Novas and supernovas effect on our habitat

In sci.astro message , Sat, 14 Aug 2010
18:23:17, Yousuf Khan posted:

A Roche Limit is mainly something applied to planetary bodies (i.e.
solid or liquid), not stars. It requires a rigidity factor to be
factored in, and there aren't good numbers for gaseous bodies like gas
planets or stars. The rigidity factor depends on density of the
objects.

The essence of the normal Roche Limit is that the strength of the
secondary is at most unimportant.

Read URL:http://www.merlyn.demon.co.uk/gravity6.htm#Roche and Roche's
paper, which it links to.

However, general rules of thumb apply and that usually means that the
two stars have to be at least within 1 AU of each other to affect each
other to the point of pulling material off of each other.

That will very much depend on the sizes of the stars.

--
(c) John Stockton, nr London, UK. Turnpike v6.05 MIME.
Web URL:http://www.merlyn.demon.co.uk/ - FAQqish topics, acronyms & links;
Astro stuff via astron-1.htm, gravity0.htm ; quotings.htm, pascal.htm, etc.
No Encoding. Quotes before replies. Snip well. Write clearly. Don't Mail News.

On 15 Aug, 00:23, Yousuf Khan wrote:
On 10-08-14 05:27 PM, JT wrote:

Well this you certainly did read wrong, what the article says is that
Binary Systems white dwarfs may pull matter from the prime star in
this case Sirius A.

If the article said Sirius B is pulling gas off of Sirius A, then it is
wrong. As I said, they are 20 AU apart, way too far to affect each other
like that. White dwarfs can pull gas off of companion stars, but they
have to be close in, and the Sirius system doesn't fit that description.

So Sirius B pull matter from Sirius A and is able to go Nova if the
star Sirius A is overflowing its roche lobe.

So please read again until you understand.. What was your 1 AU
estimated on the roche lobe?

A Roche Limit is mainly something applied to planetary bodies (i.e.
solid or liquid), not stars. It requires a rigidity factor to be
factored in, and there aren't good numbers for gaseous bodies like gas
planets or stars. The rigidity factor depends on density of the objects.

However, general rules of thumb apply and that usually means that the
two stars have to be at least within 1 AU of each other to affect each
other to the point of pulling material off of each other. Sirius doesn't
qualify. If you want to pull material off of a star at 20 AU you need at
least a galactic-scale supermassive blackhole.

* * * * Yousuf Khan

And i told you the closest distance is about 8 AU according to data,
if i did read right 2044 is next time that will happen.

JT

On 16/08/2010 5:39 PM, Dr J R Stockton wrote:
In sci.astro , Sat, 14 Aug 2010
18:23:17, Yousuf posted:

A Roche Limit is mainly something applied to planetary bodies (i.e.
solid or liquid), not stars. It requires a rigidity factor to be
factored in, and there aren't good numbers for gaseous bodies like gas
planets or stars. The rigidity factor depends on density of the
objects.

The essence of the normal Roche Limit is that the strength of the
secondary is at most unimportant.

ReadURL:http://www.merlyn.demon.co.uk/gravity6.htm#Roche and Roche's
paper, which it links to.

In solid planetary bodies, the rigidity factor is usually very close to
each other, so a simplified equation can be used.

The following link shows how to get Roche limits for both rigid and
fluid satellites, but not for gaseous.

Roche limit - Wikipedia, the free encyclopedia
http://en.wikipedia.org/wiki/Roche_l...of_the_formula

However, general rules of thumb apply and that usually means that the
two stars have to be at least within 1 AU of each other to affect each
other to the point of pulling material off of each other.

That will very much depend on the sizes of the stars.


We're talking about a white dwarf in conjunction with a main sequence
star. The white dwarf will usually be in the range of 0.5 - 1.4 solar
masses. Beyond 1.4 it'll be a neutron star rather than a white dwarf.

Yousuf Khan

On 17/08/2010 9:26 AM, JT wrote:
And i told you the closest distance is about 8 AU according to data,
if i did read right 2044 is next time that will happen.

Still not close enough.

Look at it this way, Jupiter is a gas planet, the closest thing we have
to another star in the system. Jupiter is only 5 AU from the Sun. The
Sun is a bit heavier than the white dwarf in Sirius. Yet the Sun's
gravity at that distance doesn't stretch Jupiter out to an egg shape or
draw any gas from Jupiter.

Yousuf Khan

On 16/08/2010 5:00 AM, JT wrote:
On 15 Aug, 01:08, Yousuf wrote:
There are much better candidates for nova watching than Sirius. Look up
the term, "recurrent nova", and especially look up the star system known
as "U Scorpii", it's already erupted several times since 1863 including
once earlier this year (1863, 1906, 1936, 1979, 1987, 1999, and 2010).
It's been observed so often, that scientists actually predicted that it
would go off sometime this year.

Well maybe i am just hooked on an idea that Sirius B going nova again
and again, if it would how big would it be in the sky? Three to ten
times our Sun i guess even bigger, or just a red star object?

Not at all, a nova is not that big in terms of luminosity. It's 8.5 ly's
from here, so it might be equal to some large fraction of the light of
the full moon. If it were a supernova, however, then it would be visible
even in the daylight. But at that distance, it's radiation would've
toasted us.

Yousuf Khan

On 16/08/2010 5:09 AM, JT wrote:
It is interesting to see how the 13th and 14the centurys black plague
also was plagued with Vaticans hunt for Necromancers and Witches,
maybe radiation toasted alot of brains, left earth with alot of numb
zoombies and they caretakers that Vatican falsly took for
necromancers.

I think you're putting two and two together and coming up with five.

Yousuf Khan

On 17 Aug, 19:40, Yousuf Khan wrote:
On 16/08/2010 5:09 AM, JT wrote:

It is interesting to see how the 13th and 14the centurys black plague
also was plagued with Vaticans hunt for Necromancers and Witches,
maybe radiation toasted alot of brains, left earth with alot of numb
zoombies and they caretakers that Vatican falsly took for
necromancers.

I think you're putting two and two together and coming up with five.

* * * * Yousuf Khan

Well i think it was five all the long, sadly that times physics,
doctors and priest did not know about neither radiation, relatied
sicknesses nor about the hazards from being exposed to X-rays and
Gamma rays depending on the amount of incoming gamma rays your brain
will be toasted in matter of hours to a few days. And if you also
consider that there will be no em field to slow down and deflect
Cosmic rays and particles. The brain get a bit spongy after particles
at near lightspeed penetrate head and go stratight thru.

No wonder ancient cultures did like their pyramids built in Sandstone
some even argue that it in some cases is molded concrete slabs.
Probably earths crust will pick up alot of radation if a nearby nova
disturb earths magnetic feld.

JT

On 17 Aug, 18:55, Yousuf Khan wrote:
On 16/08/2010 5:39 PM, Dr J R Stockton wrote:

In sci.astro , Sat, 14 Aug 2010
18:23:17, Yousuf *posted:

A Roche Limit is mainly something applied to planetary bodies (i.e.
solid or liquid), not stars. It requires a rigidity factor to be
factored in, and there aren't good numbers for gaseous bodies like gas
planets or stars. The rigidity factor depends on density of the
objects.

The essence of the normal Roche Limit is that the strength of the
secondary is at most unimportant.

ReadURL:http://www.merlyn.demon.co.uk/gravity6.htm#Roche *and Roche's
paper, which it links to.

In solid planetary bodies, the rigidity factor is usually very close to
each other, so a simplified equation can be used.

The following link shows how to get Roche limits for both rigid and
fluid satellites, but not for gaseous.

Roche limit - Wikipedia, the free encyclopediahttp://en.wikipedia.org/wiki/Roche_limit#Derivation_of_the_formula

However, general rules of thumb apply and that usually means that the
two stars have to be at least within 1 AU of each other to affect each
other to the point of pulling material off of each other.

That will very much depend on the sizes of the stars.

We're talking about a white dwarf in conjunction with a main sequence
star. The white dwarf will usually be in the range of 0.5 - 1.4 solar
masses. Beyond 1.4 it'll be a neutron star rather than a white dwarf.

* * * * Yousuf Khan

Well the gravitational pull is dependent upon both the suns solar
masses, Sirius A have almost 2 solar masses and Sirius B have 1 solar
mass. If Sirius B dense mass start pulling on Sirius A it possibly
also could become a Neutron star one day.

JT

On 17 Aug, 19:39, Yousuf Khan wrote:
On 16/08/2010 5:00 AM, JT wrote:

On 15 Aug, 01:08, Yousuf *wrote:
There are much better candidates for nova watching than Sirius. Look up
the term, "recurrent nova", and especially look up the star system known
as "U Scorpii", it's already erupted several times since 1863 including
once earlier this year (1863, 1906, 1936, 1979, 1987, 1999, and 2010).
It's been observed so often, that scientists actually predicted that it
would go off sometime this year.

Well maybe i am just hooked on an idea that Sirius B going nova again
and again, if it would how big would it be in the sky? Three to ten
times *our Sun i guess even bigger, or just a red star object?

Not at all, a nova is not that big in terms of luminosity. It's 8.5 ly's
from here, so it might be equal to some large fraction of the light of
the full moon. If it were a supernova, however, then it would be visible
even in the daylight. But at that distance, it's radiation would've
toasted us.

* * * * Yousuf Khan

Now i think there is a little to much wishfull thinking on your part,
here is a comparission between suns.
http://www.co-intelligence.org/newsl...mparisons.html

Aldebaran is 2.5 times the size of your sun, from that you should be
able to draw some conclusions about how big the size of Sirius B +1
solar mass will look on the sky when it goes Nova just (8AU) 5 LY
away.

It willl look spectacular and big like a second sun, maybe even
bigger.

JT

On 8/18/2010 4:38 AM, JT wrote:
Well the gravitational pull is dependent upon both the suns solar
masses, Sirius A have almost 2 solar masses and Sirius B have 1 solar
mass. If Sirius B dense mass start pulling on Sirius A it possibly
also could become a Neutron star one day.


No, it won't, there is a very specific evolutionary sequence for white
dwarfs already set down. If a white dwarf pulls a little matter from a
companion star, it'll go nova. If a white dwarf pulls a lot of matter
from a companion star, then it'll turn into a Type Ia supernova, which
leaves nothing behind after the explosion. The white dwarf gets
completely obliterated after that explosion.

This is exactly analogous to a toilet bowl flush system. Pour a little
water into the bowl with cup or a glass, and nothing really happens, the
water level goes up a little and then levels out. Pour a bucket of water
down the bowl and the familiar flush sound happens, with a chain
reaction of water swirling down the drain.

Yousuf Khan