# Lensing from compact remnants in the Galactic Center

## Jun 2, 2022 08:54 · 337 words · 2 minute read astronomy science research

I sometimes have research ideas that I think are cool, but that don’t make sense for me to pursue. I generally just make a note of them and move on. This is the seventh post in a series describing some of the ideas I’ve accumulated.

## Lensing from compact remnants in the Galactic Center

### What’s the idea?

It’s thought that the Milky Way used to host an AGN disk. AGN disks likely contain many stars, and those stars very preferentially evolve into black holes. Many of those black holes should still be around after the disk dissipates, so there could be $\sim 10^4$ black holes in the inner parsec of our galaxy. As these pass in front of other objects they lens them, and that’s something large surveys might be able to observe.

### Why is this interesting?

We have relatively few direct observational handles on stellar evolution in AGN disks, or on the properties and structure of AGN disks. From the rate of galactic center lensing events it should be possible to back out the number of black holes in the galactic center, and even just knowing that would constrain both AGN star evolution and black hole migration rates through the AGN disk.

Even better would be knowing the spatial distribution of those black holes, which could more directly probe the structure of the disk that was once there, but that may be too much to ask for.

### How can I get started?

The first thing to do is probably to work out the rate of observable lensing events from $\sim 10^4$ black holes in the inner $\sim 1\mathrm{pc}$, and then to check if large surveys like LSST should be able to see events from this population. After that the real work begins, which at first probably looks like figuring out how to identify events of interest, thinking about ways those events could be spurious, and putting together predictions for rates and spatial distributions from different models of AGN disks and different models of how embedded stars evolve.

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