NYUAD Physicist Assists in Black Hole Discovery

A lone tree silhouetted against the backdrop of the Milky Way.

Cosmologists have calculated that, on occasion, a star's orbit will be disturbed in such a way that it passes very near the super-massive black hole at the center of its galaxy — but not so close that it is captured whole.

Such a star will be torn apart by the extreme tidal forces it experiences: the force of gravity on the near side of the star is so much stronger than that on the far side that the gravitational force holding the star together is overwhelmed, causing the star to simply come apart. While some of the star's matter falls into the black hole, much of it continues in chaotic orbits, crashing into itself and producing intense radiation lasting days to months.

These phenomena are called stellar tidal disruption flares, or TDFs. The researchers uncovered sound evidence for the presence of two TDFs while repeatedly observing more than 2 million galaxies over 10 years. Sjoert van Velzen, the study's lead author, said, "Searching through 2.6 million galaxies was actually a lot of fun — there is so much to discover! Based on our search criteria and observing two TDFs that met those criteria, the rate of TDFs is about once per 100,000 years, per galaxy. It's quite thrilling to have been able to make such a measurement."

NYU Abu Dhabi physicist Joseph Gelfand was part of a team of researchers that found evidence of black holes destroying stars — a long-sought phenomenon — providing a new window into general relativity. The research, reported in the latest issue of the Astrophysical Journal, also opens up a method to search for the possible existence of a large population of presently undetectable "intermediate mass" black holes, which are hypothesized to be precursors to the super-massive black holes at the centers of most large galaxies. Gelfand assisted with the study, which was carried out primarily by Glennys Farrar and Sjoert van Velzen at New York University's Center for Cosmology and Particle Physics.