Most extreme white dwarf binary system found with orbit of just 5 minutes

Mar 08, 2010

(PhysOrg.com) -- An international team of astronomers, including Professor Tom Marsh and Dr Danny Steeghs from the University of Warwick, have shown that the two stars in the binary HM  Cancri definitely revolve around each other in a mere 5.4 minutes. This makes HM Cancri the binary star with by far the shortest known orbital period.  It is also the smallest known binary. The binary system is no larger than 8 times the diameter of the Earth which is the equivalent of no more than a quarter of the  distance from the Earth to the Moon.

The consists of two . These are the burnt- out cinders of stars such as our Sun, and contain a highly condensed form of helium, carbon and oxygen. The two white dwarfs in HM Cancri are so close together that mass is flowing from one star to the other. HM Cancri was first noticed as an X-ray source in 1999 showing a 5.4 minutes periodicity but for a long time it has remained unclear whether this period also indicated the actual orbital period of the system. It was so short that astronomers were reluctant to accept the possibility without solid proof.

The team of astronomers, led by Dr Gijs Roelofs of the Harvard-Smithsonian Center of Astrophysics, and including Professor Tom Marsh and Dr Danny Steeghs at the University of Warwick in the UK, have now used the world's largest telescope, the Keck telescope on Hawaii, to prove that the 5.4 minute period is indeed the binary period of the system. This has been done by detecting the velocity variations in the spectral lines in the light of HM Cancri. These velocity variations are induced by the , caused by the orbital motion of the two stars revolving around each other. The Doppler effect causes the lines to periodically shift from blue to red and back.

The observations of HM Cancri were an ultimate challenge due to the extremely short period that needed to be resolved and the faintness of the binary system. At a distance of close to 16,000 light years from Earth, the binary shines at a brightness no more than one millionth of the faintest stars visible to the naked eye.

Professor Tom Marsh from the University of Warwick said; “This is an intriguing system in a number of ways: it has an extremely short period; mass flows from one star and crashes down onto the equator of the other in a region comparable in size to the English Midlands where it liberates more than the Sun's entire power in X-rays. It could also be a strong emitter of gravitational waves which may one day be detected from this type of star system.”

Dr Danny Steeghs of the University of Warwick, said " A few years ago we proposed that HM Cancri was indeed an interacting binary consisting of two white dwarfs and that the 5.4 minute period was the orbital period. It is very gratifying to see this model confirmed by our observations, especially since earlier attempts had been thwarted by bad weather."

The article describing the observations of HM Cancri entitled 'Spectroscopic Evidence For a 5.4 Minute Orbital Period in HM Cancri' will be published in the Astrophysical Journal Letters of March 10, 2010

"This type of observations is really at the limit of what is currently possible. Not only does one need the biggest telescopes in the world, but they also have to be equipped with the best instruments available", explains Professor Paul Groot of the Radboud University Nijmegen in the Netherlands.

"The binary HM Cancri is a real challenge for our understanding of stellar and binary evolution," adds Dr Gijs Nelemans of the Radboud University."We know the system must have come from two normal stars that somehow spiralled together in two earlier episodes of mass transfer, but the physics of this process is very poorly known. The system is also a big opportunity for general relativity. It must be one of the most copious emitters of gravitational waves. These distortions of space-time we hope to detect directly with the future LISA satellite, and HM Cancri will be a cornerstone system for this mission."

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User comments : 19

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HealingMindN
1 / 5 (2) Mar 08, 2010
If it's an exact period of 5.4 minutes, does that make a quasi-pulsar?
Switch
not rated yet Mar 08, 2010
I would like to know the obital velocity of this system.
dan42day
2.3 / 5 (3) Mar 08, 2010
Well if the system is 8 times the diameter of the earth, then about 315 km/s.
frajo
5 / 5 (1) Mar 09, 2010
If we assume equal masses for both components then they'll move around their common center of mass on a circumference of roughly PI*10**5 km within roughly PI*10**2 s. Thus we have a velocity of about 1000 km/s for each one.
antialias
not rated yet Mar 09, 2010
However we have mass flowing from one to the other, so they're not of equal mass. But still: 5.4 minutes is extremely short. Just imagine the forces that must act on these masses whipping around each other.
frajo
1 / 5 (1) Mar 09, 2010
It would be interesting to know whether the flow of mass reverses after some time.
Hungry4info2
not rated yet Mar 09, 2010
If it's an exact period of 5.4 minutes, does that make a quasi-pulsar?


No, pulsars are neutron stars with strong emissions from their magnetic poles.

This 5.4 d periodicity is the orbital period of the binary, not the rotation period of a pulsar.

It would be interesting to know whether the flow of mass reverses after some time.


Not for this system, though it is possible in others. This is a degenerate white dwarf binary. The orbital period will continue shrinking until the two have merged because the mass transfer acts on the donor star and it looses orbital energy.
SincerelyTwo
not rated yet Mar 09, 2010
Anyone know how long before they collide? Or if they already have based on the information given?
antialias
not rated yet Mar 09, 2010
It would be interesting to know whether the flow of mass reverses after some time.


It shouldn't because the mass will flow from the body with less gravity (mass) to the one with more.

At best the flow will cease at some time in the futurte when all volatile mass from the smaller body has been sucked up by the larger one.

Since stars don't really contain any solid parts that shouldn't happen so the bigger partner will eventually acquire all the mass.
gwrede
1 / 5 (1) Mar 09, 2010
No, you wouldn't.

While it's not a black hole, the gravity still is too large to escape with any non-sci-fi starship.
danman5000
not rated yet Mar 09, 2010
Do people that post that spam garbage honestly think it works? "Quality and honest can make your bussiness flourishing!" Seriously?
S_Bilderback
not rated yet Mar 09, 2010
Well if the system is 8 times the diameter of the earth, then about 315 km/s.


I believe you would need to know the mass of each star to calculate their relative speed. I guessing its between 10 and 100 times the 315 km/s.
Royale
1 / 5 (1) Mar 09, 2010
Translate Chinese to English free. at worthless.com. you're totally right danman. i think it's amazing to picture two object so close spinning so fast out there. and yes, i bet the gravity would be pretty drastic.
Royale
not rated yet Mar 09, 2010
that's the only way to post a reacting to dan and make a comment without the admins here pulling it off for 'inane banter' it was a joke.. thanks for the one rating. never knew making fun of horrid translation could get you such a low rank.
frajo
not rated yet Mar 09, 2010
that's the only way to post a reacting to dan and make a comment without the admins here pulling it off for 'inane banter' it was a joke.. thanks for the one rating.
I didn't see the joke, sorry. I saw a template for an ad.
danman5000
not rated yet Mar 09, 2010
that's the only way to post a reacting to dan and make a comment without the admins here pulling it off for 'inane banter' it was a joke.. thanks for the one rating. never knew making fun of horrid translation could get you such a low rank.

Yeah you have to be careful what you write around here. Can't be too clever with your responses, or the admins won't get the reference and erase it.
Now, to do the same as you did:
A 5 minute rotation is pretty insane. That's probably the only celestial body with any property that short, seems like it should have ripped itself apart. What will happen as one star consumes the other? Would the period slow down and stop, leaving the remaining star in one spot (relative to the rest of the system)?
Royale
not rated yet Mar 09, 2010
that would actually be really cool. having a sun (that didnt collapse) gobble up the other body and just be sitting there, not spinning or anything because it's lost all of its inertia.
Isildur
5 / 5 (1) Mar 11, 2010
Yes velocity is about 1000km/s (it depends from the masses). No, it is not a pulsar (which is a neutron star). However, yes in an alternative model proposed years ago the system might be synchronized... the rotation period of the primary white dwarf equals the orbit period.
It is still debated whether or not mass is transferring.

Nice results, however it seems that it was already known since 8 years.

Look here

http://www.eso.or...eso0211/

Isildur
not rated yet Mar 11, 2010
At best the flow will cease at some time in the futurte when all volatile mass from the smaller body has been sucked up by the larger one.

Since stars don't really contain any solid parts that shouldn't happen so the bigger partner will eventually acquire all the mass.


True... though a white dwarf is actually more similar to a crystal rather than a gas sphere... it has only a small fraction which is volatile.

Two died stars in a binary are thought to evolve towards smaller orbital separation and will continue to shrink until the two stars will hit each other....

While it's not a black hole, the gravity still is too large to escape with any non-sci-fi starship.


Actually these two objects have masses which are a fraction of that of the Sun within a sphere with radius similar to that of the Earth. You can still escape from the white dwarf surface though not easy.

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