When is a nova not a ‘nova’? When a white dwarf and a brown dwarf collide


October 5, 2018

In July 1670, observers on Earth witnessed a “new star,” or nova, in the constellation Cygnus. Where previously there was dark sky, a bright pinprick of light appeared, faded, reappeared, and then disappeared entirely from view. Modern astronomers studying the remains of this cosmic event initially thought it heralded the merging of two main sequence stars — stars on the same evolutionary path as our sun.

New observations with the Atacama Large Millimeter/submillimeter Array (ALMA) point to a more intriguing explanation. By studying the debris from this explosion, which takes the form of dual rings of dust and gas resembling an hourglass around a compact central object, the researchers concluded that a brown dwarf (a so-called failed star without the mass to sustain nuclear fusion) merged with a white dwarf (the elderly, cooling remains of a sun-like star). hourglass star collision CK Vulpeculae. New research indicates that this hourglass-like object is the result of the collision of a brown dwarf and a white dwarf. Photo courtesy ALMA (ESO/NAOJ/NRAO)/S. P. S. Eyres Download Full Image

“It now seems what was observed centuries ago was not what we would today describe as a classic ‘nova.’ Instead, it was the merger of two stellar objects, a white dwarf and a brown dwarf," said Sumner Starrfield, an astronomer and Regents' Professor at Arizona State University's School of Earth and Space Exploration and co-author on a paper appearing in the Monthly Notices of the Royal Astronomical Society. "When these two objects collided, they spilled out a cocktail of molecules and unusual isotopes, which gave us new insights into the nature of this object.” 

According to the researchers, the white dwarf would have been about 10 times more massive than the brown dwarf, though much smaller in size. As the brown dwarf spiraled inward, intense tidal forces exerted by the white dwarf would have ripped it apart.

“This is the first time such an event has been conclusively identified,” Starrfield said.

Since most star systems in the Milky Way are binary, stellar collisions are not that rare, the astronomers note. But the new ALMA observations reveal new details about the 1670 event. By studying the light from two, more-distant stars as it shines through the dusty remains of the merger, the researchers were able to detect the telltale signature of the element lithium, which is easily destroyed in the interior of a main sequence star, but not inside a brown dwarf.

swan constellation
The Cygnus constellation, site of the stellar event: Johannes Hevelius, Figure 1 of ‘An extract of a letter of M. Hevelius,’ written to the publisher from Dantzick, August 17/27 1670, published in the Philosophical Transactions of the Royal Society, 1670, vol. 5, number 65, pp. 2087-2091; doi:10.1098/rstl.1670.0062 2053-9207.

“The presence of lithium, together with unusual isotopic ratios of the elements carbon, nitrogen and oxygen point to material from a brown dwarf star being dumped on the surface of a white dwarf. The thermonuclear ‘burning’ and an eruption of this material resulted in the hourglass we see today,” said Stewart Eyres, deputy dean of the Faculty of Computing, Engineering and Science at the University of South Wales and lead author on the paper.

Intriguingly, the hourglass is also rich in organic molecules such as formaldehyde and formamide, which is derived from formic acid. These molecules would not survive in an environment undergoing nuclear fusion and must have been produced in the debris from the explosion. This lends further support to the conclusion that a brown dwarf met its demise in a star-on-star collision with a white dwarf.

“Such collisions are probably not rare and this material will eventually become part of new solar systems, implying that they will already contain the building blocks of organic molecules as they are forming,” Starrfield added. 

The National Radio Astronomy Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc.

ALMA, an international astronomy facility, is a partnership of the European Organisation for Astronomical Research in the Southern Hemisphere (ESO), the U.S. National Science Foundation (NSF) and the National Institutes of Natural Sciences (NINS) of Japan in cooperation with the Republic of Chile. ALMA is funded by ESO on behalf of its member states, by NSF in cooperation with the National Research Council of Canada (NRC) and the National Science Council of Taiwan (NSC) and by NINS in cooperation with the Academia Sinica (AS) in Taiwan and the Korea Astronomy and Space Science Institute (KASI).

alma satellite field
High on the Chajnantor plateau in the Chilean Andes, the European Southern Observatory, together with its international partners, is operating the Atacama Large Millimeter/submillimeter Array (ALMA) — a state-of-the-art telescope to study light from some of the coldest objects in the universe. ALMA comprises 66 high-precision antennas, spread over distances of up to 16 kilometers. This global collaboration is the largest ground-based astronomical project in existence. Photo courtesy ALMA (ESO/NAOJ/NRAO)/W. Garnier (ALMA)

ALMA construction and operations are led by ESO on behalf of its member states; by the National Radio Astronomy Observatory (NRAO), managed by Associated Universities, Inc. (AUI), on behalf of North America; and by the National Astronomical Observatory of Japan (NAOJ) on behalf of East Asia. The Joint ALMA Observatory (JAO) provides the unified leadership and management of the construction, commissioning and operation of ALMA.

ASU Library writing the next chapter in the 'Future of Print'

How print books are displayed, curated and delivered is the focus of a new initiative


October 5, 2018

When Hayden Library, Arizona State University’s largest library, re-opens in 2020, its open-stack print collections will have a whole new look. 

The future display, curation and delivery of books at ASU, and how those books interact with the heavily digital-dwelling community in which they are present, is the focus of the Future of Print initiative, an exploration into the behaviors, needs and expectations of 21st-century academic library users. Health Humanities Horizon display A new collection on the Downtown Phoenix campus looks at the intersection of health and humanities. Download Full Image

Led by ASU Library, the initiative addresses specific needs of today’s public universities, and has resulted in a widely shared white paper and a three-year grant from the Andrew W. Mellon Foundation.

Lorrie McAllister, Associate University Librarian for Collections Services and Analysis, and Shari Laster, head of Open Stack Collections, are now leading the Future of Print into its next phase: experimentation.

Here, Laster discusses these experiments and how they aim to inspire new thinking around the design of inclusive, high-quality and user-focused print collections for research and learning. 

Question: This fall, the library is experimenting with a series of collection experiments. Can you tell us more about them?

Answer: ASU Library has a lot of ideas about how people and books get connected together. We came up with a list we are calling “10 Compelling Ideas” and we’re trying out some of these ideas in different library locations and in other spots on campus. This fall, we have several mini-projects, or experiments, in motion.

Surprise Me! is a collection of poetry and drama at Fletcher Library on the West campus. The books in this collection are being shelved spine-backward in order to invite students to explore an unexpected collection. Another project, Vamos Argentina! Books, Tango and Meteors, is an exciting series of talks and events that will draw attention to the collection of Argentine literature currently housed at Noble Library on the Tempe campus. At the Downtown Phoenix campus, we are featuring Health Humanities Horizons, a collection curated in collaboration with faculty whose research and teaching intersects with the CLASCollege of Liberal Arts and Sciences certificate program in interdisciplinary health humanities.

We’re also cooperating with Barrett, The Honors College to assemble a mini-library in a student-friendly environment, in addition to planning a mini-collection for Hayden Library that’s all about the act of collecting, what we collect and why we collect. 

Q: With digital interfacing consuming more of our time and attention, what are some unique strengths of the print medium?

A: Books mean different things to different people. While digital content certainly has many advantages, accessing and using a book in print format is a specific experience that can bring about a different form of interaction with the content. We all have different ways of learning and absorbing information. We hope that allowing for the possibility of a book to “catch the eye” of a passerby will enrich the experience of our spaces.

Books also have a physical presence in library spaces. Print books are often considered an essential component to creating a thriving learning environment. For example, they can make a room more conducive to study and focus. This project takes into consideration which books we are presenting in and around spaces where students study and learn. By making parts of our collections more visible, we add another layer of learning where users can physically be immersed in the collections.

Q: University libraries have always been a source of academic support for students. How does this initiative, focusing on print materials, connect to the success of ASU students?

A: When Hayden Library reopens in 2020, it will be a destination on the Tempe campus for studying, research and classroom learning. It will also be a place for the campus community to relax, take a break and explore new ideas. We want to create collections that make library spaces more welcoming and inviting. We also want to use print books to present new perspectives on academic disciplines and research, and to inspire innovation and discovery. By helping everyone who enters the library to see our collections in a new light, we also give them a new way to explore ideas that matter to their success at ASU.

Q: How can people participate in these experiments/mini-projects?

A: Visit the collections and leave us feedback! Visitors can expect to see emoji stickers for a quick shortcut to speaking your mind. Anyone can borrow the books on display, so pick up and check out what looks interesting to you. 

We also want to hear from the ASU community about the library collections that make you feel welcome in our spaces. Anyone is welcome to send me a note at shari.laster@asu.edu.

Britt Lewis

Communications Specialist, ASU Library