An international team of astronomers has uncovered a supermassive black hole in unlikely isolation at the centre of galaxy NGC 1600. National Research Council of Canada (NRC) astronomers working out of the Dominion Astrophysical Observatory (DAO) contributed the critical observational data required to map and model the unexpectedly sparse environment around the black hole.
This black hole ranks among the largest ever measured and is the first of its size to be found outside of a dense cluster of galaxies. Its discovery poses intriguing questions about how early supermassive black holes formed, and how they have grown in different parts of the universe.
Astronomers can detect the presence of a black hole by the effect of its gravitational pull on the orbits of nearby stars. However, due to the extreme distances from Earth to other galaxies, detailed spectroscopic observations are required, using instruments with superb angular resolution to identify the black holes at the galaxy centre.
While the galaxy NGC 1600 has been subject to previous investigations, this recent breakthrough black hole discovery was made possible by the bigger and more powerful optical capabilities of the Gemini Multi-Object Spectrograph (GMOS). This instrument resides atop Maunakea in Hawai'i, within the Gemini North 8-meter telescope.
"The power of GMOS lets astronomers actually measure the velocity of stars at close to the centre of giant elliptical galaxies where black holes are known to reside," says Nancy Levenson, Gemini Observatory Deputy Director and Head of Science. "Gemini is one of the few telescopes in the world with the power to collect enough starlight and sufficiently fine resolution to make meaningful observations at the centre of an elliptical galaxy."
NRC is part of an international consortium that helps operate and manage Canada's interests in the Gemini Observatory, and was one of the lead organizations that helped build GMOS.
"To confirm the black hole's existence, we had to compare the surface brightness profile of the galaxy and line-of-sight velocity distributions to numerical models of stellar orbits in the center of the galaxy," said Nicholas McConnell, NRC Research Associate, who led the data acquisition, reduction and analysis effort. "GMOS gave us the data needed for this critical measurement, and thanks to extensive experience using the Gemini Observatory, our team was able to analyze the data with unprecedented speed and thoroughness.
Critical observational data also relied on images from the Hubble Space Telescope (HST). "Archival HST data gave the brightness profile of the galaxy," notes John Blakeslee, NRC Astronomer. Dr. Blakeslee's work with the images of NGC 1600 extends through a long history of astronomers at NRC using HST data to survey galaxies and uncover fine details of their structure.
"Astronomy is fundamentally a global discipline, and Canada's prominent role in large international observatories like Gemini strengthens our position at the cutting edge of research and exploration," notes Dennis Crabtree, Director of NRC's Dominion Astrophysical Observatory. "Through these contributions, Canada is helping shine light into the depths of black holes at the centre of distant galaxies, and advancing our understanding of the Universe."