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Mark Hollands

I am a postdoc in the Warwick Astronomy and Astrophysics group. I am currently working with Pier-Emmanuel Tremblay and Boris Gänsicke on white dwarfs in the Gaia survey. My academic CV can be found here.


I study white dwarfs, the ultra-dense remains of burnt out stars—in particular I study those that have traces of metals in their atmospheres. The intense gravitaional fields of white dwarfs cause elements heavier than helium to sink out of the atmosphere in relatively short-order. Therefore the detection of metals in the photospheres of >25% of white dwarfs indicates this material must have been accreted externally.

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.

Dusty white dwarf

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

Talks Given

  • Revisiting the white dwarf local sample in the era of Gaia - presented at the 21st European white dwarf workshop (Austin, 2018)
  • 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)

Additional "Research"

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.


Astronomical Music

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



Write to:

Mark Hollands

Department of Physics,
University of Warwick,
Coventry CV4 7AL

Contact details:

E-Mail: M.Hollands AT