Astronomer Tom Bolton found compelling evidence of a black hole’s existence

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“Black holes are out of sight!” So says a popular astronomy bumper sticker. Black holes are objects whose gravity is so strong that nothing can escape, not even light. They are part of popular culture, and the most inscrutable things in the cosmos. They strain the brains of notable theorists like the late Stephen Hawking, not to mention science fiction writers. But do black holes exist?

In 1972, Dr. Tom Bolton, a young University of Toronto astronomer, published strong evidence that a faint star in the constellation Cygnus orbited a massive black hole. Independent observations by British astronomers pointed to the same conclusion. Dr. Bolton died this month at the age of 77.

Charles Thomas Bolton was born on a military base in Tennessee on April 15, 1943, and raised in Illinois where he was a star athlete in high school. He was a lifelong baseball fan. He studied at the University of Illinois and the University of Michigan, receiving a PhD in 1970. There, he became an expert in stellar spectroscopy, a technique whereby starlight is broken up into its component colours by a diffraction grating to reveal the star’s chemical composition, atmospheric temperature and pressure, motion, and more.

In 1970, he left for the University of Toronto – part of Canada’s 1970s “brain gain” (though he never gave up his U.S. citizenship). The university’s David Dunlap Observatory (DDO) in Richmond Hill, with the largest telescope in Canada, was ideally suited for his research.

In those days, space astronomy was blossoming. A high-altitude research rocket flight in 1964 had identified a strange source of X-rays in the constellation Cygnus, designated Cygnus X-1. Further space-based and ground-based observations localized it coincident with a faint, catalogued star HDE226868. But stars are not supposed to emit X-rays. With regular access to the DDO telescope, Dr. Bolton began studying the motion of HDE226868 in 1971 and showed that it was a normal star, in a 5.6-day orbit around a massive, unseen object. All evidence suggested that the companion was a black hole.

Gases from the normal star swirled around and into the black hole. Their gravitational energy was converted into intense heat, and then into high-energy X-ray radiation. The black hole was the remains of a massive companion star to HDE226868. At the end of its life, it had run out of nuclear energy, and therefore internal heat and pressure, and had collapsed under its own weight to almost infinite density.

While Dr. Bolton was doing this ground-breaking research, he was employed in a series of temporary positions. In 1973, he was offered a tenure-stream position, quickly tenured, and promoted to the highest rank, full professor, in 1980. In 1985, he was elected a Fellow of the Royal Society of Canada for “remarkable contributions” to the arts or sciences.

Dr. Bolton continued his research on HDE226868/Cygnus X-1 and, between 1982 and 1986, he and graduate student Douglas Gies published a series of comprehensive studies of that star system. Meanwhile, he was contributing to many other areas of stellar astronomy, almost as exciting as black holes – at least to astronomers. This included hot, massive stars which explode as supernovas, seeding our galaxy with the elements of life, and leaving neutron star or black hole remnants behind.

He and his students were especially interested in binary star systems like HDE226868 which, among other things, enable black holes to be detected and weighed. They also published dozens of papers on topics such as “runaway stars,” flung into interstellar space by near-collisions with other stars; “magnetic stars” with ultra-strong magnetic fields; stars with complex surface vibrations; and stars with massive winds which disrupt their environment and perhaps trigger the formation of new stars.

Dr. Bolton supervised, mentored and inspired about 40 undergraduate and graduate research students, collaborated with dozens of other astronomers, published well over 100 research papers, gave invited lectures to astronomers around the world, taught courses on both stellar astronomy and planetary astronomy, as well as introductory astronomy, and provided leadership and sage advice to dozens of national and international organizations and committees.

He was also deeply committed to public education and outreach, and did countless media interviews and appearances and public presentations, most often about black holes. Cygnus X-1 made him something of a celebrity. His vanity license plate was CYG X-1. In 1977-8, the Canadian rock band Rush recorded its two-part song series Cygnus X-1 – perhaps the ultimate form of recognition. Beneath his sometimes-gruff exterior, and southern drawl, there was a droll sense of humour, and a heart of gold. He loved nature, and cats.

His first marriage had ended in divorce but, in 1985, he met amateur astronomer Susan Challenger through the Toronto branch of the Royal Astronomical Society of Canada (RASC). They married in 1986. She lit up his life, and brought great joy and comfort to him, especially in the difficult times that were to follow.

Light pollution is the bane of an astronomer’s existence, whether they are a professional researcher or a backyard stargazer. Light pollution is the illumination of the night sky by artificial lights that shine or leak light upward, rather than just downward where needed. It is a sign of inefficient, ineffective lighting, as well as a barrier to our view of the universe. Dr. Bolton worked closely with Richmond Hill and with lighting associations to combat light pollution. In 1986, he received a Volunteer Achievement award from Richmond Hill, and was instrumental in writing and implementing a light pollution bylaw in Richmond Hill in 1995 – the first such municipal bylaw in Canada, and a model for other countries.

In middle age, at the height of his career, Dr. Bolton developed a thyroid disorder which, among other things, led to depression. The suicide of one of his graduate students also deeply affected him. And the future of DDO weighed on his mind.

Although Dr. Bolton was continuing his research, other astronomical research and training was being moved to observatories under clearer, darker skies in Chile and Hawaii. He used these facilities, and facilities in space but, unfortunately, much of his work required regular access to a telescope over weeks and months. A few hours of time on an over-subscribed telescope on a distant mountaintop was not always sufficient. He appreciated the power and value of a “local” observatory.

The university’s hope was to sell the DDO lands for development, and invest the proceeds in a new astronomy institute on the downtown campus. According to the terms of the original Dunlap bequest, however, the lands would revert to the Dunlap family if they were no longer used for astronomy. Lengthy negotiations ensued.

The views of local residents on the possible sale of the DDO lands were varied and conflicting. Debate and protest was vigorous, and at times acrimonious. Dr. Bolton was a founding member of the DDO Defenders, a grass-roots community group that sought heritage status and protection for the observatory. Ultimately, the DDO lands were sold for development in 2008, with the agreement of the Dunlap family. The proceeds were used to create a new Dunlap Institute on campus, bringing the Dunlap name and bequest into the 21st century. Its research, training, and public outreach are already well known internationally. The DDO telescope and buildings are now owned by Richmond Hill, and operated as a public education centre by community groups including the DDO Defenders, and the Toronto branch of the RASC.

The university’s sale of the DDO broke Dr. Bolton’s heart. As his physical and mental health deteriorated, he retired and became professor emeritus, and retreated to his home in Richmond Hill. He never got to bask in the glory and recognition that other senior academics enjoy. But his research data and findings live on. His collaborators included him as a co-author of many research papers in the years after he retired.

Dr. Bolton died of unspecified causes at his home in Richmond Hill on or before Feb. 4. His wife, Susan, died of amyotrophic lateral sclerosis (ALS) in 2012. His survivors include four stepsons, David, Stephen, Craig and Bill Hodges, and their partners and children. Information on his other survivors was not available.