In this series of posts, we sit down with a few of the keynote speakers of the 241st AAS meeting to learn more about them and their research. You can see a full schedule of their talks here, and read our other interviews here!
About a dozen years ago, Professor Richard Mushotzky was invited to a conference on elemental abundances. After plenty of talks on stars and the interstellar medium, it was his turn to speak: “Thank you so much for inviting me – I’m going to talk about the 90% of the Universe that you folks have not talked about.” The silence was “stunning.”
Over the past fifty years, Prof. Mushotzky – formerly of NASA’s Goddard Space Flight Center and now at the University of Maryland – has established himself as one of the pre-eminent x-ray astronomers. According to Prof. Mushotzky, the importance of x-ray astronomy is two-fold: not only do x-rays provide a window into the “most exciting phenomena in the Universe” – like neutron stars and black holes – but they also allow us to see the hot material that makes up 90% of the Universe’s luminous matter. “If you want to study the Universe as a whole, you have to study those hot baryons in the x-ray.”
A lifetime of eminence in x-ray astronomy
Prof. Mushotzky got involved with x-ray astronomy just as the field was blooming. In 1970, when he was a second-year graduate student at UCSD, the first x-ray satellite, Uhuru, was launched. With x-ray instrumentation transitioning from balloons and rockets to satellites, high-energy astrophysics saw rapid developments: “The results that [Uhuru] poured forth were just amazing – things that … no one ever thought existed.” For the first forty years of its existence, x-ray astronomy was driven by “the discovery of new and unanticipated things;” having been at the forefront of many of these discoveries, Prof. Mushotzky is now being awarded the AAS Henry Norris Russell Lectureship, an honor chosen annually “on the basis of a lifetime of eminence in astronomical research.”
Throughout his career, Prof. Mushotzky has made contributions to x-ray instrumentation and has advanced our knowledge of active galactic nuclei (AGN), clusters of galaxies, and more. With Harvey Moseley and Dan McCammon, he co-invented the x-ray microcalorimeter, an “imaging x-ray spectrometer” where each pixel contains both an image and a high-resolution x-ray spectrum, similar to an Integral Field Unit for optical astronomy. In the realm of AGN, Prof. Mushotzky has been involved in research that has explored the fundamental properties of AGN spectra (driving theories about “what produces the photons that produce x-rays” in galactic nuclei), that has vastly expanded the set of known AGN via deep x-ray surveys, and that has demonstrated that star formation is inhibited in AGN hosts. With respect to galaxy clusters, his work has shown that the plasma in clusters is metal-enriched out to high redshift and that the metallicity gradient within clusters is extremely weak – in Prof. Mushotzky’s words, “there’s an awful lot of iron in them there clusters!”
Throughout all his work, Prof. Mushotzky remains grateful for each of his collaborators: “I tried to at least say during this [interview] the names of a bunch of my collaborators, but I left a lot of people out.” He’s also thankful for his early mentors at Goddard, including Frank McDonald, Elihu Boldt, Peter Serlemitsos, and Stephen Holt.
“Did you know that aluminum can burn?”
Prof. Mushotzky’s career has not been without its setbacks and failures, however. Prof. Mushotzky “started his life as a theorist,” studying quasars – until he was “fired” by his first Ph.D. advisor. His next project – a balloon experiment with his new advisor, Laurence Peterson – literally crashed and burned: “Did you know that aluminum can burn?” he quipped after describing the balloon payload landing in a tree and being struck by lightning. Similar setbacks have persisted throughout his career: data collection from BBXRT was cut short due to a problem with the space shuttle’s toilet, the microcalorimeter on Chandra was “thrown off … because of money,” and three of the space missions on which he collaborated with the Japanese space agency – Astro-E, Suzaku, and Hitomi – fell into the Pacific ocean, produced no data, and self-destructed, respectively.
Understandably, Prof. Mushotzky’s biggest piece of advice for early-career astronomers is “don’t give up.” Make the best you can out of things: while BBXRT’s data collection may have gotten cut short, the data was still enough to get Prof. Mushotzky’s student Kim Weaver through her PhD thesis, and while Hitomi may have exploded soon after its deployment, the early data it collected on the Perseus cluster showed “knock your socks off type results … the one data set we got has really changed our understanding of the physics of the gas in clusters of galaxies.” In the face of failure, whether its an unsuccessful research project or a rejected proposal, Prof. Mushotzky advises students not to get discouraged unnecessarily: “things have turned out well … things can turn out positive in the long run.”
Prof. Mushotzky also urges grad students to “make sure [they] have the right advisor” – he “[knows] far too many students that dislike their advisors, and that’s bad for both parties.” He acknowledges that “one of the most positive things about [his] entire career [has been] the graduate students and postdocs [he’s] had the opportunity to work with … [he’d] like to thank all [his] graduate students and postdocs who’ve helped [him] enormously.”
New frontiers in x-ray astronomy
Recently, Prof. Mushotzky has continued to explore the frontiers of x-ray astronomy. Five years ago, he led the initial study for the AXIS probe that was presented to the 2020 decadal survey. AXIS will be the successor to the Chandra X-ray Observatory, with improved collecting area and a better angular resolution averaged over the field of view: “Chandra was well-matched to what was available across the electromagnetic spectrum in the year 2000 – and a lot has happened since then. AXIS will be complementary to every other wavelength band and will be able to do unique things on its own.” When AXIS is launched, it’ll shed light on supermassive black hole formation and evolution in the early Universe, it’ll provide x-ray follow-up for transients like tidal disruption events and gravitational wave events, and it’ll take high-resolution images of the intergalactic medium, including the filaments around galaxy clusters.
For his plenary talk at AAS 241, Prof. Mushotzky will be discussing his recent work with the Swift Observatory’s Burst Alert Telescope (“BAT”). While Swift was originally built to study gamma-ray bursts, the BAT’s x-ray sensitivity has made it extremely useful for x-ray astronomy. BASS – an AGN survey coupling BAT’s x-ray detections with observations from almost every other region of the electromagnetic spectrum – has “revolutionized our understanding of active galaxies,” revealing major biases in prior AGN surveys that lacked x-ray data and illuminating components of AGN that had never been seen before. Prof. Mushotzky notes that “this is just the consequence of the follow-up of an experiment which was originally built to do gamma-ray bursts – and didn’t cost any more money to make all these discoveries.” While the future of x-ray astronomy in general remains uncertain, “the wonderful results coming out of the BASS collaboration show us that there’s a huge amount of exciting stuff based on data we’ve already obtained that hasn’t been well-mined.”
To hear more about new frontiers in x-ray studies of active galaxies, tune into Professor Mushotzky’s Plenary Lecture at 3:40 PM PT on Tuesday, January 10 at #AAS241!
Astrobite Edited by: Isabella Trierweiler
Featured Image Credit: AAS
