Andrea Ghez

Major contributions

• Led a decades-long observational programme (beginning in the mid-1990s) using adaptive-optics-corrected infrared imaging at the Keck Observatory to track the precise orbital motion of individual stars near the Milky Way's galactic centre
• Determined, through careful orbital analysis of these tracked stars, the mass and extremely compact size of the central object (Sagittarius A*), providing compelling evidence that it must be a supermassive black hole rather than any other conceivable type of object
• Made significant technical contributions to adaptive optics imaging techniques, which correct in real time for atmospheric distortion and were essential for achieving the extraordinary angular resolution required to track individual stellar orbits so close to the galactic centre
• Became the fourth woman to receive the Nobel Prize in Physics, sharing the 2020 prize (with Reinhard Genzel and Roger Penrose) for this body of work

Named concepts

Concept	Statement	Codex page
Sagittarius A* Mass Determination	~4 million solar mass central compact object	View entry

Career

Ghez has spent the great majority of her academic career at the University of California, Los Angeles (UCLA), where she led the UCLA Galactic Center Group's long-term observational programme tracking stars orbiting the Milky Way's central compact object. Working independently of, though roughly contemporaneously with, Reinhard Genzel's team in Germany, Ghez's group used the Keck Observatory's advanced adaptive optics systems to achieve the extraordinary angular resolution needed to resolve individual stellar orbits so close to the crowded, dust-obscured galactic centre.

The two independent research groups' decades of precise orbital tracking, converging on essentially the same conclusion — an extraordinarily compact central mass of roughly 4 million solar masses, consistent only with a supermassive black hole — provided some of the most direct and compelling observational evidence for supermassive black holes' existence available before the Event Horizon Telescope's later direct imaging.

Key publications

• Ghez, A.M., et al. (1998). "High Proper-Motion Stars in the Vicinity of Sagittarius A*: Evidence for a Supermassive Black Hole at the Center of Our Galaxy." The Astrophysical Journal, 509(2), 678–686.

Nobel Prize

Andrea Ghez shared the Nobel Prize in Physics for 2020 (with Reinhard Genzel and Roger Penrose) "for the discovery of a supermassive compact object at the centre of our galaxy" — becoming only the fourth woman to receive the Nobel Prize in Physics.

Historical context

Ghez's and Genzel's independent, converging results represent a notable case where two competing research teams' rigorous, carefully cross-checked observational programmes reinforced rather than undermined each other's conclusions, providing an unusually solid empirical foundation for the existence of the Milky Way's central supermassive black hole well before it could be directly imaged. Her recognition as only the fourth woman to win the Physics Nobel also highlights the continued relative rarity of women recognised by the prize, a pattern noted elsewhere in this Codex's biographical entries.