Two white dwarf stars orbiting each other every five minutes, confirmed

On Mar 11, 9:16*pm, Andrew Usher wrote:
Yousuf Khan wrote:
I think the major problem here is calculating frame dragging friction,
which requires Einstein's equations. I don't know how to do it, myself.
The 1600 light-year distance between us and this system is a negligible
calculation by comparison.

I thought it should have been calculated when this system was
discovered. Surely the merger of two white dwarfs is an interesting
occurrence! I'm wondering, if the two WDs are both ONe (making a
supernova impossible), would they become a neutron star or a black
hole?

Andrew Usher

Binary dwarfs as supposedly tidal face-locked and separated by just
80,000 km and .37 solar mass each.

At some point in the near future, their ever increasing orbital
frequency and the combined magnetic force has to take over and draw
these two similar white dwarfs together, unless it’s running like a
magnetic bearing that’s perpetually isolating one another regardless
of those substantial gravitational forces (5.7e33 N). Electrons also
repulse one another, which should also help prolong their binary
status. At only 80,000 km separation, whereas being near equal mass
is pretty much required, and otherwise I agree with Yousuf Khan.

~ BG

In article ,
Yousuf Khan writes:
http://www.space.com/scienceastronom...rs-100309.html

I can't offer an exact calculation of the time until merger, but the
paper (Roelofs et al. 2010 ApJL 711, L138) gives an orbital frequency
of about 3 mHz and derivative (df/dt) of about 3.6E-16 Hz/s.
Dividing these gives 8E12 s or about 3E5 years. This is just a very
rough estimate, of course.

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Help keep our newsgroup healthy; please don't feed the trolls.
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In sci.astro message
oglegroups.com, Wed, 10 Mar 2010 18:40:50, Andrew Usher
posted:
Brad Guth wrote:
On Mar 9, 4:29*pm, Andrew Usher wrote:
Yousuf Khan wrote:
These two white dwarfs are so close together, that they might fall into
each other some day. This would be an ideal test to see if two white
dwarfs falling into each other produce a Type Ia supernova, leaving
nothing behind. Or if they simply turn into a neutron star.

How long should it be before we see the merger?

Andrew Usher

At 1600 light years, it probably already happened as of more than a
thousand years ago.

Can anyone confirm this? Guth is hardly reliable, and I have no idea
how to calculate it myself.

Other sources have 16,000 light years. But is Guth not *consistently*
wrong?

Wikipedia http://en.wikipedia.org/wiki/HM_Cancri says that Chandra
shows that they are currently closing by about two feet per day, which
is about a tenth of a mile per year. Wiki gives the separation as
50,000 miles. The closure rate will change with distance; but it would
be IMHO remarkable if closure was expected in Guth's estimate of under
600 years, and surprising if under 16,000 years ERT.

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Web URL:http://www.merlyn.demon.co.uk/ - FAQqish topics, acronyms & links;
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On Mar 12, 12:20*pm, (Steve Willner) wrote:
In article ,
*Yousuf Khan writes:

http://www.space.com/scienceastronom...rs-100309.html

I can't offer an exact calculation of the time until merger, but the
paper (Roelofs et al. 2010 ApJL 711, L138) gives an orbital frequency
of about 3 mHz and derivative (df/dt) of about 3.6E-16 Hz/s.
Dividing these gives 8E12 s or about 3E5 years. *This is just a very
rough estimate, of course.

--
Help keep our newsgroup healthy; please don't feed the trolls.
Steve Willner * * * * * *Phone 617-495-7123 * *
Cambridge, MA 02138 USA

It could be a whole lot sooner than 300,000 years.* * The current -2
feet/day could turn into losing three, four, eight, sixteen/day and so
forth within hardly a thousand years.

"Chandra data (above, graph) from observations of RX J0806.3+1527 (or
J0806), show that its X-ray intensity varies with a period of 321.5
seconds. This implies that J0806 is a binary star system where two
white dwarf stars are orbiting each other (above, illustration)
approximately every 5 minutes.

The short orbital period implies that the stars are only about 50,000
miles apart, a fifth of the distance from the Earth to the Moon, and
are moving in excess of a million miles per hour. According to
Einstein's General Theory of Relativity, such a system should produce
gravitational waves -ripples in space-time - that carry energy away
from the system at the speed of light.

Energy loss by gravitational waves will cause the stars to move
closer
together. X-ray and optical observations indicate that the orbital
period of this system is decreasing by 1.2 milliseconds every year,
which means that the stars are moving closer together at a rate of
about 2 feet per day."
http://chandra.harvard.edu/photo/2005/j0806/
http://i.ytimg.com/vi/ryqN6dyUmJg/0.jpg

"With its extremely short orbital period, RX J0806.3+1527 is also a
prime candidate for the detection of the elusive gravitational waves,
predicted by Einstein's General Theory of Relativity. They have never
been measured directly, but their existence has been revealed
indirectly in binary neutron star systems.

A planned gravitational wave space experiment, the European Space
Agency's Laser Interferometer Space Antenna (LISA) that will be
launched in about 10 years' time, will be sufficiently sensitive to
be
able to reveal this radiation from RX J0806.3+1527 with a high degree
of confidence. Such an observational feat would open an entirely new
window on the universe."
http://www.eso.org/public/news/eso0211/

Binary dwarfs as supposedly tidal face-locked and separated by just
80,000 km and worth .37 solar mass each. At some point in the near
future (perhaps a few thousands years from now), their ever increasing
orbital frequency and the combined magnetic force has to take over and
draw these two similar white dwarfs together, unless it’s running like
a magnetic bearing that’s perpetually isolating one another regardless
of those substantial gravitational forces (5.7e33 N). Electrons
repulse one another, which should also help prolong their binary
status. At only 80,000 km separation, whereas being near equal mass
is pretty much required, and otherwise I agree with the final outcome
being a neutron star unless the merger goes into a hyper/superluminal
explosion where everything gets expelled.

It’s actually more likely that Sirius(B) gets to become a neutron star
about the same time as the human species goes extinct here on Earth.

~ BG

Dr J R Stockton wrote:

Wikipedia http://en.wikipedia.org/wiki/HM_Cancri says that Chandra
shows that they are currently closing by about two feet per day, which
is about a tenth of a mile per year. Wiki gives the separation as
50,000 miles. The closure rate will change with distance; but it would
be IMHO remarkable if closure was expected in Guth's estimate of under
600 years, and surprising if under 16,000 years ERT.

Thanks, this is what I needed. It will be over 100,000 years then, and
we will not see it.

It makes you wonder how they could have closed to the distance they
are right now. I think gravitational radiation goes as (v'')^2 or 1/
r^7. Since potential energy goes as 1/r, dr/dt ~ 1/r^5. So in the
entire age of the galaxy, they could only have closed from about 8
times as far as they are now, which is absurd. Or is there another
factor?

Andrew Usher

Yousuf Khan wrote:

I thought it should have been calculated when this system was
discovered. Surely the merger of two white dwarfs is an interesting
occurrence! I'm wondering, if the two WDs are both ONe (making a
supernova impossible), would they become a neutron star or a black
hole?

Neutron star, if they don't blow up instead.

Oxygen-neon white dwarfs are at least 1.05 Msun and up to 1.37, so the
combined mass could be 2.1-2.75 Msun. The limit for a neutron star is
thought to be about 2.2, but could it lose enough mass while colliding
to avoid becoming a black hole?

Andrew Usher

On Mar 12, 6:59*pm, Andrew Usher wrote:
Dr J R Stockton wrote:

Wikipedia http://en.wikipedia.org/wiki/HM_Cancri says that Chandra
shows that they are currently closing by about two feet per day, which
is about a tenth of a mile per year. *Wiki gives the separation as
50,000 miles. *The closure rate will change with distance; but it would
be IMHO remarkable if closure was expected in Guth's estimate of under
600 years, and surprising if under 16,000 years ERT.

Thanks, this is what I needed. It will be over 100,000 years then, and
we will not see it.

I wouldn't go with 100,000 years. My initial swag of 600 years is a
wee bit short, although a few thousand years might be more likely.


It makes you wonder how they could have closed to the distance they
are right now. I think gravitational radiation goes as (v'')^2 or 1/
r^7. Since potential energy goes as 1/r, dr/dt ~ 1/r^5. So in the
entire age of the galaxy, they could only have closed from about 8
times as far as they are now, which is absurd. Or is there another
factor?

Andrew Usher

Cosmic mergers, like the one(s) which created our galaxy and gave
birth to the likes of Sirius ABC. Also, nothing out there runs
linear. Ever heard of the golden ratio or phi = 1.618034

~ BG

Andrew Usher wrote:
Yousuf Khan wrote:

I thought it should have been calculated when this system was
discovered. Surely the merger of two white dwarfs is an interesting
occurrence! I'm wondering, if the two WDs are both ONe (making a
supernova impossible), would they become a neutron star or a black
hole?
Neutron star, if they don't blow up instead.

Oxygen-neon white dwarfs are at least 1.05 Msun and up to 1.37, so the
combined mass could be 2.1-2.75 Msun. The limit for a neutron star is
thought to be about 2.2, but could it lose enough mass while colliding
to avoid becoming a black hole?

Andrew Usher

My feeling is that the limit is thought to be 2.8 Msun between neutron
star and black hole, though I'm sure there's plenty of overlap here. The
smallest stellar mass black hole found to date is about 3.8 Msun, though
we might find smaller.

XTE J1650-500 - Wikipedia, the free encyclopedia
http://en.wikipedia.org/wiki/XTE_J1650-500

Whether a core becomes a neutron star or a black hole probably depends
on how much compression it underwent when being formed during original
blow-off phase. Usually that amount of compression is dependent on the
mass of the progenitor star, but it wouldn't surprise me that some
nuclear forces could aid gravity in the compression mechanism, thus
within certain range of masses we might see some become black holes and
some become neutron stars. Thus I don't see two white dwarfs ever
forming a black hole, because they simply don't create a compressive
force on each other's cores when they merge; in fact, I'd say it's
mostly tensile during this time.

Now as for the 2.2 Msun neutron star limit, that may just be the limit
for normal neutron stars. There are subspecies of neutron stars that
have been proposed with higher masses, such as: quark stars, strange
stars, and most recently electroweak stars.

Yousuf Khan

Andrew Usher wrote:
Thanks, this is what I needed. It will be over 100,000 years then, and
we will not see it.

It makes you wonder how they could have closed to the distance they
are right now. I think gravitational radiation goes as (v'')^2 or 1/
r^7. Since potential energy goes as 1/r, dr/dt ~ 1/r^5. So in the
entire age of the galaxy, they could only have closed from about 8
times as far as they are now, which is absurd. Or is there another
factor?

Andrew Usher

They're only this close because they have been orbiting within each
other's gas envelopes as each one took their turns becoming red giants.
Combination of aerodynamic friction and gas exchange changing up their
orbital relationships. Now that neither of them have any gas left, they
will only approach each other through the gravitational friction method.

Yousuf Khan

On Mar 13, 1:33*pm, Yousuf Khan wrote:
Andrew Usher wrote:
Thanks, this is what I needed. It will be over 100,000 years then, and
we will not see it.

It makes you wonder how they could have closed to the distance they
are right now. I think gravitational radiation goes as (v'')^2 or 1/
r^7. Since potential energy goes as 1/r, dr/dt ~ 1/r^5. So in the
entire age of the galaxy, they could only have closed from about 8
times as far as they are now, which is absurd. Or is there another
factor?

Andrew Usher

They're only this close because they have been orbiting within each
other's gas envelopes as each one took their turns becoming red giants.
Combination of aerodynamic friction and gas exchange changing up their
orbital relationships. Now that neither of them have any gas left, they
will only approach each other through the gravitational friction method.

* * * * Yousuf Khan

Plus attracted to one another by their magnetic forces (especially if
poles flip) which can be rather considerable.

~ BG