News
Paper Cakes at BU
Paper Cake is a great tradition our group has mugged from astronomers at the University of Warwick. During Paper Cake, you are encouraged to bake a cake and share it along with a discussion of a new paper posted to arXiv. Here is a celebration of a recent BUWD paper on 6 Mar 2026!
White Dwarf Envelopes and Gravitational Redshifts
In March 2026, a manuscript led by graduate student and BUWD member Stefan Arseneau (Arseneau, Hermes, Camisassa, Raddi & Bauer 2026) was accepted laying the foundations to constrain the envelope structure of white dwarfs using gravitational redshifts. The hydrogen envelope mass in most white dwarfs is poorly constrained but critically affects the inferred masses and cooling age of these stars. This work combines precise gravitational redshifts and Gaia-inferred radii for nearly 500 objects to measure the mass–radius relation. The results favor evolutionary models with thick, mass-dependent hydrogen envelopes (e.g., MIST). The manuscript has been accepted in The Astrophysical Journal.
Delayed Q Branch White Dwarfs Lack Strong Magnetism
In February 2026, a manuscript led by graduate student and BUWD member Lou Baya Ould Rouis (Ould Rouis, Hermes, Guidry et al. 2026) was accepted which we hope will change the way we think about some white dwarf merger remnants. Ultramassive white dwarfs in the Gaia "Q branch" exhibit multi-Gyr cooling delays, likely linked to merger origins, but our volume-limited spectroscopic study within 100 pc reveals unexpected trends in composition and rotation of the most delayed Q branch white dwarfs. Contrary to expectations for merger products, the most delayed objects show little magnetism or rotational variability. We also add new detections of pulsations in DAQ white dwarfs which suggest a possible extension of the DAV instability strip to hotter, thin-hydrogen atmospheres. The manuscript has been accepted in The Astrophysical Journal.
Transits (that vanish) around a white dwarf every 4.97 hr
In August 2025, a manuscript led by graduate student and BUWD member Joseph Guidry (Guidry, Vanderbosch, Hermes et al. 2025) was accepted which announced the discovery of deep, irregular, periodic transits from rocky exoplanetary debris towards the white dwarf ZTF J1944+4557. This retired star dims by more than 30% roughly every five hours, as clumps of debris block off light from the white dwarf. For the first time we have also observed transits around a white dwarf completely stop, and completely return roughly a year later, giving us a new laboratory to watch how shattered rocks evolve around dead stars. The manuscript has been accepted in The Astrophysical Journal.
Gravitational redshift bias in white dwarf spectra
In August 2025, a manuscript led by graduate student and BUWD member Stefan Arseneau (Arseneau, Hermes, Zakamska et al. 2025) was accepted which showed that substantial biases (5-15 km/s) exist in low-resolution radial velocity measurements, indicating that all the physics of line formation in high-density plasmas is not fully accounted for in state-of-the-art white dwarf model atmospheres. Using large samples from SDSS-V, we attempt to measure this bias and provide simple corrections for surveys like SDSS, DESI, and 4MOST. The manuscript has been accepted in The Astrophysical Journal.
NASA’s Hubble Uncovers Rare White Dwarf Merger Remnant
In August 2025, a manuscript led by Snehalata Sahu at the University of Warwick and including members of the BUWD group (Sahu et al. 2025) announced the discovery of carbon in the atmosphere of an otherwise normal-looking hot hydrogen-rich white dwarf, a tell-tale sign of a merger in the history of the system. The discovery could not have been made without the ultraviolet capabilities of the Hubble Space Telescope. The discovery was featured in a video summary by NASA Goddard, as well as with a NASA/ESA press release and subsequent news coverage by Popular Science and Space.com. The manuscript has been accepted in Nature Astronomy.
Probing Exoplanets Around Massive Stars
In November 2024, a manuscript led by graduate student and BUWD member Lou Baya Ould Rouis (Ould Rouis, Hermes, Gaensicke et al. 2024) was accepted which showed that the most massive white dwarfs (>0.8 solar masses) show metal pollution significantly less frequently than more normal-mass white dwarfs. Specifically, just 11% of white dwarfs that begin their lives as stars >3.5 solar masses on the main sequence show metals from remnant planetary systems, while 44% of white dwarfs that begin their lives as stars <2 solar masses show metals. We have also shown that mergers are unlikely to be the main explanation for this discrepancy. The findings likely have implications for planet formation and/or survival around massive stars on the main sequence which are hard to search for exoplanets using traditional techniques. The manuscript has been accepted in The Astrophysical Journal.
Written in the Stars
A story we ❤️about how exploring the Universe can re-ignite passion. And we don't mind that it's about looking at our white dwarf spectra in @jjhermes.bsky.social group 🤩🔭
www.bu.edu/articles/202...— Sloan Digital Sky Surveys (@sdssurveys.bsky.social) December 12, 2024 at 3:58 PM
BU White Dwarf researcher Ariyana Bonab was featured in a November 2024 video profile by The Brink magazine for her research in Summer 2024 visually classifying more than 50,000 spectra of white dwarf stars from SDSS-V. The five-minute video is well worth a watch!
Signposts of Remnant Planetary Systems
In June 2024, a manuscript led by graduate student and BUWD member Joseph Guidry (Guidry, Hermes, De et al. 2024) took a look at infrared variability of white dwarfs as seen over many years from NASA's Wide-field Infrared Survey Explorer (WISE) space telescope, discovering dozens of new infrared-variable white dwarfs that are likely to be host to remnant planetary systems. Some white dwarfs with planetary systems host dusty debris that causes an infrared excess, and collisions within the debris disks often cause infrared variability. The manuscript has been accepted in The Astrophysical Journal.
Dr. Tyler Heintz
Massive congratulations to Dr. Tyler Heintz, who successfully defended his PhD dissertation on Tuesday July 23, 2024! Tyler has been at BU throughout the entire history of the BUWD research group, and has become expert in the reliability of white dwarf cosmochronology (age-dating white dwarf stars).