Dark matter

and for having me for the lecture today.

I want to try and explain to you a little bit about dark matter today.

So dark matter is a substance that we think makes up most of the mass of the universe.

It appears to be completely invisible.

We only seem to know about it through its gravitational influence.

And if that sounds completely crazy, my one objective today is for you to not think that I'm totally mad by the time you leave this room.

And a little bit more than that, I'd like at the end of the talk, if I can, to get onto some of my own work on the subject, some recent work where we think we've uncovered evidence that dark matter can be moved around at the center of galaxies as they form.

And this is giving us new clues as to what dark matter might actually be.

But I'm more interested in using these sort of as secondary tracers because you might notice that these streams trace out what look like orbits at very large distances from their host galaxies.

And that orbital information we can then use to understand the properties of dark matter on very large scales.

So in particular, I'm most interested in using these tracers around the Milky Way, our own galaxy.

So in the Milky Way, we know of between sort of 40 and 60 of these stellar streams, depending on your threshold for believability, I would say.

So this plot came up earlier from David Hogg's talk.

This is a model of this very thin feature what we call the spur around GD1, where we think that this is an indication of an interaction between a very dense perturber, a massive perturber around the Milky Way that flew through the stream and produced this sort of offshoot of material.

So the streams are both sensitive to sort of the large-scale distribution of dark matter, but also to very thin local events like this.

So since then, we've been looking at many other streams.

Rip wants to know this.

Could dark energy or matter, dark matter or dark energy, is it possible to manipulate it, to use it as a fuel of some sort?

Interesting.

So here's the problem.

Dark energy, we don't know how to interact with it.

We just measure its effects on the universe.

Dark matter reveals itself to us through its gravity.

Okay, but it doesn't reveal itself to us in any other way that we normally interact so

Okay,

is it possible that dark energy and dark matter are stuff permeating into our universe from another nearby universe and that our matter and energy is being permeated into another universe Here's the caveat, via black holes.

So, I mean, just think about it.

Hold off on dark energy for a moment, because that's just everywhere, and it would not lend itself as well to this expectation as dark matter would.

Okay.

Okay, so dark matter is a source of gravity about which we know nothing.

Got you.

It's not black holes, it's just gravity out there.

Yeah, this is David.

hemsath from patreon he says is there a hypothesis for the interaction of dark matter and a black hole so you know i mean

yeah i mean it's just because dark matter is dark and black hole black

black

don't mean all the black and the dark gotta vote together As far as we know, they are completely separate and distinct as far as we know.

And that actually I'm not even saying very much there because we don't know what comprises dark matter.

And as I've said many times, it's the better termed dark gravity.

It's something giving us gravity and we don't know what it is.

So no, here's the thing.

It's the, if you run the history of the universe back, Whatever it is that is the dark gravity, the dark matter, whatever that is, it cannot physically interact with ordinary matter.

Because if it did, it would completely change what the universe looked like.

So it has to have gravity and not interact with us.

And that's why you're this physical thing that I can touch.

And you're a physical entity that is matter collected doing other interesting things as a collected unit.

Dark, what we call dark matter or dark gravity has no such properties.

Right.