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 dwarfs 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.

Seeing the interiors of massive A stars with TESS

By JJ HermesNovember 28th, 2020

Collaborators led by Tim Bedding at the University of Sydney published in Nature in May 2020 exciting new results from NASA's TESS mission that are some of the first convincing identifications of the oscillations of a class of massive A stars that pulsate, named after the prototype star delta Scuti. The 2-minute cadence of TESS has finally allowed astronomers to identify the pulsations in delta Scuti stars, especially those that are young. Besides a NASA press release and a Nature News & Views for more general audiences, a thread contextualizing the discovery is here:

A puzzling, fast-spinning white dwarf with emission

By JJ HermesNovember 28th, 2020
An artist's impression of a strongly magnetic white dwarf (credit ESO/L. Calçada).

In May 2020, collaborators led by PhD student Josh Reding at the University of North Carolina at Chapel Hill published in The Astrophysical Journal the fastest-rotating, isolated white dwarf. The star spins on its axis every 317 seconds, and is only the second white dwarf to show Balmer emission lines -- the origin of this emission is still puzzling, and could be connected to the induction of a current from a close-in rocky planet. A thread detailing this highly magnetic stellar remnant is here:

Pulsations & eclipses in a white dwarf

By JJ HermesNovember 28th, 2020

In March 2020, collaborators led by Steven Parsons at the University of Sheffield published in Nature Astronomy the first pulsating white dwarf ever found in a binary system that also exhibits eclipses. Having both pulsations and eclipses in this low-mass (0.325 solar-mass) white dwarf will put some exceptional constraints on the star. We already know the radius of the star to 2% precision, less than 300 km, and know its mass to better than 4% -- this will be an excellent benchmark to understand how stars are stripped of mass at the end of their lives. Aside from a press release with an artist's impression from the University of Sheffield, a thread with more details can be found here:

An old failed star

By JJ HermesFebruary 26th, 2020

Collaborators, led by PhD student ZJ Zhang at the University of Hawaii, have discovered a bound pair of stars that serve as an exciting benchmark: one is a T4 (<1300 K) brown dwarf, the other is a very cool (5100 K) white dwarf. White dwarfs can serve as useful age indicators, and so we used this very cool white dwarf (which we suspect is roughly 7.3 billion years old) to constrain the age of the pair of stars. This old age puts unique constraints on interpreting the brown dwarf -- modeling the atmosphere of these failed stars is very complicated! A thread with more information from is located on Twitter:

A class of supernova survivors

By JJ HermesFebruary 1st, 2020

Group members and collaborators have discovered a new class of zombie stars that are likely the shattered remnants of thermonuclear supernova that did not fully disrupt the white dwarf! Led by Roberto Raddi at Dr.Karl-Remeis-Sternwarte Bamberg, we have now published at least three more members of this new class of star named after the prototype LP 40-365.

The research is well summarized by Shannon Hall writing in Scientific American: This “newly discovered class of odd stars appears to have persevered through supernova explosions — providing a rare glimpse into these astrophysical catastrophes.” Another summary is detailed in a Twitter thread: