> Interestingly they’re all quite fast — hundreds of kilometers per second
I bet that the milky way could only capture these ultra fast moving stars because of dark matter.
I bet that the milky way could only capture these ultra fast moving stars because of dark matter.
That's not how we date stars. We typically date the star by it's metallic content. More non-hydrogen elements in it's spectrograph, then we know it's an older generation of stars.
It's actually the exact opposite, but yes.
In lead stars, there are so few seed nuclei (those metals) that each of the seed nuclei that are there can capture many more neutrons.
It's all time, right?
Sure, but we can measure time dilation between the peak of a mountain and the base of a mountain, due to the differing velocities. Time is relative!
So far, to my knowledge, we have not observed any. As you note, hundreds of km/s is way too small to have any appreciable effect.
https://www.space.com/fastest-star-ever-moves-8-percent-ligh...
For example, suppose the other ship is one light-second away from yours and is moving at 0.2c. You're seeing the other ship where it was one second ago, and in that time it has moved 1/5 of a light second. Plus, supposing you're firing a laser at it, the laser will take another second to get to the target, so you have to aim 2/5 of a light second away from where you're seeing the other ship. And during that time the other ship could change direction and spoil your aiming calculation. The sci-fi book series probably is making some assumptions about how fast the ships can change direction, how fast and accurately they can aim, and typical distances between ships during combat to come up with the 0.2c number.
https://en.wikipedia.org/wiki/Cosmological_horizon
"Or, more precisely, there are events that are spatially separated for a certain frame of reference happening simultaneously with the event occurring right now for which no signal will ever reach us, even though we can observe events that occurred at the same location in space that happened in the distant past.
"While we will continue to receive signals from this location in space, even if we wait an infinite amount of time, a signal that left from that location today will never reach us."
Also, “in the halo” doesn’t necessarily mean “far from the center of the galaxy”; it means “not orbiting in the disk”.[1] Some of these stars are closer to the galactic center than the Sun.
[1] And further away from the center of the galaxy than the bulge — but the bulge is much smaller than the orbit of the Sun.
An example closer to home, our orbital velocity around the Sun is 29.8km/s. Mercury is 47.9km/s (on average, it actually varies throughout its orbit). Neptune is 5.4km/s.
https://en.wikipedia.org/wiki/Galaxy_rotation_curve
```
The rotational/orbital speeds of galaxies/stars do not follow the rules found in other orbital systems such as stars/planets and planets/moons that have most of their mass at the centre. Stars revolve around their galaxy's centre at equal or increasing speed over a large range of distances. In contrast, the orbital velocities of planets in planetary systems and moons orbiting planets decline with distance according to Kepler’s third law.
```