KG’s Research


I am an assistant research scientist at the University of Michigan. My research tends to focus on black holes and their environs. I eschew the traditional dichotomy of theorist/observer. In observing, I have worked in radio, millimeter wave, near infrared, optical, ultraviolet, and X-ray. I also have more than a passing interest in gravitational waves and astrostatistics. In theory, I tend to the numerical side and use detailed models to measure black hole masses.

I used to work for (but continue to work with) Douglas O. Richstone as a member of the Nuker Group.


NGC 4258

My research in SMBHs focuses on two general areas of study. The first is the coevolution of black holes with their host galaxies. Studies of elliptical galaxies and spiral bulges have led to the discoveries that most or all hot galaxies contain massive dark objects at their centers, presumably black holes; and that there is a remarkably tight correlation between the black hole mass and properties of the kinematically hot component of the galaxy. These scaling relations suggest a strong link between black hole formation, galaxy formation, and active galactic nuclei (AGNs); and once it is understood, this link should advance our understanding of all three processes. My efforts in this area are spent studying the scaling relations themselves. This involves measuring black hole masses directly and measuring the scaling relations themselves. I do both observational (mostly in the optical and near infrared) and computational work.

M87 X-ray and radio image

The second area of my research concerns the physics of accretion and outflows. Here my work is primarily observational (X-ray and radio). Accretion onto black holes (and neutron stars and white dwarfs and protostellar cores) gives rise to powerful outflows. There is a known connection between these two phenomena, but a full understanding still eludes us. There is an especially intriguing relation among black hole mass, radio luminosity, and X-ray luminosity across many orders of magnitude. This relation is intriguing to me both as a source of insight to the physics of acrretion and as a tool for estimating black hole masses.

Details about my research on SMBHs.


image of HST/Chandra Deep field

Since black holes and galaxies appear to coevolve, understanding the properties of either of them across cosmic time requires understanding them together. I have been involved in several theoretical studies, aimed primarily at understanding black hole occupation fraction and/or AGN fraction of galaxies as a function of redshift. Understanding this helps us compare predictions of luminosity functions due to different initial black hole seed mass functions. It also includes some very cool physics such as gravitational wave recoil. Details of my research in cosmology.


Chandra image of M82

Recent observations suggest the possibility of black holes with mass, M ~ 100 to 10,000 M in stellar clusters. If true, this represents a class of black holes distinct from stellar-mass black holes (thought to be the result of a core collapse supernova) and supermassive black holes (found in the centers of galaxies). The formation of these intermediate-mass black holes (IMBHs) may also be linked to stellar-mass black hole mergers involving binary-single black hole encounters, and any IMBH in a stellar cluster is likely to undergo similar encounters. The binaries involved in these encounters are also important sources of gravitational waves detectable by Advanced LIGO and LISA. My work centers on the numerical study of three-body encounters in the astrophysical context of globular clusters. I have developed a code that can integrate post-Newtonian encounters of point-masses. This is used to simulate encounters between binary black holes and interlolping black holes. I am interested in how such encounters affect the semimajor axis and eccentricity of the binary in the high mass ratio case. The code also simulates a series of encounters that a binary would face in the core of a globular cluster until it finally merges due to gravitational radiation.

More about IMBHs.

Other research interests.

I am involved in the Swift Galactic Plane Survey (PI: Mark Reynolds, which will observe 240 square degrees of the Galactic plane (−60 ≤ ℓ ≤ +60; −1 ≤ b ≤ 1) in over 3000 exposures of 500 seconds each, reaching to a 2–10 keV flux of 3×10−13 erg s−1 cm−2, plus additional ultravioloet coverage from the onboard UVOT camera.

I am a Co-I of the HET Massive Galaxy Survey (PI: Remco van den Bosch). We have taken more than 400 hours of Hobby-Eberly Telescope time to get long-slit spectra of more than 900 galaxies to create a census of the Nothern galaxies in the local volume (D < 150 Mpc; z < 0.03). There is a lot of cool science to be done with these data, the most interesting of which (to me!) is to look for black holes.

My Past Research.

My previous work was in the realm of star formation and planetary origins. I worked primarily with Lee Mundy to observe with the Berkeley Illinois Maryland Association (BIMA) interferometer in Hat Creek, CA. I also worked as an undergraduate with David Koerner.

My Recent Papers and Publications.

See my online CV for an automated listing of all of my publications, or you can look directly at ADS and astro-ph that might have slipped through the cracks. Please note that when searching for my papers on ADS, you again have to search for both "Gultekin" and "G├╝ltekin" if you want to find all of my papers. Or not. They seem to break and fix this on a regular basis. (Not to complain about an otherwise amazing service.)

Other Links of Interest