Meet the super-speedy white dwarf binary system that's going to grav-wave our world Astronomers have discovered the fastest-known eclipsing white dwarf pair yet, with the dead stars whizzing around each other every 6.91 minutes, according to a Nature paper published on Wednesday. The binary system known as ZTF J1539+5027 was spotted by the Zwicky Transient Facility (which put the ZTF into its name) …
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Yes, it's staggeringly, mind-boggling. So close that they revolve around each other in under 7 minutes and yet it's estimated they are still 200,000 years from merging. To those of use with little to no knowledge of stellar engineering, I'd have more of a sense that colliding with each other was imminent on a human scale.
"...a sense that colliding with each other was imminent on a human scale."
200,000 years is human scale. I mean you hairy apes have been around that long, haven't you? Most things in astronomy have timescales of billions of years.
They're probably only going to collide because of gravitational losses, which are obviously small and so slow. Without that they'd be as stable as an electron orbiting an atom.
It turns out that no, there won't. You are completely correct about the origin of type 1a supernovae, but the two white dwarves here are not massive enough. The Nature letter (which seems to now be showing me the actual PDF of the thing even though it was not earlier) says that the two masses are 0.610 and 0.210 solar masses, while the upper limit for a white dwarf is 1.44 solar masses. So even after colliding they will be comfortably below the limit.
One interesting thing about this binary: if the predicted merger time is 200,000 years away then it ought to be possible to detect the orbital changes over time as the orbits decay due to gravitational waves. This was famously done for the Hulse-Taylor binary which provided an indirect test for the existence of gravitational waves. That has a spin-down time of 300,000,000 years: this is shorter by a factor of about a thousand.
One problem is that these things are not pulsars, so there's no very precise timing information as there is for a pulsar: you'd have to work from the light curves. That might make it impossible to detect, although presumably with sufficiently long-term observations you could do a lot better.
(And this also isn't really a new test, although I think it would be interesting to confirm that relatively normal objects like white dwarves (normal compared to neutron stars...) have decaying orbits as well.)
Astronomers have discovered the fastest-known eclipsing white dwarf pair yet, with the dead stars whizzing around each other every 6.91 minutes,
If they're white dwarfs, then obviously they're still "burning" and not dead yet. Or is there a definition of "dead" that I missed.
White dwarfs have ceased nuclear fusion, hence dead.
They remain luminous as they cool down from the extreme temperatures (1E7 K) reached at the end of their fusion lives, much like a heated lump of metal remains luminous for a while after being withdrawn from the heating source.
One interesting thing is how long it takes white dwarves to cool. The answer is 'long': the end state of a white dwarf once it has cooled is a thing called a black dwarf, and it's estimated that there are no black dwarves yet, because the universe is not old enough.
I think the estimated time for them to get really cool is ~ 1E15 years, but some may last much longer than this.
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