were not refering to artifical objects. I thought that one of the drafts (maybe from the previous round) specifically excluded artificial objects. Would you classify SOHO as a planet? small solar system body?

No, I do not classify SOHO as a planet as it is not massive enough for its self-gravity to overcome the rigidity of its solid component.

However, I was thinking more along the lines where a technologically advanced civilization converted a pre-existing planet, possibly the one on which they originally evolved, into a planetary mass BH. Does the final result constitute a "planet". As far as I can tell from the IAU definition it does.


Paul

[xilman]

Originally Posted by Uncwilly

So, my typing and my thinking are out of sync. Such is the burden of my life.
I meant to either say that it is not a planet, or is still a 'star', as that is a phase of stellar evolution (ooh.).

So did you calculate how long a BH would take to radiate a solar mass of energy through thermal radiation at the the temperature typical of a solar mass BH? Did you even calculate the temperature of a solar mass BH and compare it with the temperature of the CBR?

Each of those are valuable exercises, IMAO.


Paul

[Uncwilly]

Originally Posted by xilman

So did you calculate how long a BH would take to radiate a solar mass of energy through thermal radiation at the the temperature typical of a solar mass BH? Did you even calculate the temperature of a solar mass BH and compare it with the temperature of the CBR?

No, but I was aware of the scales. I have saved my self the effort and looked it up.

A solar mass BH would be 1/10.000.000 K and take 10^66 years to evaporate.
A 1.000.000.000 tonne BH would be ~120.000.000 K and should take 10.000.000.000 years to flash out if existence.

[jasong]

Originally Posted by Uncwilly

No, but I was aware of the scales. I have saved my self the effort and looked it up.

A solar mass BH would be 1/10.000.000 K and take 10^66 years to evaporate.
A 1.000.000.000 tonne BH would be ~120.000.000 K and should take 10.000.000.000 years to flash out if existence.

Possibly stupid question: As a black hole shrank, wouldn't it's temperature go down? I would think it's evaporation rate would approach zero as it shrank.

[cheesehead]

Originally Posted by jasong

Possibly stupid question:

No, it's a good question.

What happens is that, without careful attention to the equations and definitions, our "common sense" leads us astray in considering the temperature of a black hole.

See "Black Hole Thermodynamics" at http://nrumiano.free.fr/Estars/bh_thermo.html. In particular, note that a black hole's temperature is inversely proportional to its mass.

(Also, http://library.thinkquest.org/C01266...0radiation.htm
and
http://library.thinkquest.org/C00757...ance/core5.htm)

As a black hole shrank, wouldn't it's temperature go down?

Look at the diagram for Hawking radiation.
Quote: "Indeed, the smaller the black hole is, the shorter is the distance for the virtual particle to travel before it becomes a real particle. The emission rate and the temperature are hence higher for a small - i.e., light - black hole."

I would think it's evaporation rate would approach zero as it shrank.

My own explanation, which may be wrong: Small BHs have a higher gravity gradient near their event horizons than larger BHs. This makes it easier (than it would be near a larger BH) for one of the pair of virtual particles to escape, thus becoming a real particle, because for traveling a given distance away from the event horizon it experiences a greater reduction in gravity when moving away from a small BH than it would when moving away from a large BH.

It would really help to see a video simulation.