The detection of debris disks (infrared excesses) at a number of metal-rich white dwarfs, plus the recent observation of transists from a disintegrating planetesimal at WD1145+017 confirm the hypothesis that these metals come from rocky bodies such as asteroids.
Image Credit: Nasa/JPL-Caltech
By analysing white dwarf atmospheres, we can therefore directly measure the composition of rocky material formed in other star systems! Furthermore, by determining white dwarf ages, we can learn about the evolution of remnant planetary systems over billions of years. For the systems I study this means looking back into the Milky Way's past, but for the Solar System correspondsas to looking forwards as the Sun will become a white dwarf in ~6 billion years.
I am also interested in magnetic white dwarfs, including their origin, evolution, and the field geometries of individual objects.
Publications I have been involved with
- Cool DZ white dwarfs I: Identification and spectral analysis
M. A. Hollands, D. Koester, V. Alekseev, E.L. Herbert, B.T. Gänsicke, MNRAS 467, 4970 (2017)
- Evolved Planetary Systems around Very Cool and Old White Dwarfs (Proceedings for the 19th European Workshop on White Dwarfs)
M. A. Hollands, B.T. Gänsicke, D. Koester, ASPC 493, 267 (2015)
- The incidence of magnetic fields in cool DZ white dwarfs
M. A. Hollands, B.T. Gänsicke, D. Koester, MNRAS 450, 681 (2015)
- The binarity of the local white dwarf population
S. Toonen, M. Hollands, B.T. Gänsicke, T. Boekholt, A&A 602, A16 (2017)
- Multi-band photometry and spectroscopy of an all-sky sample of bright white dwarfs
R. Raddi, N. P. Gentile Fusillo, A. F. Pala, J. J. Hermes, B. T. Gänsicke, P. Chote, M. A. Hollands, A. Henden, S. Catalán, S. Geier, D. Koester, U. Munari, R. Napiwotzki, P.-E. Tremblay, MNRAS (accepted 2017)
- The white dwarf binary pathways survey - II. Radial velocities of 1453 FGK stars with white dwarf companions from LAMOST DR4
A. Rebassa-Mansergas, J. J. Ren, P. Irawati, E. Garcia-Berro, S. G. Parsons, M. R. Schreiber, B. T. Gänsicke, P. Rodriguez-Gil, X. Liu, C. Manser, S. Palomo-Nevado, F. Jimenez-Ibarra, R. Costero, J. Echevarria, R. Michel, M. Zorotovic, M. A. Hollands, Z. Han, A. Luo, E. Villaver, X. Kong, MNRAS (accepted 2017)
- When flux standards go wild: white dwarfs in the age of Kepler
J. J. Hermes, B. T. Gänsicke, Nicola Pietro Gentile Fusillo, R. Raddi, M. A. Hollands , E. Dennihy, J. T. Fuchs, S. Redfield, MNRAS 468, 1946 (2017)
- First EURONEAR NEA discoveries from La Palma using the INT
O. Vaduvescu, L. Hudin, V. Tudor, F. Char, T. Mocnik, T. Kwiatkowski, J. de Leon, A. Cabrera-Lavers, C. Alvarez, M. Popescu, R. Cornea, M. Díaz Alfaro, I. Ordonez-Etxeberria, K. Kamiński, B. Stecklum, L. Verdes-Montenegro, A. Sota, V. Casanova, S. Martin Ruiz, R. Duffard, O. Zamora, M. Gomez-Jimenez, M. Micheli, D. Koschny, M. Busch, A. Knofel, E. Schwab, I. Negueruela, V. Dhillon, D. Sahman, J. Marchant, R. Génova-Santos, J. A. Rubiño-Martín, F. C. Riddick, J. Mendez, F. Lopez-Martinez, B. T. Gänsicke, M. Hollands, A. K. H. Kong, R. Jin, S. Hidalgo, S. Murabito, J. Font, A. Bereciartua, L. Abe, P. Bendjoya, J. P. Rivet, D. Vernet, S. Mihalea, V. Inceu, S. Gajdos, P. Veres, M. Serra-Ricart, D. Abreu Rodriguez28, MNRAS 449, 1614 (2015)
- Remnant planetary systems around the oldest white dwarfs - Seminar (Caltech, 2017)
- Chemistry and evolution of the oldest white dwarf planetary systems - presented at Astrochemsitry VII IAU symposium 332 (Puerto Varas, 2017)
- Chemistry and evolution of the oldest white dwarf planetary systems - presented at Planetary Systems Beyond the Main Sequence II (Technion, 2017)
- Chemistry and evolution of the oldest white dwarf planetary systems - Seminar (Institute of Astronomy, Cambridge, 2016)
- A large sample of cool, strongly-polluted DZ white dwarfs - presented at the 20th European white dwarf workshop (Warwick, 2016)
- Metals as tracers of magnetism in old white dwarfs - presented at the Stellar End Products meeting (ESO Garching, 2015)
- Planetary systems as tracers of magnetism in old white dwarfs - presented at the workshop: Mysteries of the Suns magnetic field III: Understanding stellar activity (Warwick, 2015)
- Ancient planetary systems around white dwarfs - presented at the 19th European white dwarf workshop (Montreal, 2014)
Just for fun... A simulated transit of a white dwarf by a super-Earth sized planet as it may appear to a nearby observer. The overexposed bloom effect is somewhat artistic, but represents the effect of an imperfect camera lens exposed to a bright source. The colour of the white dwarf (seen in the halo due to 'overexposure') is calculated from its optical spectrum.
While recently reading about powered exoskeletons on Wikipedia (because they are awesome), I noted that one of the links under "see also" was titled List of films featuring powered exoskeletons. Of course, such an article is impossible to ignore. The list is presented in tabular form which can be sorted by year of release (NB. films featuring cyborgs or mechas don't count). To a scientist, this brings about the uncontrollable urge to plot things.
To my amazement the number of films released per year featuring an exoskeleton is increasing exponentially with time (note the logarithmic scale on the y-axis). Simply put this means that the total number of films featuring a powered exoskeleton doubles every 10 years. Not only the total number, but also the number of films produced per year also doubles in this characteristic time of about 10 years. In fact, we have already crossed the boundary of 1 exoskeleton film per year on average, as of about 2010.
From the resulting fit, we can make some predictions. By about 2044, the number of films with exoskeletons produced per year will exceed 10. This may reflect their increasing prevalence within society (yet still too expensive to be encountered on a day-to-day basis). Extrapolating even further, by the end of this century, approximately 500 films per year will feature a powered exoskeleton of some sort. Presumably this indicates that exoskeletons will be common-place by this point. Perhaps I will be able to fulfill my dream of battling a Xenomorph queen using a power loader within my lifetime after all.
Below is a collection of music that falls into the narrow intersection of "music I enjoy" and "astronomy related" (if only the title!). To be populated over time as I think of things to add:
Astronomy - Blue Öyster Cult
Astronomy Domine - Pink Floyd
Cosmos soundtrack - Vangelis
Cygnus X-1 Book I/II - Rush
Echoes (set to the final 25 minutes of 2001 a Space Odyssey) - Pink Floyd/Stanley Kubrick
Lunar Sea - Camel
The Planets Suite - Gustav Holst
Shine on you Crazy Diamond - Pink Floyd (evidently about white dwarfs with crystallised cores)
Space Oddity - David Bowie
Stargazer - Rainbow
White Dwarf - A-Ha