# Astro2020: From Stars to Compact Objects: The Initial-Final Mass Relation

## TL;DR

This paper discusses how astrometric gravitational lensing can be used to better understand the initial-final mass relation of stars by detecting and weighing black holes and neutron stars, which are crucial for understanding stellar death.

## Contribution

It proposes a new approach using astrometric microlensing with upcoming large surveys and telescopes to constrain the mass function of isolated compact objects.

## Key findings

- Potential to measure black hole and neutron star masses.
- Improved understanding of stellar death and supernovae.
- Constraints on the initial-final mass relation.

## Abstract

One of the key phases of stellar evolution that remains poorly understood is stellar death. We lack a predictive model for how a star of a given mass explodes and what kind of remnant it leaves behind (i.e. the initial-final mass relation, IFMR). Progress has been limited due to the difficulty in finding and weighing black holes and neutron stars in large numbers. Technological advances that allow for sub-milliarcsecond astrometry in crowded fields have opened a new window for finding black holes and neutron stars: astrometric gravitational lensing. Finding and weighing a sample of compact objects with astrometric microlensing will allow us to place some of the first constraints on the present-day mass function of isolated black holes and neutron stars, their multiplicity, and their kick velocities. All of these are fundamental inputs into understanding the death phase of stellar evolution, improving supernovae models, and interpreting LIGO detections in an astrophysical context. To achieve these goals, we require large area surveys, such as the WFIRST exoplanet microlensing survey, to photometrically identify long-duration (>120 day), un-blended microlensing events as candidate compact objects. We also require high-precision astrometric follow-up monitoring using extremely large telescopes, equipped with adaptive optics, such as TMT and GMT.