3-913, Physics and Astronomy
Positions held in the past:
Hubble Fellow, Princeton University
Research Associate, Canadian Institute for Theoretical Astrophysics
Ph.D., 1996, California Institute of Technology
Undergraduate: University of Natal, Durban
High School: St Henry's College, Durban
Curriculum vitae (PDF)
Current Graduate Students ( History )
Tze (Matt) Yu (Sixth year)
Current Undergraduate Students
Prior Graduate Students
K. Hayakawa (2022)
J.K. Zink (2021)
A.M. Vinson (2020)
S.F.N. Frewen (2015)
I.J.M. Crossfield (2012)
F.E. Koch (2009)
Chair, Comprehensive Exam Committee 2023
Guidelines for the UCLA Astronomy Comprehensive Exam can be found here .
Research Interests: Theoretical Astrophysics
are my principal subject of interest today. My students and I pursue mostly theoretical but also some observational programs on a variety of topics.
Recent theoretical work has focussed on the dynamics and origin of extrasolar planetary systems as well as to how our own Solar system fits into this broader context.
now suggest that the dominant population of planets in our galaxy may be composed of highly multiple systems of low
mass stars, especially if such systems are found around low-mass M dwarfs,
which are the dominant stellar demographic in the Galaxy. Along with Norm Murray, at CITA, I have been studying the in situ assembly of
rocky planets on sub-AU scales around stars of different mass. Our models are able to provide an encouraging match to the observed distribution,
and a much better fit that the more conventionally assumed models based on the concept of migration. More detail on this work can be
found here .
I am also interested in the dynamics of systems containing multiple giant planets. Understanding the secular structure of these systems may shed light on the formation processes, especially in those systems that exhibit substantial eccentricities and/or inclinations. I am also interested in the attendant populations, such as large moons or trojan planets, as they may also provide insight into the formation of such planets. See here for a non-technical discussion of some of these issues. I also have students working on models for the migration of giant planets ( Matt Yu ) and the production of dust in debris disks ( Kevin Hayakawa ). These two projects are done in collaboration with Yasuhiro Hasegawa at JPL.
I also have an ongoing interest in how our own Solar system fits into the framework of the planets discovered around other stars. I have
worked on the formation of the terrestrial planets and am currently working on the formation of moons in the Solar system and around other
I also maintain a long-standing interest in the existence and survival of planets around evolved stars. This dates back to my days as a graduate student, when I worked on models for the formation of the pulsar planets, and continues today with studies of planetary systems around white dwarfs. My former graduate student, Shane Frewen, studied the evolution of planetary systems around both white dwarfs and subgiant stars. More detail on this work can be found here .
On the observational side, along with my former student Ian Crossfield , and long-time collaborator Travis Barman, we have pursued a program over
the last several years to observe transmission spectra of extrasolar giant planets. These observations offer the promise of constraining the
chemical compositions of planetary atmospheres, and the techniques we develop will hopefully prove useful one day in performing similar
measurements on lower mass, earth-class planets. More detail on this work can be found here . In the last few
years, my role in this particular enterprise has diminished as Ian has successfully assumed leadership of this and related projects. A more recent student observational project is that of Jon Zink, who is working on
the production of a uniform catalogue of planets from the K2 mission, in collaboration with
Jessie Christiansen, at IPAC.
White Dwarfs are the end product of stellar evolution for most stars (except for those massive enough to explode as supernovae). As such, the study of old white dwarfs can tell us a lot about the history of star formation in our Galaxy. By the time a star has reached the white dwarf stage, it has exhausted all the nuclear burning resources with which it was born. With no remaining reservoir of energy supply white dwarfs slowly cool and fade over time. I have worked a lot on theoretical models for the evolution and appearance of white dwarfs of different kinds. With my observational collaborators, I have used these models to estimate the ages of various stellar components of our Galaxy, including both the stars in the immediate vicinity of the sun and some of the nearest globular clusters. One of our recent results is a setting a lower limit on the age of our Galaxy of approximately 11 billion years.
Neutron Stars and Black Holes are the first objects I worked on, during my PHD. My most recent interest in this subject concerns the black hole at the center of our Galaxy and the immediate environment. With my students Steve Berukoff and Elliot Koch, I have been studying the dynamics of thousand-solar mass black holes orbiting the main black hole. We believe these `intermediate mass' black holes may have played an important role in the transport of young stars to the Galactic center and they will have an important influence on the resulting dynamics.
|Recent Lead Author Publications: (last 5 years)|
``Unbound close stellar encounters in the Solar neighbourhood''
B. M. S. Hansen ,
The Astronomical Journal, 163, 44 (2022)
B. M. S. Hansen & B. Zuckerman ,
The Astronomical Journal, 161, 145 (2021)
B. Hansen & S. Naoz ,
Monthly Notices of the Royal Astronomical Society, 499, 1682 (2020)
B. Hansen ,
Science Advances, Vol 5, eaaw8665 (2019)
B. Hansen ,
Monthly Notices of the Royal Astronomical Society, Vol 475, Page 2452 (2018)
B. Hansen & B. Zuckerman ,
Research Notes of the American Astronomical Society, 1, 55 (2017)
B. Hansen ,
Monthly Notices of the Royal Astronomical Society, Vol 467, Page 1531 (2017)
J. K. Zink , K. Batygin, F. C. Adams ,
Astrophysical Journal, in press (2020)
J. K. Zink , K. K. Hardegree-Ullman; J. L. Christiansen; E. A. Petigura; C. D. Dressing; J. E. Schlieder; D. R. Ciardi; I. J. M. Crossfield, ,
Astronomical Journal, in press (2020)
J. K. Zink , K. Hardegree-Ullman, J. Christiansen, C. Dressing, I. Crossfield, E. Petigura, J. Schlieder, & D. Ciardi, , Astronomical Journal, 159, 154 (2020)
A. M. Vinson , D. Tamayo & B. M. S. Hansen ,
Monthly Notices of the Royal Astronomical Society, Vol 488, 5739 (2019)
J. K. Zink & B. M. S. Hansen ,
Monthly Notices of the Royal Astronomical Society, Vol 487, Page 246 (2019)
J. K. Zink , J. L. Christiansen & B. M. S. Hansen ,
Monthly Notices of the Royal Astronomical Society, Vol 483, Page 4479 (2019)
A. M. Vinson & B. Hansen ,
Monthly Notices of the Royal Astronomical Society, Vol 472, Page 3217 (2017)
S. N. Frewen & B. Hansen
Monthly Notices of the Royal Astronomical Society, Vol 455, Page 1538 (2016)
C. E. O'Connor & B. Hansen