Comments on: At 1,500,000 mph, twin stars in the constellation Cancer win speediest orbit award http://smithsonianscience.org/2010/03/twin-stars-in-the-constellation-cancer-win-speediest-orbit-award-hands-down/ A Web site featuring highlights of the Smithsonian Institution’s scientific research in the fields of anthropology, astrophysics, conservation biology, geology, materials science, paleontology and zoology Sat, 19 May 2012 01:15:00 +0000 http://wordpress.org/?v=2.9.2 hourly 1 By: Christine Pulliam http://smithsonianscience.org/2010/03/twin-stars-in-the-constellation-cancer-win-speediest-orbit-award-hands-down/#comment-4400 Christine Pulliam Wed, 17 Mar 2010 17:52:21 +0000 http://smithsonianscience.org/?p=4182#comment-4400 Benjamin, Thank you for your comment. I ran it past one of the lead scientists, Danny Steeghs, and this is his reply: 'Things are a little tricky. Our double white dwarfs are currently transferring gas from the lower mass WD to the more massive one. (The move shows two detached WDs without transfer). At this point the orbit is still shortening, but the mass transfer should slow that down and even turn that around, pushing the white dwarfs apart again. It doesn't take billions of years for two WDs to reach contact and start sharing gas if they are in a short period systems (<<1 hour). Binaries of periods of 5-10 hours are driven into contact on timescales of billions of years, but HM Cnc has already reached that stage. It may avoid merging the two white dwarfs thanks to this mass transfer. Future data may be able to measure this change in the period, though the timescale over which it actually turns around is expected to be a few thousand years. For the article, I would say that gravitational wave losses have already driven these two WDs into contact, and that we will aim to monitor the period change very carefully to see where it is heading. The movie shows the two WDs merging, but that it not necessarily the future fate of HM Cnc.' Sincerely, Christine Pulliam H-SCfA Public Affairs Office Benjamin,

Thank you for your comment. I ran it past one of the lead scientists, Danny Steeghs, and this is his reply:

‘Things are a little tricky. Our double white dwarfs are currently transferring gas from the lower mass WD to the more massive one. (The move shows two detached WDs without transfer). At this point
the orbit is still shortening, but the mass transfer should slow that down and even turn that around, pushing the white dwarfs apart again.

It doesn’t take billions of years for two WDs to reach contact and start sharing gas if they are in a short period systems (<<1 hour). Binaries of periods of 5-10 hours are driven into contact on timescales of billions of years, but HM Cnc has already reached that stage. It may avoid merging the two white dwarfs thanks to this mass transfer. Future data may be able to measure this change in the period, though the timescale over which it actually turns around is
expected to be a few thousand years.

For the article, I would say that gravitational wave losses have already driven these two WDs into contact, and that we will aim to monitor the period change very carefully to see where it is heading.
The movie shows the two WDs merging, but that it not necessarily the future fate of HM Cnc.'

Sincerely,
Christine Pulliam
H-SCfA Public Affairs Office

]]> By: Benjamin Franz http://smithsonianscience.org/2010/03/twin-stars-in-the-constellation-cancer-win-speediest-orbit-award-hands-down/#comment-4282 Benjamin Franz Sat, 13 Mar 2010 23:06:20 +0000 http://smithsonianscience.org/?p=4182#comment-4282 Some back of envelope calculations indicate they should merge in something around 100,000 years, not 'billions' of years. They currently orbit in 5.4 minutes and their orbit shrinks enough to shorten that time about 1.2 milliseconds per year. When it reaches roughly 3 minutes they will merge because they are so close. Arithmetic tells us that that is (order of) 117000 years - but in reality it would be quite a bit sooner than that because the orbit shrinks even faster as they get closer to each other in a highly non-linear fashion. Some back of envelope calculations indicate they should merge in something around 100,000 years, not ‘billions’ of years.

They currently orbit in 5.4 minutes and their orbit shrinks enough to shorten that time about 1.2 milliseconds per year. When it reaches roughly 3 minutes they will merge because they are so close.

Arithmetic tells us that that is (order of) 117000 years – but in reality it would be quite a bit sooner than that because the orbit shrinks even faster as they get closer to each other in a highly non-linear fashion.

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