John Wardle, Professor of Astrophysics and the Head of the Division of Science, has been playing an integral role in bringing the first-ever image of a black hole to realization. Announced today, the image of the M87 black hole is being hailed as a major scientific breakthrough. Wardle serves on four of the Event Horizon Telescope’s 23 working groups, helps analyze the polarization of the M87 black hole’s radio emissions, and serves on the publication working group. This announcement was made in a series of six papers published in a special issue of The Astrophysical Journal Letters.
On Wednesday, May 30, at 9:00 pm, Marcelle Soares-Santos, Assistant Professor of Physics at Brandeis will be a part of the premier of the PBS’ program “NOVA Wonders What is the Universe Made of?” This program provides an introduction to dark matter and dark energy. Researchers admit that, aside from being able to deduce the presence of these phenomena, they have little idea of how each works. “We have no idea what is the physics underlying it,” Marcelle says in the film, referring to dark energy.
In the program, the filmmakers travel to the Cerro Tololo Inter-American Observatory in Chile just as scientists are detecting gravitational waves. Soares-Santos participated in this discovery.
Bornholm 1959 From the left, Richard Arnowitt, Charles Misner and Stanley Deser
Today’s Physics Nobel Prize to Rai Weiss, Kip Thorne, and Barry Barish for the detection by the LIGO experiment of gravitational waves is a well-deserved recognition of a remarkable achievement through perseverance. However, it is the nature of prizes such as the Nobel that they obscure the important efforts and insights of many scientists across space and time that lead to the result in question.
The extraction of a gravitational wave signal from the output of the LIGO detector requires understanding in advance what signals can be produced; these are based on numerical simulations of astrophysical events which provide templates that a signal must match.
This is possible due to the seminal work of Brandeis emeritus faculty Stanley Deser, with his colleagues Richard Arnowitt and Charles Misner, who developed the mathematical framework known as the ADM formalism, to treat general relativity as a Hamiltonian system; with this, the evolution in time of the gravitational field can be computed from initial conditions.
In addition, Stanley was instrumental in the LIGO experiment being funded in the first place. The story is best told by him in his inimitable style (here quoted from an email, and lightly expurgated):
“Marcel Bardon, then [director] of NSF physics, made me an offer I’d better not refuse. I was nominated to some advisory committee in order to plead for LIGO in front of my betters, who would then go to Congress, if convinced. Those were dark days for waves, experimentally; we (ADM) of course knew the Lord was not evil, but 3 suns’ worth we did not expect!….It worked quite well, and was duly made a line item.”
From June 28th through 30th, about fifty former and current students, colleagues and friends of Brandeis astrophysics Professors John Wardle and David Roberts gathered in the Physics building for a symposium titled “When Brandeis met Jansky: astrophysics and beyond.” This event was organized to celebrate their achievements in astrophysics and their impact on generations of students. Their work has established Brandeis as a major player in radio astronomy.
The symposium title refers to Karl Jansky who is credited with starting an entirely new means of studying the cosmos using radio waves. Radio astronomy arrived at Brandeis with Professor Wardle in 1972. He was joined in 1980 by Professor Roberts and together they pioneered a very powerful observational technique called Very Long Baseline Polarimetry. This involves the use of telescopes separated by thousands of kilometers to produce the sharpest images available to astronomers. Their methods allow astronomers to map the magnetic fields in and near celestial objects. With their students and colleagues, John and Dave have exploited this technique to study the magnetic fields in quasars and active galaxies, and near super massive black holes far outside our Milky Way galaxy as well as black holes closer to home.
Professors John Wardle and David Roberts (front right) with former students and colleagues on the steps of the Abelson physics building (photo: Mike Lovett)
The reach of John and Dave’s work was reflected in the content of the presentations and the composition of the attendees, some of whom had traveled from as far afield as South Korea, India, and Europe. All major centers of radio astronomy were represented. At the conference dinner, several former students expressed their appreciation for the roles Dave and John have played as their mentors.
In their presentations, Dave and John described their current projects and highlighted the work of their undergraduates, graduate students and postdoctoral fellows, who have all gone on to successful careers in academia and industry.
The nineteen PhD theses produced by the Brandeis Radio Astronomy group
Professor Roberts has decided to retire at the end of August, though his retirement plans include a huge program of continuing research into unusual-shaped radio galaxies. These may represent galaxy mergers and the possible merger of their central black holes, and is being carried out with colleagues in India. Professor Wardle has no intention of retiring and is expanding his horizons so to speak — he is part of the Event Horizon Telescope collaboration, an international team of astronomers that is attempting to make the first image of the ‘event horizon’* of a black hole!
The symposium was organized by Teddy Cheung (PhD ’05, now at the Naval Research Laboratory) and Roopesh Ojha (PhD ’98, now at NASA, Goddard Space Flight Center), with generous help and support from the Physics Department.
* The boundary around a black hole beyond which nothing can escape.
On December 4, the journal Science (Vol. 350 no. 6265 p 1242) published a paper titled, “Resolved magnetic-field structure and variability near the event horizon of Sagittarius A*” (abstract). The paper reports that the Event Horizon Telescope has detected strong magnetic fields around the supermassive black hole at the center of the Milky Way galaxy. John Wardle, Professor of Astrophysics at Brandeis, is one of the lead authors. A co-author is Michael Kosowsky ’14, who worked on the project as a summer research project at the MIT-Haystack observatory as a junior physics major, and is now an NSF Graduate Research Fellow at Harvard.
Near a black hole, differential rotation of a magnetized accretion disk is thought to produce an instability that amplifies weak magnetic fields, driving accretion and outflow. These magnetic fields would naturally give rise to the observed synchrotron emission in galaxy cores and to the formation of relativistic jets, but no observations to date have been able to resolve the expected horizon-scale magnetic-field structure. The paper reports interferometric observations (made with antennas in Hawaii, California and Arizona) at 1.3-millimeter wavelength that spatially resolve the linearly polarized emission from the Galactic Center supermassive black hole, Sagittarius A*. We have found evidence for partially ordered magnetic fields near the event horizon, on scales of ~6 Schwarzschild radii, and we have detected and localized the intra-hour variability associated with these fields.
The above image is an artist’s impression. With the planned addition of antennas in Mexico, Chile, Europe and the South Pole, the Event Horizon Telescope will be able to make true images with angular resolution of a few tens of microarcseconds.
The extraction of a gravitational wave signal from the output of the LIGO detector requires understanding in advance what signals can be produced; these are based on numerical simulations of astrophysical events which provide templates that a signal must match.
Science at Brandeis 