Fastest (and Most Compact) Stellar Spinner Confirmed

gregg writes "HM Cancri has been confirmed as a binary system of two white dwarfs orbiting each other so closely that they complete one orbit every 5.4 minutes; they are separated by a mere 8 Earth diameters. '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. '"

Re:Oh my God...

[mrtommyb]

The total mass is almost certainly less than 1.4 time the mass of the sun and therefore does not have enough total mass to create supernova and a neutron star (its nowhere near massive enough to form a black hole).

Re:Mass flow is common.

[AstroMatt]

It happens in binary main sequence stars. This is only one of 2 binary white dwarf systems that have direct impact accretion (the other is named V407 Vul). Usually the accretion stream misses the primary star, and forms an accretion disk. In these systems, the accretion stream slams into the the accreting white dwarf at a velocity of about 1% the speed of light, btw!

Re:Tidal bulges

[AstroMatt]

The mass losing star is somewhat teardrop shaped, with the point pointing towards the other star - that's where mass flows through. It's a 3D analog of a spring-fed lake in a valley overflowing a saddle pass and flowing into the next valley. The mass flow in this system is likely helium mostly, and the rate is equivalent to about 100,000 Nimitz-class aircraft carriers per second. The impact velocity is about 1% the speed of light.

Re:Tidal bulges

[bcrowell]

The artist's rendition shows two spherical bodies, but there's no way that can be correct. At the orbital velocities involved these things must have tidal bulges that make Kevin Smith look positively svelte!

You're right, the artist's conception is messed up. Here [arxiv.org] is the scientific paper. Figure 3 on p. 4 has a realistic diagram, showing one star completely filling its Roche lobe.

Anyway, this is cool because this system is much closer and higher in frequency than the classic Hulse-Taylor [slashdot.org] binary pulsar. That means that it's radiating gravitational waves at a much higher rate.

Re:Mass flow is common.

[frieko]

Like this? [wikipedia.org]