- #1
Thomas Sturm
- 9
- 3
- TL;DR Summary
- Consider a fast moving (relative to its galactic neighborhood) star: would its gain in mass due to dark matter have measurable consequences?
Given the fact that our galaxy consists mostly of dark matter (accounting for roughly 70% of its mass) we know astonishingly little about the stuff. Admittedly, if I could give you a lump of dark matter, you would propably be totally underwhelmed by the "experience". First of all, you wouldn't see it. Dark matter isn't "dark" but completely and utterly invisible. It simply doesn't interact with electromagnetic forces.
It does interact with gravity, though, so you would propably anticipate being given a lump of "nothing" and feeling its weight in the palm of your hand. Only, as far as we know, it doesn't interact with your hand either, so it would pass right through you and follow the call of gravitiy towards the center of the earth. In fact it would go right through and swing backwards and forwards through the planet around its center of gravity until kingdom comes. At least, according to our "knowledge" of dark matter, this should be what happens.
If it was made out of particles - which we don't know - those particles would be moved backwards and forwards each time the lump passes the centre of the earth. In other words: the lump would "warm up", losing its kinetic energy and eventually settling down. But we don't know even that. It would, however, add to the mass of our planet, one way or another. As would any other lump of dark matter our planet ever encounters.
This wouldn't amount to much given the fact that dark matter, being gravity bound, moves around the center of the milky way just like our solar system does: so from our point of view, the whole ghostly soup should remain relatively static. This is entirely different for the few rogue stars that we find in every galaxy. Since their velocity relative to the dark matter that makes up the bulk of the mass of their host galaxy is quite high (i.e. 1200 km/s in case of "US 708"), it should "gobble up" quite a sizeable amount of dark matter over time - and this should have observable consequences. It should shrink, for starters. The fact it is getting heavier all the time should also affect its trajectory.
So my question is: have I taken a wrong turn somewhere or should it not be possible to learn something about the nature of dark matter by observing hyper-velocity stars?
It does interact with gravity, though, so you would propably anticipate being given a lump of "nothing" and feeling its weight in the palm of your hand. Only, as far as we know, it doesn't interact with your hand either, so it would pass right through you and follow the call of gravitiy towards the center of the earth. In fact it would go right through and swing backwards and forwards through the planet around its center of gravity until kingdom comes. At least, according to our "knowledge" of dark matter, this should be what happens.
If it was made out of particles - which we don't know - those particles would be moved backwards and forwards each time the lump passes the centre of the earth. In other words: the lump would "warm up", losing its kinetic energy and eventually settling down. But we don't know even that. It would, however, add to the mass of our planet, one way or another. As would any other lump of dark matter our planet ever encounters.
This wouldn't amount to much given the fact that dark matter, being gravity bound, moves around the center of the milky way just like our solar system does: so from our point of view, the whole ghostly soup should remain relatively static. This is entirely different for the few rogue stars that we find in every galaxy. Since their velocity relative to the dark matter that makes up the bulk of the mass of their host galaxy is quite high (i.e. 1200 km/s in case of "US 708"), it should "gobble up" quite a sizeable amount of dark matter over time - and this should have observable consequences. It should shrink, for starters. The fact it is getting heavier all the time should also affect its trajectory.
So my question is: have I taken a wrong turn somewhere or should it not be possible to learn something about the nature of dark matter by observing hyper-velocity stars?
Last edited by a moderator: