Hakki Boran Ögelman died in Austin, Texas, on September 4, 2011, after battling esophageal cancer for several months. Hakki was born in Ankara, Turkey, on July 8, 1940, and was the son of Salehettin Ögelman, a lawyer, and Vedya Özlem Ögelman, a schoolteacher. He had a sister, older by three years, the late Esen Yerliçi. Soon after his birth, the family moved to Istanbul, where Hakki attended the Robert College from sixth grade and obtained an international baccalaureate at age 17. In the same year, he moved to the United States to further his education at DePaw University in Indiana, where he obtained a Bachelor’s Degree in three years and developed a strong passion for physics. He was accepted as a graduate student in physics at Cornell University, where he was fortunate to have such professors as Hans Bethe and Ed Salpeter, among others. Hakkı’s advisor, Kenneth Greisen, had worked on the Manhattan Project and was a leading expert in the study of charged particles from space and gamma rays from astronomical sources. For his Ph.D., Hakki flew a balloon experiment to measure gamma rays at the highest energy, deriving from the radioactive decay of elementary particles from space. Hakki received his Ph.D. from Cornell in February of 1966.
After a postdoctoral year working on gamma ray astrophysics at the University of Sydney in Australia, Hakki accepted a fellowship at NASA's Goddard Space Flight Center where he became an expert on pulsars and wrote a series of articles published by Nature on astronomical sources of gamma rays.
At age 30, Hakki declined the offer of a civil service position at NASA and left for Turkey, feeling he wanted to give back to his home country, which had given him a strong education and instilled in him core values. After a period in the military as an officer, he was offered a position at the Middle East Technical University (METU) of Ankara, an English speaking university. After becoming a full professor at METU and spending a sabbatical year back at Goddard, Hakkı took leave from Ankara to help the development of a university in the rural area of Adana and became the Dean of Basic Sciences at Çukurova University. He established a group working on exploitation techniques of solar energy and planned for himself and his wife a solar house that was built on campus. Hakki was a member of the Turkish Academy of Sciences, served as a member of the Executive Science Board for the Scientific and Technical Research Council of Turkey from 1976–1984, and represented Turkey on international science councils and co-operations.
Turkey during those years was in turmoil, first apparently on the brink of a civil war and later governed by a strict military regime. Upsetting personal experiences convinced Hakki that Turkey had become too difficult for a free intellectual person, so he took a prolonged sabbatical at the Max Planck Institute for Extraterrestrial Physics in Garching near Munich, where he had already spent several summers and kept in touch with an international and vibrant community of scientists working on high-energy astrophysics. What started as a sabbatical stretched into almost 8 years. From gamma rays he moved to lower energies, X-rays, and made several interesting discoveries first with EXOSAT, then with ROSAT, the second imaging telescope in X-rays.
Hakki was broadly educated across many areas of physics, astronomy and science in general. He was very curious and an avid reader of science and non-science books and articles. Such broad horizons helped him think “outside the box.” He was the first to observe novae as accreting and exploding white dwarfs in binary systems in X-rays, thereby observing the “naked white dwarf” to obtain clues on its mass, chemical composition and possible evolutionary path toward a supernova Ia explosion. Hakki’s work on cooling neutron stars, pulsars and their nebulae (his main interest) was always innovative. One difficult riddle he hoped to solve was the relationship between the mass and radius of a neutron star in order to infer the equation of state of neutron stars and whether they contain exotic particles. He was particularly interested in the glitches of neutron stars (sudden small increases in the rotation speed) because these may be caused by transitions of vortices in the superfluid core of the star.
Turkey recognized Hakki as an outstanding scientist, and he was awarded the Sedat Simavi Prize in 1988 and the Turkish Scientific and Technical Research Council Prize in 1991. Eventually, Hakki returned to the U.S. where he felt that scientific life was most lively and interesting. He accepted a position as professor of physics at the University of Wisconsin in Madison at the beginning of 1991. Working with ROSAT, he made new discoveries related to neutron stars and novae. He mentored five successful graduate students and a post-doctoral associate, worked with countless collaborators, and was loved by his students in Wisconsin. He bought a house on Lake Monona in Madison because “being on water was important to him and reminded him of the Bosphorus.” He visited Turkey for a long time every summer, worked with students and collaborators there, and was instrumental in establishing the Turkish National Observatory.
In 1996, while he was at the peak of his career and his third son was just a year and a half old, Hakki’s life was disrupted by a massive stroke. He became physically handicapped and had to slow his pace somewhat. He was able to go back to teaching and still carried on independent and original research, but he had to take time to rest after each activity. He taught at the University of Wisconsin until March of 2011, even after heart surgery a year earlier. Eventually, an aggressive form of cancer caught up with his energy and love of science and life. Hakki had been married three times, each marriage lasting for more than 10 years. He is survived by three sons and a daughter-in-law, Kenan Ögelman of Austin, Texas, Nedim and Laura Ögelman of Alexandria, Virginia, and Roberto Ögelman of Madison, Wisconsin, and two grandsons, Anders and Soren Ögelman, of Alexandria, Virginia. His family, friends and colleagues will miss Hakki’s inquisitive spirit.