Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]
Groups > sci.physics.relativity > #451972
| From | Thomas 'PointedEars' Lahn <PointedEars@web.de> |
|---|---|
| Newsgroups | sci.physics.relativity |
| Subject | Re: question about mass in GR - black holes |
| Date | 2018-03-08 18:02 +0100 |
| Organization | PointedEars Software (PES) |
| Message-ID | <3655532.4eW2IdbEro@PointedEars.de> (permalink) |
| References | <6292d1f1-e309-4308-aad9-66aecb323e6c@googlegroups.com> |
alsor@interia.pl wrote:
^^^^^^^^^^^^^^^^
It is considered polite here to post using one’s real name (nicknames may be
added).
> What is mass of a black hole?
Put simply, the sum of the masses within its event horizon.
> I have in mind the famous radius of a spherical mass:
> rs = 2m, the Schwarzschild radius.
This is only true in natural units where G = c = 1:
<https://en.wikipedia.org/wiki/Natural_units>
The actual equation is
rₛ = 2 G M∕c²
[Different from the SI definition, one usually writes “M” for the mass
to indicate that it is large(r than another mass). Compare Newton’s
law of universal gravitation: F = G M m∕r².]
You could have easily found that out by yourself by reading, e.g.,
Wikipedia.
> The radius is a distance or a mass?
A distance, of course.
> For example:
> for sun the radius is equal about: rs = 3km,
(_the Sun_, or _Sol_)
The current radius of Sol is 695'500 km. The _Schwarzschild_ radius of Sol
is ca. 3 km:
rₛ = 2 G × M☉/c² ≈ 2 G × 1.9 × 10³⁰ kg∕c² ≈ 2'953 m
<http://www.wolframalpha.com/input/?dataset=&i=2+G+%C3%97+(mass+of+Sol)%2Fc%C2%B2>
This means: If all of Sol’s matter and energy would be compressed into a
sphere whose radius is ca. 3 km, it would become a black hole (BH).
> thus a mass of sun is 1.5 km, because rs = 2m, so m = rs/2 - yes?
No.
> Unfortunately in the relativity theory a distance is not invariant
> quantity,
It is not _Lorentz_-invariant.
> but a mass is invariant in GR,
Again, _Lorentz_-invariant. The mass of a BH, for example, *can* change:
matter can fall beyond a BH’s outer event horizon to increase the BH’s mass
(and thus the Schwarzschild radius and event horizon radius), and a BH
can lose mass by emitting radiation (thus shrink and eventually
“evaporate”).
> so... there is great ambiguity in the theory:
Not at all. You are just oversimplifying.
> radius of a mass is: rs = 2m
No.
> but if a distance is not invariant then the mass cannot be invariant too,
> because 2m is simply m doubled - no?
No.
PointedEars
--
Q: What did the nuclear physicist order for lunch?
A: Fission chips.
(from: WolframAlpha)
Back to sci.physics.relativity | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread
question about mass in GR - black holes alsor@interia.pl - 2018-03-07 14:23 -0800
Re: question about mass in GR - black holes Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2018-03-08 18:02 +0100
Re: question about mass in GR - black holes alsor@interia.pl - 2018-03-17 15:16 -0700
Re: question about mass in GR - black holes Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2018-03-18 17:33 +0100
Re: question about mass in GR - black holes Darryl Fletcher <lu@ewiwwe.tt> - 2018-03-18 17:05 +0000
Re: question about mass in GR - black holes Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2018-03-18 18:08 +0100
Re: question about mass in GR - black holes alsor@interia.pl - 2018-03-18 10:49 -0700
Re: question about mass in GR - black holes Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2018-03-18 21:02 +0100
Re: question about mass in GR - black holes alsor@interia.pl - 2018-03-18 14:24 -0700
Re: question about mass in GR - black holes Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2018-03-18 22:58 +0100
Re: question about mass in GR - black holes alsor@interia.pl - 2018-03-19 10:04 -0700
Re: question about mass in GR - black holes Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2018-03-20 04:43 +0100
Re: question about mass in GR - black holes alsor@interia.pl - 2018-03-20 12:42 -0700
Re: question about mass in GR - black holes Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2018-03-20 21:03 +0100
Re: question about mass in GR - black holes alsor@interia.pl - 2018-03-20 14:04 -0700
Re: question about mass in GR - black holes Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2018-03-20 23:59 +0100
Re: question about mass in GR - black holes Tom Roberts <tjroberts137@sbcglobal.net> - 2018-03-08 17:43 -0600
Re: question about mass in GR - black holes Tom Roberts <tjroberts137@sbcglobal.net> - 2018-03-08 19:51 -0600
Re: question about mass in GR - black holes Keith Stein <keithstein111@gmail.com> - 2018-03-17 10:20 +0000
Re: question about mass in GR - black holes mlwozniak@wp.pl - 2018-03-08 21:25 -0800
Re: question about mass in GR - black holes Python <python@python.invalid> - 2018-03-09 06:31 +0100
Re: question about mass in GR - black holes alsor@interia.pl - 2018-03-17 15:40 -0700
Re: question about mass in GR - black holes Tom Roberts <tjroberts137@sbcglobal.net> - 2018-03-18 01:05 -0500
Re: question about mass in GR - black holes Térov Balónky <iytn@yeicenlw.ik> - 2018-03-18 12:57 +0000
Re: question about mass in GR - black holes alsor@interia.pl - 2018-03-18 10:23 -0700
Re: question about mass in GR - black holes "David (Kronos Prime) Fuller" <fuller.david@hotmail.com> - 2018-03-18 10:35 -0700
Re: question about mass in GR - black holes alsor@interia.pl - 2018-03-18 11:11 -0700
Re: question about mass in GR - black holes "David (Kronos Prime) Fuller" <fuller.david@hotmail.com> - 2018-03-18 11:18 -0700
Re: question about mass in GR - black holes "David (Kronos Prime) Fuller" <fuller.david@hotmail.com> - 2018-03-18 11:40 -0700
Re: question about mass in GR - black holes "David (Kronos Prime) Fuller" <fuller.david@hotmail.com> - 2018-03-18 11:50 -0700
Re: question about mass in GR - black holes "David (Kronos Prime) Fuller" <fuller.david@hotmail.com> - 2018-03-18 12:29 -0700
Re: question about mass in GR - black holes alsor@interia.pl - 2018-03-18 11:43 -0700
Re: question about mass in GR - black holes "David (Kronos Prime) Fuller" <fuller.david@hotmail.com> - 2018-03-18 11:45 -0700
Re: question about mass in GR - black holes "David (Kronos Prime) Fuller" <fuller.david@hotmail.com> - 2018-03-18 11:44 -0700
Re: question about mass in GR - black holes alsor@interia.pl - 2018-03-18 11:46 -0700
Re: question about mass in GR - black holes Python <python@python.invalid> - 2018-03-18 19:40 +0100
Re: question about mass in GR - black holes Tom Roberts <tjroberts137@sbcglobal.net> - 2018-03-20 19:39 -0500
Re: question about mass in GR - black holes alsor@interia.pl - 2018-03-21 10:26 -0700
Re: question about mass in GR - black holes Tom Roberts <tjroberts137@sbcglobal.net> - 2018-03-21 19:13 -0500
Re: question about mass in GR - black holes alsor@interia.pl - 2018-03-21 17:55 -0700
Re: question about mass in GR - black holes Tom Roberts <tjroberts137@sbcglobal.net> - 2018-03-22 00:08 -0500
Re: question about mass in GR - black holes mlwozniak@wp.pl - 2018-03-22 00:05 -0700
Re: question about mass in GR - black holes alsor@interia.pl - 2018-03-22 14:06 -0700
Re: question about mass in GR - black holes "David (Kronos Prime) Fuller" <fuller.david@hotmail.com> - 2018-03-22 14:37 -0700
Re: question about mass in GR - black holes "David (Kronos Prime) Fuller" <fuller.david@hotmail.com> - 2018-03-21 18:09 -0700
Re: question about mass in GR - black holes alsor@interia.pl - 2018-03-21 18:19 -0700
Re: question about mass in GR - black holes "David (Kronos Prime) Fuller" <fuller.david@hotmail.com> - 2018-03-21 18:43 -0700
Re: question about mass in GR - black holes "David (Kronos Prime) Fuller" <fuller.david@hotmail.com> - 2018-03-21 18:46 -0700
Re: question about mass in GR - black holes alsor@interia.pl - 2018-03-21 20:22 -0700
Re: question about mass in GR - black holes "David (Kronos Prime) Fuller" <fuller.david@hotmail.com> - 2018-03-21 20:55 -0700
Re: question about mass in GR - black holes "David (Kronos Prime) Fuller" <fuller.david@hotmail.com> - 2018-03-21 21:11 -0700
Re: question about mass in GR - black holes "David (Kronos Prime) Fuller" <fuller.david@hotmail.com> - 2018-03-21 21:21 -0700
Re: question about mass in GR - black holes "David (Kronos Prime) Fuller" <fuller.david@hotmail.com> - 2018-03-21 21:26 -0700
Re: question about mass in GR - black holes "David (Kronos Prime) Fuller" <fuller.david@hotmail.com> - 2018-03-21 20:49 -0700
Re: question about mass in GR - black holes Keith Stein <keithstein111@gmail.com> - 2018-03-19 15:45 +0000
Re: question about mass in GR - black holes numbernumber1964@gmail.com - 2018-03-20 13:51 -0700
Re: question about mass in GR - black holes Odd Bodkin <bodkinodd@gmail.com> - 2018-03-20 23:02 +0000
Re: question about mass in GR - black holes numbernumber1964@gmail.com - 2018-03-20 13:54 -0700
Re: question about mass in GR - black holes Koobee Wublee <koobee.wublee@gmail.com> - 2018-03-21 10:40 -0700
Re: question about mass in GR - black holes "David (Kronos Prime) Fuller" <fuller.david@hotmail.com> - 2018-03-21 11:17 -0700
Re: question about mass in GR - black holes alsor@interia.pl - 2018-03-21 11:27 -0700
Re: question about mass in GR - black holes numbernumber1964@gmail.com - 2018-03-22 15:26 -0700
Re: question about mass in GR - black holes alsor@interia.pl - 2018-03-29 15:25 -0700
csiph-web