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Since white dwarfs have around the mass of the sun in a size comparable to the Earth, the matter in them is quite exotic. Astronomer's have speculated that thes
by autocorr 8y ago
Since white dwarfs have around the mass of the sun in a size comparable to the Earth, the matter in them is quite exotic. Astronomer's have speculated that these hypervelocity stars (moving at a few tenths of a percent the speed of light in the referenced studies case[1]) are shot out like a slingshot. The original system is a binary, so they are already under extreme circular gravitational acceleration in their orbit. When the companion explodes in a core-collapse supernova, it loses that source of acceleration and moves in a straight line like a slingshot. The Gaia satellite is able to measure the velocity vector of the star very well, and show that it points back to an old supernova remnant. The scenario isn't controversial, but it does give quite a good example that this is how they come about.
- Steel_Phoenix 8y agoThis makes me wonder about the nature of gravity. How much of the gravitational pull from the companion would disappear? How fast? It seems like a reduction in gravity would be immediately followed by a massive energy release. It's impressive that the remaining star is moving away fast enough to avoid being destroyed in the resulting blast.
- whatshisface 8y agoThe reduction in gravity isn't due to anything special, the matter in the "anchor" star is just leaving to go somewhere else. (In all directions.)
- Steel_Phoenix 8y agoThat makes it seem like gravitationally, the anchor star would just be expanding. My intuition thinks the remaining star gets slammed by debris before the direction and strength of the anchor dissipates enough to launch it away, though my confidence in my stellar intuition is low.
- whatshisface 8y agoYour intuition contains some truth: according to Gauss's law, the gravitation of the expanding nova shell shouldn't change at all until it passes by its surviving companion. The matter expanding away from the companion will gravitate less, but that will be canceled out by the increased attraction to the matter expanding towards the companion. Really, we're just assuming the hot, dense, and small dwarf can sustain the licking it gets when the remnant hits it. The smallness helps it get hit by less material, moreso if it's far away. It's gravitationally bound so it won't shatter - the most you could do to disassemble it would be to boil off its matter by raising it all to escape velocity. It takes a lot of energy to do that.
- mirimir 8y agoRight, this white dwarf is moving at ~0.8% lightspeed. I gather that objects could be ejected from Sagittarius A* at even higher velocities.
- phyzome 8y agoAhhh, this makes sense -- they're not pushed, but flung. Thank you.