Job openings at MPA (apply by Jan 8, 2021)

6 Dec

We seek people to join the new stellar department, led by Selma de Mink, at the Max Planck Institute for Astrophysics (MPA) to study questions related to the fascinating Lives, Deaths, and Afterlives of (binary) Stars. We welcome applications from anyone who can … Read More »

Award for Eva Laplace’s visualization software TULIPS

30 Nov
Eva Laplace
Eva Laplace

Eva Laplace (final year PhD student at University of Amsterdam ) has been awarded the KNMW/ET outreach award for her software project TULIPS that allows to visualize computer simulations of the lives of stars. She is an astrophysicist at the Anton Pannekoek Institute for Astronomy where she is working on her PhD thesis investigating the lives and deaths of massive binary stars.

Being frustrated with the many unintuitive and cluttered diagrams that are often used in scientific papers, she started to design her own visualizations. What started as a way for her to better analyze the results of her computer simulations of the complexities of the deep interiors of stars that are at the brink of their final explosions, quickly gave her impact when showing these to colleagues at international conferences. Being passionate about teaching and outreach, she realized quickly how her diagrams could be animated and also help students develop a better understanding of how stars work and make her results accessible to the general public.

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Stephen Justham’s textbook on Common Envelope Evolution is out

22 Nov

Group member Prof. Stephen Justham coauthored this new textbook on what is without question the least understood type of binary interaction: the common envelope phase. During this phase stars temporarily share the same outer layers. This phase is essential for a wide variety of astrophysical phenomena: including cataclysmic variables, X-ray binaries, progenitors for type Ia supernovae, and gravitational-wave mergers. Read the introductory chapter here for free:

By Natasha Ivanova, Stephen Justham and Paul Ricker. Online ISBN: 978-0-7503-1563-0 • Print ISBN: 978-0-7503-1561-6

Can Gravitational-Wave detections tell us how stars fuse Oxygen out of Carbon? – Farmer et al. (2020)

1 Oct
Prediction of the location of the black hole mass gap as a function of the assumed reaction rate of C 12+ He4 -> O16 (Farmer et al. 2020)

Stars are cosmic factories that produce most elements heavier than helium in their deep interiors through nuclear fusion. The rate at which Carbon is fused into Oxygen is notoriously uncertain. It cannot be measured at any laboratory at earth, at least not under the conditions that occur in the interiors of stars.

Rob Farmer (postdoc at UvA) showed earlier that the location of the Pair Instability mass gap is a remarkably robust prediction, more solid than anything we know about the final stages of the most massive stars.

In this new paper, he shows that this prediction depends on the assumed rate for the rate at which Carbon is destroyed by alpha particles to make Oxygen. Why? High rates basically lead the star to consume all it’s carbon prematurely, already during the helium-burning phase. Being devoid of carbon, such a start skips the Carbon burning phase and has to resort to burning Oxygen immediately. In very massive stars this ignites explosively leading to a pair-instability supernova or pulsations.

Rob Farmer
Rob Farmer (UvA)

Instead, stellar models in which a lower rate is assumed for this reaction, still have carbon that they can burn. When burning Carbon in a shell they prevent premature contraction of the star holding up the outer layers. This can prevent the explosive ignition of Oxygen. Instead, the more gentle burning calmly depletes the core of its fuel leading to an inescapable final implosion to a black hole.

Long story short, assuming that the reaction is less efficient allows more massive stars to form black holes. Reducing the rate by 3 sigma moves the lower mass gap up to 100 solar masses. The hope is that gravitational wave detections will probe the location of the black hole mass gap and will eventually allow is to start to learn about their very massive brilliant progenitor stars.

A. (Lieke) Van Son – Can binaries make Black Holes with “forbidden” masses?

1 Jul
Lieke van Son (Harvard/UvA)

The theory of (single) stellar evolution predicts that stars can end their lives as Black holes, but masses between about 45 and 130 times the mass of the Sun are “forbidden”. Stellar cores that could have made Black Holes with such masses either lose a lot of mass before they can implode to become a black hole or they explode and leave nothing behind. An exciting prediction that can now be tested with the new heavy black holes found through Gravitational Wave Searches.

Lieke van Son (PhD student at Harvard University and the University of Amsterdam) investigated if this is still true for a star that has a binary companion. Black holes formed in binary systems can, in principle, steal mass from their stellar companion and grow to become heavier. How heavy? Can they fill the predicted mass gap?

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Tom Wagg wins the Harvard Leo Goldberg prize for his senior thesis

1 Jun

Group member Tom Wagg has been awarded the Leo Goldberg prize by the Harvard Astronomy Department for the best astronomy senior thesis. He estimated the detectability of black hole–neutron star binaries with LISA, a planned future mission to detect gravitational waves from space.

Tom will continue as a research fellow in the group working on gravitational waves before starting his PhD studies in 2021.

Mind the gap: on the black holes detected by gravitational waves

1 Nov

Gravitational-wave (GW) detections are now starting to probe the mass distribution of stellar-mass black holes (BHs). We investigate the predicted gap in the BH mass distribution and find that the location of the lower edge of the gap, at 45 solar masses, is remarkably robust against model assumptions and composition variations, making it the most robust predictions for the final stages of massive star evolution we have. We do find a dependency on the reaction rates, which implies that GW detections will constrain nuclear astrophysics. The robustness implies that there is a universal maximum for the location of the lower edge of the gap insensitive to the formation environment and redshift for first-generation BHs. This is promising for the possibility to use the location of the gap as a “standard siren” across the Universe.
Farmer, Renzo, de Mink et al. (2019, ApJ in press)
Rob Farmer, the lead other, is a postdoc in my group in Amsterdam and is a visiting scientist at Harvard University.

Did stars stripped in binaries help to reionize the Universe?

31 Oct

Former Ph.D. student Ylva Götberg (now Nashman theory fellow at Carnegie observatories) estimated the relative contribution of massive stars, stars stripped in binaries and active galactic nuclei to the epoch of reionization. We estimate that stripped stars contributed tens of percent of the photons that caused cosmic reionization of hydrogen, depending on the assumed escape fractions. More importantly, stripped stars harden the ionizing emission. At high redshift, stripped stars and massive single stars combined dominate the He II-ionizing emission, but we still expect active galactic nuclei drive cosmic helium reionization.

Götberg, de Mink, Mcquinn et al. (2019, A&A in press)

Recorded Colloquium at Harvard & Smithsonian Center for Astrophysics

27 Sep
Colloquium recording Sept 26, 2019, Harvard & Smithsonian Center for Astrophysics, Cambridge, MA.

From Birth to Chirp – Astrophysics of Massive Stars as Gravitational Wave Progenitors.

Abstract: How did they form?’ is a question many asked when LIGO announced the first direct detection of gravitational waves originating from two surprisingly heavy stellar-mass black holes. With masses of about 30 solar masses each, they outweighed all of the known black holes known from X-ray binaries. Now, four years after the first detection, alerts of new triggers come in at a rate of almost one per week. The analysis of the first eleven events has been published and we learned that the first system was not exceptional: the majority of detected events involve heavy black holes. In parallel, classical telescopes have been revolutionizing our understanding of the properties of young massive stars.

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