The BU White Dwarf Group

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Welcome to the home page of the BU White Dwarf group, headquartered a few blocks from Fenway Park in Boston, MA, USA.

Our research focuses on white dwarf stars and their connection to the endpoints of stars, binary, and planetary systems. Our work is supported by Boston University, the Institute for Astrophysical Research, the National Aeronautics and Space Administration (NASA), the National Science Foundation (NSF), and the Massachusetts Space Grant Consortium.

Recent news and group updates:
Research updates can be found below and on the news page.

Testing Ages Using Spectroscopy of White Dwarfs

By JJ HermesMay 27th, 2024
An example of one widely separated pair of white dwarf stars (both marked with a yellow box), each analyzed independently to determine their ages. In this case, the two stars move together on the sky and are both at the same distance (59.5 pc); they are separated from each other by roughly 1500 au (credit Aladin / PanSTARRS survey).

In May 2024, a manuscript led by graduate student and BUWD member Tyler Heintz (Heintz, Hermes, Tremblay et al. 2024) announced the most detailed test of white dwarf ages measured from spectroscopic fits in wide WD+WD binaries. By comparing the age estimates of wide pairs of stars that should have both been born at the same time, using fits using both photometry and spectroscopy, Tyler provided one of the most reliable tests of current age-dating methods of white dwarf stars. This work shows that photometry + parallax (distance) measurements returns more reliable results for fainter white dwarfs. It also finds further evidence of a significant merger fraction among wide WD+WD binaries, where roughly 20% are inconsistent with a monotonically increasing initial-final mass relation. The manuscript has been published in The Astrophysical Journal.

Gaia’s Light Curve Prospects

By JJ HermesMay 27th, 2024
Phase-folded light curves showing Gaia epoch photometry in green for white dwarfs matching ZTF and TESS data in blue and red (credit Steen et al. 2024).

In April 2024, a manuscript led by former BU undergraduate student and BUWD member Maya Steen (Steen, Hermes, Guidry et al. 2024) detailed one of the first systematic analyses of Gaia DR3 multi-epoch light curves, this focused on white dwarfs. Roughly 1300 candidate white dwarfs have Gaia light curves (spanning roughly 1000 days with visits roughly every 44 days). Even with that sparse sampling, Maya (who is now a graduate student at New Mexico State University) showed that periodicities as short as minutes can be detected from the Gaia light curves alone! We discover 86 new objects from the 105 target sample, including pulsating, spotted, and binary white dwarfs, and even a new 68.4 min eclipsing cataclysmic variable. The manuscript has been published in The Astrophysical Journal.

JWST directly images two giant planet candidates

By JJ HermesFebruary 1st, 2024
Directly imaged candidate giant planets from JWST around two white dwarfs: WD1202-232 at top, WD2105−82 at bottom (credit Mullally et al. 2024).

In January 2024, a manuscript led by Susan Mullally from Space Telescope Science Institute and including members of the BUWD group (Mullally et al. 2024) announced that JWST has directly images giant planet candidates around two metal-polluted white dwarf stars. The two planet candidates (JWST/MIRI images shown above) are consistent with 1-7 Jupiter-mass planets on orbits that would have been similar to Jupiter or Saturn in our solar system before the host star lost mass to become a white dwarf. JWST has improved our sensitivity to such planets by an order of magnitude. If confirmed to move with the white dwarf (although unlikely, in each case the point source could be a background galaxy), these would be the oldest directly imaged exoplanets ever found, and would be direct evidence that giant planets like Jupiter survive the evolution of their host star. Because they orbit white dwarf stars, we can get reasonable estimates on their ages: WD1202-232b is likely close in age to our Sun (~5 billion years old), and WD2105−82b is between 1.4-2.4 Gyr. Some nice press coverage of the discovery was published by Science Magazine as well as Universe Today. The manuscript has been accepted in The Astrophysical Journal Letters.

USRA Distinguished Undergraduate award

By JJ HermesDecember 14th, 2023

Former BU White Dwarf researcher Madi VanWyngarden, who worked with us in Summer 2021 and helped with our discovery of many new pulsating white dwarfs in TESS, has recently been honored with a 2023 Universities Space Research Association (USRA) Distinguished Undergraduate Award. Madi is one of only five recipients of this year's award, and the first ever from Boston University!

A 23-min binary in TESS

By JJ HermesNovember 11th, 2023

In November 2023, a manuscript led by Matthew Green from the Max-Planck-Institut für Astronomie in Heidelberg, Germany and including members of the BUWD group (Green, Hermes, Barlow et al. 2023) announced the discovery of the shortest-period binary system yet found by NASA's Transiting Exoplanet Survey Satellite (TESS)! Although TESS is tuned to finding transiting exoplanets, we used the facility to discover a pair of stars orbiting one other roughly every 23 minutes, one of the brightest (and closest) AM CVn binaries ever found. This is the second system we have recently found from TESS that will be detectable in gravitational wave radiation when we launch space-based interferometers in the coming decades. The manuscript has been accepted for publication in the Monthly Notices of the Royal Astronomical Society.